Intrarater test-retest reliability of hip range of motion and hip muscle strength measurements in persons with hip osteoarthritis.

OBJECTIVE: To examine the relative and absolute intrarater test-retest reliability of muscle strength and range of motion (ROM) measurements of the hip performed in people with hip osteoarthritis.
DESIGN: Repeated measures.
SETTING: Human movement laboratory of a university. PARTICIPANTS: Participants (N=22; 10 men, 12 women; age range, 50-84y) with hip osteoarthritis.
INTERVENTIONS: On 2 separate occasions, at least 1 week apart, isometric torque measurements were obtained from the hip rotators, flexors, abductors, and extensors. Passive ROMs in hip rotation, flexion, abduction, and extension were also determined. MAIN OUTCOME MEASURES: Relative reliability was estimated using the intraclass correlation coefficient, model 2,2 (ICC(2,2)). Absolute reliability was estimated using the coefficient of variation (CV) and the standard error (SE) of measurement.
RESULTS: For measurements of muscle strength, ICC(2,2) ranged from .84 to .97, and the CV ranged from 8% to 15.7%. Hip extensors and internal and external rotators showed high ICC(2,2) (>.96) and low CV (<9.8%); hip abductors showed the lowest ICC(2,2) (.84) and the highest CV (15.7%). For ROM measurements, ICC(2,2) ranged from .86 to .97 and SE ranged from 3.1 degrees to 4.7 degrees . Hip flexion ROM showed the highest ICC(2,2) (.97) and an SE of 3.5 degrees ; hip extension ROM showed the lowest ICC(2,2) (.86) and the highest SE (4.7 degrees ).
CONCLUSIONS: Strength and ROM testing of the hip in people with hip osteoarthritis can be performed with good to excellent reliability.