The effects of femoral offset on hip abductor muscle function
MetadataShow full item record
The purpose of this study was to determine if the magnitude of femoral offset of a total hip arthroplasty (THA) influences hip abductor muscle strength as well as kinematics and electrical activation of hip abductor muscles during stepping over an obstacle. Twenty participants with a unilateral THA, 11 categorized as high femoral offset (HI-FO) and 9 as low femoral offset (LO-FO), participated in the study. Maximal isometric and concentric torques of hip abductor muscles were measured using a Cybex 6000™ dynamometer. Three-dimensional kinematic and electromyography (EMG) data were collected while the participant walked on a level surface, and while stepping over obstacles of 10% and 25% of each participant’s leg length. Comparisons of the hip abductor torques between limbs within each FO group and between LO-FO and HI-FO operated limbs were made by paired t-tests and Student’s t-tests, respectively. A 2 (FO group) x 3 (obstacle height) analysis of variance with obstacle height as a within-subject factor and FO group as a between-subjects factor was employed to test hypotheses related to the stepping over an obstacle task. Isometric and concentric abductor torques tended to be higher for the HI-FO than LO-FO group. Compared to the LO-FO group, the HI-FO group exhibited significantly less magnitude of hip abductor strength deficit of the THA limb compared to the nonoperated limb, less mediolateral sway of the body’s center of mass, less EMG activation of the THA limb gluteus medius muscle, and greater foot-obstacle clearance during negotiating an obstacle. These results confirm the use of an increased femoral offset as an effective choice to enhance hip abductor muscle functioning and promote balance control during ambulation.