There are many previous reports dealing with the relationship between the abductor moment arm or femoral offset (FO), and other factors such as the abductor muscle strength after total hip arthroplasty (THA). Moreover, there have been no studies involving quantitative examination of the influence of posterolateral reconstruction on abductor muscle strength and FO. This study was to evaluate posterolateral reconstruction including posterior capsule, piriformis tendon and external rotators in THA and the relationship among the posterolateral reconstruction, abductor muscle strength, and FO.

We arbitrarily selected 48 limbs of 24 patients who underwent unilateral THA using a posterolateral approach. In 16 patients (12 women and 4 men; mean age, 66.8 years; range 50 to 82 years), posterolateral reconstruction was not performed (non- reconstruction group). In eight patients (6 women and 2 men; mean age, 61.6 years; range 52 to 72 years), posterolateral reconstruction was performed (reconstruction group). None of the selected cases were revision cases, cases in which the patient showed marked acetabular dysplasia, or cases involving the osteotomy of the greater trochanter. We compared these two groups. FO was measured on standard antero-posterior hip radiographs. Isometric abductor muscle (N) was measured with hand-held dynamometer. Each muscle strength was converted into a ratio of force to body weight (N/kg), and this ratio was used for comparison.

The reconstruction group showed higher value than the non-reconstruction group on the abductor muscle strength (p< 0.05). The correlation was recognised in the reconstruction group between abductor muscle strength and FO (p< 0.01 r=0.68).

There have been no studies involving quantitative examination of the influence of posterolateral reconstruction on abductor muscle strength and FO. Our results suggested that posterolateral reconstruction and appropriate reconstruction of FO were important in order to obtain the improvement on the abductor muscle strength after THA.