Oxford domed lateral unicompartmental knee arthroplasty

Abstract

Aims To report mid- to long-term results of Oxford mobile bearing domed lateral unicompartmental knee arthroplasty (UKA), and determine the effect of potential contraindications on outcome. Methods A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and the presence of full-thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. Results Median follow-up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%); 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing, and 12 (4%) were revised for medial osteoarthritis (OA). Ten-year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. Conclusion Domed lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. It is recommended that the stability of the bearing is assessed intraoperatively. If the bearing can easily be displaced, the fixed rather than the mobile bearing version of the Oxford lateral tibial component should be inserted instead. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications. Cite this article: Bone Joint J 2020;102-B(8):1033–1040.

The Oxford Domed Lateral Unicompartmental Knee Replacement implant: Increasing wall height reduces the risk of bearing dislocation

“…While increasing the bearing thickness only increases the VDD medially by about 0.1/1 mm increase in bearing thickness, clinically, inserting a new bearing, which may be slightly thicker than the original 7 – 9 resolves approximately two thirds of medial bearing dislocation cases so that there is no further dislocation. Using a slightly thicker bearing might be resolving clinical dislocations by increasing the tension of the soft tissues in the lateral knee, an thereby reducing the amount that the lateral compartment can distract.…”

“…The usual treatment for a dislocation is to explore the knee, remove anything such as retained osteophytes that might have displaced the bearing, then insert a new bearing, which may be slightly thicker than the original. 7 – 9 In about two thirds of cases there is no further dislocation. Occasionally, if the bearing is very unstable or if there is a recurrent dislocation, surgeons have inserted screws into the tibial eminence to increase the apparent height of the tibial wall.…”

Biomechanical effects of fixed-bearing femoral prostheses with different coronal positions in medial unicompartmental knee arthroplasty

“…The clinical duration of fixed-bearing prostheses is relatively short. Moreover, inappropriate operation procedures can lead to prosthesis malalignment [29,30]. On the other hand, the PE insert of the fixed-bearing prosthesis is immovable so that it is impossible to adjust the abnormal stress caused by prosthesis malalignment.…”

Midterm Outcomes in Lateral Unicompartment Knee Replacement: The Effect of Patient Age and Bearing Choice

“…In the review of the current literature, there are seven series reporting on lateral UKA survivorship of 10 years or more with survival ranging from 83 to 100%. 5,6,[15][16][17] While these published rates are certainly lower than those reported for TKA, it is critical when reviewing published reports because the readers take into account the age of the cohort and length of follow-up in various studies. Our median follow-up was close to 9 years with a median age of 55 years, both factors consistent with higher revision rates.…”

“…This is supported by a recently published series of 325 consecutive lateral UKA procedures where mobile-bearing dislocation occurred in 4% of cases. 16 This led the authors to recommend having a low threshold to conversion to fixed-bearing implants intra-operatively in cases where trialing results in ease of mobile-bearing displacement. Attempts to determine the influence of postoperative alignment on PROMs including WOMAC, KOOS, and Tegner activity scale did not show any effect.…”