Assessment of hepatic inflammation after spinal cord injury using intravital microscopy.

OBJECTIVES: The liver has been shown to play a particularly important role in the initiation and progression of the early systemic inflammatory response (SIR) to spinal cord injury (SCI). The purpose of this study was to determine the time course of leucocyte recruitment to the liver, and to determine the effect of injury severity on the magnitude of leucocyte recruitment and hepatic injury. METHODS: Rats were randomly assigned to one of the following groups: uninjured, sham-injured (laminectomy and no cord injury), cord compressed or cord transected. At 30 min and 90 min after SCI rats had the left lobe of their livers externalised and visualised using intravital video microscopy. RESULTS: Thirty minutes after injury the total number of leucocytes per post-sinusoidal venule was significantly increased after cord transection compared to that in uninjured and sham-injured rats (P<0.05). Of these leucocytes, significantly more were adherent to venule walls (P<0.05). At 90 min the total number of leucocytes per post-sinusoidal venule and the number of adherent and rolling leucocytes was significantly increased after cord transection and cord compression (P<0.05). DISCUSSION: This is the first study to use intravital microscopy to visualise systemic inflammation in the liver following SCI. We have demonstrated immediate leucocyte recruitment to the liver within 30 min after injury and have shown that systemic inflammation increases with time after injury and with severity of injury.

Use of co-registered high-resolution computed tomography scans before and after screw insertion as a novel technique for bone mineral density determination along screw trajectory.

INTRODUCTION: Bone mineral density (BMD) is an important factor in the examination of the performance of bone instrumentation both in and ex vivo, and until now, there has not existed a reliable technique for determining BMD at the precise location of such hardware. This paper describes such a technique, using cadaveric human sacra as a model. METHODS: Nine fresh-frozen sacra had solid and hollow titanium screws placed into the S1 pedicles from a posterior approach. High-resolution micro-computed tomography (CT) was performed on each specimen before and after screw placement. All images were reconstructed with an isotropic spatial resolution of 308 mum, reoriented, and the pre-screw and post-screw scans were registered and transformed using a six-degree rigid-body transformation matrix. Once registered, two points, corresponding to the center of the screw at the cortex and at the screw tip, were determined in each scan. These points were used to generate cylindrical regions of interest (ROI) with the same trajectory and dimensions as the screw. BMD measurements were obtained within each of the ROI in the pre-screw scan. To examine the effect of artefact on BMD measurements around the titanium screws, annular ROI of 1 mm thickness were created expanding from the surface of the screws, and BMD was measured within each in both the pre- and post-screw scans. RESULTS: The registration process was accurate to 190 mum, with a precision of 189 mum and error in BMD measurement of +/-2% in repeated scans. BMD values in the cylindrical ROI corresponding to screw trajectories were not statistically different from side to side of each specimen (p=0.23). Metal artefact created significant differences in BMD values (p=0.001) and followed an exponential decay curve as distance from the screws increased, approaching a low value of approximately 20 mg HA cm(-3), but not disappearing completely. SUMMARY: CT in the presence of metal creates artefact, making measured BMD values near implants unreliable. This technique is accurate for determination of BMD, non-destructive, and eliminates the problem of this metal artefact through the use of co-registered scans. This technique has applications both in vitro and in vivo.

The USS pedicle hook system: a morphometric analysis of its safety in the thoracic spine. Universal Spine System.

The Universal Spine System (USS) pedicle hook design includes a fixation screw that passes obliquely in the anterocranial direction in the pedicle. The addition of the fixation screw was to address concerns with rotation of the hook and hook disengagement. This study was designed to evaluate the safety of the USS screw locked pedicle hook. Eleven cadaveric thoracic spines were instrumented posteriorly with USS pedicle hooks from T1 to T12. Spinal instrumentation was performed by a spinal surgeon experienced with the USS system. Spinal deformity was created prior to instrumentation, ranging from 0 to 55 degrees in the horizontal plane (rotation) and from 0 to 50 degrees in the frontal plane (scoliosis). Radiographs, computed tomography (CT), and segmental dissection were used for data acquisition. Morphometric CT analysis before instrumentation demonstrated that the transverse pedicular diameter was the smallest at T5 with a mean of 3.7 mm. The transverse pedicular angle (TPA) was found to always point toward the midline. The largest TPA was observed at T1 with a mean TPA of 28.4 degrees. The pedicle with the least angular deviation from the midline was T11 with a mean TPA of 7 degrees. Postinstrumentation CT analysis and segmental dissection revealed perforations of the pedicle cortex by the fixation screw in 15% of instrumented pedicles (26/172). There were 6 medial and 20 lateral perforations. Medial perforations occurred exclusively in the three most proximal spinal segments, whereas the lateral perforations occurred throughout the thoracic spine. The mean encroachment of the fixation screw was 1.67 mm medially and 1.95 mm laterally. This study demonstrates the variation in caliber and direction of the thoracic pedicles. Medial and lateral perforations of the pedicle can occur with the USS pedicle hook instrumented system.

The BWM spinal fixator system. A preliminary report of a 2-year prospective, international multicenter study in a range of indications requiring surgical intervention for bone grafting and pedicle screw fixation.

STUDY DESIGN: A prospective, international, multicenter study of 400 patients who received the BWM fixator system. OBJECTIVES: To assess the effectiveness and safety of the system in the management of various conditions requiring spinal fixation and bone grafting. SUMMARY OF BACKGROUND DATA: The BWM system was developed for the management of spinal instability of all etiologies occurring in the thoracic, thoracolumbar, and lumbosacral spine. METHODS: Patients with fracture, tumor, spondylolisthesis, spondylitis, failed back, or other degenerative conditions of the spine received the BWM instrumentation as described in the study literature and were regularly reviewed for 2 years. RESULTS: The results from the first 200 patients to complete the study showed an overall graft fusion rate of 94% (95% confidence interval: 91.3%-97.6%). There were marked improvements in measures of functional ability (P < 0.001, Wilcoxon test). Before surgery, less than half the patients were capable of outdoor activity. At 2 years, 80% were able to undertake outdoor activity. There were few perioperative difficulties reported. Postoperative complications associated with major surgery were seen in 18% patients. There were 23 (2.6%) pedicle screw failures, including two loosenings, and 13 (2.5%) spacer element failures, including three loosenings. CONCLUSIONS: Clinical failure was not necessarily a consequence of component failure. The BWM fixator provided excellent stabilization during the process of bone graft consolidation. The risks of complication or component failure were no higher than those associated with similar devices.

An anatomic, radiographic, and biomechanical assessment of extrapedicular screw fixation in the thoracic spine.

This study performed a thorough review of the pertinent thoracic spine anatomy to determine the appropriate landmarks for extrapedicular screw placement and indentified the anatomic structures at risk; assessed the safety and accuracy of the newly proposed screw insertion technique; determined the stability and strength of this new screw position through biomechanical testing; and analyzed the stability of this extrapedicular screw location with respect to bone mineral density of the vertebra.

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)

Neuropathologic changes with experimental spinal instrumentation: transpedicular versus sublaminar fixation.

Fifty-six mature beagles underwent lumbar spine destabilization, followed by fusion using four techniques. Spinal cord neuropathologic analysis was carried out to determine the number of abnormalities within each group. Group I (n = 14) had posterolateral bone grafting without instrumentation. Group IIa (n = 14) had Cotrel-Dubousset (CD) pedicle screws and rods. Group IIb (n = 14) had Steffee pedicle screws and plates. Group III (n = 14) had sublaminar wires and rods. All of the animals remained clinically neurologically normal throughout the 6 months of the study. The incidence of moderate to severe neuropathologic changes was 21% in Group I, 18% in Group II, and 64% in Group III. Thus, a significantly higher percentage of neuropathologic abnormalities occurred with sublaminar instrumentation than with no instrumentation (p = 0.027), or with transpedicular instrumentation (p = 0.027). In this controlled animal study, the theoretical advantage of pedicle screws, which should not violate the spinal canal, over sublaminar devices, which must enter the canal, was confirmed.

The influence of scoliosis and ageing on proteoglycan heterogeneity in the human intervertebral disc.

Proteoglycans (PGs) purified from 19-year-old male (19M), 53-year-old female (53F), and 15-16-year-old adolescent idiopathic scoliotic (AIS) disc tissues were characterised by their aggregation properties with hyaluronic acid (HA), glycosaminoglycan (GAG), and amino acid composition, electrophoretic mobilities by composite agarose polyacrylamide gel electrophoresis (CAPGE), and hydrodynamic size by Sepharose CL2B gel permeation chromatography. Proteoglycan levels were similar in the AIS and 53F discs, but considerably higher levels were found in the 19M discs. Proteoglycan populations assessed by the aforementioned criteria demonstrated a similar level of heterogeneity in the AIS and 53F discs but this differed with the 19M sample. Two small Mr, low buoyant density PG species were particularly prominent in AIS and 53F discs: these were similar to two nonaggregating PG species formerly reported by di Fabio et al.; however, the corresponding PG species in 19M discs were of somewhat different composition. Collectively, these data suggest similar processing of PGs in the AIS and 53F discs. Furthermore, the pattern of normal age changes in the PGs from AIS discs appears to be disturbed, most likely arising as a consequence of the abnormal biomechanical forces intrinsic to the deformity.

Hip implant evaluation in an arthritic animal model.

Animal studies can provide important information in the evaluation of new techniques and prosthetic designs in orthopedics. As a prerequisite they must parallel as closely as possible the human conditions they are modeling. An arthritic sheep model simulating the human clinical situation has previously been designed and reported by Phillips and Gurr. The present study introduces for the first time an approach that evaluates a prosthetic joint in an arthritic animal hip. Hemiresurfacing following the Tharies technique was carried out unilaterally in 12 Suffolk sheep and followed up for 2 years. Femoral loosening occurred in three cases. Only one of the 12 cases showed postoperative avascularity of the femoral head. Radiologic follow-up and histologic examination showed features consistently and strikingly similar to those seen in human practice. The sheep hip with simulated arthritis provides a sensitive, clinically reproducible model for the future study of other arthroplasty types and problems.

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.

Neuropathology with spinal instrumentation.

Neurohistologic examination of the spinal cord and cauda equina were compared for 28 beagles undergoing anterior and posterior spinal destabilization procedures--Group I (n = 7), destabilized operative controls; Group II (n = 7), posterolateral bone grafting; Group III (n = 7), Harrington distraction instrumentation and posterolateral fusion; and Group IV (n = 7), Luque rectangular instrumentation and posterolateral fusion. All dogs had appeared neurologically intact upon repeated examinations prior to death. Neurohistological abnormalities (Wallerian degeneration of the dorsal columns, corticospinal tracts, and nerve roots, focal cystic degeneration, and intraspinal central cavitation) occurred in only 1 of the 14 animals (7%) in Groups I and II (noninstrumented) and in 9 of the 14 animals (64%) in Groups III and IV (instrumented). This result is statistically significant (p less than 0.001). Transient sensory disturbances and radicular paresthesias have been described in clinical reports of spinal instrumentation. It is probable that subclinical neurologic injuries, such as intraspinal and nerve root infarction in posterior neural tissue, can occur with the use of sublaminar hooks or wires. The chondrodystrophic beagle spinal model in this study should be considered a "worst case situation," and the clinical incidence of neurohistologic changes is expected to be lower.

Roentgenographic and biomechanical analysis of lumbar fusions: a canine model.

An animal model of anterior and posterior column instability was developed to allow in vivo observation of bone remodeling and arthrodesis after spinal instrumentation. Various combinations of spinal fusions and instrumentation procedures were performed after an initial anterior and posterior destabilizing lesion was created at the L5-L6 vertebral levels in 35 adult beagles. After 6 months of postoperative observation, there was improved probability of achieving a spinal fusion if spinal instrumentation had been used. All biomechanical testing was performed after removal of instrumentation to test the inherent stiffnesses and quality of the spinal fusions. The fusions performed in conjunction with instrumentation (group V = Harrington instrumentation and posterolateral fusion; group VI = Luque instrumentation and posterolateral fusion) demonstrated the greatest axial rotation stiffnesses (group V, p less than .05); axial compressive stiffness (group V, p less than .05); and flexural stiffness (group VI, p less than .05). The results show that a spinal fusion can be more reliably achieved and will be more rigid if it is accompanied by spinal instrumentation.

Biomechanical analysis of anterior and posterior instrumentation systems after corpectomy. A calf-spine model.

UNLABELLED: To simulate the spinal instability that is found clinically after anterior corpectomy for the treatment of a fracture or a neoplasm, twelve fresh calf-spine segments, each containing five motion segments, were destabilized using a complete anterior corpectomy at the third lumbar level and anterior discectomies at the second and third and the third and fourth lumbar levels. Mechanical non-destructive cyclical testing in axial compression, rotation, and flexion was performed on each spinal segment after stabilization was accomplished. The three anterior-stabilization constructs that were compared were: (1) iliac strut grafting, (2) polymethylmethacrylate and anterior Harrington-rod instrumentation (the technique of Siegal and Siegal), and (3) the Kaneda anterior device. After anterior iliac-crest strut grafting, four types of posterior instrumentation were also tested sequentially: (1) Harrington distraction rods, (2) Luque rectangular instrumentation, (3) Cotrel-Dubousset transpedicular instrumentation, and (4) Steffee transpedicular screws and plates. Rotation, torque, axial displacement, and axial loads were measured during loading across the whole spinal segment between the grip points. Using an anterior extensometer, intervertebral displacement at the second, third, and fourth lumbar levels, and thus across the corpectomy defect at the third lumbar level, was recorded "on line" during testing in flexion and axial load. By recording the intervertebral displacement, the efficacy of each spinal construct in minimizing motion across the corpectomy defect could be quantified. The value for one-way analysis of variance for axial intervertebral displacement across the site of the third lumbar corpectomy was F = 10.5, p less than 0.001. The value for one-way analysis of variance for flexural intervertebral displacement across the corpectomy defect was F = 21.1, p less than 0.001. Homogeneous subsets of rigidity for torsional stiffness revealed that the least rigid constructs were iliac grafting alone, Harrington-rod instrumentation, and Luque rectangular instrumentation. The most rigid constructs were the anterior Kaneda device, transpedicular Cotrel-Dubousset instrumentation, and Steffee screws and plates. CLINICAL RELEVANCE: After corpectomy, spinal reconstructive surgery can restore axial, torsional, and flexural rigidity to normal levels. These experimental conclusions applied to the acute restoration of stability, rather than to rigidity after long-term cyclical loading. Using the most rigid anterior system, the Kaneda device, the fixation extended only one vertebral level cephalad and one level caudad to the corpectomy defect.(ABSTRACT TRUNCATED AT 400 WORDS)

Biomechanical analysis of posterior instrumentation systems after decompressive laminectomy. An unstable calf-spine model.

Mechanical non-destructive cyclical testing in rotation, axial compression, and flexion were performed on twelve fresh spinal segments from calves. Each segment contained five motion segments. Each spine was destabilized with bilateral laminectomy and facetectomy of the fourth and fifth lumbar vertebrae, resection of the pars interarticularis of the fourth lumbar vertebra, and resection of the disc between the fourth and fifth lumbar vertebrae. Sequential stabilization of each spine was used to compare the stiffness of: (1) Harrington distraction instrumentation of five levels, (2) Luque rectangular instrumentation of five levels, (3) modified Steffee transpedicular notched-rod instrumentation of three and five levels, and (4) Cotrel-Dubousset transpedicular instrumentation of three and five levels with and without transverse approximating rods. This in vitro study of a calf-spine model led to three reproducible conclusions: (1) after laminectomy and discectomy, the instrumented spine was more unstable in rotation and flexion than when it was subjected to axial compressive loads; (2) the most rigid implant was the Cotrel-Dubousset transpedicular instrumentation of five vertebral levels (p less than 0.05); and (3) with the Steffee or the Cotrel-Dubousset transpedicular instrumentation of three vertebral levels, it was possible to restore torsional, compressive, and flexural rigidity to the destabilized spine of the calf. Furthermore, transpedicular fixation of only three vertebral levels provided more in vitro stability than either traditional Harrington or Luque rectangular instrumentation, which require fixation of five vertebral levels to stabilize a spine after laminectomy.

Cotrel-Dubousset instrumentation in adults. A preliminary report.

In an attempt to assess the value of the Cotrel-Dubousset (CD) system for adult spinal disorders, the first 50 adult cases performed at Johns Hopkins were reviewed. Treatment of adult scoliosis with the CD system yielded results comparable to standard techniques. Curve correction was directly proportional to the preoperative flexibility with no loss of correction in any case. All patients went on to a solid arthrodesis, with only three patients requiring the use of postoperative orthoses. Operative time was initially prolonged during the phase of acquiring expertise with the system; however, blood loss and hospitalization were comparable. In both the scoliosis and kyphosis groups instrumentation and fusion incorporated the same number of levels as would have been required for conventional instrumentation systems. In the spondylolisthesis, tumor and trauma groups a total of 88 transpedicle screws was used in 18 patients without neurologic complications. Pedicle screws provided a fixation alternative in cases requiring laminectomies. In the 25 cases with tumors, spondylolisthesis, and trauma, CD instrumentation reduced the number of vertebral levels required for fixation. Compared to Harrington or Luque systems, the average number of motion segments spared per patient was 1.3 in the spondylolisthesis group, 2 in the tumor group and 2.1 in the trauma group. This study suggests that the CD system, although initially developed for idiopathic adolescent scoliosis, is versatile and can be safely and effectively applied to a variety of adult spinal conditions. In cases of spinal pathology due to neoplasm, spondylolisthesis, and trauma, CD instrumentation with the option of transpedicle fixation appeared to offer significant advantages over conventional methods, and an average of 1.6 lumbar motion segments could be preserved per case.

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.