Anatomical relationship between the intertrochanteric line and femoral neck osteotomy level in direct anterior approach total hip arthroplasty: a 3D morphometric and cadaveric validation study

AIMS: Inaccurate femoral neck osteotomy is a recognized technical challenge in direct anterior approach total hip arthroplasty (DAA-THA), largely due to limited femoral exposure and the absence of a standardized intraoperative landmark. This study aimed to investigate whether the ITL is an alternative bony landmark for femoral neck osteotomy during the DAA. PATIENTS AND METHODS: Three anatomical references, the Intertrochanteric line (ITL) height (ITL-H), ITL angle (ITL-A), and femoral saddle height (SH), were measured from 3D-CT models of 60 normal hip patients (30 males and 30 females) to simulate a cutting height of 10 mm above the LT. Twenty cadaveric hip specimens were then used to evaluate the accuracy of the proposed anatomical references. RESULTS: The mean ITL-H, ITL-A, and SH were 23 ± 4 mm, 17.4° ± 3.5°, and 26 ± 4 mm, respectively. While ITL-H showed no sex difference (23 ± 3.4 mm vs 23.1 ± 4.1 mm, P = 0.96), significant differences existed for ITL-A (15.8° ± 3.4° vs 19.9° ± 1.4°, P = 0.001) and SH (27.2 ± 3.9 mm vs 23.9 ± 3 mm, P = 0.002). ITL-H was not correlated with age (P = 0.063), femoral length (P = 0.31), or femoral neck shaft angle (P = 0.41). Femoral neck osteotomy performed 23 mm above the ITL-H could yield 80% and 100% success rates for cutting heights of 10-15 mm and > 5 mm above the LT, respectively. CONCLUSIONS: ITL-H serves as a reproducible anatomical landmark for femoral neck osteotomy during DAA-THA. An osteotomy level of approximately 23 mm above the ITL-H represents a safe lower margin to avoid excessive calcar bone resection. Nevertheless, individualized preliminary osteotomy based on preoperative templating remains necessary, with intraoperative adjustment according to patient-specific ITL-H. Video Abstract.