Modified Gallie technique versus transarticular screw fixation in C1-C2 fusion.

The effectiveness of a modified Gallie technique versus Magerl and Seeman transarticular screw fixation was compared in the management of 27 patients with symptomatic atlantoaxial instability. Twelve patients were treated using a modified Gallie technique and postoperative halo vest immobilization. Atlantoaxial arthrodesis occurred in seven (58%) patients, stable fibrous union occurred in one patient, and pseudarthrosis with recurrent instability developed in four (33%) patients. Average followup was 6.9 years. All 15 patients treated using Magerl and Seeman transarticular screw fixation and postoperative soft collar immobilization had atlantoaxial arthrodesis develop. Average duration of followup was 4 years. One patient sustained vertebral artery injury during preparation for screw placement. Magerl and Seeman transarticular screw fixation provides stability and more reliably produces atlantoaxial arthrodesis than the Gallie technique provides in patients with atlantoaxial instability without the need for rigid postoperative bracing. Potential for vertebral artery exists despite apparent accurate screw placement. To ensure that safe transarticular screw placement is possible, preoperative fine cut axial computed tomography with reconstructions is required to assess vertebral artery position and C2 isthmus anatomy. A proportion of patients have anatomy unsuitable for screw placement. Traditional wiring techniques are indicated in these patients.

The effect of spinal implant rigidity on vertebral bone density. A canine model.

An animal model of anterior and posterior column instability was developed to allow in vivo observation of bone remodeling and arthrodesis following spinal instrumentation. After an initial anterior and posterior destabilizing lesion was created at the L5-L6 vertebral levels in 63 adult beagles, various spinal reconstructive surgical procedures were performed--with or without bilateral posterolateral bone grafting, with or without bilateral oophorectomies, and with or without spinal instrumentation (Harrington distraction, Luque rectangular, Cotrel-Dubousset pedicular, or Steffee pedicular implants). Observation 6 months after surgery revealed a significantly improved probability of achieving a spinal fusion if spinal instrumentation had been used (X2 = 5.84, P = .016). Nondestructive mechanical testing after removal of all metal instrumentation in torsion, axial compression, and flexion revealed that the fusions performed in conjunction with spinal instrumentation were more rigid (P less than .05). Quantitative histomorphometry showed that the volumetric density of bone was significantly lower (ie, device-related osteoporosis occurred) for fused versus unfused spines. In addition, a linear correlation occurred between decreasing volumetric density of bone and increasing rigidity of the spinal implant (r = .778); ie, device-related osteoporosis occurred secondary to Harrington, Cotrel-Dubousset, and Steffee pedicular instrumentation. Oophorectomized dogs became more osteoporotic than their surgically matched controls (posterolateral bone grafting alone, Cotrel-Dubousset pedicular instrumentation, and Steffee pedicular instrumentation); device-related osteoporosis added to the degree of hormonally induced osteoporosis (t = 5.0, P less than .0001). This is the first study to date documenting the occurrence of stress shielding in the spine secondary to spinal instrumentation.(ABSTRACT TRUNCATED AT 250 WORDS)

Pseudarthrosis of the cervical spine after anterior arthrodesis. Treatment by posterior nerve-root decompression, stabilization, and arthrodesis.

Nineteen consecutive patients who had a symptomatic pseudarthrosis after a failed anterior cervical arthrodesis were treated by a posterior nerve-root decompression and arthrodesis. The indications for the operation were radiculopathy in the absence of myelopathy and evidence of a pseudarthrosis on lateral flexion and extension radiographs. The average duration of follow-up was forty-four months (range, twenty-four to fifty-four months). A solid fusion was achieved in all patients, and the radiculopathy was relieved in all but one. The motor weakness that had been present in four patients preoperatively resolved completely.

1989 Volvo Award in basic science. Device-related osteoporosis with spinal instrumentation.

An animal model of anterior and posterior column instability was developed to allow in vivo observation of bone remodeling and arthrodesis after spinal instrumentation. After an initial anterior and posterior destabilizing lesion was created at the L5-L6 vertebral levels in 42 adult beagles, various spinal reconstructive surgical procedures were performed--with or without bilateral posterolateral bone grafting, and with or without spinal instrumentation (Harrington distraction; Luque rectangular, or Cotrel-Dubousset transpedicular methods). After 6 months' postoperative observation, there was a significantly improved probability of achieving a spinal fusion if spinal instrumentation had been used (P = 0.058). Nondestructive mechanical testing after removal of all metal instrumentation in torsion, axial compression, and flexion revealed that the fusions performed in conjunction with spinal instrumentation were more rigid (P less than 0.05). Quantitative histomorphometry showed that the volumetric density of bone was significantly lower (ie, device-related osteoporosis occurred) for fused versus unfused spines; and Harrington- and Cotrel-Dubousset-instrumented dogs became more osteoporotic than the other three groups. The rigidity of spinal instrumentation led to device-related osteoporosis (stress shielding) of the vertebra. However, as the rigidity of spinal instrumentation increased, there was an increased probability of achieving a successful spinal fusion. The improved mechanical properties of spinal instrumentation on spinal arthrodesis more than compensate for the occurrence of device-related osteoporosis in the spine.

Quantitative histologic study of the influence of spinal instrumentation on lumbar fusions: a canine model.

UNLABELLED: Histomorphometric and microradiographic studies were performed on 28 beagle hounds 1 year of age, followed up for 6 months after an L5-L6 anterior and posterior spinal destabilization procedure--Group I (n = 7), destabilized surgical controls; Group II (n = 7), posterolateral bone grafting after destabilization; Group III (n = 7), Harrington rod instrumentation and posterolateral bone grafting after destabilization; and Group IV (n = 7), Luque instrumentation, and bone grafting after destabilization. Six months postoperatively, device-related osteoporosis occurred in spines treated with spinal instrumentation. Within the L5 vertebral body the mean trabecular width was less for the two groups with instrumentation (Groups III and IV) compared with the two groups without instrumentation (Groups I and II) (p less than 0.001). The bone formation rate [mm3/(mm3 x year)] x 10(3), which is based on the mean distance between sequenced fluorochrome labels, for Group I (destabilized, nonfused, noninstrumented dogs) was more than twice that of the other three groups, which were all equivalent (p less than 0.05). CLINICAL RELEVANCE: Stress shielding, or more correctly, device-related osteoporosis, probably can occur within vertebrae in response to rigid spinal instrumentation. However, the overall mechanical properties of vertebrae underlying spinal instrumentation are probably not at increased risk of fracture because the increase in cross-sectional area of the vertebra and incorporated fusion mass more than compensate for the loss of volumetric bone density.

A biomechanical evaluation of cervical spinal stabilization methods in a bovine model. Static and cyclical loading.

A bovine model was developed for biomechanical evaluation of surgical procedures stabilizing traumatic cervical injuries disrupting the anterior and posterior spinal column. Cervical spinal segments and C4-5 functional spinal units were tested statically, and C4-5 functional spinal units were tested cyclically in evaluation of 1) the intact cervical spine, 2) Rogers' wiring method, 3) Bohlman's triple-wire technique, 4) sublaminar wiring, 5) anterior cervical plate instrumentation, and 6) posterior hook plate stabilization. Anterior cervical plate instrumentation proved inadequate, and was the least rigid, with axial and flexural loading (P less than 0.05). There was no significant difference between each of the three posterior wiring methods, and all generally restored stability to equal that of the uninjured intact cervical spine. Posterior hook plating with an interspinous bone graft serving as an extension block was the most effective method in reducing flexural stress across the injured C4-5 segment (P less than 0.05). Cyclical in vitro testing was the most sensitive method in highlighting mechanical differences between instrumentation systems, particularly with "on-line" continuous measurement of anterior and posterior strains. Anterior cervical plate stabilization does not appear to confer enough stability in cervical facet injuries to obviate the need for posterior cervical stabilization procedures. The recently developed posterior hook plate technique offers biomechanical advantages that should be weighed against the greater technical precision needed for insertion and the increased potential for neurologic and vascular complications.

The biomechanical and histomorphometric properties of anterior lumbar fusions: a canine model.

An in vivo model was developed to compare the biomechanical stability, incidence of radiographic union, bone formation rate, and bone graft remodeling parameters of anterior interbody fusions. Eighteen 1-year-old beagles underwent anterior and posterior spinal destabilization procedures at L5-L6 to produce a reproducible amount of spinal instability--resection of the anterior longitudinal ligament, L5-L6 intervertebral disk, L5 and L6 lamina, spinous processes, zygoopophyseal joints, and ligamentum flavum. Group I (N = 6) were surgically destabilized controls; Group II (N = 6) underwent anterior L5-L6 interbody fusion with iliac crest bone graft; and Group III (N = 6) underwent anterior stabilization with a longitudinal fibular strut graft in addition to the same operative procedure as Group II. Six months postoperatively the group with the highest incidence of successful radiographic L5-L6 arthrodesis was Group III, anterior interbody fusion and fibular stabilization (p less than .10). The rank order of biomechanical stability was the same for the three groups for both torsional and axial compressive stiffness, with Group I (destabilized controls) being the least rigid, then Group II (anterior fusion with iliac crest grafting only), and the most rigid to both torsion and axial compressive loading was Group III (anterior fusion with fibular stabilization and iliac crest bone graft). The bone formation rate [mm3/(mm3 x year) x 10(3)], which was derived from the distance between fluorochrome markers, revealed that the more stable the individual spinal construct, the lower the bone formation rate. In summary, the beagle provided a successful model for studying in vivo the response of anterior bone grafts over a 6-month interval and provided comparative biomechanical and histomorphometric data on spinal interbody fusion techniques.

A comparative biomechanical study of spinal fixation using the combination spinal rod-plate and transpedicular screw fixation system.

A biomechanical study was performed comparing the stiffness and stability of the three-level combination spinal rod-plate and transpedicular screw (CSRP-TPS) fixation system with those of three anterior stabilization constructs that spanned three vertebral levels: iliac strut grafting, polymethylmethacrylate and anterior Harrington rod instrumentation (technique of Siegal et al.), and the Kaneda anterior device. The CSRP-TPS fixation system was also compared with five posterior instrumentation systems that spanned five vertebral levels: Harrington distraction rod instrumentation, segmentally wired Luque rectangular instrumentation, Cotrel-Dubousset transpedicular instrumentation. Steffee transpedicular screws and plates, and R. Roy-Camille plates under conditions of single-level instability. The relative stability of each instrumentation system was compared by mounting the fixation systems on calf spine segments containing five motion segments destabilized by complete L3 anterior corpectomies and L2-L3 and L3-L4 anterior diskectomies to simulate the two-column instability found clinically in spine fractures. Mechanical nondestructive cyclical testing in rotation, axial compression, and flexion was performed on 12 spines. All biomechanical tests were performed on a biaxial servo-controlled MTS 858 Bionix hydraulic materials testing device with a biaxial load cell. Intervertebral displacements between L2 and L4 were continuously recorded utilizing an extensometer with the knife edges placed directly adjacent to the L3 corpectomy defect during testing. This biomechanical study showed that CSRP-TPS instrumentation spanning three vertebral levels could restore the torsional, compressive, and flexural rigidity of the destabilized calf spines to that of the intact calf spines and provided more in vitro stability than either the traditional five-level Harrington distraction rod or the segmentally wired Luque rectangular instrumentation. The greatest torsional rigidity occurred with the five-level Cotrel-Dubousset instrumentation, the five-level Steffee plate and screw system, and the three-level Kaneda anterior device. In axial compression and flexural testing, the three-level CSRP-TPS system provided fixation comparable with the five-level Cotrel-Dubousset instrumentation, the five-level Steffee transpedicular screw and plate system, the five-level R. Roy-Camille plate and screw system, and the three-level Kaneda anterior device. Satisfactory levels of rigidity can be restored by three-level CSRP-TPS instrumentation under conditions of single-level instability in unstable thoracolumbar and lumbar spine fractures.