Repair of the pars interarticularis defect with a cable-screw construct. A preliminary report.

STUDY DESIGN: To report on the preliminary results of preparing and reconstructing the pars interarticularis with a cable-screw construct. The success of previous techniques to repair the pars defect has been variable. OBJECTIVES: To assess the results of a new technique for stabilizing the pars interarticularis, using the strongest materials, pedicle screws, and cables in the strongest bony elements--the pedicle and lamina. SUMMARY OF BACKGROUND DATA: Previous techniques have been inadequate structurally to stabilize the pars interarticularis effectively, or the techniques were difficult to perform. Placing a screw across the defect was technically difficult and took away from the surface area of the fusion. The Scott technique used wiring between the transverse process and spinous process; and in the Morscher Technique, a hook screw was used to repair the pars defect--a technically difficult procedure, using bulky hardware. METHODS: Patients with pars interarticularis defects were carefully selected for this technique if they had primarily low back pain that did not respond to conservative treatment. The eligible patient had Grade I or less spondylolisthesis, little or no desiccation detectable on magnetic resonance imaging, and pain reproduced with injection of the pars defect. Surgical technique involved placing a special pedicle cable-screw into the pedicle of the involved vertebra. A double cable was passed underneath the lamina, threaded through the hole of the pedicle screw, and wrapped around the spinous process. The cables were simultaneously tensioned and crimped. A tricortical bone graft was compressed between the pedicle and lamina. RESULTS: Seven patients had this technique with a follow-up of 25.5 months (range, 19-37 months). The mean age was 20.5 years (range, 12-32 years), and the mean duration of symptoms was 31 months. All patients had severe pain before surgery that prevented participation in sports and normal daily activities. After surgery, results in five were rated as excellent and in two as good, according to the Prolo score. There were no failures of the cable-screw constructs, and all of the defects appear to have united solidly. CONCLUSION: The cable-screw construct uses the strongest anchors (the pedicle and the lamina) and uses compression obtained with cables to stabilize the pars interarticularis. Early results indicate that this is a safe and effective technique for this difficult problem.

Supramalleolar osteotomy for ankle valgus in myelomeningocele.

Fifty-five supramalleolar osteotomies were performed in 35 patients for progressive hindfoot valgus in myelomeningocele. All patients were ambulatory. The most common motor level of innervation was L3 in 42 limbs. The average age at surgery was 12 years. The average follow-up was 8 years. Preoperatively, all patients experienced progressive difficulty with brace use, and anteroposterior weight-bearing ankle radiographs showed a valgus tilt of the talotibial angle (TTA) of > or = 10 degrees with an average of 18 degrees. The average postoperative correction of TTA was 17 degrees. The results were graded as follows: excellent, 42 limbs; good, eight limbs; fair, three limbs; and poor, two limbs. The fair and poor limb results were the result of loss of correction or nonunion. The best results were seen when the TTA was corrected to 5 degrees of varus.

Analysis of peridural scar formation and its prevention after lumbar laminotomy and discectomy in dogs.

STUDY DESIGN: Peridural fibrosis after lumbar laminectomy and discectomy has been implicated (not proven) as one of the factors that contribute to continuing or recurrent radicular and/or low back pain. This animal experimental study was designed to unequivocally show the stages in the development of scar tissue and to what extent, if any, scar tissue development is influenced by interposing fat grafts and Na hyaluronate of different molecular weights. METHODS: A four-level unilateral lumbar laminotomy, anular fenestration, and nucleotomy was performed in 11 dogs. In each dog, levels were selected at random: one to serve as an empty control and three to insert the following: a fat graft, a viscous (1.9%) solution of Na hyaluronate, and a 1% high molecular weight solution of Na hyaluronate solution. The animals were killed at 1 day, 2 days, and 1, 2, 4, and 12 weeks postoperatively. Immediately after the dogs were killed, the lumbar spines were frozen in situ with dry ice, the lumbar spines were harvested and sectioned with a cryomicrotome. Close-up photographs taken at submillimeter intervals at each level were digitized and postprocessed with a computer. RESULTS: In the early postoperative period a hematoma was found in the pathway of the surgical dissection. During a 2-4 week period, this hematoma was replaced by a thick, white fibrotic tissue mass. Fibrosis was markedly less pronounced at the hyaluronate levels, especially the high molecular weight subset. Two-way statistical analysis of variance without replications revealed significantly less scar formation at the 0.05 level in the hyaluronate vs. the control segments. Dunnett's test, comparing each group individually with the control, revealed no difference between the fat groups and the control subjects. There was a significant difference between 1.9% Na hyaluronate and control. CONCLUSIONS: Viscous hyaluronate solution with its semifluid properties coats the nerve roots and dura anteriorly and posteriorly and reduces peridural fibrosis in the critical anterior region where adhesions form between the nerve root and anulus fibrosus.

The use of sublaminar cables to replace Luque wires.

Sublaminar wires have been used in conjunction with posterior instrumentation to stabilize the spine. Sublaminar wiring has fallen into disfavor because of an increase in neurologic complications with the Luque technique as well as wire breakage, dural tears, and difficulty of removal. A cable system consisting of two 49-stranded stainless steel cables connected to one malleable leader was designed to overcome these shortcomings. Biomechanical testing revealed that the maximum yield strength of a single stainless steel cable loop was 2.85-2.94 times greater than a double 0.05-in. stainless steel wire loop. The fatigue tests demonstrated that the stainless steel cables required 6-22 times more cycles to failure than the stainless steel wire. Many of the titanium cables failed immediately under higher loads (0-100 lb) because of slipping of the crimp. The preliminary clinical results after a mean of 19 months of follow-up of 245 cables are encouraging. There has been no breakage or loosening of the cables and no complications associated with the use of the cables. The stainless steel cables are very strong, but more important, the cable flexibility prevents repeated contusions to the spinal cord during insertion of the rods and tightening of wires. The cable conforms to the undersurface of the lamina. This may lead to a decrease in neurologic complications.

Effects of sodium hyaluronate on peridural fibrosis after lumbar laminotomy and discectomy.

Sodium hyaluronate, 1.9% solution, was evaluated for its ability to retard peridural fibrosis after unilateral lumbar hemilaminotomy, anular fenestration, and nuclectomy in dogs. Three materials: fat grafts, gelfoam, and sodium hyaluronate, were compared with empty controls for their ability to inhibit peridural fibrosis. Each dog served as his own internal control and the formation of fibrosis was evaluated at 2, 4, 12, and 26 weeks. Sodium hyaluronate was found to inhibit fibrosis more than the other materials on both a macroscopic and microscopic level. The area of fibrosis and tenacity of the adhesions on dissection were notably less in the sodium hyaluronate group. Microscopically, the thickness of collagen and number of fibroblasts were decreased with the use of 1.9% sodium hyaluronate. The peridural fibrosis occurred equally both anteriorly and posteriorly to the nerve roots and correlated with the area of surgical dissection. Fat grafts were not effective in preventing fibrosis anteriorly, especially in the region of the exiting nerve roots. Gelfoam did not inhibit but actually appeared to increase fibrosis formation. Interposition materials currently used in humans to prevent scar formation such as gelfoam and fat grafts have only addressed the posterior scar formation, which do little to alter the fibrosis anteriorly. The adhesions between the nerve root and the anulus fibrosus bind the nerve root down anteriorly, making it more vulnerable to recurrent disc herniation. Sodium hyaluronate, 1.9% solution, with its viscous semifluid properties, coats the nerve roots and dura anteriorly and posteriorly.(ABSTRACT TRUNCATED AT 250 WORDS)