EFFECTS OF CONTRALATERAL HIP AND LUMBAR LORDOSIS ON PELVIC TILT AFTER THA FOR DYSPLASTIC HIP

Abstract

Introduction: In total hip arthroplasty, the angle of acetabular component is a critical factor for the postoperative dislocation and the longevity of prostheses. The angle is principally determined in relation to anterior pelvic plane. It is reported that the pelvis tends to tilt posteriorly along with aging. Furthermore, the pelvic tilt might change after THA. The changes might be infiuenced by the hip condition and lumbar lordosis. We measured the pelvic tilt and the lumbar lordosis, and evaluated the effects of contralateral hip and lumbar lordosis on pelvic tilt after THA.

Materials and Methods: Fifty-one unilateral patients and 30 bilateral patients were enrolled in this study. The diagnosis was dysplastic osteoarthritis in all patients. In unilateral patients, the hip was affected in one side and the other hip was normal or acetabular dysplasia without symptoms. In bilateral patients, THAs in both hips were done within two months.

Pelvic inclination angle (PIA) and lumbar lordotic angle (LLA) were measured on the standing lateral X-rays before operation and 1-month, 6-month and 1-year post-operation. The effects of patient age, BMI, ROM of the hip, preoperative PIA and LLA on the changes of PIA were statistically investigated using multiple linear regression analysis. We divided the patients into three groups with regard to pre-operative PIA (anterior group: PIA < 0, intermediate group: 0 < PIA < 10, posterior group: PIA > 10) and with regard to pre-operative LLA (insufficient group: LLA < 20, moderate group: 20 < LLA < 40, severe group: LLA > 40).

Results: Overall, significant factor was only preoperative PIA. In bilateral cases, preoperative PIA and patient age affected the changes of PIA after THA. In patients with severe lordosis, preoperative PIA and LLA were significant factors. PIA increased in anterior tilt group and PIA did not change in intermediate group, while PIA gradually decreased in posterior group. In insufficient lordosis group, PIA remarkably increased after THA compared with that in severe group.

Discussion: Pelvic tilt after THA has been reported without considering the conditions of contralateral hip and lumbar spine. By categorizing patients with regard to the conditions of hips and lumbar spine, we can prospect the tendency of the direction of PIA changes. These results indicated that pre-operative PIA was related the changes of PIA in bilateral group. PIA slightly increased in all bilateral patients, PIA tended to close each other in unilateral patients. Further investigation is necessary to prospect the estimated PIA value after THA.