Anatomical structure of the medullary cavity of proximal femur with three-dimensional computed tomography

Background The lateral femoral wall is an important anatomical parameter of the proximal femur, but intramedullary nail fixation for intertrochanteric fractures may cause iatrogenic lateral wall fractures due to population-based design differences. This study aims to measure the anatomical parameters of the proximal femoral medullary cavity and provide data to help design intramedullary nails tailored to the Chinese population to reduce the risk of complications such as lateral wall fractures. Methods Consecutive patients undergoing full-length or upper half CT scans of the femur were included from January 2010 to December 2021. The anatomical parameters of medullary cavity were defined and measured, including prominence length, canal-shaft angle and proximal minimum diameter. Intraclass Correlation Coefficient (ICC) was used to estimate the inter- and intra-observer agreements. Results A total of 168 patients, comprising 78 men and 90 women, were included. The mean prominence length was 67.4 +/- 4.9 mm (males: 70.8 +/- 3.6 mm, females: 64.4 +/- 3.9 mm). The mean canal-shaft angle was 5.5 degrees +/- 0.7 degrees (males: 5.6 +/- 0.8 degrees, females: 5.5 +/- 0.7 degrees). The mean proximal minimum diameter was 22.7 +/- 1.8 mm (males: 24.0 +/- 1.5 mm, females: 21.6 +/- 1.4 mm) at the level of 1/3 prominence length from bottom to top. Gender differences were observed in these parameters (p < 0.001) except for the canal-shaft angle (p = 0.45). The mean proximal minimum diameter was significantly larger in the group aged 50 years and older (23.1 +/- 1.7 mm) compared to the group younger than 50 years (22.4 +/- 1.9 mm) (p = 0.02). Inter- and intra-observer agreement was almost perfect for all the parameters (all ICC values > 0.8). Conclusions Males have a longer prominence length and larger proximal minimum diameter than females. The proximal minimum diameter is larger in the older population than in the younger population. The measurement results help support the design of intramedullary nails tailored to the Chinese population.