Background: Kinematic alignment for total knee arthroplasty (TKA) may be one way of improving outcomes. Previous studies have either used patient-specific instrumentation, which adds cost, or standard instrumentation, which provides no intraoperative feedback on resection alignment.
Hypothesis: To determine if computer navigation could reproduce native patient anatomy and simplify ligament balance during TKA whilst giving satisfactory improvements in functional scores at early follow-up.
Materials and methods: Computer navigation was used for kinematic distal femoral and proximal tibial cuts in 100 consecutive and unselected TKAs. Resections were modified only if measured angles fell outside a pre-defined safe range of combined coronal orientation within±3 degrees of neutral and/or independent femoral or tibial cuts within±5 degrees. Pre- and postoperative measurements of the hip-knee-ankle (HKA) angle, the lateral distal femoral angle (LDFA) and the medial proximal tibial angle (MPTA) were taken using long-leg standing radiographs. Clinical evaluation was with the WOMAC and KOOS scales.
Results: Mean follow-up was 2.4 years (range 1.0-3.7, SD 0.8). The mean pre-op LDFA was 2.1 degrees valgus (9.2 valgus to 3.7 varus, SD 2.5) and 1.8 degrees valgus post-op (5.7 valgus to 4.2 varus, SD 2.0) (P=0.41). The mean pre-op MPTA was 3.0 degrees varus (10.6 valgus to 10.2 varus, SD 3.2) and 2.4 degrees varus post-op (4.0 valgus to 6.8 varus, SD 2.2) (P=0.03). The mean WOMAC score improved from 49.4 (29-85, SD 12.8) to 24.7 (0-73, SD 16.5) (P<0.001) and the mean KOOS score from 37.1 (7.2-77.2, SD 13.0) to 65.1 (26.8-100, SD 16) (P<0.001). Five knees (5%) required additional ligament release, four with valgus OA and one with varus OA. Two knees (2%) required lateral retinacular release for patellar tracking.
Discussion: Computer navigation for kinematic TKA provides the operating surgeon with full control and feedback at each step, whilst also allowing partial correction of more extreme anatomy that might be unsuitable for recreation during TKA. This technique helps to preserve ligament isometry and produces satisfactory improvements in functional scores.
Level of evidence: IV (retrospective case series review).
Keywords: Kinematic; Knee Arthroplasty; Navigation; Outcomes; TKA; Technique.
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