Ten-year survival and patient-reported outcomes of a medial unicompartmental knee arthroplasty incorporating an all-polyethylene tibial component

Abstract

IntroductionBiomechanical studies have suggested that proximal tibial strain is elevated in UKAs incorporating all-polyethylene tibial components with concern that this leads to premature failure. This study reports minimum 10-year outcomes for a UKA incorporating an all-polyethylene tibial component to determine whether these concerns were realised.Materials and methods109 fixed bearing UKAs (97 patients, mean age 68 (range 48–87), 54/97 (56%) female) with all-polyethylene tibial components were followed up for ≥ 10 years with Oxford Knee Scores, Forgotten Joint Scores and Kaplan–Meier analysis. 106/109 implants were 7 mm, 3 were 9.5 mm.ResultsTen-year survival was 85.5% (78.6–92.4 95% CI) with the end-point failure for any reason. Unexplained pain was the commonest mode of failure (6/17) followed by lateral compartment osteoarthritis (5/17) and tibial subsidence/loosening (4/17). Revision rate was highest at 2–5 years due to revisions for unexplained pain. Ten-year survival was worse in patients < 65 years old (p = 0.035), in those with BMI > 30 (p = 0.017) and in those with postoperative increases in medial tibial sclerosis (p < 0.001 log-rank). Implant malalignment was not significantly associated with failure. Radioisotope bone scans in 16 patients all remained “hot” at mean 6.1 years (range 2.1–11.5). Relative risk of failure in patients < 65 years was 2.9 (1.2–7.0 95% CI) and when BMI > 30 was 2.9 (1.2–6.9 95% CI). In those with intact UKAs at 10 years, mean Oxford Knee Score was 34.8 ± 10.7, Forgotten Joint Score was 37.9 ± 26.7 and 96% were satisfied with their knee.ConclusionThe high rate of early failure between 2 and 5 years in this all-polyethylene tibial component UKA did not persist in the long term. Though medial proximal tibial metabolic changes appear to persist they are not necessarily symptomatic. BMI > 30 and age < 65 years were significant risk factors for revision.

Unicondylar knee replacement versus total knee replacement for the treatment of medial knee osteoarthritis: a systematic review and meta-analysis

“…High levels of activity increase the risk of implant loosening due to the production of wear which might lead to the high revision rate of UKR [25,41]. Lastly, surgeons would probably modify UKR to TKR when unexplained pain occurs in patients done with UKR since the development of OA requires TKR as the final solution [42]. The revision of UKR under such cases reflect the routine treatment of OA rather than the UKR failure.…”

Greater activity, better range of motion and higher quality of life following unicompartmental knee arthroplasty: a comparative case–control study

“…However, high levels of activity increase the risk of implant loosening due to production of wear and might affect survival rates adversely [14]. Additionally, UKAs might be more likely revised and converted to a TKA in the presence of unexplained pain, as this reflects the logically next therapeutic step from a partial to a definitive solution [27,28] There was no difference in the postoperative functional KSS between the two groups. These findings are consistent with results from a systematic review by Kleeblad et al [4].…”

The effect of malalignment on proximal tibial strain in fixed-bearing unicompartmental knee arthroplasty

“…Joint registries do not distinguish between AP and MB UKA implants. Poor survivorship of AP UKAs has been reported, 22-25 with early failures commonly experienced due to tibial loosening, subsidence, or pain. The increased sensitivity to malalignment demonstrated here in AP implants may well contribute to these modes of failure.…”