Unicompartmental knee arthroplasty: state of the art

The popularity of unicompartmental knee arthroplasty (UKA) for the treatment of isolated compartment osteoarthritis of the knee has risen over the past 2 decades. Currently, UKA covers 10% of all knee arthroplasties worldwide. Although indications have been extended, results have proven that patient selection plays a critical role in the success of UKA. From the current perspective, age, body mass index, patellofemoral osteoarthritis, anterior cruciate ligament deficiency and chondrocalcinosis are no longer absolute contraindications for UKA. Motivated by the desire to improve survivorship rates, patient-reported outcomes and reduce complications, there have been many technological advances in the field of UKA over the recent years. The aim of this review was to evaluate the current indications, surgical techniques, modes of failure and survivorship results of UKA, by assessing a thorough review of modern literature. Several studies show that innovations in implant design, fixation methods and surgical techniques have led to good-to-excellent longterm survivorship, functional outcomes and less complications. Until now, resurgence of interest of cementless designs is noted according to large national registries to address problems associated with cementation. The future perspective on the usage of UKA, in particular the cementless design, looks promising. Furthermore, there is a growing interest in robotic-assisted techniques in order to optimise result by controlled soft-tissue balancing and reproduce alignment in UKA. Future advances in robotics, most likely in the field of planning and setup, will be valuable in optimising patient-specific UKA. INTRODUCTION Clinical problem: prevalence and social impact Knee osteoarthritis (OA) is highly prevalent worldwide. It is the leading cause of musculoskeletal disability and associated with activity limitation, working disability, reduced quality of life and increased healthcare costs. 2 Partial or total joint replacement of the affected knee is a surgical intervention to treat the disease when conservative strategy fails. Both procedures are commonly performed in developed countries and the number is expected to increase dramatically in the upcoming decade. 3 Unicompartmental knee arthroplasty (UKA) has gained popularity recently because several studies have shown that it is less invasive and has a reduced operative time, larger postoperative range of motion (ROM), improved pain relief, earlier return to daily activities and sports, and cost reduction in comparison to total knee arthroplasty (TKA). National and annual registries show similar usage with an increasing incidence over the past 10 years, currently ranging from 5% to 11% globally in 2014. The aim of this review is to provide an overview of different aspects concerning UKA in terms of diagnostics, indications, patient selection, surgical techniques, clinical outcomes and geographical differences. Historical perspective of UKA and its upswing The concept of replacement of a single compartment of the knee joint originated in the 1950s, when McKeever and MacIntosh introduced the metallic tibial plateau. In 1972, the first contemporary UKA, resurfacing both the femur and tibia of a single knee compartment, was performed by Marmor. Despite the theoretical advantages of this design, the survivorship rates were disappointing with more than 30% of patients undergoing revision surgery within 10 years. Tibial loosening, subsidence and accelerated polyethylene wear were the dominant reasons for implant failure. In 1976, Insall and Walker reported similar disappointing results at 2–4-year follow-up, finding good-toexcellent results in only 11 out of 24 UKAs and a 28% conversion rate to TKA. The reasons for these dissatisfying results were malposition of the implant, insufficient correction of the leg alignment and removal of the patella due to patellofemoral osteoarthritis (PFOA). Subsequently, Laskin reported outcomes using the Marmor knee (Richards Manufacturing Company) with pain relief in only 65% of the patients and a 26% failure rate at a 2-year follow-up. Following these disappointing results, interest for UKA further decreased and UKA was discouraged. 21 In 1989, Kozinn and Scott sought to improve these outcomes by proposing the use of strict inclusion criteria. As a result, better results were reported in the literature. Berger et al applied these criteria and showed a survival rate of 98% at 10-year follow-up, using the Miller-Galante prosthesis (Zimmer, Warsaw, Indiana, USA). Clinically, outcomes were graded excellent in 78% of patients and good in 20% of patients. Simultaneously, Murray et al reported on 143 knees treated with a medial Oxford mobile-bearing UKA, revealing a survivorship of 97% with a mean follow-up of 10 years. The use of mini-invasive techniques was advocated to reduce tissue damage and improve the ease of revision surgery. However, the results have been variable regarding the accuracy and reproducibility of this approach compared with standard techniques. 26 Throughout the 1980s and 1990s, UKA usage continued, however, in varying degrees with corresponding results. Over the course of the years, surgeons sought to better understand the biomechanics and modes of failure of these devices to improve on the original UKA designs. In addition, special instrumentation was designed and better patient selection State of the Art To cite: Kleeblad LJ, Zuiderbaan HA, Hooper GJ, et al. JISAKOS 2017;2:97–107. 1Department of Orthopaedic Surgery, Sports Medicine and Shoulder Service, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, New York, USA 2Department of Orthopaedic Surgery, Medisch Centrum Alkmaar, Alkmaar, The Netherlands 3Department of Orthopaedic Surgery and Musculoskeletal Medicine, University of Otago Christchurch, Christchurch, New Zealand Correspondence to Dr Laura J Kleeblad, Department of Orthopaedic Surgery, Sports Medicine and Shoulder Service, Hospital for Special Surgery, Weill Medical College of Cornell University, 535 East 70th Street, New York, NY 10021, USA; [email protected] Received 17 November 2016 Revised 12 December 2016 Accepted 13 December 2016 Published Online First 11 January 2017 97 Kleeblad LJ, et al. JISAKOS 2017;2:97–107. doi:10.1136/jisakos-2016-000102. Copyright © 2017 ISAKOS group.bmj.com on August 27, 2017 Published by http://jisakos.bmj.com/ Downloaded from