A biomechanical study of two different pedicle screw methods for fixation in osteoporotic and nonosteoporotic vertebrae.

In reconstruction of the osteoporotic spine, patients often show poor outcome because of pedicle screw failure. This study used osteoporotic and nonosteoporotic vertebrae to determine the difference in fixation strength between pedicle screws inserted straight forward and pedicle screws inserted in an upward trajectory toward the superior end plate (i.e., end-plate screws). There is some evidence to suggest that end-plate screws have a strength advantage. The particular focus was on osteoporotic vertebrae. Thirty-three vertebrae (T10-L2) were harvested. The bone mineral density (BMD) was measured: 15 vertebrae were greater than 0.8 g/cm(2) and designated as nonosteoporotic (average BMD 1.146 ± 0.186 g/cm(2)) and 18 vertebrae were designated as osteoporotic (average BMD 0.643 ± 0.088 g/cm(2)). On one pedicle the screw was inserted straight forward and on the other pedicle the screw was inserted as an end-plate screw. The torque of insertion was measured (Proto 6106 torque screwdriver). Using an MTS Mini Bionix, two types of mechanical testing were carried out on each pedicle: (a) cephalocaudad toggling was first carried out to simulate some physiological type loading: 500 cycles at 0.3 Hz, at ±50 N; and (b) then each pedicle screw was pulled out at a displacement rate of 12.5 cm/min.There was no difference in pullout force between the pedicle screws inserted straight forward and the pedicle screws inserted as end-plate screws. This result applies whether the vertebrae were osteoporotic or nonosteoporotic. For both the straight-forward screws and the end-plate screws, a statistically significant correlation was observed between torque of insertion and pullout force. The results of this experiment indicate that pedicle screws inserted as end-plate screws do not provide a strength advantage over pedicle screws inserted straight forward, whether the vertebrae are osteoporotic or not.

Risk-benefit assessment of surgery for adult scoliosis: an analysis based on patient age.

STUDY DESIGN: Retrospective review of a prospective, multicenter database. OBJECTIVE: The purpose of this study was to assess whether elderly patients undergoing scoliosis surgery had an incidence of complications and improvement in outcome measures comparable with younger patients. SUMMARY OF BACKGROUND DATA: Complications increase with age for adults undergoing scoliosis surgery, but whether this impacts the outcomes of older patients is largely unknown. METHODS: This is a retrospective review of a prospective, multicenter spinal deformity database. Patients complete the Oswestry Disability Index (ODI), SF-12, Scoliosis Research Society-22 (SRS-22), and numerical rating scale (NRS; 0-10) for back and leg pain. Inclusion criteria included age 25 to 85 years, scoliosis (Cobb ≥ 30°), plan for scoliosis surgery, and 2-year follow-up. RESULTS: Two hundred six of 453 patients (45%) completed 2-year follow-up, which is distributed among age groups as follows: 25 to 44 (n = 47), 45 to 64 (n = 121), and 65 to 85 (n = 38) years. The percentages of patients with 2-year follow-up by age group were as follows: 25 to 44 (45%), 45 to 64 (48%), and 65 to 85 (40%) years. These groups had perioperative complication rates of 17%, 42%, and 71%, respectively (P < 0.001). At baseline, elderly patients (65-85 years) had greater disability (ODI, P = 0.001), worse health status (SF-12 physical component score (PCS), P < 0.001), and more severe back and leg pain (NRS, P = 0.04 and P = 0.01, respectively) than younger patients. Mean SRS-22 did not differ significantly at baseline. Within each age group, at 2-year follow-up there were significant improvements in ODI (P ≤ 0.004), SRS-22 (P ≤ 0.001), back pain (P < 0.001), and leg pain (P ≤ 0.04). SF-12 PCS did not improve significantly for patients aged 25 to 44 years but did among those aged 45 to 64 (P < 0.001) and 65 to 85 years (P = 0.001). Improvement in ODI and leg pain NRS were significantly greater among elderly patients (P = 0.003, P = 0.02, respectively), and there were trends for greater improvements in SF-12 PCS (P = 0.07), SRS-22 (P = 0.048), and back pain NRS (P = 0.06) among elderly patients, when compared with younger patients. CONCLUSION: Collectively, these data demonstrate the potential benefits of surgical treatment for adult scoliosis and suggest that the elderly, despite facing the greatest risk of complications, may stand to gain a disproportionately greater improvement in disability and pain with surgery.

Reliability analysis for manual radiographic measures of rotatory subluxation or lateral listhesis in adult scoliosis.

STUDY DESIGN: Retrospective observational study. OBJECTIVE: To define the inter- and intraobserver reliability of 3 measures of rotatory subluxation (RS) in adult scoliosis (AS). SUMMARY OF BACKGROUND DATA: RS is a hallmark of AS. To accurately track this measure, one must know its reliability. Reliability testing has not been performed. METHODS: PA 36" films of 29 AS patients were collected from one surgeon's practice. Three observers on 2 separate occasions measured all levels with >or=3-mm RS (60 levels, 360 measurements) on the convexity of the involved segment using 3 different techniques-midbody (MB), endplate (EP), and centroid (C). These data were then analyzed to determine the intraclass correlation coefficient (ICC) for inter- and intraobserver reliability. RESULTS: The thoracolumbar/lumbar curve (average 58 degrees ) was the major curve for the majority (62%) of patients. RS at L3/4 was most common (35%). The overall inter- and intraobserver reliability was good-excellent for all methods, but the centroid method consistently had the highest ICC. ICC correlated with observer experience. Moderate-severe arthritic change (present in 55%) and poor image quality (52%) decreased ICC, but it still remained good-excellent for each measure. The reproducibility coefficient for each measure was 4 mm for MB and 2.8 mm for C and EP. CONCLUSION: MB, EP, and C are reliable techniques to measure RS even in elderly arthritic spines, but the methods inherently produce different values for a given level. The centroid method is most reliable and least influenced by experience. The EP method is easy to perform and very reliable. Spine surgeons should pick their preferred method and apply it consistently. Changes >3 mm suggest RS progression. RS may be a useful measure in addition to Cobb angle in AS. Having defined measurement reliability, the role of RS progression in surgical indications and patient outcomes can be evaluated.

Pedicle screw fixation strength: a biomechanical comparison between 4.5-mm and 5.5-mm diameter screws in osteoporotic upper thoracic vertebrae.

The purpose of this study was to evaluate the difference between 4.5-mm and 5.5-mm diameter pedicle screws inserted into the pedicles of upper thoracic vertebrae (T2 to T5). Seven fresh human spines were obtained. The bone mineral density was measured by dual-energy radiograph absorptiometry. The 4.5-mm and 5.5-mm diameter screws were inserted alternately in the right or left pedicle of each vertebra. The insertion torque and force (applied in the cephalic direction) to produce loosening of the screw were measured. The average bone mineral density for the seven thoracic spines was 0.710 g/cm(2). All of the vertebrae were classified as osteoporotic. The torque of insertion for the 5.5-mm diameter screws was significantly greater (59% greater on average) than that for the 4.5-mm diameter screws (p =. 001). Although the average force to loosening for the 5.5-mm diameter screws was higher than the average force to loosening for the 4.5-mm diameter screws (14%), the difference was not significant (p =. 33).

Is the SRS-22 instrument responsive to change in adult scoliosis patients having primary spinal deformity surgery?

STUDY DESIGN: Multicenter study. OBJECTIVE: The purpose of this study is to prospectively analyze responsiveness of the SRS-22 to change at 1 and 2 years following primary surgery. SUMMARY OF BACKGROUND DATA: A number of efforts have been directed at validation of the SRS-22 instrument in the setting of adolescent and adult spinal deformity. However, few have extensively analyzed the ability of the instrument to detect change (brought on by surgical treatment) in adult scoliosis patients. METHODS: A multicenter prospective series of consecutive adult scoliosis patients (all primary/no revisions) were administered SRS-22, Oswestry Disability Index (ODI)and Short Form-12 (SF-12) questionnaires preoperation and 1 and 2 years postoperation. Fifty-six patients had preoperative, 1-year postoperative, and 2-year postoperative data. RESULTS: The greatest changes from preoperation to 2-year postoperation were the SRS self-image domain followed by SRS total, SRS pain, and ODI scores. SRS pain and function scores significantly (P < 0.05) improved from 1-year to 2-year postoperation. There were not substantial differences in the outcome measures according to age or curve type. All outcome measures except SF-12 mental health showed statistically significant (P < 0.05) improvement from baseline to 2-year follow-up. CONCLUSION: Based on these 3 outcome tools, the greatest responsiveness to change was demonstrated by the SRS self-image domain followed by SRS total, then SRS pain, then ODI. This suggests that the SRS tool is more responsive than ODI, which is more responsive than SF-12 to change brought on by primary surgical treatment of adult scoliosis patients. Surgical treatment in adult scoliosis significantly improved pain, self-image, and function based on the health-related quality of life measures used in this study.

Bone growth retardation in mouse embryos expressing human collagenase 1.

Cellular growth and differentiation are readouts of multiple signaling pathways from the intercellular and/or extracellular milieu. The extracellular matrix through the activation of cellular receptors transmits these signals. Therefore, extracellular matrix proteolysis could affect cell fate in a variety of biological events. However, the biological consequence of inadequate extracellular matrix degradation in vivo is not clear. We developed a mouse model expressing human collagenase (matrix metalloproteinase-1, MMP-1) under the control of Col2a1 promoter. The mice showed significant growth retardation during embryogenesis and a loss of the demarcation of zonal structure and columnar array of the cartilage. Immunological examination revealed increased degradation of type II collagen and upregulation of fibronectin and alpha(5)-integrin subunit in the transgenic cartilage. The resting zone and proliferating zone of the growth plate cartilage exhibited a simultaneous increase in bromodeoxyuridine (BrdU)-incorporated proliferating cells and terminal deoxynucleotidyl transferase-mediated X-dUTP nick-end labeling-positive apoptotic cells, respectively. Chondrocyte differentiation was not disturbed in the transgenic mice as evidenced by normal expression of the Ihh and type X collagen expression. These data demonstrate that type II collagen proteolysis is an important determinant for the skeletal outgrowth through modulation of chondrocyte survival and cartilagenous growth.

Nonsurgical resource utilization in adult spinal deformity.

STUDY DESIGN: The enrollment data were retrospectively reviewed for 1,061 patients entered into a prospective multicenter study of adult spinal deformity between January 2002 and June 2004. OBJECTIVE: The purpose of this study is to quantify and analyze the use of nonsurgical resources in patients with adult spinal deformity. SUMMARY OF BACKGROUND DATA: Limited data exist regarding the utilization of nonsurgical treatment methods for adult spinal deformity. METHODS: Demographic data, surgical history, symptom assessment, and nonsurgical treatment regimen were reviewed. Health status measures were the SF-12, SRS-29, and ODI. Nonsurgical patients were divided into low- and high-symptom subgroups based on age adjusted ODI score. Resource utilization was analyzed based on both patient and physician questionnaire responses. RESULTS: High- and low-symptom nonsurgical subgroups differed significantly on all reported health status measures (P < 0.0001). High-symptom patients used greater resources in terms of narcotics, epidural blocks, and physical agent methods (P < 0.001), analgesics (P < 0.01), pain management referral and bed rest (P < 0.02), strength training, nerve root blocks, and stabilization exercises (P < 0.05). CONCLUSIONS: The results of this study demonstrate that, within the population of adult deformity patients, distinct high- and low-symptom groups exist and can be clearly identified. While high-symptom patients used significantly greater resources, most low-symptom patients used nonsurgical resources as well.

The role of the sternum, costosternal articulations, intervertebral disc, and facets in thoracic sagittal plane biomechanics: a comparison of three different sequences of surgical release.

STUDY DESIGN: Eighteen human torsos were used in three experiments (A, B, and C) to determine the changes in sagittal motion due to three different sequences of three surgical releases. OBJECTIVES: To investigate the relative effects of releasing the intervertebral disc, the costosternal joint, the sternum, and the facet joints on sagittal thoracic motion and the consequences of altering the sequence of the releases. SUMMARY OF BACKGROUND DATA: The biomechanics of the thoracic spine are different from the cervical and lumbar spine particularly due to the ribs and sternum, which contribute to stability and control motion. The role of the sternum and costosternal articulation in the biomechanics of thoracic sagittal motion has not been well studied. The effects of releasing each of these structures, whether alone or with discectomy and/or facetectomy, is potentially relevant in the surgical correction of thoracic deformities, such as severe kyphosis, and in the biomechanics of thoracic fracture. METHODS: In Experiment A, the release sequence was back to front: total facetectomy (T4-T8), then radical discectomy (T4-T8), then costosternal release, then sternal osteotomy. In Experiment B, the release sequence was front to back: sternal osteotomy, then costosternal release, then radical discectomy, and finally total facetectomy. In Experiment C, the release sequence was: radical discectomy, then sternal osteotomy, then costosternal release, then total facetectomy. The different sequences allowed separate analysis of each component and the synergistic patterns. In each of the three experiments, the torso was flexed then extended each time by an applied force (25 N) before and after each release. The extent of flexion and the extent of extension were measured each time and compared with the intact condition, after each release. RESULTS: The results obtained for sternal osteotomy were combined with the results obtained for costosternal release to give "sternal release." Radical discectomy provided the greatest increase (P < 0.05) in range of motion (ROM) compared with the other two single releases, no matter what the sequence. For paired release combinations, the radical discectomy and sternal release (as in Experiments B and C) provided a significant (P < 0.05) increase in total sagittal ROM compared with the combination of radical discectomy and total facetectomy (Experiment A). In Experiment A, sternal release accounted for 42% of the total sagittal ROM compared with only 26% related to the total facetectomy (Experiment B). In general, all of the releases allowed more extension than flexion. CONCLUSIONS: Sagittal plane motion in the thoracic spine is influenced by all three structures tested in this experiment. Overall, the radical discectomy provides the greatest increase in total ROM and in extension compared with the other two releases. The second most influential release is the combination of sternal osteotomy plus costosternal release (i.e., sternal release), particularly in extension (correction of kyphosis). When two releases are done in sequence, radical discectomy plus sternal release provides the greatest increase in total ROM and in extension. Overall, total facetectomy is the least effective release. These data have relevance for surgical strategies in the correction of thoracic kyphosis or lordosis and suggest a potential role for sternal osteotomy and costosternal release in severe and rigid upper thoracic kyphosis.

Spondylolytic spondylolisthesis: a study of pelvic and lumbosacral parameters of possible etiologic effect in two genetically and geographically distinct groups with high occurrence.

STUDY DESIGN: An anatomic and radiographic study of archeological skeletal remains from two genetically and geographically distinct groups with high occurrence rates of spondylolytic spondylolisthesis was done. Specimens were Aleut (27% known occurrence rate, n = 48) and Arikara Plains Indians (9% occurrence, n = 250+ of 1,062). OBJECTIVE: To evaluate three radiographic parameters highly correlated with spondylolisthesis (pelvic incidence [PI], sacral table angle [STA], and lumbar index [LI]) in genetically homogeneous populations to determine which may be etiologic or most predictive for lysis. SUMMARY OF BACKGROUND DATA: LI has been known to vary with the percentage of slip in lytic spondylolisthesis. Recent clinical studies have shown that PI is also significantly higher in high-grade slips, and a possible etiologic effect has been ascribed to this association. STA has also been shown to vary between normals, those with only lysis, and those with lysis and slip. The etiologic significance of STA is unknown. METHODS: Radiographic and direct morphologic measurement of PI, LI, and STA was done on L5 and reassembled sacra and ilia. Statistical analysis of these three parameters among all groups was done. RESULTS: 1) There is a genetically determined difference in the upper sacral tilt (STA) that may be etiologic. 2) Genetically homogeneous groups with a lower STA in normal specimens have an increased occurrence rate of spondylolysis. 3) When there has been pars lysis, changes in the STA occur as well as deformity more caudal in the sacrum. 4) These changes are likely related to remodeling with epiphyseal growth related to changed axial stresses secondary to pars lysis. 5) PI is not a primary etiologic factor in the process. CONCLUSIONS: The STA in the normal population for each genetic group varies and relates significantly to the occurrence rate and is thus probably etiologic. STA is more highly associated with the occurrence of pars defect than is PI. Upper sacral deformities appear due to the growth plate response to the changed pressure gradients across the epiphyseal plate rather than interosseous remodeling of the ilium and acetabular area. Thus, changes in PI would be secondary.

Is there an optimal patient stance for obtaining a lateral 36" radiograph? A critical comparison of three techniques.

STUDY DESIGN: Scoliosis patients were prospectively x-rayed in three positions with independent analysis. OBJECTIVES: To determine if one positioning technique provides superior visualization of critical landmarks (C7, T2, T12, L5-S1) and to determine any position dependent variations in regional measures or sagittal balance. SUMMARY OF BACKGROUND DATA: Different techniques for positioning patient's arms are used for 36" lateral radiograph with no data on relative effects. METHODS: A total of 25 scoliosis patients were prospectively studied with 36" lateral radiographs in three positions varying arm location (straight out, partially flexed, and the "clavicle" position). Films were analyzed independently by three surgeons. Vertebral landmarks were scored for clarity; and lordosis, kyphosis, and global balance were analyzed. Statistical analysis was done with a General Estimating Equations model. RESULTS: The overall visualization score for the clavicle position was superior to either the 60 degrees or 90 degrees positions (clavicle vs. 60 degrees, P < 0.0001; clavicle vs. 90 degrees, P < 0.0003). Analysis of vertebral landmarks showed significantly better visualization of T2 with clavicle versus 90 degrees (P < 0.047), better visualization of T12 with clavicle versus either 60 degrees (P < 0.006) or 90 degrees (P < 0.049), and better visualization of L5-S1 with clavicle versus 90 degrees (P < 0.02). Regional measures showed no differences, but sagittal balance was significantly more positive in the 60 degrees position than either clavicle (P < 0.04) or 90 degrees (P < 0.015). CONCLUSIONS: The clavicle position for obtaining lateral 36" radiographs produces significantly better overall visualization of critical vertebral landmarks. Regional measures do not differ between the three positions, but global balance is more positive with the 60 degrees position. Clinically, the clavicle position may result in more accurate radiographic measures and may minimize repeated radiograph exposures.

The validity of the SRS-22 instrument in an adult spinal deformity population compared with the Oswestry and SF-12: a study of response distribution, concurrent validity, internal consistency, and reliability.

STUDY DESIGN: Prospective analysis of a consecutive cohort of adult spinal deformity patients queried over a 12-month period. OBJECTIVES: To assess the SRS-22 instrument compared with the SF-12 and Oswestry. SUMMARY OF BACKGROUND DATA: Very few reports in the literature have applied the SRS-22 to adult spinal deformity patients. METHODS: Consecutive adult spinal deformity patients were applied the SRS-22, SF-12, and Oswestry. Four analyses were done: 1) floor/ceiling effect; 2) Pearson's correlation coefficients between the SRS-22, SF-12, and Oswestry; 3) Cronbach's alpha analysis for internal consistency within the SRS-22; and 4) test/retest. RESULTS: Floor/ceiling range for the SRS-22 compared favorably with the SF-12 and Oswestry. The Pearson's coefficients correlating the two questionnaires relative to the SRS-22 were > 0.7. The Cronbach's alpha within each domain for the SRS-22 were > 0.7, except for pain (0.67). Test/retest correlation coefficients ranged from 0.84 to 0.95 for the subscales. CONCLUSIONS: The SRS-22 is a disease-specific instrument with the capacity to demonstrate change in health status more effectively than the SF-12 and in more domains than the Oswestry. The SRS-22 showed high criterion validity with the SF-12 and Oswestry based on Pearson's coefficients. High Cronbach's alpha scores suggested a high internal consistency within each domain of the SRS-22, except for pain (0.67). Test/retest reliability was excellent.

A two-cage reconstruction versus a single mega-cage reconstruction for lumbar interbody fusion: an experimental comparison.

BACKGROUND: Interbody cages are used as an adjunct to anterior lumbar interbody fusion, but exposure and insertion of two cages can be difficult. A biomechanical study was performed to compare the stability and exposed surface for fusion obtained with interbody reconstruction using two traditional cylindrical cages (18-mm diameter) vs. a single expanded mega-cage (24-mm diameter). A single-cage technique could result in safer exposure, shorter operating time, and less cost. STUDY DESIGN: nondestructive testing of L5-S1 motion segments with cages compared the two configurations, and direct measure of the size of the fusion bed was made. PATIENT SAMPLE: 16 human cadaveric lumbar motion segments. OUTCOME MEASURES: significant differences in motion segment stiffness and cancellous surface areas were compared using a Wilcoxon rank sum test. Motion segments were biomechanically tested intact, and then tested again after insertion of two interbody cages (n=8) or a single mega-cage (n=8). Nondestructive biomechanical loading was performed consisting of: (1) compression (maximum load 900 N); (2) Flexion, extension, left and right lateral bending (maximum moment 18 Nm); and (3) left and right torsion (maximum moment 10 Nm). From the load-deformation curves obtained, stiffness values were calculated to compare the two-cage and the single mega-cage reconstructions. After testing, the specimens were disarticulated and the surface area of the endplate bed created in the cancellous bone (of both vertebrae) was measured to compare the potential vascular surface for osteogenesis with both constructs. RESULTS: The averages of the normalized values of stiffness were significantly greater for the two-cage group as compared to the mega-cage group in flexion only (1.08 vs. 0.74, p<0.05). For extension, torsion and lateral bending there was no significant difference in stiffness. In compression the two-cage group was stiffer, although not significantly (0.92 vs. 0.68, p<0.07). The average cancellous bed surface area was slightly greater for the single-cage reconstruction (1,208 mm(2) vs. 1,155 mm(2)), although this difference was not significant. CONCLUSIONS: The stiffness with a single anterior mega-cage was significantly lower in flexion compared with two standard cages. However, in all other modes of testing the constructs were statistically equivalent, although neither construct was significantly stiffer than the intact specimen. Additionally, the single mega-cage provides an equivalent cancellous bed for fusion as compared to dual cages. While this study is not sufficient to recommend human application, these results and our previous experience with the successful in vivo use of a single cage in rhesus monkeys [4] suggest that the single expanded anterior cage may be an acceptable concept although subsidence risk needs further investigation. The potential advantages of a single mega-cage (safer for the foramen, safer for the vessels, more consistent decortication and possibly cheaper) further suggest that examination should be given to this method as an approach to anterior interbody reconstruction in selected patients.