Background A clinical and radiographic review was undertaken to evaluate technical causes for limb-length discrepancy (LLD) after total hip arthroplasty and the resultant effect on function. We hypothesized that limb lengthening most commonly occurs as a result of low placement of the acetabular implant.

Methods A sample of 116 primary total hip arthroplasties performed between 2005 and 2007 with complete 1-year postoperative clinical outcomes scores and appropriate radiographs available on the Picture Archiving and Communication System were identified from a prospective arthroplasty database. Significant limb lengthening was defined as lengthening of more than 8 mm as compared with the contralateral limb postoperatively. Preoperative and 1-year postoperative anteroposterior bilateral hip radiographs were reviewed by two orthopaedic surgeons and one orthopaedic resident. Preoperative and postoperative LLD as well as the respective acetabular and femoral contribution to any postoperative LLD (if present) were measured.

Results Nineteen of 116 (16.4%) patients had limb lengthening of more than 8 mm, of which the majority were women (14 of 19, P=0.015). Of those over-lengthened, the mean difference from preoperative to postoperative LLD was 1.3 mm (SD 7.6 mm). A mean of 6.2 mm (SD 6.2 mm) of lengthening was contributed by the femoral stem, and 5.3 mm (SD 6.3 mm) by low placement of the acetabular implant (P=0.738). Lengthening and femoral placement of the stem (r=0.489, P=0.000), and lengthening and low cup placement (r=0.596, P=0.000) were significantly correlated. There was no correlation between LLD and Harris Hip or Oxford Score at 1-year postoperatively.

Conclusions Limb lengthening results from a combination of low acetabular implant and high femoral stem placement but did not result in inferior outcomes in the current study.