Muscle synergies during dynamic and static balance tasks in patients with knee osteoarthritis before and after total knee arthroplasty.

OBJECTIVE

This study aimed to investigate alterations in muscle synergy patterns during dynamic and static balance tasks in patients with moderate-to-severe knee osteoarthritis (KOA) before and after total knee arthroplasty (TKA).

METHODS

Forty KOA patients scheduled for TKA and twenty-one age- and BMI-matched healthy controls were enrolled. Ten patients were measured at the 3-month and 6-month follow-up postoperatively. Surface electromyography (EMG) was recorded from six lower-limb muscles during the Five-Times-Sit-to-Stand and static balance test. Muscle synergies were extracted using non-negative matrix factorization and compared across preoperative, 3-month, and 6-month postoperative stages and between the KOA and control groups.

RESULTS

Preoperative KOA patients exhibited significantly impaired static balance, with greater center-of-pressure displacement and larger envelope areas than controls (p < 0.05). The number of synergies during static balance was higher preoperatively (3-5) and normalized (3-4) at 3 months postoperatively. Abnormal synergy patterns of preoperative KOA patients were characterized by reduced activation of the quadriceps and hamstrings and compensatory overactivation of the gastrocnemius (p < 0.05). After TKA, muscle weightings progressively normalized, with muscle activation patterns resembling those of healthy controls at 6 months postoperatively (p > 0.05).

CONCLUSION

Alterations in muscle synergy patterns, specifically in muscle weightings, were observed in KOA patients during the execution of static and dynamic balance tasks; however, TKA may promote the realignment of these neuromuscular control strategies toward physiological norms. These findings highlighted the need for targeted quadriceps and hamstring strengthening in postoperative rehabilitation to enhance recovery of functional motor control.