Multiple level III and IV studies have been completed to ascertain the survivorship of UKA in young patients, and there are mixed results in the literature. The evidence is mixed between the designer center series, cohort groups, and national registries. In 2011, Pandit et al. published a retrospective review of their first 1000 phase three Oxford medial UKAs implanted at the designer center and subdivided the patients into those younger (245 patients) and older than 60 (755 patients) at age of implantation. They found no difference in 10‐year survivorship between the two groups, 97.3% (91.3–100%) and 95.1% (90.8–99.3%), respectively, with functional scores equal or better in the under 60 years of age group.¹ Several other case series have been published with similar outcomes and survivorship beyond 10 years.²–⁵ A 2018 systematic review by Kleeblad et al. aimed to compare outcomes and revision rates between UKA and TKA in patients under the age of 65.⁶ To calculate revision rates, the authors identified 21 cohort studies reporting data on 2224 UKAs and 33 cohort studies reporting data on 4737 TKAs. The overall UKA revision rate was 8.2% at a mean follow‐up of 9.8 years and an annual revision rate (ARR) of 1.00 (95% confidence interval [CI]: 0.77–1.30). Alternatively, the overall TKA revision rate was 6.95% at a mean follow‐up of 8.4 years and an ARR of 0.53 (95% CI: 0.36–0.78). Few studies have specifically assessed survivorship of UKA in very young patients. Parratte et al. performed a retrospective review of 25 patients under the age of 50 who underwent medial UKA, and although they found that the mean KSS score improved from 54 to 89 preoperatively, their 12‐year survival rate was 80.6%.⁷ The 2018 annual report of the Australian Orthopaedic Association National Joint Replacement Registry looking at 52 000 primary UKAs reported the cumulative percent revision of primary UKAs and found that patients aged between 55–64 had a 15.9% (range 15.3–16.6%) revision rate at 10 years and 30.4% (range 28.0–33.0%) at 17 years. Further, patients with UKA under the age of 55 had a cumulative percent revision of 22.8% (21.7–23.9%) at 10 years and 39.4% (36.6–41.4%) at 17 years.⁸ Conversely, TKA patients between the ages of 55 and 64 had an 11.8% (11.1–12.5%) revision rate and patients less than 55 had a 17.8% (16.4–19.3%) revision rate at 17 years.

Regarding functional outcomes, in the Kleeblad et al. systematic review, significantly higher overall ROM (125° vs 114, p = 0.004) as well as higher Knee Society Scores at long‐term follow‐up were found in the UKA group compared to the TKA group (88.1 and 85.8, respectively, p = 0.04).⁶ A retrospective case series by Walker et al. of 118 consecutive Oxford medial UKAs in patients aged 60 or younger found that 93% of patients returned to activity postoperatively at minimum two‐year follow‐up and 62% of patients were defined as “very active” based on the UCLA score of ≥7.⁹ Von Keudell et al. performed a retrospective age matched cohort analysis of 485 knee surgeries with a minimum three‐year follow‐up and found that in patients between the ages of 55 and 64 higher satisfaction was found in the UKA group with 93% of patients having excellent/good patient satisfaction compared to 89% in the TKA group.¹⁰ In those under the age of 55, 96% of patients with UKA had excellent/good patient satisfaction compared to 81% in the TKA group. Goh et al. published a retrospective matched cohort analysis of 160 patients under the age of 55 who underwent TKA and found that at both six months and two years patients in the UKA group had significantly greater ROM than those who underwent a TKA (128° ± 11° vs 117° ± 15°, respectively, at two years, p <0.001). They did not, however, identify any difference in functional outcomes or patient satisfaction scores.¹¹

At this time, UKA in patients under the age of 60 requires careful patient selection, meticulous surgical technique, and adequate surgical experience and also benefits from a shared decision‐making process between the patient and surgeon. To this end, several authors have developed surgical decision tools to provide support and information to patients deciding between undergoing TKA and UKA.¹²–¹⁴ Prospective randomized studies, some of which are ongoing, are required to better answer this question.¹⁵