Onlay tibial implants appear to provide superior clinical results in robotic unicompartmental knee arthroplasty.
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) all-polyethylene inlays and (2) metal-backed onlays.


OBJECTIVE
The aim of this study was to determine whether there are any differences in clinical outcomes with inlay versus onlay tibial components.


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.
Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021 USA.
Brian P
BP
Gladnick
Department of Orthopaedic Surgery, Washington University School of Medicine, 660 South Euclid Ave., Campus Box 8233, St. Louis, MO 63110 USA.
Denis
D
Nam
Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021 USA.
Saker
S
Khamaisy
Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021 USA.
Sophia
S
Paul
Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021 USA.
Andrew D
AD
Pearle
inlay; onlay; robotic surgery; tibial resurfacing; unicompartmental knee arthroplasty