The effect of body weight on interfragmentary fracture strain in plate fixation of distal femur fractures: A finite element analysis.

INTRODUCTION: Distal femur fractures are difficult to successfully treat due to high rates of nonunion. Obesity is an independent prognostic risk factor for nonunion. Advances in finite element analyses (FEAs) have allowed researchers to better understand the performance and behavior of constructs at the bone-implant interface under a variety of conditions. The purpose of this study is to determine the impact of body weight on fracture strain in a lateral locking plate construct for supracondylar femur fractures and whether additional construct rigidity is beneficial to optimize fracture strain in high body mass patients. HYPOTHESIS: We hypothesized that increased loads would produce a higher interfragmentary strain (IFS), which could be decreased by shortening the working length of the construct. MATERIALS AND METHODS: A 3D finite element analysis was performed on two separate femur models with a comminuted supracondylar distal femur fracture fixed with a lateral distal femoral locking plate in bridging mode with Ansys software. Axial forces were varied to recreate the effect of load from normal and high body mass patients. Working length and screw density of the construct were varied for each condition. Measurements of interfragmentary strain and shear motion (SM) were compared. RESULTS: Doubling the axial load from 70kg (control) to 140kg (high body mass) increased the interfragmentary strain by an average of 76% for the three working lengths (3.38%±1.67% to 4.37%±0.88% at the baseline working length (BWL), 1.42%±1.00% to 2.87%±2.02% at the intermediate working length (IWL) and 0.62%±0.22% to 1.22%±0.42% at the short working length (SWL)). On average, decreasing the working length in the 140kg load reduced the mean IFS to within 15% of the mean IFS of the 70kg load at the longer working length (2.87%±2.02% at IWL 140kg versus 3.38%±1.67% at BWL 70kg and 1.22%±0.45% SWL 140kg versus 1.42±1.00% IWL 70kg). DISCUSSION: Increased axial load increases interfragmentary strain in an AO/OTA 33A distal femur fracture fixed with a lateral distal femoral locking plate. Decreasing the working length of the fixation construct in the high body mass model decreased interfragmentary strain. Higher loading conditions reflective of high body mass patients should be considered in studies investigating optimization of fracture strain. LEVEL OF PROOF: V; Finite Element Analysis (FEA).

Direct Anterior Versus Posterior Approach for Total Hip Arthroplasty Performed for Displaced Femoral Neck Fractures.

OBJECTIVES: To compare perioperative, 90-day, and 1-year postoperative complications and outcomes between the direct anterior approach (DAA) and the posterior approach for total hip arthroplasty in geriatric patients with displaced femoral neck fractures (FNFs). DESIGN: Retrospective cohort study. SETTING: Multicenter Health care Consortium. PATIENTS: Seven-hundred and nine patients 60 years or older with acute displaced FNFs between 2009 and 2021. INTERVENTION: Total hip arthroplasty using either DAA or posterior approach. MAIN OUTCOME MEASUREMENTS: Rates of postoperative complications including dislocations, reoperations, and mortality at 90 days and 1 year postoperatively. Secondary outcome measures included ambulation capacity at discharge, ambulation distance with inpatient physical therapy, discharge disposition, and narcotic prescription quantities (morphine milligram equivalents). RESULTS: Through a multivariable regression analysis, DAA was associated with significantly shorter operative time ( B = -6.89 minutes; 95% confidence interval [CI] -12.84 to -0.93; P = 0.024), lower likelihood of blood transfusion during the index hospital stay (adjusted odds ratios = 0.54; 95% CI 0.27 to 0.96; P = 0.045), and decreased average narcotic prescription amounts at 90 days (B = -230.45 morphine milligram equivalents; 95% CI -440.24 to -78.66; P = 0.035) postoperatively. There were no significant differences in medical complications, dislocations, reoperations, and mortality at 90 days and 1 year postoperatively. CONCLUSION: When comparing the DAA versus posterior approach for total hip arthroplasty performed for displaced FNF, DAA was associated with shorter operative time, lower likelihood of blood transfusion, and lower 90-day postoperative narcotic prescription amounts. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Impact of High-intensity Zones on Their Corresponding Lumbar Spine Segments: A Propensity Score-matched Analysis.

STUDY DESIGN: Retrospective radiographic study. OBJECTIVE: The aim of this study was to compare disks with and without high-intensity zones (HIZ) to understand the impact of an HIZ on the stability of corresponding lumbar spinal segments. SUMMARY OF BACKGROUND DATA: Previous studies have established a relationship between back pain and the presence of HIZ on T2-weighted images of magnetic resonance imaging. These previous studies, however, used either plain radiographs or static (neutral position) magnetic resonance imaging to assess their chosen variables. MATERIALS AND METHODS: We retrospectively reviewed 140 consecutive patients with MR images taken in weight-bearing neutral, flexion, and extension positions. We separated segments into those with HIZ and without HIZ and assessed the grade of disk degeneration for each segment. Subsequently, a matched control group was selected from the segments without HIZ. Multiple factors were compared in a univariate analysis. A multinomial logistic regression analysis was conducted to assess the association between angular range of motion (ROM) >10 degrees and translational motion >2 mm with multiple independent variables. RESULTS: Upon assessment of the 700 lumbar segments, 70 (10%) segments had an HIZ and 68 patients had a single HIZ. On univariate analysis, the presence of an HIZ was not found to be significantly associated with degree of fatty muscle degeneration (P=0.969), muscle volume (P=0.646), degree of facet joint osteoarthritis (P=0.706), intervertebral disk height (P=0.077), Modic change (P=0.951), lower endplate shape (P=0.702), upper endplate shape (P=0.655), or degree of disk degeneration (P=0.607). Multifactorial analysis showed that none of the independent variables significantly correlated with angular ROM >10 degrees. For translational motion, the only significant correlation was the Goutallier classification (P=0.017). CONCLUSIONS: The presence of HIZ did not significantly affect spinal stability as measured by angular ROM and translational motion and was not associated with significant changes in several quantitative measurements of spine pathology.

RDH1 suppresses adiposity by promoting brown adipose adaptation to fasting and re-feeding.

RDH1 is one of the several enzymes that catalyze the first of the two reactions to convert retinol into all-trans-retinoic acid (atRA). Here, we show that Rdh1-null mice fed a low-fat diet gain more weight as adiposity (17% males, 13% females) than wild-type mice by 20 weeks old, despite neither consuming more calories nor decreasing activity. Glucose intolerance and insulin resistance develop following increased adiposity. Despite the increase in white fat pads, epididymal white adipose does not express Rdh1, nor does muscle. Brown adipose tissue (BAT) and liver express Rdh1 at relatively high levels compared to other tissues. Rdh1 ablation lowered body temperatures during ambient conditions. Given the decreased body temperature, we focused on BAT. A lack of differences in BAT adipogenic gene expression between Rdh1-null mice and wild-type mice, including Pparg, Prdm16, Zfp516 and Zfp521, indicated that the phenotype was not driven by brown adipose hyperplasia. Rather, Rdh1 ablation eliminated the increase in BAT atRA that occurs after re-feeding. This disruption of atRA homeostasis increased fatty acid uptake, but attenuated lipolysis in primary brown adipocytes, resulting in increased lipid content and larger lipid droplets. Rdh1 ablation also decreased mitochondrial proteins, including CYCS and UCP1, the mitochondria oxygen consumption rate, and disrupted the mitochondria membrane potential, further reflecting impaired BAT function, resulting in both BAT and white adipose hypertrophy. RNAseq revealed dysregulation of 424 BAT genes in null mice, which segregated predominantly into differences after fasting vs after re-feeding. Exceptions were Rbp4 and Gbp2b, which increased during both dietary conditions. Rbp4 encodes the serum retinol-binding protein-an insulin desensitizer. Gbp2b encodes a GTPase. Because Gbp2b increased several hundred-fold, we overexpressed it in brown adipocytes. This caused a shift to larger lipid droplets, suggesting that GBP2b affects signaling downstream of the ß-adrenergic receptor during basal thermogenesis. Thus, Rdh1-generated atRA in BAT regulates multiple genes that promote BAT adaptation to whole-body energy status, such as fasting and re-feeding. These gene expression changes promote optimum mitochondria function and thermogenesis, limiting adiposity. Attenuation of adiposity and insulin resistance suggests that RDH1 mitigates metabolic syndrome.