Single-stage bilateral knee arthroplasty, even when unicompartmental, remains controversial, chiefly due to the risk of peri-operative complications. The primary objective of this study was to compare the short-term complication rate and cost of single- vs. two-stage bilateral unicompartmental knee arthroplasty (UCA). The secondary objective was to compare total hospital stay lengths and motion-range recovery.

Single-stage bilateral UCA is a cost-saving alternative that is not associated with higher complication rates compared to two-stage bilateral UCA.

This single-centre retrospective comparative study included 70 patients of any age managed between 2010 and 2016. Among them, 44 (88 UKAs) had single-stage surgery (1S group) and 26 (52 UCAs) two-stage surgery (2S group). The two groups were comparable for age, body mass index, gender distribution, compartment replaced, ASA score, and Charlson comorbidity index. The following were evaluated: operative time, haemoglobin level before and after surgery, major and minor complication rates, motion-range recovery, and the radiographic hip-knee-ankle (HKA) angle. Costs were estimated based on the standard codes assigned to the procedures by the national statutory health insurance system (GHM 08C24 for knee arthroplasty to treat knee osteoarthritis and NFKA006 for unicompartmental tibio-femoral or femoro-patellar arthroplasty), modulated according to the concomitant diagnoses.

No differences were found for the haemoglobin level change, time to motion-range recovery, or HKA angle. The complication rates per patient were not significantly different between the groups: major complications, 9.1% (n=4) in the 1S group and 15.4% (n=4) in the 2S group (p=1.00); minor complications, 4.5% (n=2) in the 1S group and 3.8% (n=1) in the 2S group (p=1.00). Cost of the total hospital stay was significantly higher in the 2S group than in the 1S group (11,766.7€) and 5626.4€, respectively; p<0.001). Mean total hospital stay duration per patient was 6.7 days with single-stage surgery and 13.4 days with two-stage surgery.

Single-stage bilateral UCA is not associated with a higher rate of peri-operative complications compared to the two-stage alternative and is substantially less costly. Financial incentives from the healthcare authorities are warranted to increase the use of the single-stage procedure.

III, case-control study.