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

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).

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.

Post-ΔHKAA was significantly correlated with preoperative mLDFA (pre-mLDFA, r = -0.30, p < 0.001), pre-aHKAA (r = 0.22, p = 0.02), pre-mHKAA (r = 0.21, p = 0.03) and post-mMPTA (r = -0.29, p = 0.004). Multivariable linear regression analyses revealed that pre-mLDFA (β = -0.20, p = 0.02) and post-mMPTA (β = -0.32, p = 0.01) were independently associated with post-ΔHKAA. These results indicate that performing TKA in cases with severe femoral varus alignment and placing the tibial implant in valgus relative to the original joint surface leads to increased postoperative coronal varus alignment in the standing position.

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 Ⅳ.