Onlay Tibial Implants Appear to Provide Superior Clinical Results in Robotic Unicompartmental Knee Arthroplasty

Abstract

Background: Unicompartmental knee arthroplasty (UKA) is an increasingly popular option for the treatment of single-compartment knee osteoarthritis (OA) in adults. Two options for tibial resurfacing during UKA are (1) allpolyethylene inlays and (2) metal-backed onlays. Questions/ Purposes: The aim of this study was to determine whether there are any differences in clinical outcomes with inlay versus onlay tibial components. Patients and Methods: We identified 39 inlays and 45 onlays, with average 2.7-and 2.3-year follow-up, respectively, from a prospective robotic-assisted surgery database. The primary outcome was the Western Ontario and McMaster University Arthritis Index (WOMAC), subcategorized by the pain, stiffness, and function subscores, at 2 years postoperatively. The secondary outcome was the need for secondary or revision surgery. Results: Postoperative WOMAC pain score was 3.1 for inlays and 1.6 for onlays (p= 0.03). For 25 inlays and 30 onlays with both preoperative and postoperative WOMAC data, pain score improved from 8.3 to 4.0 for inlays versus from 9.2 to 1.7 for onlays (p=0.01). Function score improved from 27.5 to 12.5 for inlays versus from 32.1 to 7.3 for onlays (p=0.03). Four inlays and one onlay required a secondary or revision procedure (p=0.18). Conclusions:We advise using metal-backed onlays during UKA to improve postoperative clinical outcomes.

Survivorship and clinical outcome of the minimally invasive Uniglide medial fixed bearing, all-polyethylene tibia, unicompartmental knee arthroplasty at a mean follow-up of 7.3years

“…Fixed bearing designs have been shown in several studies to have equivalent clinical and radiographic outcomes compared to mobile-bearing implant designs at mid and long term follow up [15]. A fixed bearing eliminates the risk of bearing dislocation, however some studies have shown higher revision rates for all-polyethylene tibial components compared to those that utilize metal-backed implants [16][17][18]. Clear advantage of this implant is low cost.…”

Mid-Term Outcomes of Metal-Backed Unicompartmental Knee Arthroplasty Show Superiority to All-Polyethylene Unicompartmental and Total Knee Arthroplasty

“…Fewer studies have assessed functional outcomes of inlay and onlay components. Gladnick et al compared inlay versus onlay components at the 2-year follow-up [ 19 ]. Patients in their study underwent, similar to this current study, robotic-assisted UKA surgery, and the authors also reported superior WOMAC scores in patients undergoing metal-backed.…”

“…1 a) whereas onlay components are cemented on top of the flat tibial cut with a metal baseplate and therefore rely on the cortical bone as well as on the subchondral bone (Fig. 1 b) [ 19 , 43 ]. Studies have shown that inlay components have higher peak stress at the tibial surface compared to onlay components [ 49 , 61 ], which could be explained by the fact that onlay components rest on the cortical bone and that the metal backing distributes forces over the tibia [ 49 , 61 ].…”

“…It has further been suggested that this increased stress can cause pain and inferior outcomes [ 19 , 48 ]. Although one study reported inferior clinical outcomes with inlay components at short-term follow-up, at mid-term follow-up no clear significant or clinically relevant difference between both components is seen in functional outcomes [ 20 , 22 ].…”

Metal-Backed Tibial Components Do Not Reduce Risk of Early Aseptic Loosening in Unicompartmental Knee Arthroplasty: A Systematic Review and Meta-Analysis

“…In addition, we extended the research to the reference list of all relevant articles. At this point, a stepwise exclusion of studies not meeting aforementioned inclusion criteria was conducted, such as studies comparing biomechanical behavior in knee model, 11,12 comparative data of implants with different geometry (onlay vs inlay), [14][15][16] and studies with follow-up < 24 months (►Fig. 1); moreover, no data from national registries were included, 8,17 to minimize possible bias, such as different implant design, cementation technique, and surgeons' experience.…”