Instruments for carrying out an operating procedure on a joint

The invention concerns instruments for carrying out an operating procedure on the joint of a patient, in particular a finger joint. In addition the invention concerns an operating method of replacing a joint of a patient, in particular a fin- ger joint, preferably a finger middle joint.

In any gripping function by the hand the middle joint (the PIP joint) of the finger implements almost the greatest and most important part of the bending power of the finger and is therefore indispensable in its ability to operate for the es- sential forms of gripping action by the hand (gripping items forcibly, gripping large items, gripping keys gripping combs, gripping writing implements and so forth) . If the function of the PIP joint is reduced due to pain and/or a restriction on movement ultimately the overall function of the hand also suf- fers . Pain cannot be permanently treated with medication as medications loose their effectiveness and often cause undesired incompatibilities and have side-effects.

External immobilisation is extremely impracticable and uncomfortable in everyday life, and in addition the function of the finger is markedly impeded. That ultimately applies also to 'internal' immobilisation of the injured joint, which immobilisation was and still is implemented in the form of a functionally appropriate or individually desired position by means of what is referred to as arthrodesis of the PIP joint, that is to say bone fusion of the middle and base joint. Freedom from pain can in that way actually always be achieved, but the stiffening of the joint is actually not acceptable having regard to the

above-outlined enormous importance of the PIP joint in terms of the overall functioning of the hand. In that respect it is in principle to be considered that increasingly also and in particular older people are reliant on proper operability of their hands as many cannot manage for themselves and their own wish for independence and the necessity for independence are continually on the rise.

Many different endeavours have been made over many years to arrive at suitable solutions for joint replacement on the fingers. Hitherto however it has not yet been possible for any design to prove crucially successful as none adequately complies with all important target criteria.

Implants used at the present time suffer from certain disadvantages and do not meet the target criteria. On the one hand Swanson Silastic spacers are used, which in spite of the induction of foreign body granuloma, the risk of material fracture and guidance instability, often give astonishing results, in particular in relation to rheumatoid arthritis. Those movable spacers which actually do not repre- sent a joint have therefore certainly a firm place in relation to this indication. The limit of what is viable however is rapidly reached therewith, with a high level of substance loss and advanced destruction.

Present coupled 'genuine' joint implants such as for exam- pie the St. George endoprosthesis are inserted dorsally and cemented in place, but frequently exhibit loosening effects and often involve a poor function, which is to be attributed to the high tensile and frictional forces, for which reason that method is inadequate. Nowadays the idea of surface replacement with reconstruction of the utmost accuracy of the predetermined anatomy is favoured, and non-coupled implants in the form of the pyrocar- bon endoprosthesis and the moje ceramic implant are the leading representatives. As anatomically the middle joint is also not a pure hinge joint but involves a rotational-sliding movement, the endeavour is ultimately the most natural motion without

potentially harmful tensile and rotational forces. The previous operational observations and investigations however could not demonstrate that as a rule the endoprostheses involve bony integration, on the contrary they rather do not grow into place, and exhibit migration and bone extension phenomena which prevent a good functional result.

In addition those endoprostheses have to be fitted by a stretching apparatus, which precisely signifies injury to that enormously sensitive functional structure, with the conse- quences of limited early functionality, fibroses and deformations which possibly necessitate further interventions for releasing the joint, as well as shrinkage phenomena which sometimes result in stretching contraction. The attempt to implant the endoprosthesis by way of the flexural side is intended to represent an alternative, but here crucially sensitive tissue is also injured, which can limit the function due to healing effects .

The partially necessary removal of such joints then also impressively shows that, due to the respective prosthesis shank, bone substance has scarcely remained besides the cortical 'sheath' of the phalanges, a hollow tube which requires a great deal of sound bone substance for an arthrodesis which is then necessary.

The indications in respect of such implants arise out of the described facts: lack of early mobilisation mean that contracted, pre-operated joints with tendon deformation and adhesions appear inappropriate, and equally joint instabilities are not a suitable condition.

Long years of surgical activity on hands mean that the critical operator is always discontent with the fact that the motor functional structures on the fingers, the extension and flexing tendons in their complexity and the sensitivity linked thereto, in spite of the most careful treatment, always leave behind healing symptoms with the environment, which often cru- cially limit the finger function. Secondary tendon dissolutions are linked to extreme risks and can often leave behind results

which are equally poor as previously. If exercise is taken too early after a tendon suture the tissue possibly does not stick together but then there is a functional limitation due to suture insufficiency. It would be best for those structures not to be surgically treated at all if that does not have to be done .

In addition in the case of a disturbance to a finger function finger reconstruction by joint replacement should not be ruined by sound tissue being damaged in the course of the op- eration.

The object of the present invention is therefore that of providing instruments for the insertion of a finger joint prosthesis, and a treatment method which is capable of performing the flexing and elongation function of the joint, in particular the PIP joint, at best in the sound anatomically predetermined extent of movement and direction of movement so that the harmonic juxtaposition and co-operation of the fingers in regard to the gripping functions are not disturbed. The alloplastic joint must be anchored in the bone in such a way that it does not depart from its intended position and thus would again endanger the function involved. It should not further destroy the remaining bone (the phalanges do not afford here an excessively great resource) due to use of the joint and it should be stable in its functional form so that the finger can be sub- jected to load.

That object is attained by an instrument for carrying out an operating procedure on the joint of a patient, in particular on a finger joint, which includes at least the following components : - a fixing frame for fixing a finger n a straight position in the course of an operation for milling out a joint cylinder of the finger with a rigid structure for forming a receiving space for the finger and a drilling slide which is displaceable on the structure and which is fixable in any reference posi- tions and which has a positioning bar with a guide opening for relatively movably receiving a joint milling cutter or a cen-

tering sleeve and a plurality of positioning holes,

- a drilling slide with a positioning bar which extends in a longitudinal direction and which has a guide opening extending transversely through same and laterally of said guide open- ing positioning holes, and which is provided with means for guiding engagement into the fixing frame, as well as a spacer element which extends transversely with respect to the positioning bar and with which the positioning bar is fixable in various reference positions which can be selected as desired in relation to the fixing frame,

- a centering sleeve comprising a cylindrical main body adapted for insertion into the guide opening of the drilling slide which at one end has a peripherally extending shoulder and centrally has a receiving opening for an aiming wire, and - a rotary axis aiming device for exactly milling out the joint cylinder.

That instrument set makes it possible to achieve particularly accurate positioning and fixing of the joint for precisely carrying out the operating procedure. The rigid fixing frame serves in that case as a fixing means for precisely positioning the joint in the extended position.

The material of the endoprosthesis used is preferably biocompatible and 'low-wear ¹ so that the tissue is not subjected to secondary damage in another way. The endoprosthesis must technically be fitted in such a way that as far as possible sound 'tissue resource' of any kind is also always treated carefully. That must apply in particular to the extremely sensitive functional structures of the flexing and extension tendons. The joint should be capable of being moved as early as possible after the implantation operation so as to avoid sticking and healing adhesions in respect of the specified functional structures. Finally the endoprosthesis should have long durability in the bone, it should cover an indication spectrum which is as comprehensive as possible and it should have a secure reliable technical implantation route.

The invention is based on the essential concept of later-

ally implanting the endoprosthesis: lateral access to the finger circumvents the 'at-risk ¹ extending and flexing side of the finger and leaves the above-mentioned functional tissue substantially unaffected. It is only necessary to remove a lateral ligament of the finger joint, then the joint is there. All operative necessities can be implemented by way of that access, such as for example removing osteophytes, and even tendon dissolution in relation to joints which have stiffened as a result of post-operative trauma. To maintain as much bony substance of the phalanges as possible, in accordance with the invention only the joint is removed and an anchoring option is provided for the endoprosthesis, which is so stable that early post-operative exercise of the joint becomes a possibility. The joint fitted in accordance with the invention is stable and preferably made from a material which is inert and easily incorporated by the bone.

Even if anatomically no hinge is involved, nonetheless it was possible from innumerable experience with care results after middle joint fractures to speculate that nature tolerates 'minor errors'. As at least in a few cases after implantation of a St. George hinge endoprosthesis it was possible to identify very good results (in spite of all the above-mentioned problems!), the mechanism of the hinge alone could not be the limiting factor.

Thus in accordance with the invention in the context of the 'constructive avoidance strategy' a coupled titanium hinge endoprosthesis, coated with hydroxyapatite and having a polyethylene contact surface was developed, which is implanted from the mediolateral side of a finger and which is primarily stably screwed in the bone.

Thus in accordance with the invention, according to the previous clinical experience, the target criteria are achieved at least in the short term: - avoiding injury to the tendons,

- as little bony substance loss as possible,

- stable guidance for the implant,

- preferably biocompatibility of the implant,

- technically secure placement,

- high level of bony integration capability in spite of early mobility of the joint,

- very good mobility and load-carrying capability on the part of the implant, and

- a broad indication spectrum.

Clinical study hitherto shows that a quite wide indication spectrum applies, in a placement of this endoprosthesis.

Firstly the ideal indication is the painful 'normal' joint arthrosis with motion deficit and loading pain. Even large osteophyte structures do not represent a major obstacle. 'Inflammatory' arthroses do not form an exception with good bone substance as synovialectomies are possible by way of the me- diolateral access without any problems.

In addition it is possible to treat post-traumatic arthroses even with axis errors. As the endoprosthesis is me- diolaterally implanted from both sides, axis corrections are possible in that way. Hinge damage with contraction and tendon healing adhesions represent a further indication as even extensive tendon dissolutions are possible by way of the access, while maintaining the structure, and the early mobilisability then also makes indispensable exercise treatment for promoting and maintaining the joint function possible.

Post-infection damage to the joint represents a relative indication. In some cases the overall complex of bone substance, functional apparatus and soft partial sheathing has to be assessed. Further details, advantages and features of the invention will be apparent from the part of the description hereinafter, in which an embodiment by way of example of the device according to the invention is described in greater detail by reference to three drawings in which: Figures 1 to 39 show the operating procedure according to the invention,

Figure 40 shows a perspective view of a fixing frame, Figure 41 shows a perspective view of a drilling slide, Figure 42 shows a perspective view of an adjustment nut of the size M4, Figure 43 shows a perspective view of a centering sleeve, Figure 44 shows a perspective view of a saw blade, Figure 45 shows a perspective view of an extraction tool, Figure 46 shows a perspective view of a clamp for connection to the proximal end of the extraction tool, Figure 47 shows a perspective view of a joint milling cutter,

Figure 48 shows a perspective view of a milling gauge, Figure 49 shows a perspective view of a slotted sawing block, Figure 50 shows a perspective view of a retractor wound hook,

Figure 51 shows a perspective view of a holding clip for connection to the fixing frame, and

Figure 52 shows a perspective view of the rotary axis aiming device.

In accordance with the view in Figure 1 access is effected mediolaterally and radially at a middle finger 2 at the right over a length of about 4-5 cm. The skin soft partial sheath is prepared, with the vessel and nerve structures being carefully treated. That is then followed, as shown in Figure 2, by presentation of the Landsmeer ligament, severing thereof, and dorsal displacement of the extension apparatus after the opening of the joint 4.

Then, as shown in Figure 3, that is followed by the re- moval of joint osteophytes with the hollow gouge forceps and as shown in Figure 4 resection of the radial collateral ligament.

After resection of the collateral ligament 6 a rotary axis aiming wire 8 which is preferably of a diameter of 1.2 mm, for the rotary axis of the joint 4, is placed on the lateral base phalanx head in such a way that the axis of the joint 4 is in palmar-proximal relationship. That adopts a central position in

respect of the rotary axis which in principle actually moves. In Figure 6 the rotary axis aiming device 10 which is shown in greater detail in Figure 54 is set in place for checking the size and position of the joint cylinders to be resectioned. As shown in Figures 7 and 8, the correct position of the rotary axis is checked in both planes by the use of an image converter. In that respect the size and position of the joint cylinder to be resectioned is also again checked.

Figure 9 shows the positioning operation by way of the rotary axis target device for precisely milling out the joint cylinder in accordance with the established rotary axis and Figure 10 shows fixing of the fixing frame 12 according to the invention as a means for fixing the finger 2 in the straight position by way of four Kirschner wires 14 in predetermined holes in the drilling slide 14 on the base and middle phalanges. The fixing frame 12 can additionally be provided with a holding hoop 162 bridging thereover on the top side, for receiving and fixing retractor wound hooks 156. In that respect the wires 14 must engage the countercorticalis . The correct position of the fixing frame 12 is ensured by way of a centering sleeve 18 which can be fitted into a drilling slide 16, by way of a rotary axis aiming wire 8.

Now, referring to Figures 11 and 12, the joint 4 can be milled out with a cylindrical joint milling cutter 12 after removal of the centering sleeve 18 and the rotary axis aiming wire 8. In that case the operator can very well feel the milling depth with the finger on the contralateral side of the joint 4, and check the situation there. The milled-out joint cylinder is already removed in Figure 12. In Figure 13 the respective outer fixing wires 22, 24 have remained, the fixing frame 12 has been removed to provide space for the milling gauge (Figures 14 and 15) . That milling gauge is in the form of an elongate metal block which on the outside has slots 28, 30 for the fixing wires 22, 24. A guide slot 32 extending in the longitudinal direction is provided between those slots 28, 30. That guide slot 32 is adapted to receive a

sawing block 144 which also has a sawing slot 154 extending in the longitudinal direction in relation to the block 144, for guiding a stepped saw 34. The milling gauge 26 serves as a 'template' for correct slot milling in the middle and base phalanges of the finger 2 for receiving the respective prosthesis arm.

In Figure 16, the milling gauge 26 has been inserted, by way of which the hard corticalis of the middle and base phalanges is 'broken' by way of the stepped saw 34 shown in Figure 17. That saw 34 comprises an angled saw blade 36, with a saw surface 38 at the front end. The slot milling operation is markedly facilitated therewith (Figures 17 and 18) .

In Figure 19, it is possible to clearly see, after removal of the sawing block, the sawn slot 40, by way of which, with a now predetermined direction, the slot can be increased stepwise to the necessary depth and width with the milling cutter 42, as shown in Figure 20.

The guide for the milling cutter 42 is of such a configuration that tilting is prevented. The milled slot 44 which is enlarged through the milling gauge can be clearly seen in Figure 24.

In Figure 23 the bony mounting for the endoprosthesis is now prepared. It can be clearly seen from Figure 24 that the flexing and extension apparatus can be left completely intact! Referring to Figure 25, the hinge prosthesis 50 is now inserted in the straight position, with the prosthesis holding forceps 58 according to the invention.

If a post-improvement to the bony prosthesis mounting 50 should still be necessary, either for post-milling of the slots or for the resection of bones at the respective palmar bone edge in relation to the prosthesis cylinder (free space is important for enabling flexing capability! ) the endoprosthesis 50 can be removed again with the extraction instrument 52 according to the invention without in that case damaging the prosthesis 50.

The endoprosthesis 50 is correctly inserted in the

straight position at the left in Figure 27, and the flexing position is being checked in Figure 28. That position properly attains 90 degrees and it is only then that the movement is impeded by bone contact . Although the endoprosthesis 50 is inserted with a press fit, it is anchored distally in the short arm and proximally in the long arm with a respective titanium screw 62 fixedly in the bone. That permits early, non-loaded functional exercise of the joint . As shown in Figures 33 and 34 the position of the endoprosthesis 50 is checked in both planes and documented by means of the X-ray image converter, before closure of the wound.

Referring to the view in Figure 35, after closure of the wound the clinical flexing function is checked: free flexing without rotational errors.

Figure 36 shows the hand operated on, 8 weeks after the operation; the middle finger 2 is only still slightly swollen and active extension is free as shown in Figure 37. Finally the flexing shown in Figures 36 and 37 is better than in the pre- operative condition. That very good function is in particular pain-free !

By an X-ray examination Figures 38 and 39 show postoperatively no lysis symptoms post-operatively four weeks (Figure 38) and eight weeks (Figure 39) , and the calcium salt con- tent increases.

The instruments used and shown in detail in Figures 40 to 42 are made from medical high-quality steel.

Figures 40 to 52 show the individual component parts of the instrument set according to the invention for carrying out the operating procedure according to the invention.

Figure 40 shows a perspective view of the fixing frame 12 which is made from surgical high-quality steel and has a rigid main frame defining a box-like receiving space, with a plurality of longitudinal bars 64, 66, 68 extending parallel to each other in the longitudinal direction and transverse bars 70, 72, 74, 76 extending transversely with respect to the longitudinal

bars and also extending parallel to each other. Formed between the bars 64 - 76 extending only at the edges are openings so that the interior of the fixing frame 12 is accessible to the operator at all sides. The fixing frame 12 can also be formed with a bridge-shaped hoop 162 which is shown on an enlarged scale in Figure 51 and which extends over the dorsal opening, having a plurality of mutually juxtaposed receiving recesses 164 for receiving the wound hooks 156 shown in Figure 50. For that purpose, insertion openings 54, 56 are provided at the dorsal side of the fixing frame 12 on both sides of the upper opening .

In the middle the longitudinal bar 66 has a semicircular recess 77 into which an adjusting nut 134 shown on an enlarged scale in Figure 44 can be rotatably inserted. Screwed into the central screwthread opening 136 of that adjusting nut 134 is a spacer bar 78 of the drilling slide 16, by means of a corresponding male screwthread, so that rotary movement of the adjusting nut 134 produces a defined adjusting movement of the drilling slide 16 in relation to the fixing frame 12. The drilling slide 16 has a positioning bar 82 which extends in the longitudinal direction and which centrally has a guide opening 84 extending transversely therethrough for receiving the guide sleeve 94 or the joint milling cutter 20 and, laterally of that guide opening 84, positioning holes 86, 88 for the fixing wires 22, 24. The ends of the positioning bar 82 are each formed with a respective right-angled guide abutment 90, 92 which in the installation position bear at the inside and the top side against the transverse bars 70, 76 for affording parallel guidance for the drilling slide 16 on the fixing frame 12 in the adjustment movement. The positioning openings 86, 88 serve for inserting the fixing wires 22, 24 into the finger bones in accurate positions .

The centering sleeve 94 which is shown on an enlarged scale in Figure 45 can be inserted into the guide opening 84 of the drilling slide 16. That centering sleeve comprises a cylindrical metal body, the outside diameter of which corresponds to

the inside diameter of the guide opening 84 and which, at its upper end in Figure 47, has a radially outwardly enlarging shoulder 98 which in the installation position bears at the outside against the guide opening 84 of the drilling slide 16. Centrally the centering sleeve 94 has a receiving opening 100 extending therethrough for the rotary axis aiming wire 8.

The saw blade 102 which is shown on an enlarged scale in Figure 44 and which is of a double-angled configuration, for breaking open the corticales comprises a double-bend metal plate 103 which extends in the longitudinal direction and which is of a thickness of preferably 0.64 mm, having a saw 104 at its front cutting end. At the rear fixing end the saw blade has a semicircular fixing ring 37 for being clamped in a gripping device. From the plane of the saw blade 36 which extends from the front sawing surface 38 to the fixing ring 37 it is angled upwardly approximately at three quarters of the distance involved, preferably through about 36 degrees, to form a step 39, and then goes to the fixing ring again into an end extending parallel to the front portion, so that a double-bent saw blade 36 with a central step 39 is formed. That step 39 forms an abutment when the saw blade 36 is pushed into the slot of the saw block 144 shown in Figure 51 (see also Figure 18) .

Figure 45 shows a perspective view on an enlarged scale of the extraction instrument 108 for removing the finger joint prosthesis after placement in a finger. The extraction instrument 108 comprises an outer hollow body 110 which is adapted for relatively movably receiving a slider 112 arranged therein. The clip 114 shown on an enlarged scale in Figure 44 can be screwed to the proximal end of the slider 112. The clip 114 has hooks 116 which project radially towards each other in dia- metrally opposite relationship and which are hookable in the outer peripheral frame of the joint prosthesis 50. The lower end of the clip 114 has a male screwthread 118 which can be screwed into the lower proximal end of the slider 112. In that way the extraction instrument 52 according to the invention, by changing the clips 114, can be easily converted for extracting

finger joint prostheses of different sizes, involving different outside diameters. A coil spring 120 is operative between the upper end of the slider 112 and the inside of the hollow body 110. Actuation of the extraction instrument 52 is effected by way of two laterally radially protruding gripping members 122, 124 which are screwed in place. By relative movement of the gripping members 122, 124 in relation to the hollow body 110 (see Figure 26) against the spring force of the coil spring 120, the slider 112 is moved in relation to the hollow body 110 to remove the joint prosthesis from the finger gently.

Figure 47 shows the joint milling cutter 20 according to the invention, comprising a cylindrical metal body of hardened high-quality steel. At the front end the joint milling cutter 20 is equipped with a milling head 128 and thereafter extending towards the fixing end goes into two radial enlargement portions, wherein the adjoining insertion end 130 for insertion into the drilling machine narrows markedly once again in relation to the central region of greatest width. The insertion end 130 is formed in the region of the rear portion ^' with a periph- erally extending groove 132 for fixing in the drilling machine in positively locking relationship.

Figure 48 shows a perspective view of the milling gauge 26 according to the invention which substantially comprises a high-quality steel block which is bone-shaped in a front view, of a length of about 45 mm, a height of about 20 mm and a width of about 19 mm. A centering pin 138 for insertion into the joint bore is provided at the rear centrally on the longitudinal side. In the direction of its longitudinal extent, the milling gauge 26 has the guide slot 32 for guiding the milling cutter 42. Also on the front side, the milling gauge 26 has a slightly larger trough-shaped recess 142, into which the saw block 144 shown as a perspective view in Figure 51 can be inserted. Also provided on the milling gauge 26 on both sides beside the guide slot 32 are slots 28, 30. Those slots serve as tolerance compensation to prevent unwanted tilting upon non- aligned placement on the Kirschner wires 14 fixed on both sides

of the joint bore in the finger. The saw block 114 is accordingly also provided with positioning openings 150, 152 which extend transversely with respect to the longitudinal direction and which in the installation position in the inserted condi- tion in the front recess 142 of the milling gauge 136 sit on the Kirschner wires 14. Extending in the longitudinal direction between the positioning openings 150, 152, the saw block is provided with a saw slot 154 serving as a guide for the saw blade 36 shown in Figure 46. In that respect the cranked cen- tral portion 104 of the saw blade bears on the outside against the front side of the saw block 144 and thereby limits the depth of penetration of the saw blade 36.

Figure 50 shows a perspective view on an enlarged scale of the substantially bar-shaped wound retractor hook 156 which at its front end has a plurality of claw-like fingers 158 extending in parallel relationship, for hooking engagement into the tissue. The longitudinal shank of the wound hook 156 has at regular spacings ball-shaped enlarged portions 160 which are hookable in various positions as shown in Figures 9 to 12 into the holding loop 162 which is shown as a perspective view in Figure 53.

That holding loop 162 comprises a high-quality steel arcuate portion which is bent substantially in a U-shape and which at its free ends has pin-shaped projections for insertion into the insertion openings 54, 56, at the top side, of the fixing frame 12. In the installation position the holding loop 162 extends bridge-like over the upper opening of the fixing frame 12 in the manner shown in Figures 9 to 12. The holding loop 162 is provided at its front side with a plurality of regularly spaced receiving recesses 164, each of those receiving recesses 164 being only slightly wider than the width of the shank of the wound hook 156.

Figure 52 shows a perspective view on an enlarged scale of the rotary axis aiming device 10 used in Figures 6 to 8. Sub- stantially it comprises a cylindrical central element for receiving an aiming wire 8, from the outer peripheral surface of

which extend a proximal directional bar 170 and a distal directional bar 172, with the inclusion of an angle of about 120 degrees. The directional bars 170, 172 each include respective radial extension portions which extend radially outwardly from the central element and which define a first vertical plane, and then go at an angle of 90 degrees into axial extension portions which extend at a spacing relative to the centre line of the central element and define a horizontal plane.

In the present embodiment the central element comprises an inner ring 168 extending in co-linear relationship with the longitudinal direction, for receiving the aiming wire 8, with three connecting struts extending spoke-like therefrom to an outer ring 169. The inside diameter of that outer ring 169 corresponds to the outside diameter of the hinge prosthesis 50. Formed integrally on the outer ring are the proximal directional bar 170 and the distal directional bar 172, with the inclusion of an angle of about 120 degrees therebetween. They firstly extend with radial extension portions radially outwardly and then go at an angle of 90 degrees into axial exten- sion portions extending coaxially with the centre line of the inner ring 168.

With the rotary axis aiming device 10 the operator, using the image converter, can determine the correct orientation of the aiming wire 8 and the directional bars 170, 172 in the axial direction. The operator can determine the position of the rotary axis aiming device, at the inside of the outer ring. When the orientation is correct, the operator sees the joint gap of the bone and the correct dorsal and radial orientation of the directional bars 170, 172. As mentioned hereinbefore all component parts of the instruments according to the invention are preferably made from a surgical high-quality steel. The set of instruments is usually presented to the operator in an apertured insert holder, the corresponding openings in the drilling slides, the centering sleeves, the rotary axis aiming devices and the joint milling cutters preferably being of diameters of 6, 7 and 8 mm.

Although the invention has been described by reference to a finger joint the advantages according to the invention can also be achieved in regard to the placement of implants in other joints. The subject-matter of the present invention arises not only out of the subject-matter of the individual claims but also the combination of the individual claims with each other. All features and details disclosed in the documents - including the Abstract - , in particular the three-dimensional configura- tions shown in the drawings, are claimed as essential to the invention insofar as they are novel individually or in combination over the state of the art.

Instruments for carrying out an operating procedure on a joint

List of references

2 middle finger

4 joint

8 aiming wire

10 rotary axis aiming device

12 fixing frame

14 Kirschner wire

16 drilling slide

18 centering sleeve

20 joint milling cutter

22 fixing wire

24 fixing wire

26 milling gauge

28 slot

30 slot

32 guide slot

34 stepped saw

36 saw blade

37 fixing ring

38 saw surface

39 step

40 saw slot

42 milling cutter

44 milling cutter slot

48 prosthesis holding forceps

50 hinge prosthesis

52 extraction instrument

54 insertion opening

56 insertion opening

62 titanium screw

64 longitudinal bar

66 longitudinal bar

68 longitudinal bar

70 transverse bar

72 transverse bar

74 transverse bar

76 transverse bar

77 recess

78 spacer bar

82 positioning bar

84 guide opening

86 positioning hole

88 positioning hole

90 guide abutment

92 guide abutment

94 centering sleeve

96 metal body

98 shoulder

100 receiving opening

110 hollow body

112 slider

114 clip

116 hook

118 male screwthread

120 coil spring

122 gripping member

124 gripping member

128 milling head

130 insertion end

132 groove

134 adj usting nut

138 centering pin

140 longitudinal slot

142 recess

144 saw block. 150 positioning opening

152 positioning opening

154 saw slot

156 wound retractor hook

158 finger 160 enlarged portion

162 holding loop

164 receiving recess

168 inner ring

169 outer ring 170 proximal directional bar

172 distal directional bar