Leg extensor power and quadriceps strength: an assessment of repeatability in patients with osteoarthritic knees

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Abstract
Objective: To assess the repeatability of two muscle function measures – leg extensor power (LEP) and isometric quadriceps force (IQF) – in a population of patients with osteoarthritis of the knee. Design: Repeat measures of LEP and IQF at 25° and 50° knee flexion were taken within seven days. Both legs were measured and a numerical rating scale was used to assess pain on the two occasions. Subjects: Patients who were on a waiting list for a primary unilateral knee replacement for osteoarthritis were invited to take part in the study. Setting: The physiotherapy department of a National Health Service Orthopaedic Hospital in Oxford, UK. Intervention: Subjects were measured using a Kin-Com dynamometer to assess maximum isometric force and a leg extensor power rig to assess maximum single leg explosive power. Results: Twenty-six patients (mean age: 72 years; SD: 8 years; range: 50–87 years) were included in the study following informed consent. A weak relationship was found between LEP, IQF and pain scores which reached the 5% significance level for the LEP measures only. The level of repeatability for both measures was found to be acceptable. Conclusion: Both LEP and IQF are recommended as repeatable measures for assessment of muscle function in patients with osteoarthitis of the knee. However, the LEP rig has the added advantage of being quicker, cheaper and simpler to use in the clinical setting.