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

TL;DR

A modified knee replacement technique called JLO-KA improves joint alignment in patients with a specific knee deformity, leading to better outcomes compared to traditional methods.

Contribution

The study introduces JLO-KA, a modified kinematic alignment technique that reallocates correction to the tibial side, improving alignment in apex-distal joint line obliquity.

Findings

JLO-KA significantly increased lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) compared to true KA.

JLO-KA resulted in increased femoral component rotation and a more neutral joint line obliquity.

JLO-KA achieved neutral joint line obliquity in 80% of cases versus 13% with true KA.

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 (Δ = 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 p > 0.05). Postoperatively, JLO‐KA increased LDFA to 90.4° ± 2.3° versus 87.0° ± 1.9° (Δ = +3.4°, 95% confidence interval [CI]: 1.9–4.8; p < 0.0001), MPTA to 88.0° ± 1.4° versus 85.6° ± 2.0° (Δ = +2.4°, 1.1–3.7; p = 0.0015), and FCR to 3.1° ± 2.0° versus 0.1° ± 2.0° (Δ = +2.9°, 1.5–4.3; p = 0.0002), while aHKA was similar (−2.4° ± 3.1° vs. −1.4° ± 2.8°; Δ = −1.0°; p = 0.324). JLO was closer to neutral with JLO‐KA (178.4° ± 2.2° vs. 172.7° ± 2.8°; Δ = +5.8°; p < 0.001). Neutral‐JLO CPAK types (IV–VI) occurred in 16/20 (80%) versus 2/15 (13%) (p = 0.00013). The restricted KA 90° ± 5° range for LDFA and MPTA was met by 19/20 (95%) versus 7/15 (47%) (p = 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.

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