BACKGROUND OF THE INVENTION
This invention relates to surgical spinal implant systems, and particularly to those using spinal rods contoured for connection at various locations along the spinal column.
Spinal fractures often occur at the thoracolumbar junction. Most of these fractures are burst injuries, which are particularly dangerous because retropulsed bone fragments can cause spinal cord or caudal equina injuries. Posterior fixation has long been the primary approach for traumatic spinal injuries of this type.
The development of posterior internal fixation procedures for burst fractures was a substantial improvement over early approaches of bed rest and body casts. Several disadvantages to posterior fixation were, however, discovered. For example, this approach fails to reduce kyphosis or allow complete clearing of the spinal canal. Other complications include psuedoarthroses, late rod disengagement and inadequate reduction. Some posterior instrumentations require the fusions to extend at least two levels above and below the injury, particularly at the thoracolumbar junction. The posterior approach is also limited in the viability for use in burst fractures because in such fractures, neural compression generally occurs from the anterior direction. Therefore, it is generally better to decompress and fuse the spine from the anterior.
There are several advantages to anterior internal fixation. An anterior approach allows complete clearance from the spinal canal of bone fragments and for total resection of a tumor. It also permits fusion of a minimal number of motion segments. Yet in spite of these advantages, the use of anterior approaches has been limited by the risk of complications or other disadvantages.
Several plate and screw systems have been designed for anterior instrumentation of the spinal column. The Syracuse I-Plate may use rigid or semi-rigid screws in combination with a plate. But distraction or compression of the bone graft is not possible with this system. The CASF Plate marketed by AcroMed is designed to be used in a semi-rigid manner. This device, as well, does not permit compression or distraction of the bone graft and in addition cannot be used in a rigid construct. The Stafix Plating System marketed by Daruma of Taipei, Taiwan is an anterior thoracolumbar plate designed to address similar indications. This plate incorporates slots and holes as well as permitting quadrilateral placement of screws. The Anterior Thoracolumbar Plating System (Medtronic Sofamor Danek) is a slotted plate designed to attach to the anterior lateral aspect of the vertebral body. The plate allows distract and/or compression through the use of two screws and two bolts.
Several modular spinal instrumentation systems have also been developed for anterior procedures. One such device, the Kaneda device, is shown in FIGS. 1 to 6. As shown, the device extends fixation one vertebral level cephalad and one level caudal to the vertebra in question. A typical construct has two vertebral body staples A, four vertebral screws B, two rods C, eight nuts (one on each side of a screw) and two transverse fixators F. Each vertebral body staple A has four spikes, one on each corner of the staple, to initially secure the staple to a vertebra. Vertebral screws B are then placed through holes H1 and H2 into the cephalad and caudal vertebrae. Rods C are located in the holes I in each screw B with the internal nuts D loosely threaded on each rod. The external nuts, also identified as “D” are then threaded onto the rods. Thereafter, the surgeon tightens all nuts against each side of a screw with the surgeon applying compressive or distractive forces as required. The anterior and posterior rods C are then coupled with transverse fixators F. Specific indications for such modular devices may include deficient anterior bone mass due to trauma, tumor, infection, degenerative disease, congenital causes, or deformity.
The Kaneda system is not entirely satisfactory, largely resulting from the design of vertebral staple A. The staple is used to stabilize screw B much the same way as a washer is used to stabilize a bolt in most any mechanical attachment. These staples, however, are placed on a vertebra, not a uniformly flat surface. Hence, the staple curvature should ideally match the contour of the surface of the vertebra before use. And even if the fit is perfect, it may still be unsatisfactory if the spikes on one end, say the two near hole H1, are pulled from the vertebra when a screw is tightened in the hole on the other end, H2 in our example. This “rocking” effect is depicted in FIG. 7.
Further details regarding staples in a spinal fixation device can be found in Kiyoshi Kaneda, Kaneda Anterior Spinal Instrumentation for the Thoracic and Lumbar Spine, Spinal Instrumentation, Williams & Wikins, (Baltimore, Hong Kong, London, Munich, Philadelphia, Sydney, Tokyo), pp. 413 et seq, the disclosure of which is specifically incorporated into this specification by reference.
As a result, there is a need for a vertebral staple in a modular system that can be more easily contoured to the surface of a vertebra, and that does lift spikes on one side of the staple from the vertebra when the other side is tightened. The following is one solution to this need.
SUMMARY OF THE INVENTION
In one aspect, this invention is a vertebral staple with a plate having at least two apertures to receive a spinal bolt, and at least two legs (also identifiable as prongs or spikes) integrally mounted to the bottom of the plate and wherein all legs mounted on the bottom of the plate are closer to one particular aperture for passing a spinal bolt than another aperture for passing a spinal bolt.
In another aspect, this invention is a vertebral staple with a plate having at least two apertures to receive a spinal bolt. The bottom of the plate has at least one leg (also identifiable as a prong or a spike) integrally mounted near the lateral edge of the plate, and at least one leg integrally mounted on the interior of the plate, with all legs mounted on the bottom of the plate closer to one particular aperture for passing a spinal bolt than another aperture for passing a spinal bolt.
In yet another aspect, this invention is a vertebral staple with a plate having a groove therein dividing the plate into a first portion and a second portion. Each of the first and second portions have at least one aperture for passing a bone bolt through the plate and into the vertebra to which the staple is attached. In addition, the bottom of the first portion of the plate has at least two legs (also identifiable as prongs or spikes) integrally attached to the plate, while no legs are mounted on the bottom of the second portion of the plate.