SHAPE VARIABILITY OF THE MEDULLARY CANAL OF THE HUMAN PROXIMAL FEMUR

Proximal femoral morphology is crucial in cementless femoral stem design and placement in total hip arthroplasty, particularly due to inter-patient variability resulting from genetics, lifestyle, and disease. Therefore, a comprehensive understanding of the medullary morphology is essential to optimize the performance of standard and personalized cementless femoral stems in terms of stress transfer, migration, and micromotion. This study investigated the geometric characteristics of the human proximal femoral medullary canal and whether its shape can be adequately described by a small number of parameters. CT scans of the proximal region of the femur of 763 individuals (389 female, 374 male) aged 20 to 92 years were used to evaluate medullary radius (R med ), roundness index of the cross-section (MRI), orientation of the cross-section (f), flare index as a ratio of the largest and smallest cross-sectional radius, and normalized curvature with respect to the shaft (L/R cur ), and related to sex and age. In addition, a statistical shape model (SSM) was developed using principal component analysis (PCA). The geometric parameters demonstrated sex- and age-specific variation, possibly due to alterations in bone architecture resulting from endosteal resorption and periosteal formation in response to altered musculoskeletal loading. Specifically, the differences in R med /L between age groups are more pronounced in women with a slower increase toward the proximal contours (Figure 1). MRI demonstrated a comparable trend between the age groups in both men and women, exhibiting two minima in the distal region of the gluteal tuberosity and the top of the lesser trochanter and a maximum in the distal area of the lesser trochanter. Phi exhibited a significant difference between age groups only in the female cohort (p<0.01). The flare index varied with age and sex, demonstrating significantly higher values for the male cohort in the middle-aged and elderly (p<0.001) (Figure 2). L/R cur showed significant sex- and age-dependency particularly in men and in the elderly (p<0.01). With respect to the SSM, the first three PCs accounted for 68.4% of the total variation, with each component being associated with at least one of the investigated geometrical parameters. The generated new shapes could facilitate custom canal shape matching by reducing the need for manual geometric adjustments and material usage.