Effect of native Posterior condylar axis-Transepicondylar axis variability on femoral component rotation using robotic total knee arthroplasty.

purposeAccurate femoral component rotation in total knee arthroplasty (TKA) is critical for flexion balance, patellofemoral tracking, and implant longevity. Conventional techniques apply a fixed 3° external rotation relative to the posterior condylar axis (PCA), assuming a constant relationship with the transepicondylar axis (TEA). However, anatomical variability challenges this assumption. This study evaluated whether robotic-assisted TKA individualizes femoral rotation according to native PCA-TEA anatomy rather than applying a fixed rotational target. MATERIALS AND

methodsThis retrospective study included 52 patients (72 knees) undergoing primary CT-based robot (MAKO) assisted TKA for primary osteoarthritis of the knee. Preoperative CT scans were used to determine the native PCA-TEA angle. Intraoperative femoral component rotation relative to PCA and TEA was recorded using robot-generated measurements. Correlations were assessed using Spearman's coefficient, with subgroup analysis across PCA-TEA strata.

resultsThe median PCA-TEA angle was 2.3° (range -1.9 to 8.7°). Median femoral rotation was 3.9° (range -1.2 to 9.6°) relative to PCA and 1.1° (range -3.4 to 4.9°) relative to TEA. A strong positive correlation existed between PCA-TEA angle and rotation relative to PCA (ρ = 0.8, p < 0.001), while a moderate negative correlation was observed relative to TEA (ρ = -0.5, p < 0.001). Knees with negative PCA-TEA anatomy demonstrated significantly lower rotation than the conventional 3° target (p < 0.05).

conclusionRobotic functional alignment adapts femoral component rotation to native PCA-TEA anatomy within predefined rotational boundaries rather than adhering to a fixed 3° paradigm. While this demonstrates patient-specific rotational adaptation, whether such adaptation provides a clinical benefit remains to be demonstrated.