Accuracy and early outcomes in medial unicompartmental knee arthroplasty performed using patient specific instrumentation.

Unicompartmental knee arthroplasty (UKA) is a technically demanding procedure and poor implant positioning has been identified as a factor in early failure. The aim of this study was to evaluate the accuracy and clinical outcomes of the patient specific instrumentation implementation technique with a fixed bearing UKA. We carried out a prospective study of 41 patients (44 procedures) between December 2011 and April 2013. The preoperative planned sizes of implants used were accurate to within one implant size change in 96% of cases. The mean post-operative limb alignment was 3.8° varus. The Oxford Knee Scores (OKS) (0-48) improved from a mean preoperative score of 23.8 to 35.6 at six weeks and 44.5 at one year. The mean improvement in OKS from preoperative to one year was 20.7. The mean one year FJS (0-100) was 80.6. At a mean follow-up of 24 months there were no complications identified and there was a 100% survivorship. This technique may offer a particular advantage to surgeons who perform lower volumes of UKA with the potential to improve both clinical outcomes and implant survivorship in UKA to achieve greater consistency of results.