Does Total Knee Arthroplasty Change Frontal Plane Knee Biomechanics During Gait?

Background Dynamic knee varus angle and adduction moments have been reported to be reduced after TKA. However, it is unclear whether this reduction is maintained long term.

Questions/purposes We therefore asked whether (1) the dynamic knee adduction angle and moment remain reduced 1 year after TKA, (2) if changes in adduction moment are related to static alignment and varus angle during gait 6 months and 1 year after TKA, and (3) if these changes in loading pattern are related to changes in Knee Society scores.

Methods We performed gait analysis on 15 patients (17 TKAs) before surgery and 6 months and 1 year after TKA. Weightbearing radiographs were used to assess coronal plane knee alignment.

Results TKA corrected static knee alignment from 2.2° (2.5°) varus to 3.5° (2.7°) valgus at 6 months. Peak varus angle during gait was reduced from 9.7° (6.5°) to 3.6° (5.8°) at 6 months and 5.2° (7.6°) at 1 year. Peak adduction moment was reduced to 85% of the preoperative level at 6 months but increased to 94% of the preoperative level at 1 year. We observed a correlation between the increase in dynamic varus angle and increase in adduction moment from the 6-month to 1-year followups.

Conclusions TKA improves knee adduction moment at 6 months, but this effect is lost with time (1 year).

Clinical Relevance Despite restoration of static knee alignment, knee adduction moment remains high presumably predisposing to medial polyethylene wear as noted by retrieval studies.