Changes in Lateral Femoral Bowing and Varus Alignment During 10-Year Follow-Up After Total Knee Arthroplasty

It is unclear whether bone morphology remains stable over time following total knee arthroplasty (TKA). This study aimed to evaluate lower limb bone morphological changes 10 years after TKA.

This retrospective study included patients who underwent TKA between 2008 and 2015 with both immediate postoperative and 10-year follow-up standing anteroposterior whole leg radiographs. Patients who had other prostheses in the lower limbs and underwent additional surgery or had inappropriate radiographs were excluded. Among the 419 TKAs screened, 177 TKAs with two whole leg radiographs were identified. After 73 exclusions, 104 lower limbs were analyzed. The primary outcomes were changes in bone morphological parameters (femoral lateral bowing angle [FLBA], mechanical lateral distal femoral angle, tibial lateral bowing angle, mechanical medial proximal tibial angle [mMPTA], hip-knee-ankle angle [HKAA], and joint line convergence angle) between the two time points, which were evaluated using paired t-tests. Except for mMPTA, larger values indicated varus deformity. Postoperative factors related to the 10-year increase in FLBA were examined using multiple linear regression.

After 10 years, the mean FLBA increased by 2.0 ± 2.3° toward lateral bowing (P < 0.001). The mean HKAA shifted by 2.1 ± 2.5° toward varus (P < 0.001), accompanied by varus changes in the mechanical lateral distal femoral angle (1.1 ± 2.7°, P < 0.001) and mMPTA (-0.6 ± 1.9°, P < 0.001). Multiple linear regression analyses of the FLBA increase identified the postoperative ipsilateral FLBA (b = -0.21), contralateral FLBA (b = 0.18), HKAA (b = 0.13), and joint line convergence angle (b = 0.23) as significant independent predictors (R² = 0.30).

Over the 10-year follow-up period, the FLBA increased, accompanied by a varus shift in the HKAA. These findings suggest that both bone morphology and coronal alignment can change after TKA, highlighting the importance of accounting for long-term morphological changes when formulating alignment strategies.