Dan M. Spengler

A prospective study of work perceptions and psychosocial factors affecting the report of back injury

A longitudinal, prospective study was conducted on 3,020 aircraft employees to identify risk factors for reporting acute back pain at work. The premorbid data included individual physical, psychosocial, and workplace factors. During slightly more than 4 years of follow-up, 279 subjects reported back problems. Other than a history of current or recent back problems, the factors found to be most predictive of subsequent reports in a multivariate model were work perceptions and certain psychosocial responses identified on the Minnesota Multiphasic Personality Inventory (MMPI). Subjects who stated that they “hardly ever” enjoyed their job tasks were 2.5 times more likely to report a back injury (P = 0.0001) than subjects who “almost always” enjoyed their job tasks. The quintile of subjects scoring highest on Scale-3 (Hy) of the MMPI were 2.0 times more likely to report a back injury (P = 0.0001) than subjects with the lowest scores. The multivariate model, including job task enjoyment, MMPI Scale-3, and history of back treatment, revealed that subjects in the highest risk group had 3.3 times the number of reports in the lowest risk group. These findings emphasize the importance of adopting a broader approach to the multifaceted problem of back complaints in industry and help explain why past prevention efforts focusing on purely physical factors have been unsuccessful.

Spinal pedicle fixation: reliability and validity of roentgenogram-based assessment and surgical factors on successful screw placement.

The increased popularity of pedicle fixation prompted research to address two issues: the reliability and validity of roentgenograms as a technique for evaluating the success of pedicle fixation, and the effects of surgical factors on successful fixation. Thus, does approach—the point and angle of screw insertion, surgeon experience, practice, level of the spine involved, and screw size—effect success of pedicle fixation? Eight fresh thoracolumbar spines were harvested and cleaned of all soft tissues. Two surgeons, one more experienced in pedicle fixation than the other, used two pedicle fixation approaches (Weinstein and Roy-Camille) on both the left and right sides at levels T11–S1 of each specimen. All screws were placed under anteroposterior (AP) and lateral c-arm control. For specimens 1 to 3, 5.5 mm screws were used at T11–L1, and 7.0 mm screws at L2–S1. Unacceptable failure rates at L2 and L3 for the first three specimens resulted in a change of instrumentation for the remaining specimens, with 5.5 mm screws used at T11–L3 and 7.0 mm screws at L4–S1. When surgeons completed the fixations for a specimen, AP and lateral roentgenograms were taken and both surgeons independently evaluated the films to assess the success of each fixation. Failure was defined as evidence of any cortical perforation on any side of the pedicle in or outside of the spinal canal. After completing the roentgenogram evaluation, the specimen was transected in the midline, and the success of each pedicle fixation was evaluated by visual/tactile inspection. There were no disagreements between surgeons on the visual/tactile evaluations of the specimens. In contrast, inter-rater adjusted percent agreement for roentgenograms ratings was 74, judged to be less than satisfactory when considering that the ratings were on a 2-point scale (S or F). The overall failure rate was approximately 21% (26/124). Of the 26 failures, 92% represented cortical perforations within the spinal canal. Discrepancies between visual/tactile and roentgenogram-based evaluations were not encouraging. Occurrence of false-positive results was at rates of 8.1% and 6.5%, and false-negative results occurred at a rate of 14.5% amd 12.9% for the more and less experienced surgeons, respectively. In general, success rate was independent of surgical factors. Success was not significantly related to approach, surgeon experience, screw size, or spine level. There was, however, an appreciable practice effect, χ2 = 8.84, P < 0.003. Failure rates were 26.4% compared to 6.4% for specimens 1–4 and 5–8, respectively. Also of interest was a trend for success to be related to approach, depending on the region of the spine involved, F1,100=3.38, P<0.07. Examination of relative success rates indicated no significant differences between the Weinstein and Roy-Camille approach in the upper lumbar spine (T11–L2), but a trend toward greater success with the Weinstein approach in the lower lumbar spine (L3–S1); a 93.1% success rate for the Weinstein, compared with 78.6% for the Roy-Camille approach. Roentgenograms were found to produce unacceptably high rates of false-positive and false-negative evaluations. The lack of differences in success rates between the surgeons with different levels of experience in conjunction with a strong relationship between success rate and practice is consistent with poor roentgenogram evaluation. Surgeons cannot be expected to improve with experience when their tools (roentgenograms) do not allow accurate evaluation of their performance. However, significant improvement in success rate can be expected when accurate evaluation is provided. Unfortunately, this research exposes the inadequacies of current evaluation procedures without providing viable alternatives. The trend toward superior success rates with the Weinstein approach in the lower lumbar spine is particularly important since the approach is believed to have the added advantage of providing less interference with uninvolved adjacent motion segments. Such an advantage would be of little value if the success rate was not at least as good as demonstrated for other approaches.

Matrix metalloproteinase-7–dependent release of tumor necrosis factor-α in a model of herniated disc resorption

Herniated disc (HD), one of the major causes of low back pain, is often resolved spontaneously without surgical intervention. Resorption is associated with a marked increase in infiltrating macrophages, and the matrix metalloproteinases (MMP) MMP-3 and MMP-7 have been implicated in this phenomenon. We developed a murine organ culture model in which intact intervertebral discs were cocultured with peritoneal macrophages to investigate the role of MMPs in HD resorption. Using macrophages isolated from MMP-null mice, we report that macrophage-produced MMP-7 was required for proteoglycan degradation, loss of wet weight, and macrophage infiltration of cocultured discs. The inability of MMP-7-deficient macrophages to infiltrate discs could not be attributed to a defect in macrophage migration. MMP-7 was required for the release of the cytokine TNF-alpha from peritoneal macrophages. The generation of soluble TNF-alpha was essential for the induction of MMP-3 in disc cocultures, which in turn is required for the generation of a macrophage chemoattractant and subsequent macrophage infiltration. TNF-alpha release from macrophages was necessary but insufficient for disc resorption, which required macrophage infiltration. We conclude that there is extensive communication between macrophages and chondrocytes in HD resorption and that an essential component of this communication is the requirement for MMPs to release soluble bioactive factors.

Relationship between vertical ground reaction force and speed during walking, slow jogging, and running.

OBJECTIVE: To obtain descriptive information between vertical ground reaction force (GRF)-time histories and gait speed, running style, and gender. DESIGN: GRF-time history measurements were obtained from male and female subjects during walking, slow jogging, jogging and running on an indoor platform. BACKGROUND: Previous studies have established GRF descriptor variables for male subjects running at speeds from 3 to 6 m s(-1), but very little descriptive data exists for slower or faster running, nor have previous studies reported GRF descriptors separately for female subjects. METHODS: GRF-time histories were recorded for 13 male and 10 female recreational athletes during walking and slow jogging at speeds between 1.5 and 3.0 m s(-1), and running at speeds between 3.5 and 6.0 m s(-1). Vertical GRF-time data for trials with speeds within 0.2 m s(-1) of the prescribed speed were analysed to determine thrust maximum GRF (F(z)) and loading rate (G(z)). RESULTS: In both male and female subjects, F(z) increased linearly during walking and running from 1.2 BW to approximately 2.5 BW at 6.0 m s(-1), remaining constant during forward lean sprinting at higher speeds. F(z) was linearly correlated to G(z), the latter ranging from 8 to 30 BW s(-1) over this speed range. Slow jogging was associated with a > 50% higher F(z) and G(z) in comparison to walking or fast running. CONCLUSIONS: Similar GRF descriptor data and velocity relationships were obtained for male and female subjects. Impact forces were greatest when the subjects adopted a higher, less fixed centre of gravity during slow jogging. RELEVANCE: These results suggest that vertical GRF norms can be established for male and female subjects alike, and that slow or fast running with a lower, fixed centre of gravity decreases impact forces.

Back injuries in industry: a retrospective study. II. Injury factors.

To evaluate the impact of back injury on industry, the authors conducted an extensive retrospective analysis of injuries among hourly employees of The Boeing Company, the largest industrial manufacturer in western Washington. The Boeing Company provided injury information on 31,200 employees for a 15-month period from July 1, 1979 to September 30, 1980. From this information, we analyzed 4,645 injury claims filed as of February 28, 1981 by 3,958 different employees. There were 900 back injuries in this group. Claims were categorized according to total incurred cost (TIC), made up of the medical costs and indemnity costs. High-cost claims were defined as those with a TIC greater than

The pathomorphology of spinal stenosis as seen on CT scans of the lumbar spine.

10,000, and low-cost claims were those with a TIC less than

Back Injuries in Industry: A Retrospective Study: III. Employee-related Factors

10,000. Among 857 claimants with 900 back injuries, lifting or material handling was much more commonly considered the cause of injury than accidents such as slips or falls. Accidents, however, had a much greater tendency to result in an expensive claim. The authors could not make reliable conclusions regarding injuries and 32 job skill classifications. The rate of injury did not vary according to day of the week or month, but a significantly higher rate of high-cost back injuries was noted on the day shift than on the evening or night shifts.

Matrix metalloproteinase-3–dependent generation of a macrophage chemoattractant in a model of herniated disc resorption

This study examines different morphologic measurements in the evaluation of patients with lumbar spinal stenosis. Preoperative CT scans from 24 patients who underwent surgery for central lumbar stenosis were analyzed. No correlation was observed between the size of the bony spinal canal and the size of the dural sac. A new measurement, the transverse area of the dural sac, is introduced. Normal values are provided. Correlation between the cross-sectional area of the dural sac and the anteroposterior diameter of the dural sac was excellent.

Reduced surgical site infections in patients undergoing posterior spinal stabilization of traumatic injuries using vancomycin powder

To evaluate the impact of back injuries on industry, the authors conducted a retrospective analysis of injuries occurring among a group of 31,200 employees of The Boeing Company, a large industrial manuacturer in Western Washington. They analyzed 4,645 injury claims (including 900 back injuries) made by 3,958 different employees. Two previous articles give an overview of the study, provide a detailed analysis of the costs associated with these back injuries, and analyze the characteristics of the injury. This article focuses on employee-related factors associated with back injuries. Claims were categorized according to severity, as indicated by total incurred cost (TIC), the sum of the medical costs, and indemnity costs. High-cost claims were defined as those with a TIC >

Role of computed tomography and myelography in the diagnosis of central spinal stenosis.

10,000 and low-cost claims as those with a TIC <