“You can't teach an old dog new tricks”
Edward C. Benzel
Edward C. Benzel
✓ The short-rod/two-claw (SRTC) technique of spine instrumentation was recently introduced for the treatment of thoracic and lumbar spine fractures. The use of this technique in 10 patients harboring wedge compression or burst fractures of the thoracic or lumbar spine is described.
Of three patients treated with the construct placed in a distraction mode, the average follow-up loss of angle (the difference between the immediate postoperative and follow-up midsagittal angle as measured on x-ray films) was 18.3°. Of the seven patients in whom the instrumentation was placed in a compression mode, the average observed loss of angle at follow-up examination was 1.6°. Two patients had a preoperative scoliotic deformity at the fracture site. and both deformities were exaggerated by the placement of the SRTC technique in compression. Although no patient experienced an adverse outcome and all achieved a solid fusion, the application of the SRTC technique of universal spine instrumentation in distraction was associated with an exaggerated loss of angle. Loss of angle and deformity exaggeration are not desirable and are preventable by strict patient selection and by applying the construct in a compression mode. It is emphasized that few patients are candidates for this form of instrumentation. When applicable. however, the advantages of decreased pain and stiffness and the elimination of the need for instrumentation removal make the SRTC and related short-segment techniques desirable alternatives to traditional methods of spinal fixation.
Edward C. Benzel
Edward C. Benzel
✓ A three-quarter prone position for the lateral extracavitary operative approach to the thoracic and lumbar spine is described. This approach has been used in 40 patients with anterior spinal cord compressive lesions in the thoracic and/or lumbar region. In this patient population, it has allowed a safe ventral decompression of the spinal cord. It also allows placement of spinal instrumentation through the same incision. Both the operating surgeon and the assistant have an excellent view of the operative site, including the dural sac. Patient positioning and the operative approach are described and illustrated.
Nevan G. Baldwin and Edward C. Benzel
✓ Secure fixation of the sacrum is technically challenging. The bone of the dorsal sacral surface is often thin, making hook fixation tenuous. The use of bone screws in the sacral pedicles has gained popularity, but rigidity is often not achieved and screw pullout is common. Solid constructs have been achieved using angled rods to stabilize the ilium, but these methods are technically difficult and time-consuming to perform.
A technique is described that achieves rigid sacral fixation by adding a bone screw placed through both cortical surfaces of the ilium. This bone screw is a new type that allows attachment to a rod at variable angles. It permits easy attachment to an appropriately contoured rod, which is affixed to sacral hooks or screws. The resulting configuration of the bone-metal interface creates a tripod for load distribution. Additionally, the splayed geometry of these purchase sites provides a significant biomechanical advantage preventing the instrument from being pulled out. The technique for this fixation method, particularly for patients with complex spinal disorders, is described. Use of this new technique provides significant advantages to the spine surgeon in situations in which substantial sacral fixation integrity is necessary.
Edward C. Benzel
Edward C. Benzel and Nevan G. Baldwin
✓ An ideal spinal construct should immobilize only the unstable spinal segments, and thus only the segments fused. Pedicle fixation techniques have provided operative stabilization with the instrumentation of a minimal number of spinal segments; however, some failures have been observed with pedicle instrumentation. These failures are primarily related to excessive preload forces and limitations caused by the size and orientation of the pedicles.
To circumvent these problems, a new technique, the crossed-screw fixation method, was developed and is described in this report. This technique facilitates short-segment spinal fixation and uses a lateral extracavitary approach, which provides generous exposure for spinal decompression and interbody fusion. The technique employs two large transverse vertebral body screws (6.5 to 8.5 mm in diameter) to bear axial loads, and two unilateral pedicle screws (placed on the side of the exposure) to restrict flexion and extension deformation around the transverse screws and to provide three-dimensional deformity correction. The horizontal vertebral body and the pedicle screws are connected to rods and then to each other via rigid crosslinking. The transverse vertebral body screws are unloaded during insertion by placing the construct in a compression mode after the interbody bone graft is placed, thus optimizing the advantage gained by the significant “toe-in” configuration provided and further decreasing the chance for instrumentation failure.
The initial results of this technique are reported in a series of 10 consecutively treated patients, in whom correction of the deformity was facilitated. Follow-up examination (average 10.1 months after surgery) demonstrated negligible angulation. Chronic pain was minimal. The crossed-screw fixation technique is biomechanically sound and offers a rapid and safe form of short-segment three-dimensional deformity correction and solid fixation when utilized in conjunction with the lateral extracavitary approach to the unstable thoracic and lumbar spine. This approach also facilitates the secure placement of an interbody bone graft.
Edward C. Benzel and Lee Kesterson
✓ A technique of posterior cervical interspinous compression wiring and fusion, which offers significant immediate stability, is presented. Its efficacy in 50 consecutive cases illustrates its utility. The technique involves the passage of an interspinous cerclage wire. Rather than placement of onlay laminar and facet grafts, a split-thickness tricortical iliac-crest graft is compressed against the involved medial laminae and spinous processes bilaterally. These grafts are held in place by a compression wire, which encircles the grafts and thus sandwiches the spinous processes between them. This virtually ensures subsequent bone fusion and offers substantial acute stability. The compression wire offers an added advantage of encircling the cerclage wire, thus pulling it dorsally. This significantly diminishes translational mobility at the unstable segment. It also minimizes hyperextension at the unstable segment via medial compression of the grafts into the interspinous space.
The fusion of a minimal number of spinal segments is emphasized. This substantially diminishes the chance of flexible kyphosis and degenerative changes, both above and below the fusion site. A three- or four-level fusion was performed in only 11 patients. The remaining 39 patients underwent two-level fusion. A solid bone fusion was achieved in all cases, with a follow-up period of at least 6 months. In one patient, the spinous process fractured, necessitating an anterior fusion procedure. The technique presented here appears to acutely offer a very stable construct and, in addition, is a simple and straightforward procedure for the treatment of the unstable cervical spine.