Effect of knee and hip position on hip extension range of motion in individuals with and without low back pain

A 2-group, nonrandomized, mixed design with 1 between-subjects factor (group) and 2 within-subjects factors (knee and hip position). To determine the amount of passive hip extension during changes in the knee angle in the sagittal plane, and the hip angle in the frontal plane in back-healthy (BH) subjects and subjects with low back pain (LBP). Information regarding the specific contributions of hip flexor muscles to limitations in hip extension range of motion (ROM) is necessary for the prescription of appropriate treatment. Thirty-five BH subjects (24 women and 11 men, mean age = 31.37 +/- 11.36) and 10 subjects with LBP (6 women and 4 men, mean age = 33.70 +/- 9.31) participated in the study. The passive length of the one- and two-joint hip flexor muscles was tested in 4 different conditions in which the positions of the knee and the hip were varied. The knee was positioned passively in full extension or 80 degrees of flexion while the hip was positioned passively in zero abduction or full abduction. Subjects with LBP displayed less passive hip extension than BH subjects (LBP, -5.61 degrees +/- 4.30; BH, -2.57 degrees +/- 4.18). Both groups had less hip extension when the knee was in flexion of 80 degrees than when the knee was fully extended (flexed, -5.51 +/- 4.50; extended, -0.98 degrees +/- 4.65), and when the hip was in zero hip abduction than when the hip was fully abducted (zero, -7.55 degrees +/- 5.03; full, 1.06 degrees +/- 4.31). The contribution of the different hip flexors to a hip extension limitation differed between BH and subjects with LBP. BH subjects demonstrated an effect of knee angle on hip extension when the hip was in zero abduction (flexed, -11.43 degrees +/- 5.81; extended, -2.49 degrees +/- 5.39), but not when the hip was in full abduction (flexed, 1.74 degrees +/- 3.91; extended, 1.89 degrees +/- 3.94). Subjects with LBP demonstrated an effect of knee angle on hip extension when the hip was in zero abduction (flexed, -12.60 degrees +/- 4.91; extended, -6.65 degrees +/- 5.03) and when the hip was in full abduction (flexed, -3.10 degrees +/- 5.53; extended, -0.10 degrees +/- 5.18). The results of this study provide evidence that changing the knee joint angle in the sagittal plane and the hip joint angle in the frontal plane, during the hip flexor length test, can affect the amount of passive hip extension ROM. The contribution of specific hip flexor muscles to a hip extension limitation may differ depending on the individual's mo