Support for the human spine

The invention is an elongated plate made of deformable, body-compatible material, which is to be anteriorly attached to at least a pair of adjacent vertebrae. The plate has specially placed holes to receive bone screws to be screwed into the vertebrae.

FIELD OF THE INVENTION 
The present invention relates to a sustaining means for correcting and/or 
stabilizing injured or deficient vertebras of the human spine according to 
the preamble of claim 1. 
DESCRIPTION OF RELATED ART 
German petty patent 87 11 317 discloses so-called Schanz screws which are 
screwed in the vertebra through the pedicels to reposition healthy and/or 
fractured vertebras. The Schanz screws are secured to a sustaining means 
which provides an adjustment of the Schanz screws with respect to all 
three degrees of freedom. The known sustaining means, however, are not 
able to bridge more than a vertebra or to provide for a multi-segmental 
treatment of multiple fractures. To provide for an implantation, the 
Schanz screws must be cut off after securing to the sustaining means. 
Consequently, burs are formed at the end of the screws. Due to the need of 
substantial space, the known sustaining means may not be used in the upper 
range of the spine, in particular in the cervical vertebra zone. 
SUMMARY OF THE INVENTION 
A number of vertebras may be bridged by a so-called Harrington rod to which 
hooks or pedicel screws are attached. However, a Harrington rod cannot be 
individually adjusted to the particular shape of the spine in the zone 
where it is applied. Therefore, it has been known to use a threaded wire 
cooperating with pedicel screws. This known sustaining means, however, 
does not provide a primary stable support because it exhibits 
non-sufficient strength. Therefore it can be used mainly for spines which 
are stable per se and of which the course has to be corrected for 
orthopedic reasons. 
German petty patent 88 02 112 discloses a sustaining means for the human 
spine, wherein between adjacent pedicel screws a tension Jack is provided 
which ends include clamping faces for clamping to the head of a pedicel 
screw. By adjusting the axial distance of the belts with respect to each 
other, for example by means of a threaded sleeve, the attachment points of 
the pedicel screws may be adjusted. Still further the bolts provide for a 
rotation of the pedicel screws about the bolt axis at a desired angle. 
Furthermore, the pedicel screws may be pivoted about an axis normal to the 
axis with respect to the attachment points to be fixed in a desired 
position. The pedicel screw may thus take any desired position in space 
and can be fixed in this position. The known sustaining means provides for 
screwing pedicel screws into each desired vertebra to fix desired 
vertebras of a spine portion with respect to each other. The sustaining 
means described is thus suited to primarily stabilize the spine, when one 
or more vertebras are fractured. However, even this sustaining means which 
is dorsally implanted, which means a relatively small stress to the 
patient is not suited to be used for the upper spine zone, in particular 
for the cervical vertebras. 
Accordingly, the invention is based on the object to provide a sustaining 
means for the correction and/or stabilization of injured or deficient 
vertebras of the human spine, which may be used in the upper zone of the 
spine. 
The object referred to is solved by the features of claim 1. 
According to the invention the sustaining means consists of an elongated 
plate made of deformable, body-compatible material, which is anteriorly 
attached to at least a pair of adjacent vertebras. The plate comprises 
holes to receive bone screws to be screwed in the vertebrae. The plate 
further comprises weakening zones and/or thickness dimensions and/or a 
selection of material such that it may be adjusted to the contour of the 
vertebras. 
According to the invention the plate is suited to be pre-shaped before the 
operation to conform to the contour of the vertebras or to be shaped by 
the surgeon right during the operation. Thereafter, the plate is fixed by 
bone screws to the vertebras whereby screw holes are formed substantially 
in the center axis of the plate and additionally towards the edge which is 
bent in the longitudinal axis to fit to the vertebra. To fit the plate to 
the depressions in the vertebra, the plate is further bent around a normal 
axis so that the plate obtains a substantial stability due to the 
different bending which stability is sufficient for a primary setting of 
fractured or deficient vertebras, for example. 
Attaching the plate is performed anterior, i.e. from the front side so that 
it is particularly suited for the cervical vertebras of the spine. The 
attachment does not involve particular problems and needs extremely little 
space thus being less detrimental to the patient. The bone screws are 
either anchored in the vertebra only or additionally in the pedicels of 
the vertebras or in the pedicels exclusively. 
The plate of the invention must represent a sufficient deformability on the 
one hand and a sufficient stiffness on the other. According to the 
invention a weakening of the plate to facilitate deformability is provided 
by a plurality of preferrably round holes having a diameter which is 
smaller than the diameter of the screw holes. A weakening of this type is 
relatively easy to manufacture. Therefore, a further embodiment of the 
invention provides to arrange the screw holes or the weakening zones of 
the plate and thus of the smaller holes such that the plate is stiffer in 
its central longitudinal zone than towards the longitudinal edge. 
Therefore, the plate may be more easily deformed along the length edge 
than towards the central portion which feature facilitates fitting the 
plate to the contour of the vertebras. 
To prevent weakening the plate too much, the number of holes should be 
limited. According to an embodiment of the invention, the distance or the 
multiple of the distance of the screw holes in the length axis of the 
plate substantially corresponds to the center distance of adjacent 
vertebras, possibly taking into account the shaping along a normal axis or 
length axis to fit to the contour of the vertebras. Particularly in the 
cervical vertebra range the bone screws are more easily screwed centrally 
in the vertebra than in the lower or upper range. 
The length of the plate depends on the size of the injured range. Possibly 
a plate covering two vertebras is sufficient. However, as the case may be, 
the length of the plate may be selected substantially larger. To prevent 
preparing an individual plate for each length, the invention provides for 
an endless plate which may be cut. Thus, the surgeon may determine the 
length of the plate which is cut from a suitable stock. 
According to a further embodiment of the invention the screw holes in the 
end areas of the plate are elongated tapering towards the end thereof to 
become more narrow and the edges of the holes are sloped to cooperate with 
the conical underside of the screw head. In this way a compression force 
may be created when the conical undersides of the screw heads cooperate 
with the elongate holes. 
A further embodiment of the invention provides ear-like projections along 
the edges of the plate including small holes. The holes may accomodate 
wires, for example to obtain an additional fixing.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a plate 10 made of flat material of a body-compatible 
material, for example titane. Along the edges and at the corners the plate 
10 comprises small ear-like projections 12 including including small 
circular holes 14. The plate 10 further comprises four lines of screw 
holes 16 to receive bone screws. Smaller circular holes 18 are formed 
between the screw holes 16. The distance of the screw holes 16 in the 
lines approximately corresponds to the central distance of adjacent 
cervical vertebras, for example. By the individual holes and/or the 
selection of material, the plate 10 is suited to more or less closely fit 
to the contour of cervical vertebras. The shaping may be performed before 
the operation or during the operation. By means of bone screws not shown 
the plate 10 is then fixed to adjacent vertebras, wherein a part only of 
the screw holes is used. A wire used for an additional fixing may be 
pulled through the holes 14 in the ear-like projection 12. 
The plate 20 of FIG. 2 is of similar structure as the plate 10 of FIG. 1. 
Alike, it comprises ear-like projections 12a including holes 14a and lines 
of screw holes 16a and smaller holes 18a therebetween. Furthermore, 
elongated holes 22 are provided in a predetermined distance, which are 
narrowed towards the end of plate 20. The edge of the holes 22 is conical, 
as FIG. 3 shows so that by means of a conical screw head a compression may 
be exerted on the vertebra in which the screw in the elongated holes 22 
are screwed in. The plates 20 may be made of an endless material as 
indicated at 23 and from this material a desired length is cut off, in 
particular by the surgeon. 
FIG. 4 shows vertebras 24 of cervical vertebras which are connected to each 
other by a plate 26. The structure of the plate 26 corresponds to the 
plate 10 of FIG. 1, i.e. the plate comprises rows of screw holes 16b and 
rows of holes 18b having a smaller diameter to facilitate shaping. The 
plate 26 is bent along its length axis, in particular in the edge zone and 
in addition thereto along its normal axes to better fit to the outer 
contour of the vertebras 24. Only the screw holes 16b located in the 
center of the vertebras 24 accomodate bone screws 28. 
The plate 30 shown in FIG. 5 is provided with rows of screw holes 16c 
wherein rows with three screw holes 16c alternate with rows of two screw 
holes 16c. The distance between the rows with three screw holes 16c or, 
respectively between the rows with two screw holes 16c approximately 
corresponds again to the center distance of adjacent vertebras of the 
cervical spine. Between the screw holes, rows of through holes 18c of 
smaller diameter are provided. One realizes, that by providing the screw 
holes 16c, the plate 30 is stiffer in its central region than towards the 
longitudinal edges. This is augmented by selecting the distance of both 
the central holes 18c larger than between a central and an outer hole 18c 
of the row. Thus, a relatively high ductibility is obtained in the edge 
zone, whereas the central region is substantially stiffer. 
Preferrably, the plate 30c is made endless so that the surgeon cuts off a 
suitable length.