Smaller Lateral Gap Than the Medial Gap in Deep-Flexion was Associated with Lower Patient Satisfaction in Robotic-Assisted Restricted Kinematically Aligned Cruciate-Retaining Total Knee Arthroplasty.

BACKGROUND: Medio-lateral soft-tissue balance influences clinical outcomes after total knee arthroplasty (TKA). The purpose of this study was to investigate the intraoperative medial-lateral gap difference pattern in restricted kinematically aligned (rKA) TKA and its associations with radiographic parameters and clinical outcomes.

METHODS: A total of 110 knees were retrospectively analyzed. Robotic-assisted rKA TKA using a cruciate-retaining implant was performed to restore the native joint surface. Preoperative and postoperative radiographic parameters were measured. Intraoperative component gaps were assessed during the implant trial stage. Medial-lateral gap balance was defined as the lateral gap minus the medial gap, with positive values indicating a larger lateral gap than the medial gap. Knees were classified into three groups; group 1 (n = 83; medial gap less than lateral gap consistently), group 2 (n = 11; medial gap greater than lateral gap from extension to mid-flexion), and group 3 (n = 16; medial gap greater than lateral gap from mid-range to deep flexion). Clinical outcomes were evaluated at one year postoperatively using the Knee Society Score (KSS) satisfaction, Western Ontario and McMaster Universities Arthritis Index (WOMAC), and Forgotten Joint Score-12.

RESULTS: Compared with group 3, group 1 showed a significantly higher satisfaction score (30.9 versus 23.5, P < 0.001) and a significantly lower WOMAC pain score (3.4 versus 5.8, P = 0.032). Multiple regression analyses showed that significant risk factors for smaller medial-lateral gap balance were a smaller preoperative angle between the surgical epicondylar axis and the posterior condylar axis (SEA-PCA) (P = 0.003) and the change in SEA-PCA (P < 0.001).

CONCLUSION: A smaller lateral gap than the medial gap from mid-range to deep flexion was associated with lower patient satisfaction in robotic-assisted rKA TKA. Femoral component rotation based on gap simulation may help achieve the target medial-lateral gap pattern during flexion.

LEVEL OF EVIDENCE: III.