THE SHOULDER TO CENTRE OF ROTATION OF STEM DISTANCE: A NOVEL TECHNIQUE TO REDUCE LEG LENGTH DISCREPANCY IN TOTAL HIP ARTHROPLASTY

Limb length discrepancy (LLD) is the commonest cause of patient dissatisfaction and litigation after total hip replacement (THR). We present a new technique using the shoulder to centre of rotation of stem distance (SCRD) to reduce LLD. SCRD was calculated for the most common stems in the NJR. All patients who underwent THR only for primary osteoarthritis between June 2023 and 2024 were included in this prospective study. THR for other indications was excluded. Depth of insertion of the stem was determined by SCRD of the stems used at our unit and varus/valgus/neutral position of the native neck of the operative or opposite side. Post-operative radiographs were analysed for LLD using the inter-teardrop and inter-lesser trochanter line by 3 independent observers and intra and inter-observer variability was analysed using SPSS version 29.0(IBM). 50 patients with a mean age of 70 years (57 to 92) were included. The mean LLD 2.5±1.2mm. The intra-observer coefficient was very good for rater 1,0.78 (0.448 – 0.900); excellent for raters 2 & 3, 0.962 (0.930 to 0.980) and 0.881 (0.777 to 0.937) respectively(p<0.001). The inter-rater reliability was excellent 0.835 (0.723 to 0.9) p<0.001. SCRD is an excellent technique to reduce LLD in THR. It can be used in the absence of templating software and had good intra and inter-observer reliability.