EARLY FAILURE IN UNICOMPARTMENTAL KNEE ARTHROPLASTY

Abstract

Introduction: Unicompartmental knee arthroplasty (UKA) remains a cost effective option for treatment of medial compartment osteoarthritis of the knee. In carefully selected patients survival rates exceed 90% survivorship at ten years. Main indications for revision include progressive osteoarthritis in other compartments, component loosening and polyethylene bearing failure. However, within those patients who have been revised, there is a cohort of patients who are revised early, usually under seven years. Mechanical mal-alignment has been cited recently as a reason for early failure and revision. The introduction of computer assisted surgery (CAS) has allowed us to more accurately restore the normal mechanical axis of the limb in UKA.

Aims and Hypothesis: The aim of this study was to identify whether, within our cohort of early failures, the failure mechanism differed from patients in the late revision group and specifically to examine whether mechanical mal-alignment contributed to the mechanism of early failure.

Materials and Methods: We undertook this retrospective review of a single surgeon series of 87 revised unicompartmental knee replacements carried out over 15 years. We collated the indications for revision, mechanisms of failure, and methods of revision from medical notes and compared the early and late revisions by mechanism of failure. We considered an early failure to be any UKA revised before seven years

Results: There were 50 late failure UKAs and 37 early failures. We found no significant differences between groups in age, activity or demographics at time of primary UKA. The main implants in the late failure group were 19 (38%) Miller Galante, 22 (44%) PCA Duracon, and 9 (18%) others while the early failures consisted 21 (57%) Miller Galante, 5 (14%) Oxford, 3 (8%) PCA Duracon, and 8 (22%) others. 60% of late failures were cemented while 89% of early failures were cemented. Mechanism of late failure was 46% bearing wear, 22% progression of OA, 14% malalignment and 14% loosening, while mechanism of early failure was 41% loosening, 27% bearing wear and 14% malalignment.

Discussion: Many historical bearing failures were due to oxidised polyethylene following sterilization. These should now have been eliminated by modern polyethylene and sterilization techniques. Mechanical mal-alignment is also now measurable and preventable by the use of CAS. We believe that avoidance of these two pitfalls will have an impact on the rate of early revision of UKA.

Conclusion: We conclude that patients who underwent early UKA revision had a different failure mechanism from late UKA revisions. In the early failure group the main mechanisms were mechanical loosening and bearing wear. In the late revision group, bearing failures, progressive osteoarthritis and component loosening were the main reasons for failure. Mechanical malalignment failed to differ between the groups.