No direct intra-operative measurement to determine the ideal size of the femoral component of Oxford unicompartmental knee replacement (UKR) is currently present. The aim of this study is to assess the accuracy of patients' shoe size as a predictor of femoral component size.
A retrospective study was conducted to identify the correlation between patients' shoe size (British system) and the femoral component size. After excluding patients who died (n = 2) and patients in whom the implanted femoral component size was inaccurate (n = 13), the remaining cases (93 UKR in 88 patients) formed the study sample. Postoperative radiographs were reviewed to determine femoral component fit.
We found positive correlation between shoe size and femoral component size. In females; a shoe size from 2.5 to 6 predicted a small femoral component and shoe size from 6.5 to 8.0 predicted a medium femoral component. In males, a shoe size from 6 to 9.5 predicted a medium femoral component and a shoe size from 10 to 13 predicted a large femoral component. This relation predicted the femoral component size accurately in 80% of cases. A subgroup analysis, after excluding patients who changed their shoe size during adulthood after foot surgery or pathology (n = 20), showed an accuracy rate of 81%.
Shoe size is a simple method that predicts femoral component size more accurately than other methods currently used such as templating, tibial component size and height based on gender.