Patient, observer and instrument variation in the measurement of strength of shoulder abductor muscles in patients with rheumatoid arthritis using a modified sphygmomanometer.

We describe the use of a modified sphygmomanometer to measure the strength of shoulder abductor muscles. Using a 5 x 5 Greco-Latin square design we compared the measurements of 5 physical therapists taken on 5 patients with rheumatoid arthritis with 2 cuff adaptations. The design variables explained 96.4% of the pressure readings, with patients accounting for 76.6%. There was no significant variation due to order of testing, cuff preparations …