Bilateral Knee Strength Asymmetry and Functional Performance in Older Women With Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease that commonly affects the knee, especially in individuals over 50. It leads to pain, reduced mobility, and functional decline. In bilateral knee OA, muscle imbalances, especially in the quadriceps and hamstrings, worsen functional limitations and increase the risk of falls. These imbalances are caused by pain, joint instability, and cartilage damage, affecting muscle strength and coordination. In older women, these issues are more pronounced, increasing their risk of functional decline compared to men.

Emerging research highlights the role of muscle strength asymmetry (differences between the left and right leg) in functional difficulties, such as poor balance, walking issues, and difficulty with daily tasks. This study aims to explore how these muscle imbalances in knee extensors and flexors impact overall functional abilities, such as balance and walking efficiency in women with bilateral knee OA.

The study seeks to examine how bilateral strength asymmetry in the knee muscles affects dynamic balance, gait efficiency, and mobility in older women with knee osteoarthritis. The hypothesis is that greater muscle imbalance will lead to worse balance, slower walking, and reduced mobility.

• Isokinetic Strength Testing (Other), also known as Pain Assessment, Dynamic Balance Measurement, Functional Mobility, Gait Speed: Bilateral knee strength asymmetry was assessed using a Biodex System 4 Pro isokinetic dynamometer (Biodex Medical Systems, USA). Participants were securely positioned, and knee extensor and flexor strength were measured at angular velocities of 120°/s and 180°/s. Each participant performed five maximal concentric contractions per limb, with the highest peak torque values recorded.

Primary outcomes

• Isokinetic Strength Testing [From enrollment to the end of evaluation in 1 hour]: Bilateral knee strength asymmetry was assessed using a Biodex System 4 Pro isokinetic dynamometer (Biodex Medical Systems, USA). Participants were securely positioned, and knee extensor and flexor strength were measured at angular velocities of 120°/s and 180°/s. Each participant performed five maximal concentric contractions per limb, with the highest peak torque values recorded. Higher asymmetry values indicated greater strength imbalances between limbs
• Functional Mobility [From enrollment to the end of evaluation in 1 hour]: The 30-second Sit-to-Stand test was used to assess lower limb functional strength and endurance. Participants were instructed to stand up and sit down as many times as possible in 30 seconds from a standard chair (seat height: 46 cm) without using their arms. The total number of completed repetitions was recorded. A lower Sit-to-Stand score indicates reduced quadriceps endurance, decreased functional independence, and a higher fall risk in older adults.

Secondary outcomes

• Pain Assessment [From enrollment to the end of evaluation in 1 hour]: Knee pain intensity during daily activities and strength testing was evaluated using the 10-cm Visual Analog Scale, a widely validated tool for assessing subjective pain perception in bilateral knee osteoarthritis patients
• Dynamic Balance Measurement [From enrollment to the end of evaluation in 1 hour]: Dynamic balance was assessed using the Biodex Balance System (Biodex Medical Systems, Shirley, NY, USA), a validated system for evaluating postural control and stability. Participants performed the Limits of Stability (LOS) test, which measures movement control in eight directions, quantifying reaction time, movement velocity, endpoint excursion, and directional control
• Gait Speed [From enrollment to the end of evaluation in 1 hour]: Gait speed was assessed using a 4-meter walk test, a reliable measure of functional mobility and fall risk in older adults. Participants were instructed to walk at their usual pace, and the time (s) was recorded. Slower gait speed is associated with higher fall risk, reduced mobility, and lower physical function in knee osteoarthritis patients

Sex: Female, ages: 50 Years to any

Inclusion Criteria:

* women gender
* aged 50 years or older
* diagnosed with bilateral knee osteoarthritis (Kellgren-Lawrence grade II-III),
* capable of independent walking without assistive devices.

Exclusion Criteria:

* severe knee osteoarthritis requiring total knee arthroplasty
* neurological conditions affecting gait or balance
* severe musculoskeletal disorders
* uncontrolled systemic diseases
* cognitive impairments (Mini-Mental State Examination < 24)

• Sema Aktürk, MD Professor, Study chair, Inonu University