Plate for covering a drill hole in a skull cap and for fixing a cranial bone cover

A plate for covering a drill hole in a skull cap and for fixing a cranial bone cover comprises a plurality of vanes (16a-16e) extending radially with respect to a center (12) and slots (20a-20e) between the vanes. For receiving bone screws holes (18a-18e) are provided in the respective region of the outer periphery of the vanes.

In neurosurgical, plastic and craniofacial operations on or through the 
vault of the human skull, after detachment of the soft parts covering the 
cranial vault frequently large-area bone segments of the skull cap are 
detached and secured again at the same point of the skull cap or in a 
different position at the end of the surgical operation (refixed). 
In the surgical treatment of craniofacial abnormalities, frequently one or 
more bone segments of the skull cap are removed and after modelling 
corresponding to the desired cosmetic result refixed again in a displaced 
position. Such operations, which are frequently carried out in infancy, 
serve the purpose of correcting bone malformations of the skull cap in 
order to permit unobstructed growth of the brain and at the same time also 
to improve the cosmetic appearance of the patient. 
In neurosurgical operations bone covers of the skull are lifted off in 
various regions and sizes to permit access to the brain. As a rule, the 
bone segments removed in this manner (hereinafter referred to as cranial 
bone covers) are refixed in the original position after completion of the 
socalled soft part operation (i.e. the operation on the brain). 
The operating technique employed in such operations frequently includes a 
socalled bow incision (from ear to ear over the highest point of the skull 
cap) through the soft parts, whereafter a subpereosteal undermining is 
carried out and the largest soft part lobes are folded forwardly or 
rearwardly. 
Depending on the size, location and geometrical form of the bone cover to 
be lifted off, several holes are drilled through the cranial vault. If the 
bone cover to be removed is for example a triangular skull cap segment, as 
a rule three holes are drilled at the corner points of the bone cover. 
Thereafter, by means of a saw (which is provided with a guide nose in 
order to avoid dura mater injuries) the socalled connecting osteotomies 
are made between the drill holes; with a triangular form of the bone cover 
to be lifted off the connecting osteotomies are thus the sides of a 
spherically curved triangle. Thereafter the bone cover can be lifted off 
to carry out the further operation. 
After completion of the operation the previously removed bone covers have 
to be refixed again, i.e. secured again at the desired location. Various 
aids are known in the prior art for this refixation of the bone cover. EP 
0 290 138 A2 and EP 0 291 632 A1 describe for this purpose socalled small 
bone plates of body-compatible material, for example titanium or a 
chromium-cobalt-molybdenum alloy, which are made strip-like and at 
intervals are provided with holes for receiving bone screws. These 
elongated plates are so designed that they can be deformed by the surgeon 
to adapt them to the bone in the area to be treated. 
EP 0 347 658 A1 described a bone plate for osteosynthesis having holes to 
receive bone screws and a gear mechanism between the plate parts for 
adjusting the relative position of the plate parts 
German utility models DE 85 28 003 U1 and DE 87 06 912 U1 describe bone 
plates employed for fixing a cranial bone cover. 
The elder application published as DE 40 28 021 C1 describes an 
osteosynthesis grid with holes for receiving bone screws (i.e. securing 
screws which are screwed into the bone). 
Another implant is the socalled mesh systems, in particular according to 
Dumbach. Here, relatively large-area perforated discs (for example of 
titanium) which are flexible in order to be exactly fitted by the surgeon 
are used as implant for bone fixation, primarily in the jaw region. The 
aforementioned drill holes made at the start of a trephination present 
particular problems. For several reasons, among others for protecting the 
brain covered postoperatively only by the soft parts and for improving the 
cosmetic result, the drill holes should also be closed after the 
operation. When the drill holes are made using conventional drills or 
trephines, as a rule however no bone plug is formed which could be 
refixed; on the contrary, due to the cutting action of the rotating 
instrument only bone meal is formed. In the prior art, the following 
attempts are made to solve the problem of the drill holes: 
The drill holes remain unclosed. However, after the healing phase this 
gives a mostly unsatisfactory cosmetic result because, in particular in 
the region of the forehead, visible "dents" result beneath which 
frequently the pulsation of the brain is even visible. The covering of the 
drill holes simply by means of the soft parts does not provide adequate 
protection of the brain from injuries. 
The bone meal forming when making the drill holes can be partially 
collected and used for covering the perforation. However, with this method 
adequate stability of the bone and a predictable positive cosmetic result 
cannot be ensured. Also, no immediate protection of the brain is obtained. 
It is further known to use alloplastic materials, such as bone waxes, bone 
cement, etc. However, these materials do not provide reliable protection 
of the brain either and in addition as a rule they are exogenous 
implantation materials which remain in place and are not surrounded 
naturally in the course of time so that infections or other undesired 
reactions of the body can occur. 
Finally, it is further known in the prior art to use plastic covers which 
project over the edge of the drill hole and are clamped in the drill hole 
itself. With this method as well no cosmetically satisfactory result is 
ensured (the plastic covers can project over the contour of the bone). 
Furthermore, due to its softness plastic does not offer reliable 
protection against puncture wounds. The invention is based on the problem 
of providing means for solving the problems explained above and permitting 
refixation of cranial bone covers which ensures both a reliable protection 
against injury and a cosmetically predictable and desired result. 
This problem is solved in a plate of the type mentioned at the beginning by 
a plurality of vanes which extend racially with respect to a centre and 
which are separated from each other by slots, and of which at least some 
comprise at their outer peripheral portions in each case a hole for 
receiving a bone screw. 
The plate according to the invention covers the drill hole and its outer 
contour is preferably substantially round, in particular circular, or 
polygonal. The preferably slightly concavely formed cover plate is made 
available in various sizes and arranged by the surgeon concentrically over 
the drill hole and can then be anchored securely to the cranial bone by 
means of bone screws. 
The bone screws are led through holes in the plates according to the 
invention which are arranged at the outer peripheral portions of the 
vanes, i.e. readily adjacent (inside or outside) said portions. This 
optimizes the mechanical stability of the refixation. 
Preferably, the holes for receiving a respective bone screw are arranged on 
a circle of which the centre point coincides with the centre of the plate. 
Along the periphery of the plate according to the invention the holes for 
receiving the bone screws are preferably arranged at regular intervals, at 
least three holes for receiving screws being necessary and provided, in 
order to achieve a fixation-stable three-point anchoring. Additional holes 
for receiving screws increase the anchoring possibilities of the plate. 
The vanes of the plate according to the invention are joined together in 
the interior of the plate. The entire plate is made integrally from a 
single material, such as titanium, niobium, etc. 
The individual vanes of the plate according to the invention are separated 
from each other by radially extending slots. The slots extend however 
preferably only over a portion of the radius of the plate in order to 
achieve good stability in the refixation. Preferably, the slot length 
corresponds to approximately half the radius of the plate with an allowed 
deviation of +/- 30%, the radius being related to the solid part of the 
plate, i.e. without any possibly provided additional rings at the exterior 
of the plate for accommodating holes for receiving screws. 
According to a preferred embodiment the slots between the vanes of the 
plate are formed conically. 
The slots have inter alia two functions: 
The surgeon can employ the slots as "inspection slots" and through them can 
see the drill hole disposed therebelow, thereby enabling the plate to be 
anchored centrally with respect to the drill hole in simple manner with 
constant lateral intervals, i.e. the substantially round or 
rotation-symmetrical plate can be fixed concentrically to the drill hole. 
Preferably, the plates according to the invention are made available in a 
concave form adapted to the curvature of the skull. They can however be 
individually formed in accordance with the conditions of the specific use 
of the plate. Due to the slots between the individual vanes of the plate, 
the plates and in particular the vanes themselves can be adapted to almost 
every anatomical situation, thereby optimizing the cosmetic result 
obtained. 
Preferably, both in the inner portion and in the vanes of the plate 
according to the invention holes are provided so that postoperatively 
blood and tissue fluid can flow out of the epidural space unrestricted. 
According to another embodiment of the plate according to the invention, in 
the centre thereof a central screw hole is provided for the case that a 
possibly obtained bone plug is to be additionally screwed to the lower 
side of the plate. 
The plate according to the invention is preferably so configured that it 
has as flat a profile as possible and the bone screw heads used to secure 
the plate are as far as possible countersunk in the plate without 
projection. 
The plate according to the invention thus has a double function: Firstly, 
it serves as drill hole cover and secondly it serves for fixation of the 
bone cover. At least one, preferably two, screws connect the plate to the 
bone cover, whilst the remaining screws establish a connection over the 
drill hole to the rest of the cranial vault. A large number of differently 
dimensioned bone covers can be fixed to the skull cap in all regions of 
the skull by using at least two, preferably three plates. An additional 
stabilizing of the skull segments by the alternative fixation 
possibilities according to the prior art described at the beginning is not 
necessary but is available additionally to the surgeon if required.

FIG. 1 shows schematically a skull cap SD in which bores B are formed. 
Between the bores B incision lines extend (cf. also FIG. 6) so that a 
cranial bone cover D can be removed. To remedy the osseous malformations 
visible in FIG. 1 portions T.sub.1, T.sub.2, T.sub.3 of the skull are 
removed. 
The present invention relates to refixation of the cranial bone cover D and 
covering of the drill holes B. 
FIG. 2 shows a first example of embodiment of a plate for covering a drill 
hole B in a skull cap SD and for fixation of a cranial bone cover D. The 
plate 10 serves as implant and is made integrally from a biocompatible 
material, for example titanium or niobium. 
FIG. 2 shows in a manner similar to FIG. 3 an example of embodiment for 
covering a relatively large drill hole B having diameters up to 14 mm 
whilst FIGS. 4 and 5 show plates which are provided for smaller drill 
holes having diameters up to 7 mm. 
In FIGS. 2 to 5 corresponding components are provided with the same 
reference numerals so that only FIG. 2 need be described in detail. The 
examples of embodiment according to the FIGS. 3 to 5 will then be readily 
understandable. 
The plate 10 is rotational symmetrical with respect to its centre 12. The 
centre 12 is disposed centrally in a hoe 14. 
In the examples of embodiment illustrated the plate 10 comprises five vanes 
16a, 16b, 16c, 16d and 16e. 
Between the vanes 16a-16e respective slots 20a, 20b, 20c, 20d and 20e are 
arranged. The slots extend radially with respect to the centre 12 over 
about half the radius of the plate, the radius being measured from the 
centre 12 up to the outer peripheral portions 17a, 17b, 17c, 17d and 17e 
of the vanes 16a-16e, i.e. the radius does not include the radial 
extensions of the individual vanes in which respective holes 18a, 18b, 
18c, 18d and 18e are provided for receiving bone screws. The slots are 
made to taper conically radially inwardly. 
The entire plate 10 is provided uniformly with holes 22 so that during and 
after the operation blood and other fluids can flow off. 
The holes 18a-18e each have countersunk portions so that the heads of bone 
screws (not shown) do not project. 
The plate 10 including the vanes 16a-16e is made concave in such a manner 
that it is roughly preadapted to a skull cap SD. Due to the configuration 
of the plate 10 described and the slots between the vanes the operating 
surgeon can during the operation perform an adaptation of the shape 
depending upon the particular geometrical situation and bend the vanes and 
if necessary also the inside of the plate as desired. 
The holes 18a-18e for receiving the bone screws are provided in rings 
24a-24e which in the examples of embodiment illustrated project as 
integral projections beyond the outer peripheral portions 17a-17e of the 
vanes 16a-16e. The projections and the holes formed therein are in each 
case arranged centrally on the associated vane. 
In the examples of embodiment of plates according to the invention 
illustrated in FIGS. 2 to 5 in each case five vanes are provided. This has 
been found favourable. 
FIG. 6 shows the refixation of a cranial bone cover D to a skull cap SD 
(cf. also FIG. 1). The bone cover D has the form of a spherical triangle 
and the bores (not visible in FIG. 6 because they are covered by the 
plates) are each located at the corner points of the triangle formed by 
the incision lines 26a, 26b and 26c. The plates 10a, 10b and 10c according 
to the invention are arranged concentrically overlapping the drill holes 
and fix the cover D with respect to the skull cap SD. The fixation can be 
additionally promoted by a grid 28 known per se. 
The examples of embodiment described above having five vanes can be 
modified in that in particular three vanes or more than five vanes are 
provided. An odd number of vanes if preferred. The rotational symmetry 
shown in the examples of embodiment illustrated (with five vanes an arc 
angle of 72.degree.) facilitates handling of the plate. 
The plates according to the examples of embodiment described above are 
essentially round (except for the attached rings 24), i.e. the main body 
is substantially circular about the centre 12. Modifications are possible 
to this preferred embodiment, in particular square or rectangular main 
bodies.