Post-Market Study of Robotic-Arm Assisted Unicompartmental Knee Arthroplasty in Comparison to Traditional UKA (Fixed and Mobile Bearings)

Total knee arthroplasty (TKA) is known to have excellent long-term survivorship and clinical success in the management of degenerative joint disease, and remains the primary treatment for patients with bi- or tri-compartmental osteoarthritis. However, the patient population seeking knee arthroplasty is evolving, with patients being younger and more demanding on their prostheses (1). Recent investigations have highlighted that there remains a high incidence of residual symptoms including grinding/popping/clicking, swelling, and difficulties getting in and out of a car and chair, and 16% of patients remain "unsatisfied" following TKA (1).

Medial unicompartmental knee arthroplasty (UKA) remains a viable alternative to total knee arthroplasty in patients presenting with isolated, medial compartment osteoarthritis of the knee. Its use has increased in popularity in the United States, as the number of UKA performed over the last decade has increased by 30%(1). Proposed benefits of UKA include a smaller incision, less blood loss as well as shorter recovery time to functional level. Other benefits of UKAs include improved knee range of motion and better restoration of the knee kinematics (2, 5). These benefits are attributed to the less invasive nature of the procedure with preservation of the anterior and posterior cruciate ligaments, and minimal bony resections.

Unfortunately, historically the survival rate of UKA has been poor, with several reports demonstrating a survival rate of only 65-70% at 7-10 year follow-up (8, 9). These historically poor results have been attributed to instrumentation that was difficult to use, poor indications for the surgical procedure, and inadequate implant designs. More recent reports have shown 10-year survival rates ranging from 91% to 98% using both mobile-bearing and fixed-bearing UKA designs (7, 10-12). Mobile bearing UKA have a 92% survival rate at 20 years (5). However, the vast majority of these studies were performed at high-volume centers, and national joint registries have continued to demonstrate an increased rate of early failure and decreased survivorship of UKA versus TKA(13).

Recently, robotic-assisted UKA has been introduced to improve the accuracy of implant positioning (4). As implant positioning including alignment and translation in the coronal and sagittal planes and implant sizing are critical for success after UKA, the addition of robotic-assistance theoretically can improve radiographic alignment and clinical outcomes.

Currently, the most common robotic guidance system used in UKA is the Robotic Arm Interactive Orthopedic System (RIO; MAKO Surgical; Ft. Lauderdale, FLA). The purposes of this investigation is to 1) retrospectively review the radiographic and clinical outcomes of medial UKA using conventional techniques performed at our institution and 2) prospectively assess the learning curve, radiographic, and clinical outcomes of use of the RIO system as it is incorporated into our clinical practice.