Rotational changes of the vertebral pelvic axis after sublaminar instrumentation in adolescent idiopathic scoliosis.

STUDY DESIGN: The authors studied the rotational effect of sublaminar wiring on the spinal pelvic axis on 20 patients who were being treated for adolescent idiopathic scoliosis. OBJECTIVES: To determine if sublaminar wiring effectively derotates the scoliotic spine. SUMMARY OF BACKGROUND DATA: The correction of the rotational deformity in adolescent scoliosis via sublaminar wiring is not well quantified in the literature. The derotation maneuver of Cotrel-Dubousset has been shown to produce variable and unpredictable amounts of axial derotation. METHODS: Twenty patients who underwent posterior spine fusion for adolescent idiopathic scoliosis were evaluated using computed tomography scans and plain radiography before and after surgery and at a subsequent follow-up examination (average time of follow-up examination, 35 months after surgery). The degree of angle of vertebral rotation about the sagittal plane and that relative to the pelvis were measured before and after surgery and at a follow-up examination. RESULTS: The primary thoracic curves were not derotated significantly relative to the pelvis with sublaminar wiring. Primary thoracolumbar curves instrumented on the convexity with pedicle screws were derotated significantly relative to the pelvis (P = .001). The average initial correction was 57%. On final follow-up examination, the correction was 24% (18 of 20 twenty individuals lost axial correction by an average of 34%). In nine of 20 patients the spine was more rotated, relative to the pelvis, than it had been before surgery. No coronal or sagittal decompensation was seen in any curve type. CONCLUSIONS: Coronal and sagittal plane correction of scoliotic curves may be achieved with sublaminar instrumentation. The ability to derotate axially the scoliotic spine appears to be variable, however, and, in most cases, curve-type dependent. Over time, much correction appears to be lost, and in many patients the scoliosis actually becomes worse than it was before surgery. Nonetheless, the apical derotation that takes place appears to be reasonably true: the percent correction of angle of rotation about the sagittal plane and the percent correction of angle of rotation about the sagittal plain relative to the pelvis were closely correlated. Derotation forces applied to the instrumented spine do not appear to be transmitted to more distal segments.

Magnetic resonance imaging and biological changes in injured intervertebral discs under normal and increased mechanical demands.

STUDY DESIGN: An animal model was used to examine the short-term tissue response to changes in the mechanical environment after the structure (disc) is mechanically injured. OBJECTIVES: To observe changes in an injured intervertebral disc and the corresponding motion segment when the mechanical demands of the disc were increased by fusion of the adjacent motion segments. SUMMARY OF BACKGROUND DATA: Disc degeneration has been modeled in animals by producing a tear in the anulus via laminectomy, laparotomy, or posterolaterally. Methods of altering and quantifying the mechanics of the intervertebral joint by use of internal fixation and fusion in the canine have been developed. METHODS: Eight dogs divided into two groups (a study and a control group) had anular stab wounds (L2-L3). The study group was surgically instrumented posteriorly from L3 to L7. Magnetic resonance imaging studies were conducted for all animals before and periodically after the surgical procedures. At the end of the study, the segments were processed histologically and biochemically. RESULTS: Anular bulging was seen on magnetic resonance imaging in all control animals 4 months after injury and did not progress out until 6 months after injury. Similar changes were seen in study animals, but 75% were herniated by 6 months. Histologic changes correlated with magnetic resonance imaging changes. No significant difference in water or proteoglycan content of the disc tissue between groups was found. CONCLUSIONS: Progression from the bulging of the anulus to herniation was not evident in damaged discs not subjected to adjacent fusions. No change in water or proteoglycan content as a function of altered mechanical state was found, suggesting the short-term effect of the altered mechanics is on the mechanical structure and not on the cells or extracellular matrix.

Kinematics of the canine lumbar intervertebral joint. An in vivo study before and after adjacent instrumentation.

STUDY DESIGN: In vivo, canine lumbar spine intervertebral motion was measured before and after instrumentation of caudal segments. The three-dimensional kinematics of the intervertebral joint were described using helical axes and Fourier series. OBJECTIVE: The in vivo three-dimensional kinematics of the intervertebral joint were measured and described. An animal model where intervertebral motion could be repeatedly changed was developed. SUMMARY OF BACKGROUND DATA: The kinematics of intervertebral joints have been described from results of extensive in vitro testing, some limited in vivo testing, and clinically by evaluation of flexion/extension films. In the canine, in vivo intervertebral motion has been described previously, but the method possessed some measurement artifact. METHODS: In vivo, four canines had motion data collected (L2-L3) while the animals walked on a treadmill. L3 To L7 were instrumented in all of the animals and motion testing was repeated 1 and 12 weeks later. Helical axes of motion were determined for each gait cycle. Fourier series were fit to the motion data, helical axis parameters, and Fourier coefficients were all statistically compared (pre- and postinstrumentation). RESULTS: Vertebral rotations (coronal plane) and excursion of the L2/3 facet increased significantly (P < 0.01) after caudal instrumentation. Helical axes were oriented in a ventral direction and only the angle of rotation about the axis changed significantly (P < 0.05) after instrumentation of caudal segments. The Fourier coefficients (amplitudes) showed a significant (P < 0.05) increase in the coronal plane rotations only, after adjacent instrumentation. CONCLUSION: The in vivo kinematics of the intervertebral joint have been completely defined in this study. Some motion characteristics compare very well to human motion. Since motion at an intervertebral joint now can be repeatedly altered, this animal model shows promise as a useful tool for investigation of tissue response to changes in motion at a joint.

Results of intervertebral diskectomy without fusion at L4-5 versus L5-S1.

The results of diskectomy without fusion at L4-5 were compared with those at L5-S1. Strict indications for surgery had been applied to each group. Evaluation was carried out using the Oswestry Disability scale, as well as a modified Smiley-Webster scale, and a subjective improvement rating scale, as well as documenting work status, whether any future surgery was required, and other factors. Results were placed into categories based on these evaluation methods and were analyzed statistically. Average follow-up was 51 months with a minimum of 24 months. Overall excellent and good results occurred in 81% of patients in both groups. No difference in reoperation rate was detected between the two groups. Women were more likely to undergo a subsequent procedure, usually fusion. Equally satisfactory results can be obtained at L4-5 and L5-S1 if strict selection criteria are used.

Biomechanical analysis of facet and graft loading in a Smith-Robinson type cervical spine model.

OBJECTIVE: This study determined the effect of change in graft height on the forces across a Smith-Robinson graft as well as across the posterior elements of the same motion segment. STUDY DESIGN: The study utilizes a strain gauge technique for the measurement of facet joint loading and a subminiature load cell for the measurement of graft loads. SUMMARY OF BACKGROUND DATA: A number of cases of Smith-Robinson procedures have had some form of collapse of the interspace and graft material after surgery. Some patients with collapse of the graft go on to have prolonged sclerotomal-type pain or pseudarthrosis. The appropriate amount of distraction is not well defined in the literature and may affect the outcome. METHODS: Cervical spines (C5-C6) were instrumented by placing strain gauges bilaterally on the pedicles of C6 (to measure the forces across the posterior elements). A miniature load cell with matching metallic shims was used to measure the force across the graft site and to distract the segment. Forces across the posterior elements and the graft site were measured, during flexion loading, and compared as the disc space was distracted. RESULTS: The ratio of posterior element load to graft load with increasing disc space distraction significantly decreased from 1.06 +/- 0.65 (1.4 mm distraction) to 0.30 +/- .13 (4.6 mm distraction) (P < .03). The posterior element load decreased significantly after the same distraction, from 46.1 +/- 22.0 to 18.7 +/- 9.7 N/Nm (P < .05). CONCLUSIONS: In spondylotic specimens (4-5 mm disc heights) disc space distraction in excess of 3.0 mm from preoperative height caused a significant decrease in both the ratio of posterior element to graft loading and posterior element loads. These findings may help explain recent clinical reports of a limit of effective disc space distraction.

Comparison of in vivo and in vitro adjacent segment motion after lumbar fusion.

STUDY DESIGN: For in vitro studies, there is no basis for choosing a "load control study" over a "displacement control" study. This study qualitatively compared results from in vitro and in vivo tests, allowing the authors to address the experimental assumptions that in vitro testing contributes to the understanding of the in vivo condition. OBJECTIVES: To compare motion changes at segments adjacent to fusions for in vitro and in vivo tests. SUMMARY OF BACKGROUND DATA: Investigators have measured the effects of spinal fusions on the adjacent segment in a human cadaver model and found greater adjacent facet joint load after fusions. Others have found significant increases in motion and facet loads at segments adjacent to in vitro lumbosacral and long fusions, when the same range of motion was repeated before and after immobilization of lumbar segments. METHODS: L2-L3 motion was measured in vitro by an instrumented spatial linkage under load and displacement control before and after immobilization of segments (L3-L7). In vivo, L2-L3 motion was measured while animals walked on a treadmill. L3-L7 was fused and the L2-L3 motion testing was repeated. The change in in vivo adjacent segment motion was qualitatively compared with the in vitro change under "load" and "displacement" control. RESULTS: Under "load" control, in vitro facet motion did not significantly change after immobilization, whereas under "displacement" control, the facet motion significantly increased from 2.2 +/- 0.4 mm to 4.1 +/- 0.6 mm. Post-instrumentation, in vivo L2-L3 facet motion increased significantly. This change in vivo related better to the changes seen in the in vitro "displacement" control test than to the in vitro "load" control test.

Arthroscopic subacromial decompression and rotator cuff debridement for stage II and stage III impingement.

Arthroscopic subacromial decompression and rotator cuff debridement was performed on 61 consecutive patients with either stage II or stage III impingement syndrome: 27 with no actual tear of the cuff (group IIa); 21 with a partial-thickness tear (group IIb); and 13 with full-thickness tears (group III). Patients were seen in follow-up at a minimum of 2 years (mean 27.7 months). Apical oblique and outlet radiographic views of the shoulder were used to evaluate both preoperative subacromial pathology and to document removal of adequate bone postoperatively. Patients were evaluated pre- and postoperatively using both the UCLA Shoulder Rating Scale and Neer's criteria: Twenty-four of the 61 cases were compensation related. Mean motion improved postoperatively for all stages of impingement. For all patients, preoperative UCLA and Neer ratings were unsatisfactory. In group IIa, postoperative UCLA and Neer ratings improved in 22 patients to an 81% satisfactory result rate. In group IIb, 17 patients had major improvement in UCLA and Neer ratings (also an 81% satisfactory result rate). In group III, there were 10 satisfactory and three unsatisfactory results for a 77% satisfactory result rate. Of the 10 satisfactory results, eight were in patients who were either retired or worked at sedentary jobs that did not demand above-shoulder activities and strength, and whose principal preoperative complaint was pain. All 10 of these patients had relief of their pain; the three unsatisfactory results were all compensation cases in manual laborers, one later having a satisfactory result from an open cuff repair.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence from cadavers suggestive of entrapment of fifth lumbar spinal nerves by lumbosacral ligaments.

Lumbosacral spines from 51 geriatric-age cadavers (25 men and 26 women) were examined both grossly and under the dissecting microscope for evidence of compression of fifth lumbar spinal nerves by their respective lumbosacral ligaments. These ligaments were found to extend from the transverse process and body of L5 to the ala of the sacrum in 97% of the specimens, and from the transverse process and body of L5 to the promontory of the sacrum in 3% of the specimens. Anterior primary rami of the fifth lumbar spinal nerve were observed to be compressed in 11% (11 of 102) of the specimens examined grossly and under the dissecting microscope. Histologic evidence of chronic compression, as suggested by perineurial and endoneurial fibrosis, peripheral thinning of myelin sheaths, or subjective evidence of a shift in fiber diameter to a population of smaller size fibers was found, deep to the lumbosacral ligament, in three of the 11 nerves judged to be compressed. The information derived is of interest to the clinician whose patient presents with L5 root signs and a myelogram, discogram, and computed tomographic scan which do not show any abnormality. The possibility of extraforaminal compression must be considered as a possible source of the clinical signs.

Morphometry of the lumbar spine: anatomical perspectives related to transpedicular fixation.

The pedicles of lumbar vertebrae were measured both directly and radiographically to determine the differences between the sexes and the accuracy of radiographic measurement. The lumbar pedicles of cadavera of forty-nine patients--twenty-four men and twenty-five women--who died between the ages of sixty and ninety-eight years were measured directly and on radiographs. The pedicles of lumbar vertebrae from fifty-one patients--twenty-three men and twenty-eight women--between the ages of twenty and fifty years who had low-back problems were measured on radiographs and computerized tomographic scans. Comparison revealed that the average transverse and sagittal diameters of the pedicles and the distance from the posterior aspect of the laminar cortex to the anterior aspect of the cortex of the vertebral body along the central axis of the pedicles were 5 to 20 per cent greater in men, but the transverse and sagittal angles of the pedicle did not differ significantly between the sexes. Measurements on radiographs and computerized tomographic scans of the transverse angles of the pedicles and of the distances from the posterior aspect of the laminar cortex to the anterior aspect of the cortex of the vertebral body from the second to the fifth lumbar vertebra were greater than direct measurements, even without magnification. Direct measurements of the diameters of the transverse and sagittal diameters of the pedicle of the fifth lumbar vertebra, however, were greater than the radiographic measurements.

Degenerative joint disease: multiple joint involvement in young and mature dogs.

Radiologic, pathologic, and ancillary methods were used to determine the occurrence of degenerative joint disease involving multiple joints of immature and adult dogs. Animals were selected for the development of hip joint dysplasia and chronic degenerative joint disease. Of disease-prone dogs, 82% (45 of 55 dogs) had radiologic changes, indicative of hip dysplasia, by 1 year of age. At necropsy, more abnormal joints were identified than by radiographic examination. Among 92 dogs between 3 to 11 months of age that had joint abnormalities, 71% had hip joint involvement; 38%, shoulder joint involvement; 22%, stifle joint involvement; and 40% had multiple joint involvement. Polyarthritis was asymptomatic and unexpected. Radiographic examination of older dogs also revealed evidence of degenerative joint disease in many joints. Multiple joint involvement was substantiated at necropsy of young and mature dogs. A similar pattern of polyarticular osteoarthritis was revealed in a survey (computer search) of necropsy reports from medical case records of 100 adult and elderly dogs. Usually, the joint disease was an incidental observation, unrelated to the clinical disease or to the cause of death. The frequent occurrence of degenerative changes in several joints of dogs aged 6 months to 17 years indicated that osteoarthritis may be progressive in these joints and raises the possibility that systemic factors are involved in the disease process.