Preoperative coronal alignment and tibial implant positioning affect condylar lift-off in BCS-TKA.

Purpose: Condylar lift-off is the phenomenon in which the femoral component lifts off from the polyethylene insert. In some cases, the mechanical hip-knee-ankle angle (mHKAA) appears more varus than the arithmetic hip-knee-ankle angle (aHKAA) in a standing position, which is thought to be related to lift-off. This study analyzed factors influencing the difference between postoperative aHKAA and mHKAA in bi-cruciate-stabilized total knee arthroplasty (BCS-TKA). Methods: This study included 100 knees that underwent BCS-TKA. Full-length standing radiographs of both lower extremities were obtained preoperatively and 1-year postoperatively. The mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), and mHKAA were measured and aHKAA (mMPTA-mLDFA) was calculated. The difference between postoperative aHKAA (post-aHKAA) and post-mHKAA was defined as post-ΔHKAA (post-mHKAA-post-aHKAA). Correlations between post-ΔHKAA and the measured parameters were analyzed, and multivariable linear regression analyses were performed to identify independent predictors of post-ΔHKAA. Results: Post-ΔHKAA was significantly correlated with preoperative mLDFA (pre-mLDFA, Conclusion: In BCS-type TKA, postoperative condylar lift-off in standing positions is more likely to occur in cases with severe preoperative femoral varus alignment or with valgus tibial implant placement. Level of Evidence: Level Ⅳ.