The use of density mapping in the analysis of thigh pain after total hip arthroplasty in patients with well-fixed tapered wedge stems

Purpose:The mechanisms underlying thigh pain in patients with well-fixed cementless femoral components after total hip arthroplasty (THA) remains unclear. We hypothesized that the thigh pain is correlated with the initial contact state of the stem and aimed to investigate the relation between thigh pain and the initial contact state.Materials and methods:A total of 209 hips of 184 patients were analysed in this retrospective case–control study. The patients were divided into a thigh pain group ( n = 13 hips) and a control group (without thigh pain, n = 196). Post-operative stem contact images were three-dimensionally visualized by a density mapping function using computed tomography data, which quantified the stem contact area according to Gruen zones. Thigh pain was defined as anterior or anterolateral pain upon loading at 3-month post-operatively.Results:Thirteen hips (6.2%) had thigh pain; however, all the hips demonstrated stable bony ingrowth radiographically. The thigh pain group had a significantly lower contact area in zone 2 ( p = 0.014). The multivariate logistic regression analysis showed that the contact area of zone 2 was negatively correlated with thigh pain [odds ratio (OR): 0.858, p = 0.018], and the canal flare index was negatively correlated with the development of thigh pain (OR: 0.336, p = 0.026).Conclusions:We identified an association between the initial contact state and post-operative thigh pain. Our data demonstrated that proper lateral contact prevents the occurrence of thigh pain in THA using a tapered wedge stem.