Does laxity alter the relationship between strength and physical function in knee osteoarthritis?

Area of Science:

• Orthopedics
• Biomedical Engineering
• Physical Therapy

Background:

• Knee osteoarthritis (OA) interventions targeting muscle strength show suboptimal functional improvements.
• Joint laxity is known to influence muscle activity and biomechanics.

Purpose of the Study:

• To investigate the relationship between knee extensor and flexor strength and physical function in patients with knee OA.
• To determine if joint laxity modifies the association between muscle strength and physical function in knee OA.

Main Methods:

• 164 knee OA patients underwent assessments for quadriceps and hamstring strength, varus-valgus laxity, and functional status (WOMAC-PF, chair-stand).
• Patients were categorized into high and low laxity groups based on the sample median.
• Multivariate analyses examined the interaction between laxity, strength, and function.

Main Results:

• Muscle strength positively correlated with chair-stand performance (r=0.44-0.52) and negatively with WOMAC-PF scores (r=-0.21 to -0.36).
• Higher varus-valgus laxity was significantly associated with a weaker relationship between muscle strength and physical functioning measures.
• This effect was consistent across both quadriceps and hamstring strength assessments.

Conclusions:

• Varus-valgus laxity diminishes the strength-function relationship in knee OA.
• Future research on strengthening interventions for knee OA should consider stratifying by laxity levels.
• Optimizing interventions for knee OA may require addressing the passive restraint system's status alongside muscle strengthening.