The use of modular components for hip and knee arthroplasty, available since the late 1970’s, has become increasingly popular. Modularity increases the inventory of components required for arthroplasty with the increased possibility of implantation of mismatched components.

All members of the New Zealand Orthopaedic Association were sent a confidential questionnaire asking whether they had selected mismatched components for arthroplasty within the last five years and if so, how often. Information was requested on which components were involved, how and when the mismatch was discovered and what action was taken once mismatch identified. Surgeons were asked to comment on factors contributing to the mismatch occurring and their standard practise to avoid this possibility occurring.

One hundred and forty eight questionnaires were sent out and 120 replies received giving a response rate of 81%. Twenty-eight surgeons (23%) had implanted mismatched components within the last five years, occurring during total hip arthroplasty in 20 cases, knee arthroplasty in six and others in four. The mismatch was discovered prior to wound closure in 39%, during the admission in 51% and after discharge in a further 10%. The mismatch led to a further surgical procedure in 13 patients (46%). The elements contributing to the mismatch will be discussed.

Modular arthroplasty is popular and enables the surgeon to modify the components to the individual patient. This is valued by surgeons accordingly and is unlikely to diminish in frequency. The mismatch rate may be higher than recognised as some mismatches may not have been noted if there was no clinical problem. Strategies to avoid this complication occurring will be discussed.