Mechanical axis correction after total knee arthroplasty alters ankle alignment but does not affect ankle function.

Area of Science:

• Orthopedic surgery
• Biomechanics
• Radiology

Background:

• Total knee arthroplasty (TKA) aims to restore knee function.
• Coronal plane deformities corrected during TKA may influence adjacent joint biomechanics.
• The effect of TKA-induced knee alignment changes on the ankle remains unclear.

Purpose of the Study:

• To investigate the clinical and radiological effects of altered knee alignment after TKA on the ankle.
• To determine if changes in knee alignment post-TKA impact ankle function and radiographic parameters.

Main Methods:

• Prospective observational study of 158 patients undergoing TKA, with 128 completing 1-year follow-up.
• Clinical outcomes assessed using multiple validated questionnaires (MOXFQ, KSS, WOMAC, EuroQol, FJS-12).
• Radiographic parameters including mechanical axis and ankle joint orientation angle (AJOA) measured preoperatively and postoperatively.

Main Results:

• Significant improvement in mechanical axis from 5.8° varus to 1.3° varus (p < 0.001).
• A significant change in AJOA from -0.8° to 0.8° (p = 0.001) was observed.
• Moderate positive correlation between AJOA change and knee axis correction (rho = 0.4, p < 0.001); no significant correlation with MOXFQ scores.

Conclusions:

• TKA-induced mechanical axis correction alters ankle radiographic alignment.
• Ankle function is not significantly affected at 1 year post-TKA in patients with moderate deformities.
• Patient-reported functional outcomes improve after TKA, irrespective of alignment changes.