Brain oxygenation declines in elite Kenyan runners during a maximal interval training session.

PURPOSE: The purpose of this study was to characterise the cerebral oxygenation (Cox) response during a high-intensity interval training session in Kenyan runners, and to examine any relationship with running performance. METHODS: 15 Kenyan runners completed a 5-km time trial (TT) and a Fatigue Training Test on a treadmill (repeated running bouts of 1-km at a pace 5% faster than their mean 5-km TT pace with a 30-s recovery until exhaustion). Changes in Cox were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxy-haemoglobin (Δ[O2Hb] and Δ[HHb]), tissue oxygenation index (TOI), and total hemoglobin index (nTHI). RESULTS: The number of 1-km repetitions achieved by the participants was 5.5 ± 1.2 repetitions at a mean pace of 20.5 ± 0.7 km h-1. Δ[O2Hb] measured at the end of each running repetition declined progressively over the course of the trial (p = 0.01, ES = 4.59). Δ[HHb] increased during each running bout until the end of the Fatigue Training Test (p < 0.001; ES = 6.0). TOI decreased significantly from the beginning of the test (p = 0.013, ES = 1.83), whereas nTHI remained stable (ES = 0.08). The Cox decline in the Fatigue Training Test was negatively correlated with the speed at which the test was completed (p = 0.017; r = -0.61), suggesting that the best performers were able to defend their Cox better than those of lower running ability. CONCLUSIONS: In conclusion, this study suggests that elite Kenyan runners cannot defend cerebral oxygenation when forced to exercise to their physiological limits. This emphasises the critical importance of pacing in their racing success.

Impact of social norms and social support on diet, physical activity and sedentary behaviour of adolescents: a scoping review.

The prevalence of non-communicable diseases (NCDs) in adulthood is rapidly increasing, and it is essential that risk factors for NCDs be addressed in adolescence, both for the health of individuals during adolescence and for their health in later life. These risk factors include diet, physical activity and sedentary behaviour. No literature has been published that comprehensively summarizes the impact of social norms and social support on these behaviours among adolescents. Therefore, a scoping review was conducted to determine the extent of recent (since 2000) literature available on this topic. A comprehensive search strategy was used to search PubMed and EMBASE for eligible reviews. Review papers (narrative reviews, systematic and non-systematic reviews) published in English in peer-reviewed journals from 2000 to February 2013 were included in the overview. Two of the authors screened the titles and abstracts of the search results independently. Thirty reviews were included in the scoping review. This scoping review has shown sufficient evidence for parental influences, and especially the positive impact of an authoritative parenting style, on healthy behaviours of adolescents, although the evidence is somewhat more compelling for diet than for physical activity and sedentary behaviour. More research is needed to investigate parental and family influences on physical activity and sedentary behaviour. And the effect of peer influences on diet, physical activity and sedentary behaviour of adolescents requires further investigation. The evidence presented affirms the consideration of social norms and social support in the development of interventions to address these behaviours in adolescents. The evidence regarding parenting style provides some concrete guidance for such interventions.

Nutritional interventions for reducing morbidity and mortality in people with HIV.

BACKGROUND: Adequate nutrition promotes and maintains optimal immune function. Dietary support may, therefore, improve clinical outcomes in HIV-infected individuals by reducing the incidence of HIV-associated complications and attenuating progression of HIV disease, thereby improving quality of life and ultimately reducing disease-related mortality. OBJECTIVES: To evaluate the effectiveness of various macronutrient interventions, such as a balanced diet or high protein, high carbohydrate, or high fat diets given orally, in reducing morbidity and mortality in adults and children living with HIV infection. SEARCH STRATEGY: We searched CENTRAL (up to March 2006), MEDLINE (1966 to March 2006), EMBASE (1988 to March 2006), LILACS (up to March 2006), and AIDSearch (up to March 2006). We also scanned reference lists of articles and contacted authors of relevant studies and other researchers. SELECTION CRITERIA: Randomised controlled trials evaluating the effectiveness of macronutrient interventions compared with no nutritional supplements or placebo in the management of adults and children infected with HIV. DATA COLLECTION AND ANALYSIS: Three reviewers independently applied study selection criteria, assessed study quality, and extracted data. Effects were assessed using weighted mean difference and 95% confidence intervals. Meta-analysis employed a fixed-effect model, except when the chi-square test for heterogeneity was significant (p<0.1). MAIN RESULTS: Eight trials (with a total of 486 participants), met the criteria for inclusion in our review. None of the studies reported on mortality, morbidity, or disease progression. Overall, macronutrient supplementation (with or without nutritional counselling) significantly improved energy intake (5 trials; n=254; WMD 367 kcal.day-1; 95% CI: 217 to 516) and protein intake (3 trials; n=128; WMD 17 g.day-1; 95% CI: 8 to 26) compared with no nutritional supplementation or placebo. There was no evidence of an effect on body weight (8 trials; n=423; WMD 0.24 kg; 95% CI: -0.6 to 1.1), fat mass (6 trials; n=305; WMD -0.73 kg; 95% CI: -1.83 to 0.37), fat-free mass (5 trials; n=311; WMD 0 kg; 95% CI: -2.3 to 2.4) or CD4 count (6 trials; n=271; WMD 0.23 cells.mm-3; 95% CI: -40.2 to 40.6). AUTHORS' CONCLUSIONS: Given the current evidence base, which is limited to a few small trials in high-income countries, no firm conclusions can be drawn about the effects of macronutrient supplementation on morbidity and mortality in people living with HIV.

Nutritional supplements for people being treated for active tuberculosis: A technical summary.

Tuberculosis and nutrition are intrinsically linked in a complex relationship. Altered metabolism and loss of appetite associated with tuberculosis may result in undernutrition, which in turn may worsen the disease or delay recovery. We highlight an updated Cochrane review assessing the effects of oral nutritional supplements in people with active tuberculosis who are receiving antituberculosis drug therapy. The review authors conducted a comprehensive search (February 2016) for all randomised controlled trials comparing any oral nutritional supplement, given for at least 4 weeks, with no nutritional intervention, placebo or dietary advice only in people receiving antituberculosis treatment. Of the 35 trials (N=8 283 participants) included, seven assessed the provision of free food or high-energy supplements, six assessed multi-micronutrient supplementation, and 21 assessed single- or dual-micronutrient supplementation. There is currently insufficient evidence to indicate whether routinely providing free food or high-energy supplements improves antituberculosis treatment outcomes (i.e. reduced death and increased cure rates at 6 and 12 months), but it probably improves weight gain in some settings. Plasma levels of zinc, vitamin D, vitamin E and selenium probably improve with supplementation, but currently no reliable evidence demonstrates that routine supplementation with multi-, single or dual micronutrients above the recommended daily intake has clinical benefits (i.e. reduced death, increased cure rate at 6 and 12 months, improved nutritional status) in patients receiving antituberculosis treatment. In South Africa, most provinces implement a supplementation protocol based on nutritional assessment and classification of individuals rather than on disease diagnosis or treatment status.

Maintained cerebral oxygenation during maximal self-paced exercise in elite Kenyan runners.

The purpose of this study was to analyze the cerebral oxygenation response to maximal self-paced and incremental exercise in elite Kenyan runners from the Kalenjin tribe. On two separate occasions, 15 elite Kenyan distance runners completed a 5-km time trial (TT) and a peak treadmill speed test (PTS). Changes in cerebral oxygenation were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxyhemoglobin (Δ[O2Hb] and Δ[HHb]), tissue oxygenation index (TOI), and total hemoglobin index (nTHI). During the 5-km TT (15.2 ± 0.2 min), cerebral oxygenation increased over the first half (increased Δ[O2Hb] and Δ[HHb]) and, thereafter, Δ[O2Hb] remained constant (effect size, ES = 0.33, small effect), whereas Δ[HHb] increased until the end of the trial (P < 0.05, ES = 3.13, large effect). In contrast, during the PTS, from the speed corresponding to the second ventilatory threshold, Δ[O2Hb] decreased (P < 0.05, ES = 1.51, large effect), whereas Δ[HHb] continued to increase progressively until exhaustion (P < 0.05, ES = 1.22, large effect). Last, the TOI was higher during the PTS than during the 5-km TT (P < 0.001, ES = 3.08; very large effect), whereas nTHI values were lower (P < 0.001, ES = 2.36, large effect). This study shows that Kenyan runners from the Kalenjin tribe are able to maintain their cerebral oxygenation within a stable range during a self-paced maximal 5-km time trial, but not during an incremental maximal test. This may contribute to their long-distance running success.

Insulin sensitivity measured by the minimal model: no associations with fasting respiratory exchange ratio in trained athletes.

The aim of this study was to examine the role of fasting insulin concentrations and tissue insulin sensitivity on whole-body substrate oxidation in 61 well-trained subjects. Subjects underwent a frequently sampled intravenous glucose tolerance test (FSIVGT) after a 10- to 12-hour overnight fast. Minimal model analysis was used to determine insulin sensitivity (S(i)). A week later, fasting (10- to 12-hour) respiratory exchange ratio (RER) was measured at rest and during exercise at 25%, 50%, and 70% of peak power output (W(peak)). Prior to these measurements, training volume, dietary intake, and muscle fiber composition, substrate concentrations, and enzyme activities were determined. The average fasting plasma insulin concentration was 7.3 +/- 2.4 microU/mL (4.0 to 10.5 microU/mL), and the mean S(i) was 14.0 +/- 6.1 x (10(-4) min(-1) x microU(-1) x mL(-1)) (2.6 to 26.3 x 10(-4) min(-1) x microU(-1) x mL(-1)). There was no significant correlation between fasting plasma insulin concentration and S(i) (r = -.14, P =.336) or between these measurements and fasting RER, measured at rest and during exercise at 25%, 50%, and 70% W(peak). Only VO(2max) and the proportion of type 1 muscle fibers were significantly correlated with S(i) (r =.30, P =.045 and r =.34, P =.026, respectively), and waist-to-hip ratio (WHR) was significantly correlated with fasting plasma insulin concentration (r =.35, P =.006). In conclusion, S(i) and fasting plasma insulin concentration were not associated with fasting RER at rest and during exercise of increasing intensity in trained athletes who have high S(i).

Intervertebral disc herniation in the adolescent.

Twenty-nine patients between 14 and 20 years of age underwent surgical treatment for intervertebral disc herniation over a 10-year period. Trauma was a significant factor in 59%. Back pain was a major complaint in all cases, and all but one had significant sciatic distress. Typical painful, restricted forward flexion was found in 22 cases. All patients had definite signs of nerve root tension. Nerve compression signs were present in 41%. Myelography was done in all cases, and discography was performed on 22 patients to aid in diagnosis and planning of definitive treatment. Twenty-three patients were followed over an average of 5.3 years. Excellent or good results were found in 89%. One patient required a further surgical procedure. Analyzing 12 procedures performed at the L5-S1 level demonstrated excellent results in all patients undergoing lumbosacral fusion combined with discotomy at this level in the presence of a normal L4-5 discogram.

Multidirectional stability of the Graf system.

STUDY DESIGN: To assess the biomechanical influences of the Graf fixation system on the spine, motion segments were tested. In normal spines, destabilized and restabilized with the Graf system conditions, the range of motion and flexibilities were found under various loading conditions. OBJECTIVES: These results should explain how the Graf Fixation system affects the biomechanical response of a motion segment. METHODS: Motion segments (L2-3) and (L4-5) were subjected to these loading conditions: compressive loading, flexion-extension, lateral bending, and axial rotation moments. During the loading, the main and coupled motions were measured, and flexibilities were computed. The position of the balance point in axial loading was also determined. The motion segments were tested under three conditions: intact, destabilized, and restabilized. The destabilization consisted of a bilateral total laminectomy (pedicle-to-pedicle). Restabilization was affected with the Graf stabilization system, consisting of polyester bands between pedicle screw implants. RESULTS: The total laminectomy significantly changed the balance point location by moving it forward. The restabilized motion segment had a balance point more similar to normal conditions. The mean compressive compliance was significantly less after application of the Graf system compared with destabilization. The range of motion for flexion-extension and axial rotation was significantly reduced for the main motion with the Graf system. For lateral bending, the main and coupled rotations were affected significantly, with lateral bending and flexion-extension motion reduced and axial rotation increased after restabilization. Restabilization decreased the flexibility of the destabilized motion segment for all of the moments. CONCLUSIONS: The Graf fixation system reduced the range of motion and the flexibility values in some loading conditions. These results only assess the immediate stabilization characteristics of this implant system in cadaveric material. Further research should address the fatigue characteristics.

Decompression for degenerative spondylolisthesis and spinal stenosis at L4-5. The effects on facet joint morphology.

Anatomic variations exist in the facet joint orientation, shape, and size at L4-5. This morphology is further modified by degenerative changes in spinal stenosis and degenerative spondylolisthesis. This study explored the morphologic alteration of "pedicle-to-pedicle" decompression on the facet joints in normal patients, spinal stenosis patients, and degenerative spondylolisthesis patients. Using computerized digitization, computed tomographic scan images of the facet joint at L4-5 and the medial border of the pedicle at L5 were superimposed. The facet joint orientation, coronal dimension, percentage, and absolute reduction in coronal dimension after pedicle-to-pedicle decompression, and residual coronal dimension after decompression at L4-5 were measured for the three groups. There is a significantly reduced coronal dimension of the facet joint in degenerative spondylolisthesis patients compared with spinal stenosis and normal patients (P < 0.01). The average reduction of the facet joint coronal dimension is 34% (SD 30%) in degenerative spondylolisthesis, and 36% (SD 25%) in spinal stenosis. The smaller preoperative coronal dimension in degenerative spondylolisthesis leads to a significantly reduced residual coronal dimension in degenerative spondylolisthesis compared with normal patients (5.9 mm [SD 4.3 mm] vs. 9.3 mm [SD 3.5 mm]), respectively. Wide variations in facet joint reduction and residual facet joint coronal dimension exist. The significantly reduced coronal dimension after decompression in degenerative spondylolisthesis may be correlated to a trend to further anterior displacement if it is treated with decompression alone. Case-specific assessment of residual facet joint morphology after decompression in both spinal stenosis and degenerative spondylolisthesis patients should be integrated into decisions about fusion for stability at the L4-5 level.

Postoperative spondylolisthesis at L4-5. The role of facet joint morphology.

Thirty-three patients underwent decompression without fusion at the L4-5 level for spinal stenosis or degenerative spondylolisthesis. Using preoperative and 1-year postoperative lateral lumbar spine radiographs, the incidence of postoperative spondylolisthesis of greater than 5% was found to be 58%. Computed tomographic scans were used to analyze the presurgical facet joint morphology and facet joint-pedicle spatial relationship. This allowed calculation of the facet joint orientation for each side; the coronal dimension of each facet joint; the amount of the facet joint coronal dimension removed if a decompression was performed up to the medial border of the L5 pedicle (facet joint reduction); and the residual coronal dimension of facet joint after such a decompression (residual facet joint). The lateral radiographs were analyzed for presurgical disc height and the presence of traction spurs or spondylophytes. A well-maintained disc height was associated with an increase slip (7.47%) compared with those cases with a narrow or complete loss of disc space before surgery (4.84% P < 0.1 trend). Presence of spondylophytes was associated with a reduced tendency to slip. When spondylophytes were controlled for there was a significant relationship between slip of greater than 10% and sagittal facet joint orientation. Although there was a lesser residual facet joint after decompression in the group that slipped these values were not statistically significant. This study suggests that the development of postoperative spondylolisthesis is related to facet joint orientation and dimensions, rather than the absolute amount of joint removed. The stabilizing effects of reduced disc height and spondylophytes were confirmed.

Etiology of spondylolisthesis. Assessment of the role played by lumbar facet joint morphology.

This study examined the role of facet joint morphology in the etiology of both degenerative spondylolisthesis and isthmic spondylolysis. To this end, the axial facet joint morphology of the lower lumbar spine in a normal population and in populations of patients with spinal stenosis or degenerative spondylolisthesis at L4-5 and in patients with isthmic spondylolysis at the L5 level were characterized. Computed tomographic scans were digitized, defining the axial morphology of the normal facet joint at five stations from proximal to distal within the joint. Assessments were made of facet joint orientation, transverse articular dimension, depth of the articular surface, and shape of the articular surface at levels L3-4, L4-5, and L5-S1. There was a gradually more coronal orientation from proximal to distal among the stations at each level, and a maximal transverse articular dimension at the level of the superior endplate of the caudad vertebra. Minimal error in the recording process at this level. In addition to the maximal joint dimension, made this level the most representative of the overall morphology and most useful for further studies. At the L4-5 level, a significantly more sagittal facet orientation was found in the degenerative spondylolisthesis group when compared to both the normal population and spinal stenosis groups (P < 0.01). At L5-S1, the only significant morphologic difference between the normal population and the patients with isthmic spondylolysis was reduced transverse articular dimension. These results support the hypothesis that patients developing degenerative spondylolisthesis are predisposed to this by a developmental sagittal orientation of the L4-5 facet joints.

Reliability of axial landmarks for pedicle screw placement in the lower lumbar spine.

STUDY DESIGN: Measurements were made on transverse-plan, computed tomography scans from three different patient groups. OBJECTIVE: To describe the correlation between two previously described pedicle screw entry points to the pedicle axis and the predicted frequency of pedicle breakthrough from the use of a 6.5-mm screw placed parallel to the pedicle axis. SUMMARY OF BACKGROUND DATA: Fluoroscopic assistance improves the accuracy of pedicle screw placement. Whether this is a result of improved accuracy of the starting point or correct directional guidance is unclear. No morphologic studies have been done to assess the accuracy of previously described entry points. METHODS: Computerized digitizing and mathematic superimposition of the images from computed tomography scans of the low lumbar spine were used to quantify facet and pedicle anatomy and the correlation between two previously described entry points and the pedicle axis. RESULTS: The two previously described entry points are significantly medial to the pedicle axis. They are most medial at the L5 pedicle in patients with L4 degenerative spondylolisthesis. CONCLUSIONS: The two previously described entry points for pedicle screws in the low lumbar spine that were studied here are not reliable and tend to direct screw placement medial to the pedicle axis enough to lead to a substantial frequency of pedicle breakthrough for screws parallel to this axis. Surgeons implanting screws should take this tendency into account and use alternative methods to obtain accurate entry to the pedicle.

The pathomechanism of isthmic lumbar spondylolisthesis. A biomechanical study in immature calf spines.

STUDY DESIGN: Anterior shearing force was applied to immature calf lumbar functional spinal units until failure. OBJECTIVES: To clarify the mechanism of slippage in immature calf lumbar spines with pars defects as a first step to understand the mechanism of spondylolisthesis in pediatric human lumbar spines. SUMMARY OF BACKGROUND DATA: Progression from lysis to olisthesis occurs during the adolescent growth spurt. However, the mechanism of slippage in the immature lumbar spine has not yet been understood clearly. METHODS: Bilateral pars defects were created at the rostral vertebra. The specimens then were assigned to one of the two groups: functional spinal units with intact disc (n = 5) and with disc dissected (n = 5). In the former group, the disc was left intact, whereas in the disc dissected group, the anterior longitudinal ligament and 75% of the anterior-to-posterior depth of the disc were incised along the mid-disc plane. Using a uniaxial MTS machine (MTS System, Minneapolis, MN), anteroposterior shearing force was applied to each specimen. Failure load and displacement at failure were calculated from the load--displacement curve. Failure sites also were assessed radiographically and histologically. RESULTS: The five functional spinal units in the intact disc group failed at 973.8 +/- 78.1 N, whereas specimens in the disc dissected group failed at 986.4 +/- 124.2 N. The data showed no significant differences between the two groups. All the specimens showed displacement through the growth plates on radiographs. Histologically, failure was observed to occur between the superior growth plate and osseous endplate of caudal vertebra, indicating that this site is the weakest link. CONCLUSIONS: The results suggest that in the pediatric immature lumbar spine with pars defects, slippage may occur between the growth plate and osseous endplate.

L4-5 isthmic spondylolisthesis. A biomechanical analysis comparing stability in L4-5 and L5-S1 isthmic spondylolisthesis.

The authors have previously reported that the L4-5 isthmic spondylolisthesis lesion often progresses more than the L5-S1 lesion in adult patients. This biomechanical study compares the in vitro stability of the L4-5 isthmic spondylolisthesis lesion compared with the L5-S1 isthmic lesion. The authors also analyzed the role of the L5 iliolumbar ligament as a contributing factor to stability. Six fresh frozen human cadaveric specimens (L4 to the sacrum including the iliolumbar ligamentous complex) were tested by applying 10 Nm flexion-extension moments. Sagittal plane motion was measured with the specimens intact and after sequential transection of the pars interarticulares at L4 and L5 and finally with the iliolumbar ligaments cut at L5-S1. L4-5 and L5-S1 both showed significant increases in rotation with the pars defect compared with normal (L4-5 = +2.0, L5-S1 = +3.2 degrees). Decreased translation of L5-S1 occurred with pars defect at this level. There were no significant differences at the L5-S1 level after sectioning of the iliolumbar ligament. Calculating the percentage difference from normal, L4-5 with a pars defect exhibited significantly greater relative motion compared with L5-S1 with the same defect; 12% more rotation, 33% more shear, and 43% more axial translation. The iliolumbar ligament did not appear to contribute to these differences because there was no significant change in the L5-S1 kinematics after its transection. These results support the hypothesis that L4-5 pars defects are more unstable than L5-S1 lesions. The iliolumbar ligament could not be implicated as the major contributing factor in these differences.

Hole preparation techniques for transpedicle screws. Effect on pull-out strength from human cadaveric vertebrae.

In each of eight thoracolumbar human cadaveric vertebrae, a hole was made through one pedicle into the vertebral body with a drill bit and through the contralateral pedicle with a probe. Identical metal screws were implanted into the holes to equal depths, and maximum pull-out force was determined for each screw. Using a paired Student t test, no significant difference (P = 0.87) was found in pull-out strength between the screws implanted into drilled holes and those implanted into probed holes. In fact, the average pull-out strengths for the two groups differed by less than 2%. The pedicular cortex was broken through during hole preparation in 5 of the 16 pedicles: 3 as a result of drilling and 2 secondary to probing. The average pull-out strength of the screws in these five pedicles was 11.0% less than the average pull-out strength of the screws implanted into the contralateral intact pedicles. Although this does not represent a statistically significant difference (P = 0.15), it suggests that damaging the pedicular cortex may weaken pedicle screw fixation.

Clinical correlates of patient satisfaction after laminectomy for degenerative lumbar spinal stenosis.

STUDY DESIGN: Prospective multicenter observational study of the outcome of surgery for degenerative lumbar spinal stenosis. OBJECTIVES: To identify correlates of patient satisfaction with the results of surgery. SUMMARY OF BACKGROUND DATA: Little published information exists on correlates of patient satisfaction after surgery for spinal stenosis. METHODS: Preoperative and 6-month follow-up data for 194 patients were analyzed. Associations between preoperative variables and satisfaction with the results of surgery were examined in univariate and multivariate models. RESULTS: In multiple linear regression models that adjusted for the effects of age, gender, individual surgeon, number of interspaces decompressed, whether a fusion was performed, depression score, and overall level of pain, the predominance of back (as opposed to leg) pain, greater comorbidity, and worse preoperative functional status were associated with lower patient satisfaction. The regression model explained just 15% of the variance in patient satisfaction. CONCLUSIONS: Patients bothered predominantly by back pain preoperatively and those with greater medical comorbidity and functional disability are significantly less satisfied with the results of surgery for degenerative lumbar spinal stenosis.

Lumbar laminectomy alone or with instrumented or noninstrumented arthrodesis in degenerative lumbar spinal stenosis. Patient selection, costs, and surgical outcomes.

DESIGN: A prospective, multicenter observational study. OBJECTIVES: 1) Identify correlates of the decision to perform arthrodesis in patients undergoing laminectomy for lumbar spinal stenosis. 2) Compare symptoms, walking capacity, and satisfaction 6 and 24 months after laminectomy alone and laminectomy with noninstrumented and with instrumented arthrodesis. BACKGROUND DATA: Few prospective studies have compared outcomes of laminectomy alone or laminectomy with noninstrumented or with instrumented arthrodesis in patients with degenerative lumbar spinal stenosis. There is uncertainty regarding the optimal use of arthrodesis and instrumentation. METHODS: Two hundred seventy--two patients undergoing--surgery for degenerative lumbar stenosis by eight surgeons at four centers were included in the study cohort. Of these, 37 had noninstrumented and 41 had instrumented arthrodesis. Logistic regression identified factors associated with arthrodesis. The principal outcomes-health status, walking capacity, back and leg pain, and satisfaction with surgery-were assessed 6 and 24 months postoperatively with univariate and multivariate techniques. Outcomes also were assessed in a restricted cohort of patients with at least 5 mm spondylolisthesis and/or 15 degrees scoliosis. Hospital costs were obtained from a computerized hospital cost accounting system. RESULTS: The major predictor of the decision to perform arthrodesis was the individual surgeon (P = 0.0001). Noninstrumented arthrodesis was associated with superior relief of low back pain at 6 months (P = 0.004) and 24 months (P = 0.01). This difference persisted in multivariate analyses, with borderline statistical significance. There were no significant differences in the other outcomes across treatment groups. Mean hospital costs of laminectomy alone and noninstrumented and instrumented arthrodesis were $12,615, $18,495, and $25,914, respectively (P = 0.0001). CONCLUSION: Findings were limited by the small number of participating surgeons, modest sample size that produced P values of borderline significance, and nonrandomized design. With these caveats in mind, the authors conclude: (1) The individual surgeon was a more important correlate of the decision to perform arthrodesis than clinical variables such as spondylolisthesis. (2) Noninstrumented arthrodesis resulted in superior relief of back pain after 6 and 24 months. (3) Instrumented arthrodesis was the most costly option. These results highlight the need for randomized controlled trials and cost effectiveness analyses of lumbar arthrodesis and instrumentation in patients with degenerative lumbar spinal stenosis.

Stability analysis of an enhanced load sharing posterior fixation device and its equivalent conventional device in a calf spine model.

STUDY DESIGN: An in vitro test of calf spine lumbar segments to compare biomechanical stabilization of a rigid versus a dynamic posterior fixation device. OBJECTIVES: To compare flexibility of a dynamic pedicle screw fixation device with an equivalent rigid device. SUMMARY OF BACKGROUND DATA: Dynamic pedicle screw device studies are not as prevalent in the literature as studies of rigid devices. These devices contain the potential to enhance load sharing and optimize fusion potential while maintaining stability similar to that of rigid systems. METHODS: Load-displacement tests were performed on intact and stabilized calf spines for the dynamic and rigid devices. Stability across a destabilized L3-L4 segment was restored by insertion of either a 6 mm x 40 mm dynamic or rigid pedicle screw fixation device across the L2-L4 segment. The screws then were removed, 7 mm x 45 mm pedicle screws of the opposite type were inserted, and the construct then was re-tested. Axial pull-out tests were performed to assess the likely effects of pedicle screw replacement on the load-displacement data. RESULTS: Results indicated a 65% reduction in motion in flexion-extension and a 90% reduction in lateral bending across the destabilized level for both devices, compared with intact spine values. Reduction in axial rotation motion was much smaller than in other modes. Axial pull-out tests showed no weakening of the bone-screw interface. CONCLUSIONS: Both devices provided significant stability of similar magnitudes in flexion, extension, and lateral bending. In axial rotation, the devices only could restore stability to levels similar to those in an intact spine. The dynamic device offers a design that may enhance load sharing without sacrificing construct stability.

Predictors of surgical outcome in degenerative lumbar spinal stenosis.

STUDY DESIGN: A prospective, observational study. OBJECTIVES: To identify outcome predictors of surgery for degenerative lumbar spinal stenosis. SUMMARY OF BACKGROUND DATA: Degenerative lumbar spinal stenosis is the most frequent indication for spine surgery in the elderly. More than 25% of surgical patients have a poor outcome, yet little is known about factors that predict the outcome of surgery. METHODS: Surgery was performed on 199 patients with degenerative lumbar spinal stenosis, and they were observed for 2 years after surgery in four referral centers. Surgery consisted of decompressive laminectomy with or without arthrodesis. Outcomes included validated measures of symptom severity, walking capacity, and satisfaction with the results of surgery. Potential predictors of outcome included sociodemographic factors and physical examination, as well as radiographic, psychological, social, and clinical history variables. RESULTS: The proportion of patients with severe pain decreased from 81% before surgery to 31% by 2 years afterward. The most powerful preoperation predictor of greater walking capacity, milder symptoms, and greater satisfaction was the patient's report of good or excellent health before surgery. Low cardiovascular comorbidity also predicted a favorable outcome. CONCLUSIONS: Patient's assessments of their own health and comorbidity are the most cogent outcome predictors of surgery for spinal stenosis.

The pathomechanism of spondylolytic spondylolisthesis in immature primate lumbar spines in vitro and finite element assessments.

STUDY DESIGN: Immature Chacma baboon (Papio ursinus) spine specimens were used to determine load-displacement behavior as related to disc injury. This was accomplished through the application of A-P shear force until failure of FSUs with pars defects. Several finite element models (FEMs) of the FSU were developed to study the mechanism of slippage in immature baboon lumbar spines. OBJECTIVES: The purpose was to show that spondylolisthesis (olisthesis) always occurs through the growth plate using a model similar to immature human lumbar spines. Using FEMs, the roles of facet orientation, pars interarticularis thickness, and a weak growth-plate in producing slippage were examined. SUMMARY OF BACKGROUND DATA: Progression from spondylolysis (lysis) to olisthesis occurs, most often, during the adolescent growth spurt. The biomechanical literature dealing with the slippage mechanism in the immature lumbar spine does not provide a clear understanding and is sparse. METHODS: Several groups of FSUs were subjected to A-P shear force until failure. The results provided displacement at failure as a function of disc injury and flexion-extension fatigue. A bilateral pars defect was created in each specimen prior to application of A-P shear force using an MTS machine. Failure sites were assessed radiographically and histologically. A nonlinear 3-D FEM of the intact L4-L5 was created from CT scans. The model was modified to predict the effects of a pars fracture, a thin pars, a weak growth plate, and facet orientation on the shear load through the growth plate and stresses in the pars. RESULTS: Experimentally, failures always occurred through the growth-plate in the disc intact and disc-incised groups. In the intact FEM, the growth plate carried21% of the applied A-P shear force. The load increased when the facets were more sagittally oriented. The effect of thin pars and/or weaker growth plate was an increase in stresses in the pars. Changes in the load through the growth plate were minimal. CONCLUSIONS: The weakest link in immature baboon lumbar functional spinal units (FSUs) with lysis during an A-P shear load was the growth plate, between the cartilaginous and osseous end plates. Surgeons may assess this lesion on MRI views, thereby predicting the possible development and preventing progression of olisthesis. Finite element model results predict that more sagittally orientated facets and/or a pars fracture are prerequisites for olisthesis to occur.