Effect of femoral offset and limb length discrepancy on hip joint muscle strength and gait trajectory after total hip arthroplasty

Backgroud: Femoral offset (FO) and limb length discrepancy (LLD) are important perioperative considerations when performing THA. Decreased FO prevents improvement of gait and muscle recovery and residual LLD has a prominent influence on patient satisfaction with THA, while few studies have investigated the relationship between FO and/or LLD and gait disturbances. We investigated the association between these two factors and hip muscle strength and the results of 3-D gait analysis after THA. Methods: We evaluated 92 patients (including 20 patients who underwent gait analysis) in whom total hip arthroplasty was performed for unilateral evere osteoarthritis of the hip joint. FO and LLD were measured on a standard anteroposterior radiograph of the pelvis. Hip muscle strength was evaluated by isometric hip flexion (in the manner of straight leg raising test: SLR) and hip abduction strength. To evaluate 3-D walking trajectory, we used a portable gait analyzer. Results: Reduction of global FO by> 5 mm after THA compared to the contralateral hip was associated with hip abductor muscle weakness. On the other hand, LLD <= 20 mm had no influence on hip abductor muscle strength and SLR strength. In gait analysis, SLR strength showed a significant difference between the sagittal plane symmetrical and asymmetrical groups. Conclusion: Postoperative global FO > 5 mm less than that of the contralateral hip was associated with hip abductor muscle weakness. And, from the results of 3-D gait analysis, SLR weakness may increase gait asymmetry in the sagittal plane.