Osteogenic protein versus autologous interbody arthrodesis in the sheep thoracic spine. A comparative endoscopic study using the Bagby and Kuslich interbody fusion device.

STUDY DESIGN: Using an in vivo interbody arthrodesis model, the efficacy of the Bagby and Kuslich (BAK) device packed with recombinant human osteogenic protein-1 (rhOP-1) was evaluated. OBJECTIVES: To compare the efficacy of osteogenic protein with that of autograft for interbody arthrodesis, with fusion success based on biomechanical, histologic, and radiographic analyses. SUMMARY OF BACKGROUND DATA: The use of recombinant human bone morphogenetic proteins (rhBMPs) as osteoinductive bone graft substitutes or expanders has recently gained considerable research interest, particularly when applied in posterolateral arthrodesis. However, whether these results can be extrapolated to a successful interbody spinal arthrodesis remains uncertain. METHODS: Twelve sheep underwent a multilevel thoracic spinal decompression by thoracoscopic approach. Three noncontiguous destabilization sites (T5-T6, T7-T8, T9-T10) were prepared and randomly treated as follows. Control group treatments were nonsurgical, destabilization alone, and empty BAK. Experimental groups were treated with autograft alone, BAK device packed with autograft, or BAK device packed with rhOP-1. Four months after surgery, interbody fusion status was quantified by biomechanical testing, computed tomography, microradiography, and histomorphometry. RESULTS: Results of biomechanical analysis showed statistically higher segmental stiffness levels when comparing the control and experimental groups with four of the five testing methods (P < 0.05). Computed tomography and microradiography characterized destabilization alone as producing one fusion in six preparations; the empty BAK, two in six;, autograft alone, four in eight; BAK with autograft, five in eight; and BAK with rhOP-1 group, six in eight-all evidenced by woven trabecular bone spanning the fusion sites. Histomorphometry yielded significantly more trabecular bone formation at the fusion sites in the three experimental groups than in the two control groups (P < 0.05). CONCLUSIONS: Interbody spinal fusions showing biomechanical and histomorphometric equivalency to autologous fusions have been achieved with rhOP-1. The functional unit stability and histologic osteointegration evidenced by the BAK/rhOP-1 complex shows this interbody arthrodesis technique to be a viable alternative toconventional autologous iliac crest, thereby obviating the need for an iliac crest donor site and associated patient morbidity.

The effects of rigid spinal instrumentation and solid bony fusion on spinal kinematics. A posterolateral spinal arthrodesis model.

STUDY DESIGN: Spinal kinematics after the implementation of rigid spinal instrumentation or the achievement of a solid fusion was studied using a sheep posterolateral spinal arthrodesis model. OBJECTIVE: To investigate the effects of rigid spinal instrumentation or solid fusion on spinal kinematic parameters. SUMMARY OF BACKGROUND DATA: Numerous studies have attempted to define spinal instability in terms of kinematics. Recent in vitro studies have documented the neutral zone, or a measure of spinal laxity, as more sensitive to spinal instability than the range of motion. METHODS: Seven skeletally mature sheep underwent a single-level posterolateral lumbar arthrodesis using autologous bone graft augmented with transpedicular screw fixation. The animals were killed 4 months after surgery. The identical surgical procedures were performed in seven sheep cadaveric spines, which served as acute postoperative controls. Each functional spinal unit was tested biomechanically before and after hardware removal. The experimental control groups consisted of destabilized spines and spines that underwent transpedicular screw fixation alone, whereas the fusion groups included spines that underwent posterolateral fusion alone or posterolateral fusion with instrumentation. RESULTS: Rigid instrumentation and solid fusion significantly decreased the neutral zone and range of motion in all testing modes. In axial rotation and lateral bending, solid fusion reduced the range of motion significantly more than transpedicular screw fixation alone. However, in all testing modes, the neutral zones showed no statistical difference between transpedicular screw fixation alone and fusion groups. CONCLUSIONS: The range of motion was an equivalent or better indicator of fixation or fusion stability compared with the neutral zone. Moreover, the immediate postoperative fixation stability, even if using transpedicular screw fixation, was less than the stability present after a solid fusion.

Maturation of the posterolateral spinal fusion and its effect on load-sharing of spinal instrumentation. An in vivo sheep model.

UNLABELLED: We investigated the temporal relationship among the biomechanical, radiographic, and histological properties of a posterolateral spinal fusion mass to elucidate the changes in load-sharing of the spinal instrumentation and that of the fusion mass throughout the healing process. Destabilization of the posterior spinal column and transpedicular screw fixation at the segments between the third and fourth and the fifth and sixth lumbar vertebrae was performed in twenty-four sheep. A posterolateral spinal arthrodesis with use of autologous corticocancellous bone graft was done randomly at one of the two segments; the other segment (without bone graft) served as the instrumented control. Six animals each were killed at four, eight, twelve, and sixteen weeks postoperatively. Biomechanical testing showed that the posterolateral fusion mass had increased mechanical stiffness after the fourth week. The strain on the hardware, measured with use of rods instrumented with strain-gauges, decreased significantly (p < 0.01) beginning at eight weeks. Radiographically, three independent observations of each of the six animals at each time-period showed that, although all of the fusion masses were considered solid unions at sixteen weeks, bridging of trabecular bone was noted during only ten of eighteen observations at twelve weeks, three of eighteen observations at eight weeks, and none of eighteen observations at four weeks. Computerized tomography and histomorphometric analyses demonstrated that mineralization in the fusion mass increased in a linear fashion even after eight weeks. Histologically, the fusion mass consisted predominantly of woven bone at eight weeks; thereafter, it was gradually trabeculated. CLINICAL RELEVANCE: We found a great discrepancy between biomechanical stability and histological maturation of the posterolateral fusion mass. The biomechanical properties of a stable spinal fusion preceded the radiographic appearance of a solid fusion by at least eight weeks, suggesting that immature woven bone provided substantial stiffness to the fusion mass. The spinal instrumentation was subjected predominantly to bending stress rather than to axial stress, and the load-sharing of the spinal instrumentation decreased concurrently with the development of the spinal fusion.

Prevalence of perioperative complications after anterior spinal fusion for patients with idiopathic scoliosis.

Anterior spinal fusion (ASF) has been proven to improve curve correction, save motion segments, and decrease the rate of pseudarthrosis when compared with posterior spinal fusion alone. However, in patients with idiopathic scoliosis, the complication rate of the anterior approach to the spine using current techniques has only been scantly defined in the literature. This is a retrospective review of consecutive patients who underwent primary ASF for idiopathic scoliosis to determine the prevalence and types of complications specifically related to the anterior approach. All patients who underwent primary ASFs for idiopathic scoliosis done by one of two orthopaedic surgeons between October 1986 and July 1992 were reviewed. Adequate records were available for 98 of 103 patients. The average age at time of surgery was 22 years (range, 10-60 years). Complications were divided into three groups: major (resulting in permanent sequelae or necessitating a second major operation); minor (resulting in a prolonged hospital stay, necessitating a minor operation, and/or resulting in a significant temporary hardship or persistent minor problem); and insignificant (anything less than minor). One of 98 patients had a major complication (a pelvic deep venous thrombosis that required operative thrombectomy). Twenty-five of 98 patients had 28 complications classified as minor, and 28 of 98 patients had 30 complications classified as insignificant. Smoking was a significant risk factor for the development of minor complications. There was no statistically significant relationship between the development of complications and the degree of curve, the approach used, the procedure performed, or the performance of rib resections. The anterior approach to the spine in patients with idiopathic scoliosis in this series was very safe, with only one major complication in 98 patients. However, minor and insignificant complications were quite common, occurring in 45 of 98 patients (46%). Smoking was a significant risk factor for minor complications.

In vitro biomechanical comparison of multistrand cables with conventional cervical stabilization.

STUDY DESIGN: The biomechanical stability of six different methods of cervical spine stabilization, three using multistrand cables, were evaluated in a bovine model. OBJECTIVES: To quantify and compare the in vitro biomechanical properties of multistrand cables used for posterior cervical wiring to standard cervical fixation techniques. SUMMARY OF BACKGROUND DATA: Fixation of the posterior cervical spine with monofilament stainless steel wire is a proven technique for stabilization of the cervical spine. Recently, multistrand braided cables have been used as a substitute for monofilament stainless steel wires. These cables, made of stainless steel, titanium, or polyethylene, are reported to be stronger, more flexible, and fatigue resistant than are monofilament wire based on mechanical testing. However, no in vitro biomechanical studies have been performed testing a standard posterior cervical wiring technique using multistrand cables. METHODS: Thirty-six fresh frozen cervical calf spines consistent in size and age were mounted and fixed rigidly to isolate the C4-C5 motion segment. Six different reconstruction techniques were evaluated for Rogers' posterior cervical wiring technique using: 1) 20-gauge stainless steel monofilament wire, 2) stainless steel cable, 3) titanium cable, 4) polyethylene cables, 5) anterior locking plate construct with interbody graft, and 6) posterior plate construct. Six cervical spines were included in each group (n = 6), with each specimen statically evaluated under three stability conditions: 1) intact, 2) reconstructed, and 3) postfatigue. The instability model created before the reconstruction consisted of a distractive flexion Stage 3 injury at C4-C5. Nondestructive static biomechanical testing, performed on an material testing machine (MTS 858 Bionix test system, Minneapolis, MN), included axial compression, axial rotation, flexion-extension, and lateral bending. After reconstruction and static analysis, the specimens were fatigued for 1500 cycles and then statically retested. Data analysis included normalization of the reconstructed and postfatigue data to the intact condition. The calculated static parameters included operative functional unit stiffness and range of motion. RESULTS: Posterior cervical reconstruction with stainless steel monofilament wire proved inadequate under fatigue testing. Two of the six specimens failed with fatigue, and this construct permitted the greatest degree of flexion-extension motion after fatigue in comparison with all other constructs (P < 0.05). There were no significant differences in flexural stiffness or range of motion between stainless steel, titanium, or polyethylene cable constructs before or after fatigue testing. The posterior cervical plate constructs were the stiffest constructs under flexion, extension, and lateral bending modes, before and after fatigue testing (P < 0.05). CONCLUSIONS: Multistrand cables were superior to monofilament wire with fatigue testing using an in vitro calf cervical spine model. There were no failures or detectable differences in elongation after fatigue testing between the stainless steel, titanium, and polyethylene cables, as shown by the flexion-extension range of motion. The posterior cervical plate construct offered the greatest stability compared with all other constructs.

Minimally invasive surgical techniques to treat spine infections.

Minimally invasive techniques including closed laparoscopy and thoracoscopy as well as video-assisted procedures using limited open incisions provide an excellent alternative for treating vertebral osteomyelitis and tuberculous infections in the thoracic and lumbar spine. The traditional principles of surgical debridement and a stable interbody fusion are unchanged when applying endoscopic techniques. In the future, the spinal endoscopist will have available a larger selection of endoscopic instruments, more sophisticated video technology, and the development of anterior instrumentation systems to allow for rigid internal fixation. These advances, along with the surgeon's endoscopic experience and refined techniques, will further establish minimally invasive surgical techniques in the field of spinal surgery.