Kinematic alignment without femoral cartilage-wear compensation for apex-distal joint line obliquity: Effects on component alignment.

Abstract

Pronounced apex-distal joint line obliquity (JLO) complicates total knee arthroplasty (TKA) by challenging patellofemoral tracking and medial tibial bone support. Joint line obliquity-modified kinematic alignment (JLO-KA)-a selective modification of kinematic alignment (KA) that omits femoral cartilage-wear compensation and reallocates correction to the tibial side-was developed. This study quantified postoperative component and limb alignment with JLO-KA versus true KA. Retrospective comparison of 20 JLO-KA knees and 15 true-KA knees with preoperative apex-distal JLO (CPAK I-III). Pre-/postoperative computed tomography (CT) measured lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), femoral component rotation (FCR), arithmetic hip-knee-ankle angle (aHKA), and JLO; postoperative Coronal Plane Alignment of the Knee (CPAK) distribution was analysed (<i>Δ</i> = JLO-KA minus true KA). Groups were similar at baseline: preoperative LDFA 87.7° versus 87.6°, MPTA 83.5° versus 83.5°, aHKA -4.3° versus -4.1°, JLO 171.2° versus 171.2° (all <i>p</i> > 0.05). Postoperatively, JLO-KA increased LDFA to 90.4° ± 2.3° versus 87.0° ± 1.9° (<i>Δ</i> = +3.4°, 95% confidence interval [CI]: 1.9-4.8; <i>p</i> < 0.0001), MPTA to 88.0° ± 1.4° versus 85.6° ± 2.0° (<i>Δ </i>= +2.4°, 1.1-3.7; <i>p</i> = 0.0015), and FCR to 3.1° ± 2.0° versus 0.1° ± 2.0° (<i>Δ </i>= +2.9°, 1.5-4.3; <i>p</i> = 0.0002), while aHKA was similar (-2.4° ± 3.1° vs. -1.4° ± 2.8°; <i>Δ</i> = -1.0°; <i>p</i> = 0.324). JLO was closer to neutral with JLO-KA (178.4° ± 2.2° vs. 172.7° ± 2.8°; <i>Δ</i> = +5.8°; <i>p</i> < 0.001). Neutral-JLO CPAK types (IV-VI) occurred in 16/20 (80%) versus 2/15 (13%) (<i>p</i> = 0.00013). The restricted KA 90° ± 5° range for LDFA and MPTA was met by 19/20 (95%) versus 7/15 (47%) (<i>p</i> = 0.0019). Reallocating cartilage-wear compensation from the medial femur to the medial tibia within the same calliper-verified workflow reduced femoral valgus, limited tibial varus, and increased femoral external rotation by ≈3° while maintaining aHKA. Shifts were consistent with lateralizing the prosthetic trochlear groove and preserving medial tibial bone support, positioning JLO-KA as a targeted option for apex-distal knees (CPAK I-III). Level III, retrospective comparative study.