Impact of Joint Line Displacement on Function and Quality of Life After Primary Total Knee Arthroplasty

Background/Objectives: Total knee arthroplasty (TKA) is one of the most common surgeries among people over 60. Joint line restoration plays an important role in knee biomechanics, with joint line elevation or depression after TKA being associated with poorer postoperative outcomes, although there is no consensus regarding the threshold at which these variations become clinically relevant. The objectives of this study were to evaluate whether a joint line variation greater than 4 mm after primary TKA affects postoperative outcomes, and to assess the concordance between different radiographic methods used to measure joint line height. Methods: A retrospective study was conducted including patients over 60 who underwent primary TKA for knee osteoarthritis. Joint line height variations were evaluated preoperatively and postoperatively using three radiographic measurements: lateral femoral epicondyle-fibular head (LEFH) distance, adductor tubercle-joint line (ATJL) distance, and Blackburne-Peel index. Quality of life was assessed using the Short Form-12 (SF-12) questionnaire, and functionality using the Knee Society Score (KSS). Statistical analysis was carried out using R software. Results: Seventy-three patients were included. No statistically significant associations were found between joint line displacement and functional outcomes (KSS), quality of life (SF-12), or postoperative complications. Concordance analysis between radiographic methods showed a significant but weak correlation between the LEFH and ATJL measurements (ρ = 0.419; p < 0.001). Conclusions: Joint line displacement after primary TKA was not associated with poorer postoperative outcomes in this cohort. These findings suggest that its clinical impact may depend more on its magnitude than on its mere presence and may also be influenced by additional factors. The weak concordance observed between radiographic measurement methods highlights the need for standardized criteria.