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

Online First Article

Brian P. Gladnick, MD

Department of Orthopedic Surgery, Hospital for Special Surgery

Denis Nam, MD

Department of Orthopedic Surgery, Hospital for Special Surgery

Saker Khamaisy, MD

Department of Orthopedic Surgery, Hospital for Special Surgery

Sophia Paul, BA

Department of Orthopedic Surgery, Hospital for Special Surgery

Andrew D. Pearle, MD
Andrew D. Pearle, MD

Assistant Attending Orthopaedic Surgeon, Hospital for Special Surgery

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.

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.

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).

We advise using metal-backed onlays during UKA to improve postoperative clinical outcomes.

Level of Evidence: Level III

This article appears in the HSS Journal: Volume 11, Issue 1.
View the full HSS Journal article at

About the HSS Journal

HSS Journal, an academic peer-reviewed journal published three times a year, February, July and October. The Journal accepts and publishes peer reviewed articles from around the world that contribute to the advancement of the knowledge of musculoskeletal diseases and disorders.


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