Total Knee Arthroplasty Versus Unicondylar Knee Arthroplasty: a Randomized, Double-blind Multicenter Trial

Background Knee osteoarthritis (OA) is a common joint disease, which may cause severe pain and lead to a reduced quality of life. It has been shown that the prevalence of symptomatic OA in those aged 60 and above was 9.6% in men and 18% in women. Primary treatment of knee OA is conservative including physical activity, exercise and analgesics. Meta-analysis shows small to moderately sized effects of exercise on pain and function. Total knee arthroplasty (TKA) is the gold standard option for the treatment of painful OA of the knee when conservative treatment is not sufficient.

Unicondylar knee arthroplasty (UKA) can be used as the treatment of knee OA isolated to a single compartment instead of TKA. Both UKA and TKA have been used for decades as a treatment of knee OA. However, operative indications for TKA and UKA overlaps, but they are not similar. Therefore, the outcome or survivorship of these procedures cannot be compared directly.

Some advantages of UKA over TKA have been reported, including faster recovery time, reduced perioperative morbidity and mortality, a subjective preference of feeling more normal knee, lower cost and improved return to work and sport. On the other side national arthroplasty registers like the National Joint Registry of England and Wales (NJR), the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), the Swedish Knee Arthroplasty Register (SKAR), and the Finnish Arthroplasty Register (FAR) consistently report around a threefold increase in crude cumulative revision rate at 8 to 10 years for UKA compared with TKA 7-10. Few reports have been published about patient-perceived outcomes following TKA compared with UKA. Newman et all compared fixed bearing UKA to TKA and published better range of movement (ROM) after UKA. Sun PF et all compared mobile bearing UKA to fixed bearing TKA. They didn't had significant difference in ROM or Knee Society score (KSS) postoperatively after mean 52 months follow-up, but in TKA group had significantly more postoperative deep vein thrombosis and more blood loss.

A study comparing cemented UKA (Oxford, Biomet) and TKA, have been published using patient-perceived outcome measures, but the study protocol lacks of blinding. There is no published randomized controlled, double-blind trial which compares patient-perceived outcomes after TKA and UKA.

Oxford mobile bearing UKA is most used unicondylar prosthesis according to national registries. The most common reason for revision of UKA according to NJR is aseptic loosening, accounting for up to 48% of all UKA revisions. Other reasons for UKA revision in Finland where malalignment, prosthesis fracture, instability, infection, fracture, patella complication and other reasons (35%). A randomized controlled trial of 62 knees comparing cemented and cementless Oxford UKA has demonstrated a greatly reduced incidence of tibial radiolucencies with similar functional outcomes at 1 year 15. Cementless Oxford unicondylar knee is relative new product and was developed to address problems related to cement fixation, and has been demonstrated in a randomised study to have similar clinical outcomes with fewer radiolucencies than observed with the cemented device. New Zealand Joint Registry (NZJR) data shows revision rate 1,37/100 component years for cemented Oxford phase 3 and 0,72/100 component years for cementless Oxford phase 3 UKA. The uncemented Oxford UKA has a significantly lower revision rate than the overall mean of 1.27 /100 observer component years. Also the NJR show better survivorship for cementless unicondylar arthroplasty compared to cemented unicondylar arthroplasty. On the other hand cementless TKA shows lower survivorship compared cemented TKA in Finnish Arthroplasty Register (FAR). There are no published randomized controlled, double-blind trial which compare patient-perceived outcomes after cemented TKA and cementless Oxford UKA.