Load transfer characteristics between posterior spinal implants and the lumbar spine under anterior shear loading: an in vitro investigation

STUDY DESIGN.: A biomechanical human cadaveric study. OBJECTIVE.: To determine the percentage of shear force supported by posterior lumbar spinal devices of varying stiffnesses under anterior shear loading in a degenerative spondylolisthesis model. SUMMARY OF BACKGROUND DATA.: Clinical studies have demonstrated beneficial results of posterior arthrodesis for the treatment of degenerative spinal conditions with instability. Novel spinal implants are designed to correct and maintain spinal alignment, share load with the spine, and minimize adjacent level stresses. The optimal stiffness of these spinal systems is unknown. To our knowledge, low-stiffness posterior instrumentation has not been tested under an anterior shear force, a highly relevant force to be neutralized in the clinical case of degenerative spondylolisthesis. METHODS.: The effects of implant stiffness and specimen condition on implant load and intervertebral motion were assessed in a biomechanical study. Fifteen human cadaveric lumbar functional spinal units were tested under a static 300 N axial compression force and a cyclic anterior shear force (5-250 N). Implants (high-stiffness [HSI]: ? 5.5-mm titanium, medium-stiffness [MSI]: ? 6.35 × 7.2-mm oblong PEEK, and low-stiffness [LSI]: ? 5.5-mm round PEEK) instrumented with strain gauges were used to calculate loads and were tested in each of 3 specimen conditions simulating degenerative changes: intact, facet instability, and disc instability. Intervertebral motions were measured with a motion capture system. RESULTS.: As predicted, implants supported a significantly greater shear force as the specimen was progressively destabilized. Mean implant loads as a percent of the applied shear force in order of increasing specimen destabilization for the HSI were 43%, 67%, and 76%; mean implant loads for the MSI were 32%, 56%, and 77%; and mean implant loads for the LSI were 18%, 35%, and 50%. Anterior translations increased with decreasing implant stiffness and increasing specimen destabilization. CONCLUSION.: Implant shear stiffness significantly affected the load sharing between the implant and the natural spine in anterior shear ex vivo. Low-stiffness implants transferred significantly greater loads to the spine. This study supports the importance of load-sharing behavior when designing new implants.     

Can Group Medical Clinics Improve Lipid Management in Diabetes?

Background

Group medical clinics may improve diabetes and hypertension control, but data about dyslipidemia are limited. We examined the impact of group medical clinics on lipids among patients with uncontrolled diabetes and hypertension.

Methods

Prespecified secondary analysis of 239 veterans randomized to group medical clinics or usual care. Lipids were assessed at study baseline, midpoint, and end. We used linear mixed models to compare lipid levels between arms and generalized estimating equation models to compare low-density lipoprotein cholesterol (LDL-C) goal attainment. An additional post hoc analysis examined intensification of cholesterol-lowering medications in both arms.

Results

At baseline, mean total cholesterol was 169.7 mg/dL (SD 47.8), LDL-C 98.2 mg/dL (SD 41.7), and high-density lipoprotein cholesterol (HDL-C) 39.3 mg/dL (SD 13.0). Median baseline triglycerides were 131 mg/dL (interquartile range 122). By study end, mean total cholesterol and LDL-C in group medical clinics were 14.2 mg/dL (P = .01) and 9.2 mg/dL (P = .02) lower than usual care, respectively; 76% of group medical clinic patients met goals for LDL-C, versus 61% of usual care patients (P = .02). Triglycerides and HDL-C remained similar between study arms. Treatment intensification occurred in 52% of group medical clinic patients, versus 37% of usual care patients between study baseline and end (P = .04). The mean statin dose was higher in group medical clinic patients at study midpoint and end.

Conclusions

Group medical clinics appear to enhance lipid management among patients with diabetes and hypertension. This may be a result of greater intensification of cholesterol-lowering medications in group medical clinics relative to usual care.     

Nonprocedural bleeding after left atrial appendage closure versus direct oral anticoagulants: A subanalysis of the randomized PRAGUE-17 trial

Introduction

Observational studies have shown low bleeding rates in patients with atrial fibrillation (AF) treated by left atrial appendage closure (LAAC); however, data from randomized studies are lacking. This study compared bleeding events among patients with AF treated by LAAC and nonvitamin K anticoagulants (NOAC).

Methods

The Prague-17 trial was a prospective, multicenter, randomized trial that compared LAAC to NOAC in high-risk AF patients. The primary endpoint was a composite of a cardioembolic event, cardiovascular death, and major and clinically relevant nonmajor bleeding (CRNMB) defined according to the International Society on Thrombosis and Hemostasis (ISTH).

Results

The trial enrolled 402 patients (201 per arm), and the median follow-up was 3.5 (IQR 2.6–4.2) years. Bleeding occurred in 24 patients (29 events) and 32 patients (40 events) in the LAAC and NOAC groups, respectively. Six of the LAAC bleeding events were procedure/device-related. In the primary intention-to-treat analysis, LAAC was associated with similar rates of ISTH major or CRNMB (sHR 0.75, 95% CI 0.44–1.27, p = 0.28), but with a reduction in nonprocedural major or CRNMB (sHR 0.55, 95% CI 0.31–0.97, p = 0.039). This reduction for nonprocedural bleeding with LAAC was mainly driven by a reduced rate of CRNMB (sHR for major bleeding 0.69, 95% CI 0.34–1.39, p = .30; sHR for CRNMB 0.43, 95% CI 0.18–1.03, p = 0.059). History of bleeding was a predictor of bleeding during follow-up. Gastrointestinal bleeding was the most common bleeding site in both groups.

Conclusion

During the 4-year follow-up, LAAC was associated with less nonprocedural bleeding. The reduction is mainly driven by a decrease in CRNMB.     

Failure of chronic experimental hyperinsulinism to alter insulin binding to hypothalamic receptors in the rat

We have previously shown that [125I]insulin binding to medial hypothalamic receptors is attenuated following 14 days of food restriction. Such rats are characterized by considerably reduced circulating insulin levels with unchanged hypothalamic insulin concentration. The present data demonstrate that, in contrast to the effects of starvation, [125I]insulin binding to hypothalamic receptors from rats made hyperinsulinaemic by daily injections of protamine zinc insulin (4-6 U/rat/day for 14 days) is unaffected by this manipulation, even though hypothalamic insulin concentration in insulin-injected animals was significantly higher than in saline-injected controls. Insulin binding to partially purified membranes from the medial hypothalamic region was significantly greater than that from the lateral area, confirming a finding in our earlier study. Insulin treatment was associated with slight reductions in maximal insulin-binding capacity of medial hypothalamic receptors, a tendency which appeared to be compensated by reciprocal changes in receptor affinity for this hormone. The data indicate that hypothalamic insulin receptors are not regulated by peripheral or even central insulin levels per se; it appears, rather, that some other, as yet unidentified, correlate(s) of significantly altered food intake and/or body weight can modify hypothalamic insulin receptor function. Perhaps such modifications could, in turn, participate in the activation of regulatory mechanisms involved in correcting energy imbalance.