Abstract
Introduction
The revision rate of unicompartmental knee replacement (UKR) in national joint registries is much higher than that of total knee replacements and that of UKR in cohort studies from multiple high-volume centres. The reasons for this are unclear but may be due to incorrect patient selection, inadequate surgical technique, and inappropriate indications for revision. Meniscal bearing UKR has well defined evidence based indications based on preoperative radiographs, the surgical technique can be assessed from post-operative radiographs and the reason for revision from pre-revision radiographs. However, for an accurate assessment aligned radiographs are required. The aim of the study was to determine why the revision rate of UKR in registries is so high by undertaking a radiographic review of revised UKR identified by the United Kingdom's (UK) National Joint Registry (NJR).
Methods
A novel cross-sectional study was designed. Revised medial meniscal bearing UKR with primary operation registered with the NJR between 2006 and 2010 were identified. Participating centres from all over the country provided blinded pre-operative, post-operative, and pre-revision radiographs. Two observers reviewed the radiographs.
Results
Radiographs were provided for 107 revised UKR from multiple centres. The recommended indications were not satisfied in 30%. The most common reason was the absence of bone-on-bone arthritis, and in 16 (19%) the medial joint space was normal or nearly normal. Post-operative films were mal-aligned in 50%. Significant surgical errors were seen in 50%, with most errors attributable to tibial component placement and orientation. No definite reason for revision was identified in 67%. Reasons for revision included disease progression (10%), tibial component loosening (7%), dislocation of the bearing (7%), infection (6%) femoral component loosening (3%), and peri-prosthetic fracture (2% - one femur, one tibia).
Discussion and Conclusion
This study found that improper patient selection, inadequate surgical technique, inappropriate revisions and poorly taken radiographs all contributed to the high revision rate. There is a misconception that UKR should be used for early OA. Bone-on-bone arthritis is a requirement and was definitely not present in about 20%. There were many surgical errors, particularly related to the tibial cut: The new instrumentation should reduce this. There was a high prevalence of mal-aligned radiographs. Revisions should be avoided unless there is a definite problem, as the outcome of revision is usually poor in this situation.
80% of UKR revisions could potentially be avoided if surgeons adhered to the recommended indications for primary and revision surgery, and used the recommended surgical techniques. This study therefore suggests that if UKR was used appropriately the revision rate would be substantially lower and probably similar to that of TKR.
