Field of the Invention This invention relates to orthopedics, particularly to therapeutic helmets for treating plagiocephaly and for postoperative protection of the infant cranium .

Background of the Invention Referring to FIGURE 1, the cranium 10 or brain case of a human infant is made up of frontal 12, parietal 14, temporal 16, and occipital 18 bones that encase and protect the brain (not shown). These bones are separated by membranous intervals 20 until brain growth is complete, at about eighteen to twenty-four months of age. During that time period, pediatricians routinely monitor the accompanying growth of the cranium by measuring the maximum circumference of the cranium 10, the so-called occipital-frontal cir¬ cumference 22 that goes .around the cranium 10, for comparison with tabulated average values for the population. See, for example, Nellhaus, G., Composite International and Interracial Graphs, Pediatrics 41:106, 1968, hereby incorporated by reference. During the first eighteen months of age, the mean head circumference 22 increases from about 34 to about 48 cm for boys, and from about 34 to about 47 em for girls. After about twenty-four months of age, thickening of the cranial bones accounts for subsequent head growth.

Referring to FIGURE 2, two additional reference lines are commonly established with respect to the infant cranium 10. A midsagittal line 24 runs through the mandibular symphysis 26 .and the interpupillary mid¬ point 28. Extending line 24 back through the inion 29, the most prominent point of the external occipital protuberance, defines the midsagittal plane 30 that, in a normal infant, bisects the cranium 10 into substantially exact halves. As discussed below, judgments concerning cranial symmetry or asymmetry are typically made with reference to plane 30.

As also shown in FIGURE 2, for the purpose of orienting the head for cranial com out ed tomography (CT), a transverse plane 32 is established

through a pair of supraorbital-meatal reference lines or baselines 34, which typically run through the supraorbital arch 36 and the external auditory mleatus 38 on either side of the cranium 10. Referring now to FIGURE 3, an infant's cranium 10 is shown in a section view taken along the midsagittal plane 30, as in a standard Horz (LAT) pilot scan in cranial computed tomography. Representative transverse planes 34a-i are shown parallel to the supraorbital- meatal baseline 34. Such transverse planes 34a-i conform with the standard CT twain ^slices" that fire taken for various ^diagnostic purposes. For example, see A.G. Lurus, et al., CT Application Guide, Picker International, 595 Miner Road, Highland Heights, Ohio, hereby incorporated by reference.

As mentioned, the normal infant cranium 10 is symmetrical with respect to midsaggital plane 30. However, a condition known as plagiocephaly, characterized by a rhomboid-shaped head, occurs in at least one in 300 live born infants. Such cranial asymmetry usually results from late gestational or postnatal deformation. When an infant's rapidly growing head Is maintained in a nearly fixed position against the uterine wall or the mattress, the cranium 10 progressively flattens. Such deformational plagiocephaly generally will improve within a few months after birth, especially if a full range of neck movement can be rapidly achieved. However, for perhaps ten percent of affected infants, plagiocephaly may persist into adulthood as a permanent, mild-to-severe cosmetic disability.

Applicant previously reported that individualized plastic helmets x ^» oύld- remold the rhomboid-shaped head into a more usual form. Clarren, S. K., et al., The Journal of Pediatrics 94(l):43-46, 1979. In that preliminary study, individually fitted plastic helmets, similar in style to football helmets, were designed to fit snugly against the prominent aspects of an infant's cranium and to be loose fitting where the head is shallow. The patients wore their helmets continuously for two to three months. Cranial asymmetry dramatically improved as the' atient's brain ^" grew and the head filled out the helmet and thus acquired a more usual shape. Again, such helmets were individually fitted, that is, made from a precise impression of each patient's plagiocephalic cranium. A thin cotton cap was placed over the patient's head, and this was then covered with plaster to make a east. After the cast had been removed and thoroughly dried, a replica of the patient's head shape was obtained for filling the cast with modeling clay or plaster of Paris. The cast was then cut away and discarded. Modeling clay or plaster slurry was then used to build up the flattened areas of the model head until a more ideal shape was achieved. No additions were place over the prominent aspects of the model so as to assure a snug helmet fit i

those areas. The occipitofrontal circumference was increased by no more tha 3 cm, as otherwise the helmet was reportedly too loose for effective wea Standards for growth in head height were not available, but allowance for growt in this plane was also required and was estimated. A polypropylene sheet wa then vacuum formed over this individually sculpted mold to produce th particular patient's helmet.

Applicant subsequently reported the results of additional helme treatments, using the above-described individually fitted helmets, in which a attempt was made to objectify the degree of plagiocephaly through standar superior and frontal photographs of each potential subject's head. Such photo graphic measures were reportedly arbitrary and prone to some error. Clarren S. K., The Journal of Pediatrics 98(l):92-95, 1981.

Of less direct interest, other than their off-the-shelf availability are protective helmets that employ adjustable padding to suspend the craniu within the helmet cavity. Such bicycle- type helmets have been employed fo children following cranial reconstructive surgery. H. E. James, et al., Concept pediat. Neurosurg. 5:41-47, 1985.

It would be advantageous, for treating plagiocephaly, to provid helmets that need not be individually molded and fitted. It would also b advantageous to provide an improved off-the-shelf helmet for protecting infant who are at risk for brain injury from minor trauma, such as following crania surgery.

Summary of the Invention

The invention provides, in one aspect, a method of helmet treat ment for deformational cranial asymmetry in which the dimensions of th therapeutic helmet cavity are prescribed in relation to specific CT scan section of the infant's cranium. A graded series of sized helmets is provided for suc treatments. Each helmet cavity is configured to accommodate and effectivel treat infants of specified ages and degrees of plagiocephaly. By employing th subject off-the-shelf helmets, the ti e-consuming and labor-intensive fitting o individualized helmets is obviated.

To prescribe an appropriate therapeutic helmet, horizontal an transverse CT scans are made of the plagiocephalic infant's cranium. Th transverse scans are generated parallel to a supraorbital-meatal baseline. From among the transverse scans, the section having the cranial outline with th longest anterior-posterior dimension is selected. Certain critical helme dimensions are measured from this selected section, as described below, in cluding the maximum circumference, maximum lateral axis, anterior-posterio

axis, and maximum chord. From a horizontal CT scan, the maximum height of the helmet cavity is taken. A helmet is then prescribed for the infant's ' treatment having a cavity that substantially conforms in sTiape to a normal infant cranium and that is dimensioned to at least equal and exceed by no more than 4 and preferably 2 cm the corresponding measured values of the plagio¬ cephalic cranium. The availability of a graded series of sized helmets permits the attending physician to prescribe and order an appropriate therapeutic Λeltoet, on the basis of data generated-from standard CT scans, from a location remote from the helmet manufacturer and distributor. Brief Description of the Drawings

FIGURE 1 is a lateral view of the human skull at birth showing the bones that make up the cranium and indicating the maximum occipital-frontal circumference by which head growth is conventionally monitored;

FIGURED is an oblique ήew of an infant's nead illustrating two reference planes, the midsaggital plane and a transverse plane parallel to a supraorbital-meatal baseline, that are commonly used to assess cranial symmetry and orient the head for CT scanning, respectively;

FIGURE 3 is another lateral view of the infant skull illustrating the locations of representative transverse planes, parallel to a supraorbital-meatal baseline, that conform with standard CT brain scan views, and furthermore showing how the subject helmet height dimension is determined;

FIGURE 4 is a schematic view of a representative transverse CT brain 'scan of a plagiocephalic patient, showing how the other critical helmet dimensions are determined; FIGURE 5 is a schematic section through a representative therapeutic helmet of the invention; and,

FIGURE 6 is a view similar to FIGURE 4 but showing a preferred method of determining the maximum diagonal chord for fitting the subject helmet. Detailed Description of the Preferred Embodiment

The invention provides, in one aspect, a method of helmet treat¬ ment for deformational cranial asymmetry in which the dimensions of the therapeutic helmet cavity are prescribed in relation to specific CT scan sections of the infant's cranium. A graded series of sized helmets is provided for suc treatments. Each helmet cavity is configured to accommodate and effectively treat infants of specified ages and degrees of plagiocephaly. By employing th subject off-the-shelf helmets, the time-consuming and labor-intensive fitting o individualized helmets is obviated. Purther ore, since the subject helmets ar

prescribed on the basis of data generated from standard CT scans, the attendin physician can prescribe and order a suitable helmet, from a location remote from the helmet manufacturer or distributor, with relatively minor inconvenience an expense to the patient and patient's family. Standard procedures are followed for the CT scanning. The infant is positioned supine, nose up, with the head placed securely in a head holder. Th midsagittal line 24 (but, for the plagiocephalic patient, not necessarily the inion 29 and plane 30) is aligned with the instrument's midline laser. Th instrument's horizontal laser is aligned conventionally with the inter pupillary midpoint 28. A horizontal or lateral scan is made with the horizontal laser centered at the mandibular symphysis 26, to produce a view such as shown in FIGURE 3. Representative slices through transverse planes 34 to 341 are then taken after aligning the tilt line parallel with the supraorbital-meatal base- line 34, which in this embodiment passes through the supraorbital arch 36 and the external auditory meatus 38. Other baselines 34, such as a baseline 34 used to generate brain slices at an angle of about 20° cephalad from the orbital-meatal line, can alternatively be employed here. Transverse planes 34a-i can be on the order of eight to ten millimeters apart, and uniform slice thicknesses of that magnitude can be set with the instru ent. The superior limit, or last slice 34i, is typically set at the vertex 52 of the cranium 10. Following this procedure, the horizontal scan and transverse views are developed in standard fashion.

Pursuant to the invention, data from the standard CT scans are used to assure that the following critical helmet dimensions are met. From the horizontal scan, the maximum height (MH) of the infant's cranium 10 is measured along the line 54 (FIGURE 3), perpendicular to the supraorbital-meatal baseline 34, that intersects the vertex 52, that is, the longest such line 54 that can be drawn perpendicular to baseline 34 within the confines of the cranium 10.

The other critical helmet dimensions are measured from the transverse section, parallel with the supraorbital-meatal baseline 34, that has the greatest anterior-posterior dimension. A representative section 34c is shown in FIGURE 4. The maximum anterior-posterior dimension 56, parallel to the plane 57 that results from alignment of the instrument's midline laser with midsagittal line 24, is measured within this section 34c. That dimension 56 is then compared with similar dimensions 56 in the other sections to select the section (34c, in this illustrative embodiment) from which to prescribe the additional helmet dimensions. For most plagiocephalic infants, the third to fifth, and typically the fourth section superior to baseline 34, assuming 10-mm slice

thicknesse's, will have the greatest anterior-posterior dimension 56 and so can be used t prescribe the other helmet dimensions.

Once selected, the circumference 58 of the section 34c is measured t define the maximum circumference 58 (MC) of the infant's cranium 10 parallel to th transverse plane 32. The maximum (i.e., longest) lateral axis (ML) 60, perpendicular t plane 57, - s also selected and measured. Then the anterior-posterior axis (AP) 6 perpendicular to and bisecting the maximum -lateral axis 60 is selected and measure Next, the maximum chord (mc) 64 passing through the intersection 66 of the maximu lateral axis 60 and the anterior-posterior axis 62 is selected and measured, and the chor angle 65 with respect to axis 62 is measured.

From the foregoing measurements, a helmet 68 for the plagiocephali infant's treatment is prescribed. A representative helmet 68 is shown in FIGURE Helmet 68 is shaped in outward appearanee much like a football of bicycle helme having an outer shell 70 of lightweight, high-impact material such as polypropylen and/or a cellular plastic 72. However, the helmets 68 of this invention lack the intern padding of such conventional protective helmets, which padding is typically adjustable t suspend the cranium substantially uniformly within a cushioning airspace within th helmet. In contrast, the internal cavity 74 of the subject helmet 68 is designed t substantially conform in shape to a normal infant cranium and furthermore has maximum circumference, maximum lateral axis, anterior-posterior axis, maximum chor and -maximum height at -least equal to and ot more than about four cm greater than t foregoing values measured from the infant's CT scans. The subject helmet 68 will als typically be provided with a chin strap 76 and associated fasteners 78, and with plurality of air holes 80 for ventilation. In another aspect, the invention provides a graded series of sized helmets 6 ranging in maximum circumference 58 from about forty to about fifty-two centimeter in one- .or. two-centimeter^intervals. Such a sized series is selected to encompass t tenth to ninetieth percentiles of infant head size at the age levels spanning ten eighteen months. These standard helmets 68 are made from helmet prototypes usi conventional manufacturing techniques, such as by pneumatic thermoforming. T helmet prototypes can be fabricated from molds of the heads of normal control infant Selection of the controls is based upon two criteria. First, a control infant's cranium must not exhibit plagiocephaly, that is, -the control cranium 10 must be symmetrical shaped about the midsaggital plan 30. Second, the occipital-frontal circumference

of normal infants who meet the first criterion should be measured, as a roug index of the disclosed circumference 58, in order to select a graded series o controls that approximately exhibit the aforementioned one- or two-centimete intervals between the tenth and ninetieth percentiles. A plaster cast is made o the cranium 10 of each selected normal infant, .and from that cast a plaste prototype of the cranium 10 is made. Confirmation of the suitability of th assembled normal prototypes, for achieving the requisite fit and effectiv treatment when prescribed as disclosed herein, is made by preparing standard CT scans of the plaster prototypes, using the same orientations as if the prototypes were actual craniums 10. From the resulting data, final helmet prototypes are selected which conform with each of the following graded sizes.

Size MC ML AP me MH

1 40 10.3 14.0 13.75 9

2 41 10.7 14.3 14.25 9

3 42 11.0 14.5 14.50 9

4 43 11.3 14.8 14.75 10

5 44 11.7 15.3 15.00 10

6 45 12.0 15.8 15.75 10

7 46 12.3 16.3 16.25 10

8 47 12.7 16.8 16.50 10

9 48 13.0 17.0 16.75 10

10 49 13.0 17.3 17.00 10

11 50 13.3 18.0 ^• 17.75 10

12 51 13.5 18.4 18.00 11

13 52 14 18.8 18.50 11

Once the graded normal prototypes are selected, as described above, the prototypes can serve as the templates for large-scale manufacture of therapeutic helmets 68 having cavities 72 of the stated dimensions. Representative manufacturing techniques include thermoforming and other plastic molding methods known in the art.

A physician, even at a location remote from the plagiocephalic infant patient, can prescribe a helmet 68 from the foregoing series on the basis of a standard ~CT series- of the patient's cranium 10. After measuring the critical dimensions from the patient's CT scans, as described above, the appropriate helmet is selected which has each of the listed dimensions at least equal to and no more than four centimeters greater than the measured dimensions. Preferably, the listed dimensions should each exceed the measured dimensions by nodworethan two cm, in order to avoid unnecessary loos enessof fit and to assure that the treatment will be completed as rapidly as possible. Referring now to FIGURE 6, in a preferred embodiment the maximum chord 64 is selected from the group of six chords passing 10°, 20°, and 30° on both sides of the anterior-posterior axis 62 in the transverse section 34c having the greatest circumference 58. From the patient's CT scan data, a helmet _s selected shaving a cavity with at least the following corresponding dimensions, none of which can exceed the patient-specific dimensions by 4 cm, and preferably by no more than 2 cm. mc

Size MC ML AP __ 20° 30° MH

1 40 10.3 14.0 13.75 13.50 13.25 9

2 41 10.7 14.3 14.25 13.75 13.5 9

3 42 11.0 14.5 14,5 14.25 14.0 9

4 43 11.3 14.8 14.75 14.25 14.0 10

5 44 11.7 15.3 15.00 14.75 14.50 10

6 45 12.0 15.8 15.75 15.5 15.25 10

7 46 12.3 16.3 16.25 16 15.5 10

8 47 12.7 16.8 16.5 16 15.75 10

9 48 13.0 17.0 16.75 16.5 16.5 10

10 49 13.0 17.3 17.0 16.75 16.0 10

11 50 13.3 18.0 17.75 17.50 17.25 10

12 51 1-3.5 18.4 18.0 17.5 17.0 11

13 52 14 18.8 18.5 18.0 17.75 11

For convenience, reference can be similarly made to other chord ang (measured as indicated by reference numeral 65 in FIGURE 4), such as 15° and 25° either side of the anterior-posterior axis 62 in section 34c, in order to size the off-th shelf helmet to the individual patient. While the invention has been described with reference to data generated cranial computed tomography (also known as computerized axial tomography, CAT), a imaging technique that can delineate the shape of the cranium as set forth above can used to practice this invention. Such alternative imaging techniques include nucle magnetic resonancy (NMR), or even particle emission tomography (PET) scanning. Following certain neurological procedures, especially when bone is n replaced over the dura, postoperative protection may be required. The subject infa helmets 68 can advantageously provide such protection, and are preferable to bicycl type helmets, as helmets 68 are lighter in weight, closer fitting and hence less clumsy wear, and are better tolerated by infant patients. While the present invention has been described in conjunction with preferred embodiment, one or ordinary skill after reading the foregoing specification w be able to effect various changes, substitutions of equivalents, and alterations to t subject matter set forth herein. It is therefore intended that the protection granted Letters Patent hereon be limited only by the definitions contained in the appended clai and equivalents thereof.