Can the intra-operative measurement of the diameter of the femoral head help surgeons to choose the best size of the acetabular cup?

Purpose We hypothesized that the intra-operative measurement of the femoral head may increase the accuracy of the acetabular cup size optimal selection in total hip arthroplasty (THA). The purpose of this clinical research was to analyze the correlation between the estimated cup size from intra-operative measurement of the femoral head and the pre-operative templated cup size. Methods A prospective observational single-center study was conducted from June 2019 to January 2020 including primary THA ( n = 100). All cases were pre-operatively templated. The measurement of the anterior–posterior diameter of the femoral head was routinely intra-operatively performed. Any definitive implanted cup was considered as “oversized” when the size was > 4 mm than the diameter of the native head. Results The median (interquartile range) size of the implanted cup, pre-operative planned cup size, and diameter of the femoral head were measured 52 (50–54) mm, 50 (48–54) mm and 49 (45–51) mm, respectively. Pre-operative planned size cup accurately predicted the implanted cup or differed in only one size (2 mm) in 77 (78%) cases. Otherwise, intra-operative femoral head measurement method accurately predicted the implanted or differed in only one size (2 mm) in 51 (87%) cases ( p = 0.097). Conclusion The intra-operative femoral head measurement is a simple and reliable tool to help the surgeons choose the best size of the acetabular cup and is as reliable as the pre-operative templating in order to avoid cup oversizing in THA. Utmost caution is warranted whenever the cup reamer is > 4 mm than the anterior–posterior diameter of the native head.