Sizing accuracy of the OPSTM dynamic planning system for total hip arthroplasty.

Presenting Author – Sanjeev Gupta
Introduction The use of cementless stems in total hip arthroplasty is increasing. Correct sizing is critical with cementless implants, with under-sizing leading to subsidence and loosening. Stems that are oversized can lead to leg length inequality and fractures. 3D templating has been shown to be more accurate than using 2D imaging. The aim of this study was to measure the accuracy of the OPSTM planning software in predicting the implanted acetabular cup and femoral stem size. Methodology The senior author’s first twenty-one patients receiving OPSTM pre-operative planning were analysed. OPSTM is a pre-operative, dynamic, patient-specific modelling system for acetabular and femoral implant positioning. The system requires a pre-operative CT scan which allows patient specific implant sizing as well as positioning. All patients received a Trinity cementless acetabular component (Corin, UK) and a cementless MetaFix femoral component (Corin, UK). Review of the operative notes provided the actual sizes of implants used, which was retrospectively compared to the planned sizes in the pre-operative OPSTM reports. Results Of the 21 MetaFix stems, 95% were within one size of that predicted. 52% were the predicted size, 43% were within one size of the predicted, and 5% within two sizes. Of the acetabular components, 100% were within one size of that planned. 67% were the planned size, with the remaining 33% within one size of that planned. Conclusions • The results are similar to those of other 3D templating systems, showing more than 95% of implanted stems/cups within one size of that planned. • There is significant value in prediction of sizes of implants pre-surgery, both as an indicator to the surgeon as to the size expected, and for reducing the inventory supplied to the hospitals, thus reducing costs.