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

PURPOSE: Accurate 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 METHODS: This 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. RESULTS: The 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). CONCLUSION: Robotic 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.