Modified bony landmark measurement to deal with leg length discrepancy during total hip arthroplasty

Abstract

Objective To evaluate the clinical application of modified bony landmark measurement (MBLM) to deal with leg length discrepancy (LLD) during total hip arthroplasty (THA). Methods We retrospectively analyzed the 36 patients in whom MBLM was used to deal with LLD during THA from January 2014 to May 2015 at Department of Orthopaedics, The Second Hospital of Fuzhou. They were 17 men and 19 women, aged from 42 to 78 years (average, 68.7±10.1 years). They were divided into 3 groups according to their pre-operative LLD value (d): 16 cases in group A with d ≤ 10 mm, 11 cases in group B with 10 mm 20 mm. After the sizes of prosthetic cup and femoral component and the location of implant were determined using preoperative X-ray, a special formula was used to calculate the prosthetic length of femoral head neck and the osteotomy area at the femoral neck. MBLM was used to measure the leg lengths before hip joint dislocation and after placement of the hip implant. The neck length and depth of the femoral component was adjusted according to the measurements. Post-operative X-ray was used to measure the LLD (d＇). The value of MBLM in judgment of LLD during THA was assessed by comparison of d and d＇and analysis of distribution of d＇. Results The postoperative d＇(6.0±3.0 mm) was significantly shorter than the preoperative d (11.0±5.0 mm) (t=5.145, P 20 mm. The cases with d＇≤ 10 mm were significantly more than those with d ≤ 10 mm and the cases with d＇> 20 mm significantly fewer than those with d>20 mm (χ2=15.500, P=0.000). Conclusion MBLM used during THA is a reliable method to judge the leg lengths so that LLD can be effectively reduced after THA. Key words: Arthroplasty, replacement, hip; Hip prosthesis; Retrospective studies; Leg length discrepancy; Bony landmark measurement