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

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 degrees and 50 degrees 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.