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



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.

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Conflict of Interest

Brian P. Gladnick, MD, Denis Nam, MD, Saker Khamaisy, MD and Sophia Paul, BA have declared that they have no conflict of interest. Andrew D. Pearle, MD reports personal fees from Pipeline Orthopaedics, stock options from Blue Belt Technologies and research grants from MAKO Surgical, outside the work.

Human/Animal Rights

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008 (5).

Informed Consent

Informed consent was obtained from all patients for being included in the study.

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Corresponding author

Correspondence to Brian P. Gladnick MD.

Additional information

Level of Evidence: Level III

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Gladnick, B.P., Nam, D., Khamaisy, S. et al. Onlay Tibial Implants Appear to Provide Superior Clinical Results in Robotic Unicompartmental Knee Arthroplasty. HSS Jrnl 11, 43–49 (2015).

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  • unicompartmental knee arthroplasty
  • tibial resurfacing
  • inlay
  • onlay
  • robotic surgery