Does the Instability of Pertrochanteric Fractures in the Elderly Correlate With Weakened Gluteal Muscles?

Introduction Suboptimal outcomes were observed in cases of unstable pertrochanteric fractures, even when bone healing occurs without complications. This raises the question of whether factors beyond bone health integrity, such as the frailty of muscles, contribute to these less favorable results. Muscles, particularly the gluteal muscles, not only influence functional ability but also serve as a cushion that provides physical protection against external forces during falls. When gluteal muscles are thin or weak, their ability to absorb the impact from a fall diminishes, potentially leading to unstable fractures. In this study, we compared gluteal muscle-related indices, including cross-sectional area (CSA) and muscle density, between stable and unstable pertrochanteric fractures. The aim of this study was to employ a retrospective approach to investigate the causes of unstable fractures, with a focus on potential muscular pathology. It was hypothesized that reduced CSA and lower density of the gluteal muscles would be associated with unstable fractures. Material and methods Geriatric patients aged 70 years or older with pertrochanteric fractures requiring surgical intervention were retrospectively identified from databases. These fractures classified as stable (A1) or unstable (A2) based on the Revised Arbeitsgemeinschaft für Osteosynthesefragen (AO)/Orthopaedic Trauma Association (OTA) Classification were compared based on demographic variables (age, height, body mass index (BMI), and fracture laterality) as well as muscle-related indices. A multivariate logistic regression model was employed to identify predictors of unstable fractures. Independent variables included age at the time of surgery, height, BMI, and muscular metrics CSA and density of the gluteus maximus and gluteus medius. Results Out of 220 patients identified from the database, 111 patients with an average age of 88 years (ranging from 71 to 103 years) were included. This cohort consisted of 40 patients with stable fractures (A1) and 71 patients with unstable fractures (A2). Among the demographical data, only fracture laterality demonstrated a significant difference between the groups (p < 0.05). Regarding gluteal muscle data, the CSA/BMI of both the gluteus maximus and medius, as well as the density of the gluteus medius, did not show significant differences between the two groups. The only exception was the density of the gluteus maximus, which was significantly lower in the unstable group (p < 0.01). A binary logistic regression analysis was conducted to identify risk factors for unstable fractures. The analysis found that the density of the gluteus maximus was a statistically significant predictor, with an odds ratio of 0.959 (95% CI, 0.923 to 0.997; p = 0.03). To determine an optimal cut-off value, receiver operating characteristic (ROC) analysis was performed for the density of the gluteus maximus. The Youden index identified a cut-off value of 20.8 HU for the gluteus maximus density as the optimal threshold (area under the curve (AUC): 0.625; 95% CI: 0.520-0.730). Conclusion This retrospective study investigated whether unstable pertrochanteric fractures in elderly female patients were linked to weakened gluteal muscles, compared to stable fractures, and suggested this muscle weakness may contribute to poor functional outcomes. Our binary regression analysis indicated that decreased muscle density in the gluteus maximus increases the risk of unstable fractures.