LIMB LENGTH DISCREPANCY IN CEMENTED VERSUS CEMENTLESS TOTAL HIP ARTHROPLASTY

Abstract

Aims: Limb length discrepancy is a recognised complication of total hip arthroplasty (THA). Cementless THAs are increasingly being used, but in order to achieve rotational and axial stability larger implants may be required than originally templated for. This could potentially result in greater limb length discrepancy. Our objective was to determine if limb length discrepancy exists to a greater degree in cementless THA.

Methods: 166 consecutive patients undergoing elective THA between June 2007 and May 2008 were included in this retrospective study. Post-operative, digital radiographs (PACS, Centricity^®) were examined for each of these patients to determine limb length. Limb length discrepancy was calculated as the difference between the perpendicular distance between the inter-teardrop line and the most prominent points on the lesser trochanter of each limb. Magnification was determined from the measured radiographic diameter of the prosthetic heads and their actual diameters.

Results: Of the 166 patients included in this study 128 had cementless THA and 38 had cemented. The average magnification was calculated as 30%. Limb length discrepancy was found post-operatively in 93% of cases. In 65% of patients the operated limb was longer (by 0 – 29 mm) and in 28% it was shorter (by 0 – 23 mm). The mean limb length discrepancy, corrected for magnification, was 6.21 mm for cemented THA and 6.22 mm for cementless THA. A student’s T-test demonstrated no significant difference in limb length discrepancy between these operations (p = 0.996).

Conclusions: The incidence of limb length discrepancy after THA is high. However, no significant differences were demonstrated between cemented and cementless THAs in our series. Accurate and careful pre-operative templating is important in THA to minimise the risk of clinically significant limb length discrepancy.