Kinematic evaluation of lumbar fusion techniques.

STUDY DESIGN: Eight human cadaveric lumbosacral spines were biomechanically and kinematically tested in torsion and compression-flexion. They were retested after simulated posterolateral fusion, anterior lumbar interbody fusion, and circumferential fusion. OBJECTIVES: To analyze stiffness and motion in the anterior and posterior columns of the index and contiguous spinal motion units of anterior, posterolateral, and circumferential fusions. SUMMARY OF BACKGROUND DATA: Previous biomechanical studies have not incorporated analysis of motion with six degrees of freedom, consideration of contiguous levels, and comparisons of anterior and posterior column motion. METHODS: Eight human cadaveric lumbosacral spines were biomechanically tested in compression-flexion and torsion using an advanced biplanar radiography technique. Each specimen underwent either a simulated posterolateral fusion or anterior fusion followed by a circumferential fusion. Motion and stiffness at the level of the fusion and at contiguous levels were analyzed independently in the anterior and posterior columns of the spine. RESULTS: At the level of fusion, the simulated posterolateral and anterior fusions prevented more motion in torsion compared with compression-flexion. With all specimens, it was shown that circumferential fusions were stiffer than the intact specimen. Our comparison of motion in the anterior and posterior columns found no significant differences within the columns of a single vertebral motion segment. Compared with posterolateral fusions, anterior fusions were found to have the greatest effect in increasing motion at contiguous levels. The effect of circumferential fusions on adjacent level kinematics was not significantly greater than that of anterior fusions. CONCLUSION: There are major biomechanical differences between different fusion techniques. This information should be considered in patients undergoing lumbar spinal fusion.

A comparative analysis of spondylolysis repair.

STUDY DESIGN: This retrospective study compared patient outcome after two surgical techniques for pars interarticularis repair: 1) buck screw fixation and 2) the modified Morscher-designed spondylolysis distraction hook. OBJECTIVES: To determine whether one technique was associated with higher radiographic, clinical, or implant failure. SUMMARY OF BACKGROUND DATA: Both techniques have been reported as giving good clinical results. METHODS: Twenty patients were included in this study. All patients had Type IIA spondylolytic defects with either a Grade 0 or Grade I spondylolisthesis. Nine patients were treated with the Morscher hook implant, and 11 patients were treated with the Buck technique. RESULTS: Radiographic follow-up of the Morscher implants demonstrated loosening in three and breakage in one. Radiographic analysis of the Buck technique demonstrated implant failure in one. Failure of healing occurred in four instances with the Morscher implant compared with two instances with the Buck technique. Clinical outcome was assessed using the modified Prolo score. The mean outcomes were 6.33 in the Morscher group and 6.09 in the Buck group. CONCLUSIONS: In these patients, the Morscher implant had a high failure rate. Furthermore, the clinical outcome in this group of patients was poor using either technique.

Complications associated with the technique of pedicle screw fixation. A selected survey of ABS members.

A limited survey analysis of 617 surgical cases in which pedicle screw implants were used was undertaken to ascertain the incidence and variety of associated complications. The different implant systems used included variable spinal plating (n = 249), Edwards (n = 143), and AO fixateur interne (n = 101). The most common intraoperative problem was unrecognized screw misplacement (5.2%). Fracturing of the pedicle during screw insertion and iatrogenic cerebrospinal fluid leak occurred in 4.2% of cases. The postoperative deep infection rate was 4.2%. Transient neuropraxia occurred in 2.4% of cases, and permanent nerve root injury occurred in 2.3% of cases. Previously unreported injury to nerve roots occurred late in the postoperative course in three cases. Screw breakage occurred in 2.9% of cases. All other complications had an incidence of less than 2%. The authors conclude that pedicle screw placement may be associated with significant intraoperative and postoperative complications. This information is of value to surgeons using pedicle implant systems as well as to their patients. Repeat surgery is associated with greater numbers of complications.