The impact of absolute change in tibiofemoral morphology on patient reported outcome measures post total knee arthroplasty.

BACKGROUND: Reconstructing knee morphology and alignment is important for outcomes post total knee arthroplasty (TKA). Personalised alignment strategies are proposed to improve outcomes by replicating native alignment. However, how change in morphology affects patient outcomes is unclear. This study aimed to investigate the relationship between absolute change in morphological measures post-TKA and patient reported outcome measures (PROMs).

METHOD: An observational analysis of a randomised clinical trial was conducted. Participants received preoperative and postoperative CT scans and completed PROMs at six-months post-TKA. Absolute change in hip-knee-ankle angle, medial proximal tibial angle, lateral distal femoral angle, non-weightbearing joint line convergence angle, tibial and femoral rotation, and posterior tibial slope (PTS) were calculated. PROMs included visual analogue scales of pain and satisfaction (0-100), Oxford Knee Score, Forgotten Joint Score, and the Kujala Score. Regression and principal component (PCA) analyses investigated relationships between PROMs and change in morphology.

RESULTS: Sixty-one participants were included for analysis (61% women, age 66.9 ± 9.1 [mean ± SD] years, BMI 32.8 ± 6.8 kg/m2). The PCA demonstrated coronal, axial, and sagittal plane measures were interdependent, with over 65% of variability driven by change in tibial rotation (PC1) and the PTS (PC2). The regression analysis showed no relationships between morphological change and PROMs postoperatively.

CONCLUSION: Tibiofemoral morphology was interrelated across coronal, axial, and sagittal planes. However, this study suggests absolute morphological change had minimal impact upon PROMs at six-months post-TKA. Future research should clearly distinguish between osteoarthritic versus prearthritic alignment and consider the influence of soft-tissue releases upon PROMs.