Subcutaneous fat area at the upper thigh level is a useful prognostic marker in the elderly with femur fracture

Abstract

Background: The aim of this study was to evaluate prognostic value of body tissue composition at the upper thigh level for 1 year mortality in elderly patients with proximal femur fracture.

Methods: This retrospective cohort study included consecutive elderly (aged ≥65) patients diagnosed with proximal femur fracture based on the findings of pelvic bone computed tomography (CT) performed at the emergency department of a tertiary care hospital and treated with surgery between 2010 and 2017. The cross-sectional area of subcutaneous fat and skeletal muscle at the upper thigh level was measured using CT. Adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for 1 year mortality were estimated using a Cox proportional hazards model. Survival based on the SFA quartiles was assessed using nonparametric Kaplan-Meier survival analysis and compared used log-rank tests.

Results: Among 876 elderly patients included in this study, the median age was 79.0 years, and 646 (73.7%) patients were female. A total of 93 (10.6%) died within 1 year after admission to the emergency department. Survivors had a significantly higher median subcutaneous fat area (SFA) than non-survivors (170.2 vs. 133.0 cm² , P < 0.001), but no significant difference was observed between the skeletal muscle area (median, 156.7 vs. 160.3 cm² , P = 0.504) and muscle density (median, 19.0 vs. 19.1 HU, P = 0.861) of both groups. After adjustment of other clinical characteristics and body compositions, the multivariate Cox proportional hazard analysis showed that SFA (adjusted HR, 0.987; 95% CI, 0.982-0.992; P < 0.001) was independently associated with 1 year mortality. With 384 deaths during 51 322 person-months of follow-up, the median estimated survival duration of all the patients was 92.8 months (95% CI, 80.8-104.7 months). The patients with SFA in the third (165.6-195.0 cm² ) and fourth (>195.0 cm² ) quartiles showed significantly longer survival duration than those with SFA in the first (<131.4 cm² ; median survival time, 51.3 months) and second (131.4-165.5 cm² ; median survival time, 88.7 months) quartiles (P < 0.001 by log-rank test).

Conclusions: The SFAs measured at the upper thigh level and 1 year mortality are positively associated in elderly patients with proximal femur fracture. SFA may be an independent prognostic biomarker for 1 year mortality of femur fracture.

Keywords: Body composition; Elderly; Femur fracture; Mortality; Upper thigh.

Figure 1

Body morphometry analysis. The axial computed tomography image at the upper thigh level is selected. The boundary between the subcutaneous fat and skeletal muscle is drawn. Then, the skeletal muscle area (SMA) and subcutaneous fat area (SFA) are segmented using predefined thresholds (−29 to 150 HU for SMA, −190 to −30 HU for SFA). The mean density of the muscle area is calculated within the boundary of the skeletal muscle.

Figure 2

Patient flow diagram. CT, computed tomography; ED, emergency department.

Figure 3

Representative pelvic bone computed tomography images used for measurement of skeletal muscle and subcutaneous fat area and muscle density. (A) An 84‐year‐old female survivor whose axial image shows a high subcutaneous fat area of 326.6 cm² with a low skeletal muscle area of 170.9 cm². (B) An 82‐year‐old female non‐survivor whose axial image shows a low subcutaneous fat area of 120.9 cm² with a high skeletal muscle area of 248.2 cm².

Figure 4

Kaplan–Meier survival curve estimates of elderly patients with proximal femur fracture according to their subcutaneous fat area (SFA) (cm²) measured at the upper thigh level. SFA were defined as Q1: <131.4 cm²; Q2: 131.4–165.5 cm²; Q3: 165.6–195.0 cm²; and Q4 > 195.0 cm².