FIELD OF THE INVENTION

Provided herein are surgical guiding instruments for positioning a guide pin in the glenoid cavity of a scapula. Further provided herein are related surgical methods for positioning a guide pin, for example for glenoid reconstruction such as for guiding the positioning of a glenoid implant in a shoulder arthroplasty procedure.

BACKGROUND OF THE INVENTION

The shoulder joint is formed by two bony components, more particularly the glenoid cavity (cavitas glenoidalis, glenoid fossa) of the scapula and the humeral head (caput humeri), respectively forming the socket and the ball of a ball-and-socket joint. The joint is reinforced and stabilized by various muscles, including the rotator cuff muscles (musculus subscapulars, musculus teres minor, musculus supraspinatus, and musculus infraspinatus) and the musculus deltoideus.

During the lifetime of a patient, the glenoid cavity may become worn, thereby causing severe shoulder pain and limiting the range of motion of the patient's shoulder joint. To alleviate such pain and increase the patient's mobility, a shoulder arthroplasty may be performed. Arthroplasty is the surgical replacement of one or more bone structures of a joint with one or more prostheses. Shoulder arthroplasty often involves replacement of the glenoid fossa of the scapula with a prosthetic glenoid component.

Typically, the positioning of a prosthetic glenoid component involves reaming the patient's glenoid using a reamer, thereby obtaining a surface fitting the implant at the location where the implant should be placed. In a further step, the implant is placed upon the scapula, supported by the reamed surface.

Obtaining an adequate orientation and position of the implant is crucial for the outcome of the surgery. Indeed, the orientation of the implant highly influences the success or failure of the surgery, and the lifespan of the implant. When prosthesis fails, a revision surgery is carried out. However, this procedure is technically more difficult and time-consuming than the primary intervention and the outcome is often less satisfactory. Indeed, a failing prosthesis can lead to significant bone loss, resulting in a reduced bone stock for the surgeon to work on. Furthermore, with each successive joint revision, the risk of infection and symptomatic loosening of the prosthesis may increase substantially. Accordingly, one of the most important aspects of joint surgery procedures is the correct, accurate and stable placement of the primary implant. To assist the surgeon in finding the optimal orientation and/or position of the reamer and the implant, a guide pin indicating this orientation and/or position may first be inserted in the glenoid cavity. An exemplary procedure involving the use of such guide pin is described in international patent application WO 2012/129018. It is clear that in such procedure, the correct positioning of the implant position largely depends on the accuracy and precision of the guide pin positioning.

A number of different guiding instruments is available for position of guide pins. Currently, the most reliable guide pin positioning is obtained using patient-specific guiding instruments. Such instruments typically are made according to a pre-operative plan based on 3D medical images (e.g. PET/CT scans) of the patient and rely on the matching of an anatomical feature for correct positioning. Indeed, these instruments typically contain at least one surface which mates specifically with the surface of the anatomical part. Although a number of less expensive standard guiding instruments are available, these instruments are much less reliable than the patient-specific instruments.

Chinese utility model CN 201912219 describes a guiding instrument for positioning a pin onto the coracoid process of the scapula. However, this instrument does not allow for the correct positioning of a pin in the glenoid cavity.

Accordingly, there is a need for surgical guiding instruments and methods which mitigate at least one of the problems stated above.

SUMMARY OF THE INVENTION

Provided herein are surgical guiding instruments for positioning a guide pin in the glenoid cavity of a scapula. Further provided herein are related surgical methods for positioning a guide pin, for example for guiding the positioning of a glenoid implant in a shoulder arthroplasty procedure.

The present guiding instrument and method may allow for an accurate positioning of guide pins, without the need of pre-operative 3D imaging of the patient's anatomy. The guiding instrument registers on bone parts which can be localized easily by the surgeon, which may facilitate performing the surgery.

The above and other characteristics, features and advantages of the concepts described herein will become apparent from the following detailed description, which illustrates, by way of example, the principles of the invention.

The invention thus provides for the following aspects:

1 . A surgical guiding instrument for positioning a guide pin in the glenoid cavity of a scapula, comprising: a first contact element for positioning on the most medial point of said scapula;

a second contact element for positioning on the most inferior point of said scapula; a third contact element for positioning on a part of said scapula on a central point of said glenoid cavity or on the base of the coracoid process; and

- a guide sleeve for guiding said guide pin

towards said central point of said glenoid cavity; and

in or parallel with the scapular plane defined by the most medial point of said scapula, the most inferior point of said scapula, and said central point of said glenoid cavity;

wherein said first contact element, second contact element, guide sleeve, and said third contact element are interconnected.

The surgical guiding instrument according to aspect 1 , wherein

said first contact element targets a first aiming point for positioning on the most medial point of said scapula;

- said second contact element targets a second aiming point for positioning on the most inferior point of said scapula;

and wherein said first aiming point, said second aiming point, and the longitudinal axis of said guide sleeve are arranged in a single plane.

The surgical guiding instrument according to aspect 1 or 2, wherein the distance between said first contact element and said second contact element is adjustable between 105 mm and 145 mm.

The surgical guiding instrument according to any one of aspects 1 to 3, wherein the position of said first contact element and said second contact element is adjustable within said single plane in at least one direction.

The surgical guiding instrument according to aspect 4, wherein the position of said third contact element is further adjustable in at least one direction parallel to said single plane. he surgical guiding instrument according to any one of aspects 1 to 5, comprising

- a third contact element targeting a third aiming point for positioning on the base of the coracoid process; and

- a fourth contact element targeting a fourth aiming point for positioning on said central point of said glenoid cavity.

The surgical guiding instrument according to any one of aspects 1 to 6, wherein said guide sleeve further allows for positioning said guide pin in an angle of between 15° and 25° with respect to the axis defined by said most medial point of said scapula and said central point of said glenoid cavity.

The surgical guiding instrument according to any one of aspects 1 to 7, comprising a first arm comprising said guide sleeve and said one or more contact points directed at either the base of the coracoid process, or and said central point of said glenoid cavity, or both; and

a second arm, slidably interconnected with said first arm, comprising said first contact element.

9. The surgical guiding instrument according to aspect 8, wherein either said first or said second arm comprises the second contact element.

10. The surgical guiding instrument according to aspect 8 or 9, wherein said guide sleeve is removably connected to said first arm.

1 1 . The surgical guiding instrument according to any one of aspects 1 to 10, further comprising a locking mechanism for locking the relative position of said first and second arm, said first, second, third and/or fourth contact element and/or said guide sleeve.

12. A method of positioning a guide pin in a glenoid cavity of a scapula, comprising:

(a) accessing said glenoid cavity;

(b) accessing at least a part the margo medialis of said scapula;

(c) accessing at least a part of the inferior angle of said scapula;

(d) identifying a central point of said glenoid cavity;

(e) identifying the coronal scapular plane, positioning the guiding instrument according to any one of aspects 1 to 1 1 on said scapula; and

(f) positioning a guide pin in said coronal scapular plane, or parallel with said plane.

13. The method according to aspect 12, wherein said central point of said glenoid cavity is the center of the inferior glenoid circle.

14. The method according to aspect 13, wherein said guide pin is positioned in said central point of the glenoid cavity, in an angle of between 15° and 25° with respect to the axis defined by said medial point and said central point.

15. The method according to aspect 14, wherein said guide pin is positioned in said central point of the glenoid cavity, along the axis defined by said medial point and said central point.

16. A glenoid guiding block (15) specific for the left or right shoulder (15d) can have specific sizes according to the patient anatomy, reflected by a non-limiting radius of about 7 to 17 mm, (15c). This guiding block (15) typically is comprised of a half disc shape of more than 150° or 1/3 ^rd of a full disk (15b) of a certain thickness, and holds a taper connection (15a) with a diameter suitable to receive a sleeve in which a K-wire (e.g. about 0,5mm) could be positioned. The guiding blocks (15) have a version of about 93,43° and an inclination of about 1 1 1 ,36°. These different guiding blocks can be connected to the surgical guiding device, or its guiding sleeve. BRIEF DESCRIPTION OF THE DRAWINGS

The drawings depicted herein are merely for illustrative purposes and are not to be seen as limiting the invention in any particular way. All scapulas shown in said figures are left-side scapulas, but the skilled person will appreciate that the device of the present invention is in no way to be seen as limited for left side scapulas and that all embodiments can be equally designed or adapted for right side scapulas without any problem if needed, without departing from the ideas disclosed and claimed herein. FIG. 1 Ventral view of a left scapula (1 ), depicting:

a) : the glenoid cavity (2) having a gravity point (8), the coracoid process (3), the medial border (4), the lateral border (5), the most medial point (Smed, 6), and the most inferior point (Sinf, 7).

b) : the scapular plane (10) defined by three points on the scapula: (6), (7), and (8). At the intersection of said plane with the scapular spinal axis (1 1 ), a perpendicular plane can be indicated (10').

c) : axis (12) formed by the rotational centre of the humeral head (13) and the center (8) of the glenoid cavity. Axis 12 forms an angle alpha with the spinal scapular axis (1 1 ).

FIG. 2 Ventro-lateral view of a left scapula (1 ), depicting the gravity point (8) of the glenoid cavity (2), a first aiming point located at or around the most medial point (Smed, 6), a second aiming point located at or around the most inferior point (Sinf, 7), a third aiming point (9) at the base of the coracoid process (3), the scapular plane (10) defined by three points on the scapula: (6), (7), and (8), the scapular spinal axis (1 1 ), the axis (12) forming an angle alpha with the spinal scapular axis (1 1 ), and the guiding sleeve (14), pointing towards the gravity point 8, in the scapular plane (10).

FIG. 3 Position of aiming points on the left scapula: a): third aiming point (9) in view of second (7) and fourth aiming point (8); b) and c): third aiming point (9) in view of first (6), second (7) and fourth aiming point (8);

FIG. 4 Calculation methods of gravity point (8, 8', 8", or 8"') of glenoid cavity (2). a): established by generating a line from the most superior point of the glenoid rim to the most inferior point of the glenoid rim ("Sailer's line"); b): established by the center of the circle defined by the most superior point of the glenoid and two points (one anterior point and one posterior point) at the lower third of the glenoid rim; c): established by the center of the "inferior glenoid circle", this is the circle defined by three points at the rim of the inferior two quadrants of the glenoid, more particularly one inferior, one anterior, and one posterior point; d) : alternatively a specific guiding block (15) can be placed at the rim of the glenoid (2) to centre the glenoid gravity point (8"'). Such a guiding block (15) is specific for the left or right shoulder (15d) and can have specific sizes according to the patient anatomy, reflected by a non-limiting and patient specific radius of about 7 to 17 mm, (15c). It typically is comprised of a half disc shape of more than 150° or 1/3 ^rd of a full disk (15b) of a certain thickness, and holds a taper connection (15a) with a diameter suitable to receive a K-wire (e.g. about 0,5mm), The thickness at the taper connection is typically larger than the thickness at the opposite edge of the radius, resulting in a correction of the axis of the K-wire, perpendicular to the plane of the guide block surface.

FIG. 5 Schematic view of two different embodiments (5a and 5b) of the surgical guiding instrument (20) having three contact elements (26, 27, and 29) respectively targeting three aiming points (6, 7, and 9). Said contact elements are interconnected by one or more arms (31 and 32), which can be adjusted in length, e.g. through sliding/locking mechanisms (30). The instrument carries a guiding sleeve (14), which is situated in the scapular plane (10) and forms an angle alpha with the spinal scapular axis (1 1 ).

FIG. 6 Schematic view of two different embodiments (6a and 6b) of the surgical guiding instrument (20) having three contact elements (26, 27, and 28) respectively targeting three aiming points (6, 7, and 8). Said contact elements are interconnected by one or more arms (31 and 32), which can be adjusted in length, e.g. through sliding/locking mechanisms (30). The instrument carries a guiding sleeve (14), which is situated in the scapular plane (10) and forms an angle alpha with the spinal scapular axis (1 1 ).

FIG. 7 Schematic view of two different embodiments (7a and 7b) of the surgical guiding instrument (20) having contact elements (26, 27, 28, and 29) respectively targeting four aiming points (6, 7, 8, and 9). Said contact elements are interconnected by one or more arms (31 and 32), which can be adjusted in length, e.g. through sliding/locking mechanisms (30). The instrument carries a guiding sleeve (14), which is situated in the scapular plane (10) and forms an angle alpha with the spinal scapular axis (1 1 ).

FIG. 8 describes the positioning of a glenoid implant (22) using the surgical instrument according to one of the embodiments of the invention, involving the positioning of a guide pin (21 ) along the glenoid axis, i.e. through the center of the glenoid cavity (8) and perpendicular to the articulating surface of the glenoid (2). Said guide pin is positioned correctly through the guide sleeve (14) of the instrument (20).

DETAILED DESCRIPTION OF THE INVENTION

While potentially serving as a guide for understanding, any reference signs in the claims shall not be construed as limiting the scope thereof. As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. The terms "comprising", "comprises" and "comprised of" when referring to recited components, elements or method steps also include embodiments which "consist of" said recited components, elements or method steps.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments described herein are capable of operation in other sequences than described or illustrated herein.

The values as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/-10% or less, preferably +/-5% or less, more preferably or less, and still more preferably +/-

0.1 % or less of and from the specified value, insofar such variations are appropriate to ensure one or more of the technical effects envisaged herein. It is to be understood that each value as used herein is itself also specifically, and preferably, disclosed.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.

All documents cited in the present specification are hereby incorporated by reference in their entirety.

Unless otherwise defined, all terms used in disclosing the concepts described herein, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present disclosure. The terms or definitions used herein are provided solely to aid in the understanding of the teachings provided herein.

The term "longitudinal" as used herein refers to objects having an aspect ratio (length divided by width) that is greater than 1 , or of at least 2, preferably at least 3, most preferably at least 4.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment envisaged herein. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are also envisaged herein, and form different embodiments, as would be understood by those in the art. For example, in the appended claims, any of the features of the claimed embodiments can be used in any combination.

Figure 1 a provides a ventral view of a human scapula (1 ). The scapula (1 ) includes a glenoid cavity (2) that forms a socket against which the head of the humerus (not shown) articulates. The glenoid cavity (2) is delimited by a glenoid rim and has a gravity point (8). The scapula further comprises a hook-like structure on the lateral edge of the superior anterior portion of the scapula, called the coracoid process (3), and serving to stabilize the shoulder joint. Fig. 1 further shows the medial border (4) and lateral border (5) of the scapula. The medial border is also known as "margo medialis" or "vertebral border".

Located on the medial border is the most medial point (Smed, 6) of the scapula, which is a first reference point for determining the position of the coronal plane of the scapula. The term "most medial point of the scapula" as used herein refers to the point on the medial border of the scapula which is positioned in line with the spina (scapular spine, not shown). A second reference point is the most inferior point (Sinf, 7) of the scapula. As used herein, the term "most inferior point of the scapula" refers to the point on the inferior angle of the scapula, between the medial border and the lateral border of the scapula. A third reference point is the gravity point or center (Cglen, 8) of the glenoid cavity (2). Methods for determining this center are explained further in this text.

Figure 1 b shows the plane defined by the three reference points (6, 7, 8), referred to as the "coronal plane of the scapula" or simply "scapular plane" (10). The straight line defined by the most medial point (6) of the scapula and the center (8) of the glenoid cavity is referred to as the "spinal scapular axis" (1 1 ) (SSA). Perpendicular to the scapular plane (10) intersecting with the latter at the SSA, is defined herein as plane (10').

In Figure 1 c, the positioning of the glenoid axis (12) formed by the rotational centre of the humeral head (13) and the center (8) of the glenoid cavity is shown vis a vis the spinal scapular axis (1 1 ). Axis 12 forms an angle alpha with the spinal scapular axis (1 1 ).

Studying the resulting forces of the different muscles attached to the scapula, the inventors discovered that the volume of the musculus subscapularis and combined volume of musculi infraspinatus and teres minor is balanced around the coronal plane of the scapula (scapular plane). This means that the scapular plane (10) is a very important landmark for establishing a guiding instrument enabling correct reconstruction of the glenoid surface and for determining its correct orientation and position versus the humeral head.

Based on this knowledge, a guiding instrument was designed with a guiding sleeve for positioning a guiding pin (e.g. a K-wire) into the centre of the glenoid, but within the scapular plane. Figure 2 e.g. shows the desired orientation and positioning of a guiding sleeve (14), which can be used to insert a surgical guiding pin or wire such as a K-wire used to correctly position the glenoid prosthesis or implant. Said guiding sleeve (14) is positioned in the scapular plane (10) and follows axis 12 (12), forming an angle alpha with the SSA (1 1 ).

As a third aiming point (9), a point at the basis of the coracoid process of the scapula, particularly the most lateral base thereof, is envisaged. As shown in Figure 3, said aiming point (9) is situated at a distance or offset X, Y, and Z with respect to the centre of the glenoid (8). Typically, X is within the range of plus/minus 7-8 mm, Y is within the range of plus/minus 2-3 mm, and Z is within the range of plus/minus 2.5-3 cm. Looking at the lateral view of the left scapula, X and Y values would be negative, while Z value would be positive, since the third aiming point would be located to the upper left op the glenoid centre, and slightly shifted to the back with respect to the plane of the glenoid cavity.

The offsets X, Y and Z can be indicated on the guiding instrument, so as to facilitate correct positioning of the guiding sleeve above the gravity point of the glenoid (8), without the need of actually having a contacting point towards said glenoid centre (8). The offsets can e.g. be indicated with color codes or other marked areas on the arm(s) connecting the aiming and/or contacting points and guiding sleeve.

In addition, the standard positions of the arms which are slidably connected to each other can also be indicated.

Provided herein is a surgical guiding instrument which may allow for establishing the position and orientation of the glenoid cavity during surgery, and may further allow for the positioning of a guide pin indicating this position and/or orientation. The guide pin may then be used for guiding the positioning of a glenoid implant, for example as described in patent applications US 2012/0239155 and WO 2012/129019, which are hereby incorporated by reference.

More particularly, the guiding instruments provided herein may allow for (intraoperatively) determining the scapular plane and the spinal scapular axis (SSA), which are clinically relevant for establishing the position and orientation of a glenoid implant. Indeed, although the shape of the scapula typically is highly variable and dependent on factors such as the gender and age of the patient, the angle between the SSA and the straight line through the center of the glenoid cavity and the center of rotation of the humerus is relatively uniform. The angle alpha typically lies within the range of between 10 to 30 degrees, preferably 15 to 25 degrees.

Accordingly, provided herein is a surgical guiding instrument (20) for positioning a guide pin in the glenoid cavity of a scapula, said guiding instrument comprising

- at least three contact elements (26 to 29) for positioning the guiding instrument on different parts of the scapula; and

a guide sleeve (14) for guiding a guide pin within the coronal plane (10) of the scapula (1 ) to a central point of the glenoid cavity (8).

This will be explained more in detail herein below.

The guiding instrument (20) described herein comprises a guide sleeve (14) for guiding a guide pin. In preferred embodiments, the guide pin is a Kirschner wire or K-wire. However, it is envisaged that in certain embodiments, the guide pin may be another longitudinal object suitable for indicating a direction and/or position, for example a screw.

The guide sleeve (14) typically provides an opening or (through) hole, hereinafter also referred to as "channel", permitting the passage of the guide pin. The channel typically is a longitudinal channel, having a straight central axis in the longitudinal direction, thereby providing a stable orientation of the guide pin in the sleeve. The transverse cross-section of the channel typically at least partially matches the transverse cross-section of the guide pin, such that the pin is guided through the channel along its longitudinal axis.

In particular embodiments, the guide sleeve (14) may be formed as a straight (longitudinal) hollow tube which is open at both ends, and preferably providing a cylindrical channel.

In certain embodiments, the guide sleeve (14) may provide a straight longitudinal slit, thereby allowing a lateral insertion and removal of the guide pin in and from the sleeve. This may be particularly useful for removing the guiding instrument from the scapula once the guide pin is in place.

In particular embodiments, the guiding instrument (20) described herein may comprise a plurality of guide sleeves. For example, the guiding instrument may comprise two or more guide sleeves for guiding a guide pin towards the same point, but in different directions parallel to or within the coronal plane. Accordingly, in certain embodiments, the guiding instrument comprises two, three or more non-parallel guide sleeves within the same plane, wherein the longitudinal axes of the guide sleeves intersect at a single point.

The guiding instrument (20) described herein further comprises a first contact element (26) for positioning on the margo medialis of a scapula. In particular embodiments, the first contact element is for positioning on a location (on the margo medialis) near the most medial point of the scapula (6), more particularly a location at a distance of at most 1 cm of the most medial point, more preferably at most 0.5 cm. Most preferably, the first contact element is for positioning on the most medial point of the scapula. The positioning of the first contact element on or near the most medial point of the scapula aids in establishing the position and orientation of the coronal plane of the scapula.

In addition to the first contact element, the guiding instrument (20) described herein comprises a second contact element (27) for positioning on the inferior angle of a scapula. In particular embodiments, the second contact element is for positioning on a location on the scapula on or near the most inferior point of the scapula (7), more particularly a location at a distance of at most 1 cm of the most inferior point, more preferably at most 0.5 cm. Most preferably, the second contact element is for positioning on the most inferior point of the scapula. The positioning of the second contact element on or near the most inferior point of the scapula aids in establishing the position and orientation of the coronal plane of the scapula.

Additionally, the guiding instrument (20) described herein comprises an additional contact element (28 or 29) for positioning on a part of the scapula on or near the glenoid cavity. Said contact element provides additional stability to the guiding instrument when positioned on the scapula. In particular embodiments, said contact element is called the third contact element, and suits for positioning on a part of the scapula surrounding the glenoid cavity. A preferred part is the coracoid process, particularly the most lateral base thereof (9). An exemplary location on the coracoid process base for positioning the third contact element is indicated in Fig. 3a and 3b. This base of the coracoid process is easily accessible and provides a contact surface which can be reached over various angles, making it ideal for providing additional stability. Alternatively, the guiding instrument (20) described herein may comprise a fourth contact element (28) for positioning on a central point of the glenoid cavity, preferably the center of the glenoid cavity (8). Although this contact element is referred to hereinafter as "fourth contact element", it is noted that the presence of this fourth contact element on the guiding instrument is independent of the presence of a third contact element as described above. In other words, the fourth contact point can replace the third contact point, or can complement it.

The contact elements (26 through 29) described above may independently comprise a contact surface for positioning on the aiming points on the scapula; and/or a tip for contacting the scapula hereinafter also referred to as the "aiming point". A contacting point may be formed as a pin-like structure which can be used for contacting and indicating a specific location on the scapula in its respective aiming point. A contact surface typically provides a larger area for contacting the scapula compared to a contacting point. When positioned on the scapula, the contact surface may contact the scapula via the entire contact surface, or via a part thereof. In particular embodiments, the shape of a contact surface may be adapted to the shape of the part of the scapula onto which it is to be positioned. The contact surface may be a standard surface adapted to fit most scapulas, or may be a patient-specific surface at least partially matching the surface of a scapula of a certain patient.

In particular embodiments, the first contact element (26) and second contact element (27) each comprise a contacting point. In further embodiments, the first contact element comprises a first contacting point for positioning (targeting, or aiming) on the most medial point of the scapula, whereas the second contact element comprises a second contacting point for positioning (targeting, or aiming) on the most inferior point of the scapula. In this way, the contacting points directly indicate the reference points for establishing the coronal plane of the scapula, thereby greatly facilitating determining the position of this plane.

In certain embodiments, the third contact element (28) comprises a third contacting point for positioning on the coracoid process of said scapula. Although this contacting point is referred to herein as "third contacting point", it is noted that the presence of this third contact element is independent of the presence of a first and/or second contacting point as described above. In particular embodiments, the fourth contact element (29) comprises a contacting point for positioning (targeting, or aiming) on the center of the glenoid cavity. Although this contacting point is referred to herein as "fourth contacting point", it is noted that the presence of this fourth contact element is independent of the presence of a first, second, and/or third contacting point as described above.

In the guiding instrument (20) described herein, the contact elements (26 through 29) and the guide sleeve (14) described above are directly or indirectly interconnected. More particularly, the contact elements and guide sleeve may be connected through one or more structures or arms (31 and 32) which allow for bridging the gap between the contact elements when positioned on the scapula. Thus, these structures are typically such that they allow for bridging the scapula. Said arms can be bridging the scapula ventrally or dorsally, depending on the surgical strategy. In Figure 8 for example, the situation is exemplified in which one of the arms (31 ) bridges the depicted scapula on the dorsal side (interrupted lines), when using the beach-chair or lateral decubitus position.

In preferred embodiments, the guiding instrument (20) described herein is an extracorporeal guiding instrument. Accordingly, the structure(s) interconnecting the contact elements and guide sleeve preferably allow for bridging the dorsal surface of the scapula, while these structures are positioned outside the patient's body.

In particular embodiments, the guiding instrument (20) described herein comprises two or more arms (31 and 32), to which the contact elements and guide sleeve(s) are directly or indirectly connected. The arms may comprise straight, curved, and/or angled portions. More specific configurations of arms, contact elements and guide sleeve(s) are discussed further in this text. Said arm(s) (31 and 32) typically can be adjusted to position the contacting points to their desired locations on the scapula. Said adjustment however needs to be done in such a way that the guiding sleeve (14) stays in the scapular plane (10) and maintains the desired angle alpha versus the SSA (1 1 ). For this, the standard positions can be indicated on the arms through e.g. a color or other marked area, such that the device can be correctly assembled. Such so-called offsets are well known in the art and often used for correct surgical instrument assembly. Typically, the arms need to be positioned within a certain standard offset, which is e.g. indicated or marked in green for easy recognition by the physician. Other colors or types of marking, such as symbols, ribbons, slight recesses on or in the arms can equally be used for correct positioning. This will give the physician a good indication of standard assembly, yet retaining some flexibility to adjust the guiding instrument according to the specific anatomy of the patient being treated.

In certain embodiments, the guide sleeve (14) is removably connected to the rest of the guiding instrument (20). For example, the guide sleeve may be removably connected to an arm (31 or 32) as described above. A removably connected guide sleeve may facilitate removing the guiding instrument from the scapula after positioning of the pin. The guiding instrument may further comprise two or more interchangeable guide sleeves, adapted for guiding different guide pins. In this way, the surgeon can choose among different types of guide pins the one most suitable for the surgery.

In certain embodiments, one or more of the contact elements may be removably connected to the rest of the guiding instrument. For example, one or more contact elements (26 through 29) may be removably connected to an arm (31 or 32) as described above. The guiding instrument may further comprise two or more interchangeable contact elements, for example adapted for positioning on specific locations on the scapula. Accordingly, the surgeon may choose among different types of contact elements the one most suitable for the surgery.

The guide sleeve (14) may be used for positioning a guide pin towards a central point of the glenoid cavity such as the glenoid cavity center, in a direction in or parallel with the scapular plane of the scapula, preferably within the scapular plane (10). This typically implies that the guide sleeve and contact elements are of can be configured in a certain relative position. More particularly, the distance between the first contact element (26) and second contact element (27), or the distance between the first contacting point (6) and the second contacting point (7), typically ranges between 7 and 15 cm. In particular embodiments, the distance between the first contact element (contacting point) and the second contact element (contacting point) is adjustable at least between 105 mm and 145 mm, preferably at least between 100 mm and 150 mm, most preferably at least between 90 mm and 160 mm. Such range is considered suitable for most patients. As described above, the first and second contact elements may respectively comprise a first and second contacting point. In such embodiments, the first contacting point (6), the second contacting point (7), and the (longitudinal axis of the) guide sleeve (12) are typically arranged in a single plane. If provided, the fourth contacting point (8) is typically arranged in the same plane. In such a configuration, this plane corresponds to the scapular plane (10) of the scapula if:

- the first contacting point is positioned on the most medial point of the scapula;

- the second contacting point is positioned on the most inferior point of the scapula; and - the guide sleeve points towards the center of the glenoid cavity.

Accordingly, this configuration allows for a direct and accurate intraoperative determination of the scapular plane of the scapula, and ensures that the guide pin can be reliably positioned in the scapular plane.

Similarly, in particular embodiments, the (longitudinal axis of the) guide sleeve and at least a part of the first and second contact element intended for contacting the scapula are arranged in a single plane. However, this is not always required. For example, if the first contact element and/or the second contact element is not intended for positioning on a part of the scapula within the coronal plane, then these contact elements and the (longitudinal axis of the) guide sleeve may not arranged in a single plane.

In preferred embodiments, the guiding instrument described herein is a standard (i.e. not patient-specific) instrument. Accordingly, the relative position of the contact elements and the guide sleeve(s) preferably is adjustable, to allow for adjusting the relative position of the contact elements and the guide sleeve to a particular scapula. The offsets as defined herein can help in standard assembly of the device.

In preferred embodiments, the relative position of the contact elements and the guide sleeve(s) is (only) adjustable in one or more directions within or parallel with a single plane, more particularly the scapular plane. A restriction of the movement of the contact elements and guide sleeve(s) to directions parallel or within the scapular plane ensures that the orientation of the guide sleeve relative to the scapular plane is not affected by changing the relative positions of the guide sleeve and the contact elements.

Thus, in particular embodiments, the position of each of the first and second contact element relative to the guide sleeve is independently adjustable (only) in one or more directions in a single plane, more particularly the scapular plane (when the guiding instrument is positioned on the scapula). In further embodiments, the position of each of the first and second contact element relative to the guide sleeve is independently adjustable (only) in one or more directions in the plane defined by the first contacting point, second contacting point, and the (longitudinal axis of the) guide sleeve. However, it is envisaged that in specific embodiments, the relative position of the contact elements and guide sleeve are (also) adjustable in other directions.

The adjustability of the relative positions may be obtained in various ways. In particular embodiments, the contact elements and the guide sleeve(s) are slidably interconnected.

For example, the guiding instrument may have two or more slidably interconnected arms to which the contact elements and guide sleeve(s) are connected. More particularly, in certain embodiments, the guiding instrument comprises:

a first arm (31 ) comprising said guide sleeve and one or more contacting points (28, 29) directed at either the third (9) or fourth aiming point (8), or both; and

a second arm (32), slidably interconnected with said first arm (31 ), comprising said first contact element (26) directed to the first aiming point (6).

In particular embodiments, the first arm may be extendible, thereby allowing for adjusting the relative position of the first contact element and the guide sleeve. Preferably, the first arm is (only) extendable along the SSA, or in a direction parallel to the SSA. The extendible arm may comprise a telescopic system, a rail system, etc.

In certain embodiments, the first arm may further be provided with the third contact element and/or fourth contact element. However, it is also envisaged that in certain embodiments, the third and/or fourth contact may not be provided on the first arm.

In particular embodiments, the slidable connection between the first and second arm may be provided through a rail system. For example, one arm may comprise a sleeve through which a (part of) the second arm can move. Also other systems for obtaining a slidable connection may be used. As the third contact element (29) mainly serves to stabilize the position of the guiding instrument, the movement of this contact element does not directly affect the determination of the scapular plane. Accordingly, in particular embodiments, the position of the third contact element (if provided) can be adjusted in multiple directions, parallel and/or non-parallel with the coronal plane. In particular embodiments, the third contact element is interconnected to the rest of the guide instrument via one or more systems selected from a hinge, a rail, and a telescopic system. Again, offsets can be present on said arm(s).

In particular embodiments, the guiding instrument may comprise one or more locking mechanisms, for locking the relative position of said arms, said first contact element, said second contact element, said third contact element and/or said guide sleeve. Any type of locking mechanism known in the art is envisaged. Non-limiting examples can be screws, clips, clamps, springs, etc..

As described above, the guide sleeve (14) may allow for positioning a guide pin (21 ) within the coronal plane of the scapula. Depending on the envisaged surgery, a specific orientation of the guide pin within this plane may be envisaged. More particularly, it may be desired to position the guide pin in a specific angle with respect to the SSA (1 1 ).

For example, international patent application WO 2012/129021 describes the positioning of a glenoid implant (22), involving the positioning of a guide pin (21 ) along the glenoid axis, i.e. through the center of the glenoid cavity (8) and perpendicular to the articulating surface of the glenoid (2). In particular embodiments, the guiding instrument described herein may be adapted for positioning a guide pin along the glenoid axis (12), which is formed by the rotation centre (13) of the humeral head and the gravity point (8) of the glenoid. Figure 8 depicts how an exemplary surgical instrument according to the present invention could be positioned on the scapula to guide the guiding pin or wire and glenoid implant to its correct position.

Indeed, the inventors have found that the glenoid axis typically is located (almost) within the coronal plane of the scapula, wherein the angle (a) between the glenoid axis and the SSA generally is between 10 and 30 degrees, more preferably between 10 and 30 degrees, preferably between 15 and 25 degrees. More particularly, based on measurements of the scapula of 26 patients, an average angle (alpha; a) of 16.56 degrees was found, with a standard deviation of 3.46 degrees. Although obtained from a relatively small patient population, these results suggest that if the guide pin can be reliably positioned in an angle of about 14 to 19 degrees, preferably about 15 to 18 degrees, more preferably between about 16 to 17, preferably about 16.5 to 17 degrees relative to the SSA, the guide pin will on average be positioned along the glenoid axis, with a standard deviation of about 3.5 degrees. At present, better results may only be obtained using certain patient-specific instruments, which are significantly more expensive. Even better results may be obtained once more statistical information is available. For instance, different average angles (a) may be determined for specific subsets of patients (e.g. according to gender, age, symptoms, ...), thereby on average reducing the angular difference between the statistically determined average angle (a) and the actual angle (a) of the scapula.

Accordingly, the guiding instrument described herein may be adapted for positioning of a guide pin along the SSA, or in a specific angle relative to the SSA. In specific embodiments, the guide sleeve further allows for positioning said guide pin in an angle of between 15° and 25° with respect to the axis defined by Smed and Cglen.

In particular embodiments, the position of the guide sleeve is fixed to a specific angular position relative to the SSA. Alternatively, the position of the guide sleeve may be adjustable (within the coronal scapular plane) in a certain angular range relative to the SSA, preferably between 10° and 30°, more preferably between 15° and 25° with respect to the SSA. The guiding instrument may further be provided with a goniometer for determining the angle between the (longitudinal axis of the) guide sleeve and the SSA.

As described above, the guide sleeve is typically directed towards the center of the glenoid cavity. In particular embodiments, the guiding instrument described herein may comprise a fourth contact element (28) for positioning on a central point of the glenoid cavity (e.g. the gravity point (8)), wherein the (longitudinal axis of the) guide sleeve is oriented towards the fourth contact element. This ensures that the guide pin is automatically directed towards the center of the glenoid cavity whenever the contact element is positioned thereon.

In particular embodiments, the fourth contact element is provided on a distal end of the guide sleeve. In this way, it can be ensured that the guide sleeve is always oriented towards the fourth contact element, regardless of the position of the guide sleeve. However, it is also envisaged that in certain embodiments, the fourth contact element may be provided on a dedicated contact element.

In as described above, the guiding instruments described herein are typically standard instruments. In these embodiments, the adjustable relative position of the contact elements may allow for adjusting the instrument to any scapula. In particular embodiments, the guiding instrument may be a standard instrument designed for a specific subset of patients, such as male patients, female patients. The offsets can hence be adapted according to gender or age.

However, it is envisaged, that in particular embodiments, the guiding instruments may comprise patient-specific features. For example, one or more contact elements may comprise a patient-specific anatomy engagement surface which matches at least a part of the anatomy of the patient. Typically, such patient-specific surfaces are designed based on 3D information of the patient anatomy, obtained via medical imaging. In particular embodiments, the guiding instruments comprise one or more patient-specific elements, which are removably connectable to one or more (reusable) standard elements comprised by the instrument.

In particular embodiments, the guiding instrument may be dedicated for positioning on either a left scapula or a right scapula. Accordingly, further provided herein is a kit comprising two or more guiding instruments as described herein, wherein at least one guiding instrument is for positioning on a left scapula, and at least one guiding instrument is for positioning on a right scapula. The guiding instrument for positioning on a left scapula may essentially be the mirror image of a guiding instrument for positioning on a right scapula. Further provided herein is a method of positioning a guide pin and/or implant in a glenoid cavity of a scapula. As described above, the guide pin may be used for guiding the positioning of a glenoid implant. The method described herein comprises the steps of:

(a) accessing said glenoid cavity;

(b) accessing at least a part the margo medialis of said scapula;

(c) accessing at least a part of the inferior angle of said scapula;

(d) identifying a central point of said glenoid cavity;

(e) identifying the coronal scapular plane, positioning the surgical guiding instrument according to the invention on the scapula; and

(f) positioning a guide pin in said coronal scapular plane, or parallel with said plane.

The method needs not necessarily be performed in the above order. In particular, steps (a) to (c) may be performed in any order. Furthermore, steps (a) to (d) can be performed in any order, with the proviso that step (d) is not performed before step (a).

In step (a) of the method described herein, the glenoid cavity of a patient's scapula is accessed, in accordance with a desired surgical approach as known in the art.

In steps (b) and (c), at least a part of respectively the margo medialis and the inferior angle of the scapula are accessed. In particular embodiments, this may be performed through a deltopectoral approach. In preferred embodiments, step (b) includes accessing the most medial point of the scapula, and step (c) includes accessing the most inferior point of the scapula. These points are most relevant for establishing the coronal plane of the scapula. Moreover, these points are typically palpable through the patient's skin and therefore easy to locate. Accordingly, steps (b) and (c) typically require only minor incisions.

In step (d) of the method described herein, a central point of the glenoid cavity is identified. The central point may be determined by any method known in the art. The point identified by any of these methods may be regarded as the "center" of the glenoid cavity.

A number of methods for identifying the center of the glenoid cavity are known, as described by Verstraeten et al. (Verstraeten et al., Determination of a reference system for the three- dimensional study of the glenohumeral relationship, Skeletal Radiol. 2013, DOI 10.1007/s00256-013-1572-0; hereby incorporated by reference). Some of these methods have also been described in patent application US 2012/0239155, which is hereby incorporated by reference.

In particular embodiments, the geometric center (8) of the glenoid may be established by generating a line from the most superior point of the glenoid rim to the most inferior point of the glenoid rim ("Sailer's line"), as illustrated in Fig. 4A. As used herein, the terms anterior, posterior, superior, and inferior, unless otherwise specifically described, are used with respect to the orientation of the scapula 1 as depicted in FIG. 3a. A second line is generated between the most posterior point of the glenoid rim and the most anterior point of the glenoid rim. The intersection of the two generated lines is considered to be the geometric center of the area circumscribed by the glenoid rim.

In certain embodiments, the central point (8') of the glenoid is the center of the circle defined by the most superior point of the glenoid and two points (one anterior point and one posterior point) at the lower third of the glenoid rim, as shown in Fig. 4B.

In particular embodiments, the central point of the glenoid (8") is the center of the "inferior glenoid circle", this is the circle defined by three points at the rim of the inferior two quadrants of the glenoid, more particularly one inferior, one anterior, and one posterior point, as shown in Fig. 4C. As the inferior part of the glenoid rim is quasi-circular, any inferior, anterior, and posterior point on this part of the rim may be selected.

In yet an alternative embodiment, a specific guiding block (15) can be placed at the rim of the glenoid (2) to centre the glenoid gravity point (8"'). Such a guiding block (15) is specific for the left or right shoulder (15d) and can have specific sizes according to the patient anatomy, reflected by a non-limiting radius of about 7 to 17 mm, (15c). This guiding block (15) typically is comprised of a half disc shape of more than 150° or 1/3 ^rd of a full disk (15b) of a certain thickness, and holds a taper connection (15a) with a diameter suitable to receive a sleeve in which a K-wire (e.g. about 0,5mm) could be positioned. The thickness at the taper connection is typically larger than the thickness at the opposite edge of the radius, resulting in a correction of the axis of the K-wire, which is typically perpendicular to the plane of the guide block surface. The guiding blocks (15) have a version of about 93,43° and an inclination of about 1 1 1 ,36° according to previous 3D CT anatomical studies, and are left and right specific. The guiding blocks (15) are designed in such a manner that they fit the inferior two quadrants of the glenoid (2) when placed on the anterior quadrant of the inferior glenoid (cf. Figure 4C and D). The guiding blocks are designed to cover 150° of the circle on the inferior glenoid (Figure 4D). This is because a more extensively guiding block touches the more superior part of the glenoid and conflicts with a steady placement on the inferior glenoid. The size is chosen according to the size of the anterior quadrant of the inferior glenoid. These different guiding blocks can be connected to the surgical aiming device guiding sleeve.

In step (e) of the method described herein, the coronal scapular plane of the scapula is identified. Typically, this involves identifying the center of the glenoid cavity, the most medial point of the scapula, and the most inferior point of the scapula.

In preferred embodiments, step (e) involves positioning a surgical guide as described on the margo medialis and the inferior angle via its first contact element and second contact element. Then, the guide sleeve may be positioned such that it points in the direction of the center of the glenoid cavity. Once this is obtained, the coronal plane is established, such that the guide pin can be positioned. Typically, the guiding sleeve will function as a guide for reaming or drilling a hole in the glenoid cavity for introducing a guide pin such as e.g. a K- wire.

In step (f) of the method described herein, a guide pin is positioned in the glenoid cavity. If step (e) involves the positioning on the scapula of a surgical guide as described herein, then the guide pin preferably is positioned using the guide sleeve of said guiding instrument.

The pin typically is positioned within or parallel to the coronal scapular plane. Preferably, the pin is positioned within the coronal scapular plane and in the center of the glenoid cavity. In further preferred embodiments, the guide pin is positioned in said central point of the glenoid cavity, in an angle of between 15° and 25° with respect to the SSA.

After correct positioning of the guiding pin, the guiding instrument can be removed in order to facilitate reconstruction of the glenoid cavity through e.g. reaming the glenoid surface and subsequent fixation of a prosthesis (22).

The guiding instruments described herein may also be used as a surgical spreader or for supporting of a surgical spreader. Spreaders are typically used to improve the view and access to the scapula, as is known by the skilled person. Indeed, through the support on three reference points on the scapula as described above, the guiding instruments provide a frame which is sufficiently stable to spread soft tissues (muscle tissue, tendons, fat tissue, and skin) using appendages designed thereto, to increase the view on the scapula, and in particular the glenoid cavity. Accordingly, in particular embodiments, the guiding instruments as described herein may be provided with one or more appendages for spreading soft tissue which surrounds the scapula. Such appendages may comprise one or more hooks. In particular embodiments, one or more appendages may be u-shaped.

The use of a guiding instrument as described herein as a spreader or for supporting a spreader can provide the advantage that it still allows movement of the scapula. This may reduce the stress at the surrounding soft tissues while improving the accessibility of the glenoid. Conventional spreaders typically are mounted to the operation table, thereby fix the scapula.

The guiding instrument and method described herein will now be illustrated by the following, non-limiting illustrations of particular embodiments. EXAMPLES

Example 1 : Guiding instruments according to present invention targeting aiming points 6, 7, and 9.

Figure 5a shows a schematic illustration of a surgical guiding instrument (20) according to a particular embodiment of the present invention, having three contact elements (26, 27, and 29) respectively targeting three aiming points (6, 7, and 9). Said contact elements are interconnected by one or more arms (31 and 32), which can be adjusted in length, e.g. through sliding/locking mechanisms (30). The instrument carries a guiding sleeve (14), which is situated in the scapular plane (10) and forms an angle alpha with the spinal scapular axis (1 1 ).

Figure 5b shows a schematic illustration of a guiding instrument according to another particular embodiment of the present invention. The guiding instrument (20) can be positioned on a scapula (1 ) via three contact elements, as shown in Fig. 5b. More particularly, a first contact element (26) comprises a first contacting point (6) for positioning on the most medial aiming point (6) of the scapula. A second contact element (27) comprises a second contacting point (7) for positioning on the most inferior aiming point (7) of the scapula. A third contact element (29) comprises a third contacting point (9) for positioning of the most lateral aiming point of the basis of the coracoid process (3) of the scapula.

Example 2: Guiding instruments according to present invention targeting aiming points 6, 7, and 8.

Alternatively, said surgical guiding instrument (20) has three contact elements (26, 27, and 28) respectively targeting three aiming points (6, 7, and 8). Said contact elements are interconnected by one or more arms (31 and 32), which can be adjusted in length, e.g. through sliding/locking mechanisms (30). Said arms can connect the contact elements and guiding sleeve(s) in different ways as is exemplified in Figures 6a and b. The instrument carries a guiding sleeve (14), which is situated in the scapular plane (10) and forms an angle alpha with the spinal scapular axis (1 1 ).

Example 3: Guiding instruments according to present invention targeting four aiming points 6, 7, 8, and 9.

Another exemplary surgical guiding instrument is represented schematically by Figure 7. Figure 7 shows two possible guiding instruments (20), having contact elements (26, 27, 28, and 29) respectively targeting four aiming points (6, 7, 8, and 9). Said contact elements are interconnected by one or more arms (31 and 32), which can be adjusted in length, e.g. through sliding/locking mechanisms (30). Said arms can connect the contact elements and guiding sleeve(s) in different ways as is exemplified in Figures 7a and b. The instrument carries a guiding sleeve (14), which is situated in the scapular plane (10) and forms an angle alpha with the spinal scapular axis (1 1 ).

Example 4: Positioning of the surgical guiding instrument on the scapula during use.

In use, the surgical guiding instrument as defined herein is placed on the scapula as depicted in Figure 8. In said figure, the guiding instrument of Figure 5a is depicted, but all other embodiments can of course be put in use in a similar manner. In essence, the guiding instrument (20) is correctly positioned on the scapula (1 ) by targeting the different contact elements (in this case 26, 27, and 29) to their respective aiming points (in this case (6, 7, and 9) on the scapula. Said aiming points (especially aiming points 6 and 7) may have been made accessible by making small incisions through the subject's skin. Doing this, the guiding sleeve (14) is positioned correctly into the scapular plane (10) and can be adjusted in said plane to correctly target the gravity point of the glenoid cavity as defined above (8). Typically, an angle alpha is formed between the axis (12) of the guiding sleeve and the SSA (1 1 ) Next, a K-wire (21 ) or similar guiding pin can be introduced in the correct plane, e.g. to facilitate the reaming procedure in order to allow for correct placement of the implant or prosthesis (22) and subsequent reconstruction of the glenoid cavity.

Example 5: Scapula measurements.

Three-dimensional CT reconstruction studies were performed to determine position of the glenoid plane relative to other landmarks of the scapula. 5.1 Specimen preparation

38 paired shoulders and 6 single shoulders were harvested from 25 fresh-frozen human cadavers (ages ranging from 63 to 98 years). The cadavers were stored at -20 °C and thawed before dissection. Each shoulder was dissected to expose the shoulder joint. The deltoid muscle was removed and the integrity of the rotator cuff muscles, tendons, and long head of biceps were noted. The glenohumeral joints were disarticulated, the cartilage of the humeral head and glenoid were evaluated for traumatic or degenerative changes. No clinical information was available of these specimens. Twenty-four cadaveric shoulders with an intact cuff and intact glenohumeral joint were selected for the study (Table 1 ). The humeral head and rotator cuff were removed. The glenoid was denuded from all cartilage and the remaining soft tissues were removed from the glenoid neck, coracoid process and base, and the acromion. 5.2 Morphologic measurements

Measurements of the superoinferior and the (widest) anteroposterior diameter of the bony glenoid were done with sliding calipers, precise up to 0.1 mm. With an architect's device, the best fitting circle was defined on the denuded inferior glenoid rim and the diameter was determined, as described by De Wilde et al. (Karelse A, Kegels L, De Wilde L, Clin. Anat. 2007, 20, 392). The center of this circle was marked with a pin point. Each scapula was fixated in a custom-made holder held on 3 points defining the coronal scapular plane; the Clc, Sinf and Smed. A custom-made device was used for measuring the distance of various landmarks with respect to Clc; more particularly the tuberculum superius, the coracoid base, the lateral tip of the coracoid, the base of the acromion accessible straight next to the posterior glenoid rim, and the lateral tip of the acromion. The distance was measured in a plane parallel and a plane perpendicular to the coronal scapular plane as shown in Fig. 1 b. All measurements were taken with the scapula fixed in the coronal scapular plane.

For the inferior, lateral and medial point of the inferior circle the distance in the parallel plane was measured. From these measurements the inclination and version of the glenoid were calculated according to the method described by Churchill et al. (Churchill RS, Brems JJ, Kotschic H, J. Shoulder Elbow Surg. 2001 , 10, 327) and Kwon et al. (Kwon YW, Powell KA, Yum JK, Brems JJ, lannotti JP, J. Shoulder Elbow Surg. 2005, 14, 85).

From each of the scapulae different morphologic measurements were obtained:

glenoid radius (Inferior circle);

distance between the most anterior to the most posterior point on the glenoid (AP);

distance between the most superior and the most inferior point on the glenoid (SI);

distance between the center of the inferior glenoid circle and Smed (Cic-Smed);

- distance from Cic to Sinf (Cic-Sinf);

distance from Smed to Sinf (Smed-Sinf);

distance from the center of the inferior circle (Cic) to the supraglenoid tubercle (Tub Sup; insertion of the long head of biceps); and angle from Cic to Tub Sup; and depth from Cic to Tub Sup;

- distance of the center of the inferior circle (Cic) to the coracoid base, angle of Cic to the coracoid base, and depth of Cic to the coracoid base;

distance from Cic to the lateral tip of the coracoid (coracoid tip), angle from Cic to the coracoid tip, and depth from Cic to the coracoid tip; and

distance from Cic to the base of the spina scapula accessible from lateral (spina), angle from Cic to spina, and depth from Cic to spina. 5.3 Results

The results of the measurements are summarized in Table 2. The results indicate that the glenoid plane is not influenced by the position of the scapula and the measurements indicate that in particular the inferior glenoid plane has a low variability with respect to the coronal scapular plane. An accurate identification of the glenoid plane in case of glenoid erosion is essential for correct placement of a glenoid component. The guiding instruments described herein can allow for such identification, by indicating the direction perpendicular to the glenoid plane. The guiding instruments are designed to be positioned on landmarks of the scapula which are surgically accessible and provide a low variability with respect to the glenoid plane, thereby allowing for a reliable identification of the glenoid plane without the need of patient-specific instruments.

Table 1 - Summary of cadavers used in the study

Age Left (L) or Right Male (M) or female

Cadaver number

(years) (R) scapula (F)

2 87 L M

2 87 R M

4 77 L M

4 77 R M

9 90 L M

9 90 R M

10 70 L M

10 70 R M

12 87 L M

12 87 R M

14 73 L M

14 73 R M

15 87 L M

15 87 R M

18 63 L M

18 63 R M

16 94 L F

16 94 R F

17 84 L F

17 84 R F

22 69 L F

22 69 R F

26 71 L F

26 71 R F Table 2 - Summary of measurements on scapula

Distance Radius

Distance (mm)

Cadaver (mm) (mm)

number Inferior Cic- Smed-

SI AP Cic-Sinf

circle Smed Sinf

2 39 29 14 109 152 124

2 40 31 14 108 151 127

4 37 29 14 108 156 133

4 40 31 15 107 159 141

9 44 34 17 123 155 143

9 44 33 16 122 155 146

10 43 37 14 1 19 155 138

10 44 32 16 1 14 155 137

12 36 29 15 1 10 142 125

12 36 28 14 1 10 141 123

14 38 29 14 109 163 141

14 41 31 15 108 160 141

15 40 33 16 102 149 141

15 40 31 15 103 148 138

18 41 33 16 106 159 139

18 44 32 16 102 163 137

16 39 28 13 96 132 123

16 35 25 1 1 95 131 120

17 36 26 13 101 131 1 16

17 37 25 12 102 136 1 14

22 33 25 12 103 132 102

22 34 28 14 103 133 108

26 37 27 13 102 134 1 10

26 38 28 14 101 136 1 13

Average 39,0 29,8 14,3 106,8 147,0 128,3

Standard

3,3 3,1 1 ,5 7,2 1 1 ,4 12,9 deviation Table 2 (Continued) - Summary of measurements on scapula

Position of Cic relative to Position of Cic relative to

Cadaver Tub Sup Coracoid base number length angle length angle

depth depth (mm) (°) (mm) (°)

2 22,5 18 -2 31 24 3

2 24,5 -14 0 33,5 29 6

4 23,5 -5 -8 29,5 16 -3

4 25,5 9 -6 31 ,5 23 -2

9 27,5 -8 -5 34,5 7 -3

9 27,5 4 -4 30,5 16 -3

10 28,5 3 -3 33,5 18 2

10 28,5 -2 -3 34,5 20 1

12 21 ,5 -4 -2 28,5 26 3

12 23,5 2 -3 28,5 19 1

14 26,5 -15 -5 31 ,5 24 1

14 27,5 18 -5 32,5 17 1

15 25,5 -6 -8 32,5 24 1

15 25,5 7 -1 32,5 19 5

18 23,5 -27 -6 32,5 37 -8

18 23,5 26 -8 32,5 33 -6

16 22,5 -12 -6 29,5 37 0

16 21 ,5 22 -4 29,5 36 2

17 19,5 -4 -2 30,5 38 3

17 25,5 13 -4 28,5 28 4

22 21 ,5 -8 -6 26,5 17 -3

22 21 ,5 4 -6 26,5 18 -1

26 24,5 -20 -6 29,5 41 -1

26 21 ,5 16 -6 29,5 40 -1

Average 24,3 0,7 -4,5 30,8 25,3 0,1

Standard

2,5 13,7 2,2 2,3 9,2 3,4 deviation Table 2 (Continued) - Summary of measurements on scapula

Position of Cic relative to Position of Cic relative to

Cadaver Coracoid tip Spina number length angle length angle

depth depth (mm) (°) (mm) (°)

2 40,5 49 -1 1 18,5 65 16

2 43,5 53 -10 18,5 62 16

4 37,5 48 -22 20,5 45 14

4 40,5 51 -23 19,5 46 13

9 39,5 46 -23 19,5 59 16

9 43,5 54 -24 22,5 56 16

10 44,5 46 -21 24,5 48 19

10 42,5 49 -25 22,5 52 17

12 41 ,5 54 -17 20,5 44 18

12 40,5 51 -19 21 ,5 46 14

14 40,5 56 -17 18,5 48 15

14 43,5 53 -14 17,5 61 14

15 40,5 56 20 20,5 50 14

15 40,5 56 -12 22,5 59 12

18 41 ,5 65 -22 21 ,5 52 12

18 38,5 64 -20 20,5 55 1 1

16 39,5 53 -18 14,5 30 14

16 37,5 58 -12 18,5 56 13

17 38,5 46 -15 17,5 56 17

17 43,5 44 -1 1 17,5 50 17

22 40,5 45 -18 12,5 58 17

22 39,5 41 -17 17,5 67 15

26 40,5 63 -15 17,5 38 16

26 43,5 60 -13 19,5 58 14

Average 40,8 52,2 -15,9 19,3 52,3 15,0

Standard

2,0 6,4 9,0 2,7 8,7 2,1 deviation