UNICOMPARTMENTAL VS. TOTAL KNEE ARTHROPLASTY

This recommendation has been downgraded due to differing outcomes at long term versus short term. Unicompartmental knee arthroplasty (UKA) provides similar or higher patient-reported outcome measure scores of pain, function, and performance compared to total knee arthroplasty (TKA) at short to mid-term follow up when performed for the appropriate indication of isolated unicompartmental osteoarthritis. Among this patient population, UKA was also found to be associated with a higher forgotten joint score. Notably, performing UKA in this population is associated with the advantage of shorter operative time, shorter hospital stay, lower intraoperative estimated blood loss, lower postoperative transfusions, greater postoperative range of motion, higher level of activity at time of discharge, and mitigated overall minor and major 30-day complication rates. Some long-term outcomes in favor of TKA were observed; Kulshrestha (2017) found functional outcomes in favor of TKA at 2 years, Ellis (2021) found TKA was associated with less disease progression, and van der List (2016, 2017) found that 3-year post op WOMAC scores favored TKA patients.

Benefits/ Harms of Implementation

Performing UKA in an appropriately selected population affords the advantages of mitigated invasiveness, shorter operative time, length of stay, greater preservation of bone stock, knee biomechanics that are more aligned with those of the native knee and similar or superior pain and function metrics compared to TKA. Conversely, the main concern is the higher revision rates, especially at in mid-to-long term follow-up. It should also be noted that UKA to TKA conversions have been observed to be inferior in outcome versus primary total knee arthroplasty (Pearse 2012).

Cost Effectiveness/ Resource Utilization

Short term metrics indicate superior cost-effectiveness for UKA compared to TKA in appropriately selected patients. Such a difference stems from the shorter operative time, length of hospital stay, and perioperative complications in UKA versus TKA while affording similar improvement in patient-reported pain, activity and functional outcomes. A recent study (Shankar 2016) demonstrated that hospital direct costs were lower for UKA ($7893 vs. $11,156; p < 0.001) as were total costs (hospital direct costs plus overhead; $11,397 vs. $16,243; p < 0.001). Supply costs and implant costs were similarly lower for UKA ($701 vs. $781; p < 0.001, and $3448 vs. $5006; p < 0.001). This advantage extended up to the 5-year follow up according to a recent randomized controlled trial. Further investigations are required to evaluate long term cost effectiveness.

Acceptability and Feasibility

Overall, UKA has fair acceptability and feasibility among surgeons and patients. American Joint Replacement Registry (AJRR) data indicates diminishing rates reaching 2.7% of all primary knee arthroplasties reported to AJRR for 2017. However, such rates rebounded with numbers increasing to 4.2% in 2020 (AJRR 2020).

Future Research

Recent AJRR data highlighting revision risk curves show that when stratified by sex, males 65 years and above had UKA revision rates that were comparable to their TKA counterparts. Conversely, females of the same age group had statistically and clinically significant higher rates of revision UKA up to 108 months compared to TKA. Such sex-based difference after age adjustment warrants further research into factors influencing UKA survivorship including activity levels, bone quality and other patient determinants. This will aid in identifying the optimal patient subset for which UKA would be recommended for greatest survivorship and functional benefit.

Additional References:

Pearse, A. J., Hooper, G. J., Rothwell, A. G., & Frampton, C. (2012). Osteotomy and unicompartmental knee arthroplasty converted to total knee arthroplasty: data from the New Zealand Joint Registry. The Journal of Arthroplasty, 27(10), 1827-1831.