Background External contracture of the hip joint occurs with the progression of hip osteoarthritis. It can be easily imagined that improvement of the external contracture can be expected with the posterior approach as it dissociates the short external rotator muscle group and the posterior tissue. However, improvement of external contracture with the anterior approach, which does not dissociate the posterior tissue, is unclear. In this study, we examined the degree of external contracture improvement after anterolateral approach THA, its influencing factors, and the effect on lower limb function.
Methods We prospectively examined 73 patients who underwent THA using an anterolateral approach for hip osteoarthritis of Crowe type 1 and 2. Lower limb rotation, leg lengthening, and various offsets in the natural position were measured using three-dimensional templating software based on computed tomography before and two weeks after surgery; factors related to lower limb rotation were investigated by multiple regression analysis. A functional evaluation, which are gait speed, knee extensor strength, functional reach test, and the Japanese Orthopaedic Association hip score, was performed one year after surgery.
Results All functional outcomes significantly improved after THA. As for the setting of implants, the acetabular offset became shorter with the medialization of the cup as planned; the stem side could be compensated accordingly, and the global offset could be almost reproduced. The stem was inserted almost along the original anteversion. There were no postoperative dislocation cases. External contracture was improved by 4.7° ± 8.3° after anterolateral THA. Age and preoperative femoral external contracture were significant factors for the amount of improvement in femoral external contracture (adjusted R2: 0.492) and for the postoperative remaining external contracture (adjusted R2: 0.577), but they were not significantly correlated with lower limb function and the Japanese Orthopaedic Association hip score 1 year after surgery (p > 0.05).
Conclusion Even anterolateral approach THA, which does not dissociate the posterior tissue, improved postoperative external contracture of the hip joint by about five degrees, and the stronger the preoperative external contracture, the greater the improvement. However, there was no significant correlation with lower limb function one year after surgery.