Intraoperative six-axis loads during direct anterior approach total hip arthroplasty using a leg positioner: quantitative patterns across manoeuvres.

purposeThe direct anterior approach (DAA) for total hip arthroplasty (THA) commonly uses leg positioners to facilitate femoral exposure, but intraoperative lower-limb loading during these manoeuvres remains poorly understood. This study quantitatively assessed six-axis loads during femoral preparation in leg positioner-assisted DAA-THA.

methodsThis prospective observational biomechanical study included 95 hips undergoing primary DAA-THA using a leg positioner. A six-axis force sensor mounted on the operative boot recorded forces (Fx, Fy, Fz) and moments (Mx, My, Mz) at baseline and at two predefined static endpoint measurement points: the extension endpoint and the final stem position after adduction. Values were expressed relative to baseline and represented static endpoint measurements rather than peak values during dynamic manoeuvres. Measurements were standardised to a right-sided coordinate system. Repeated-measures analysis of variance with Bonferroni-corrected post hoc paired comparisons was used.

resultsAt the extension endpoint, distal traction force was greatest (Fz; 170.6 ± 51.9 N). At the final stem position after adduction, distal traction force decreased compared with the extension endpoint but remained elevated relative to baseline (126.9 ± 45.7 N), and Mx showed the greatest magnitude among the moment components. The maximum endpoint Fz relative to baseline was recorded at the extension endpoint (322.8 N). No significant associations were found between final-position Fz and age, sex, height, weight, body mass index, or diagnosis. Mean stem rasping time was 10 min 48 s ± 4 min 28 s (648 ± 268 s).

conclusionDuring leg positioner-assisted DAA-THA, the extension endpoint generated the highest distal traction force, whereas the final stem position after adduction was associated with residual distal traction force and a greater magnitude of Mx.