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system. Int J Health Care Qual Assur. 2011;24(5):366-388. 2. Hariri S, Bozic KJ, Lavernia C, Prestipino A, Rubash HE. Medicare physician reimbursement: past, present, and future. J Bone Joint Surg Am. 2007;89(11):2536-2546. 3. Kurtz S, Ong K, Lau E, Mowat F, Halpern M. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am. 2007;89(4):780-785. 4. Foran JR, Sheth NP, Ward INTRODUCTION Unicondylar knee arthroplasty (UKA) has evolved substantially since its conceptual introduction by McKeever and MacIntosh in the late 1950s.1,2 Although early results with UKA were unpredictable, this procedure restores native knee kinematics and, according to some investigators, yields patient satisfaction superior to total knee arthroplasty (TKA).3–7 Advances in prosthetic design, bearing surface technology,8 and surgical instrumentation have rendered excellent results in recent literature. Longterm survivorship has been reported to be as high as 98% 10 years after surgery.9–13 There is a general consensus that implant positioning is key to long-term survival of unicondylar arthroplasties in addition to proper patient selection.14–16 In traditional extramedullary or spacer block techniques, the femoral cutting block is positioned a Orthopaedic Foundation for Active Lifestyles, Greenwich, CT, USA; b Plancher Orthopaedics & Sports Medicine, 1160 Park Avenue, New York, NY 10128, USA; c Department of Orthopaedics, Albert Einstein College of Medicine, New York, NY, USA * Corresponding author. E-mail address: kplancher@plancherortho.com KEYWORDS Unicondylar knee arthroplasty Intramedullary technique Intramedullary guide Partial knee replacement Femur first technique Unicompartmental arthritis Arthritis Knee kinematics KEY POINTS Use of an intramedullary femoral alignment guide for unicompartmental arthroplasty is a reliable, reproducible technique. Use of intramedullary alignment for partial knee replacements mimics the distal femoral preparation of total knee arthroplasty, familiar to many surgeons, improving the likelihood of successful outcomes. The distal femur cut provides increased working space for more accurate proximal tibial resection and also allows a flexion contracture or a non-passively correctable contracture of 15 or more to be treated successfully with a UKA in carefully selected patients. UKA with intramedullary instrumentation is amenable to minimally invasive surgical approaches. Clin Sports Med 33 (2014) 87–104 http://dx.doi.org/10.1016/j.csm.2013.08.004 sportsmed.theclinics.com 0278-5919/14/$ – see front matter 2014 Elsevier Inc. All rights reserved. freehand after the proximal tibial cut has been made. These methods have been associated with radiographic inaccuracies in prosthesis positioning in up to 30% of cases.17 With intramedullary (IM) femoral guide instrumentation, the femoral cut is made first. Cadaveric models have confirmed that the use of IM instrumentation yields superior radiographic results in coronal alignment of the femoral component, sagittal alignment of tibial component, and overall satisfaction with prosthesis positioning.18 We encourage use of the long IM rod for all procedures when possible. Insertion of the short IM rod in UKA per the manufacturer’s guidelines may decrease the accuracy of the anatomic axis1 ; however, newer techniques and instrumentation have the ability to restore knee kinematics matching that of the native knee when the short IM rod must be used.5,19 Furthermore, IM instrumentation for UKA mimics that of TKA, offering a more familiar operative experience for the orthopedic surgeon.20 PREOPERATIVE EVALUATION AND MODERN SELECTION CRITERIA Patient selection has been a topic of debate. Criteria described by Kozinn and Scott were rigorous leaving most potential surgical candidates no other option than TKA.21,22 Previous research has shown discrepancies in expected outcomes between patients and surgeons.23 As a result, postoperative expectations must be discussed and managed preoperatively throughout the decision-making process to improve patient satisfaction. Thoughts are evolving that there is no ideal candidate for UKA and an individualized approach must be taken by the surgeon. Recently expanded inclusion criteria have made this a viable option for the young, active patient seeking pain relief and return to activities without compromising the prosthesis or outcomes.24–26 A diagnosis of osteonecrosis or osteoarthritis (OA) (Fig. 1) 27 in the medial or lateral compartment of the knee is understood, but weight, age, and presence or absence of the anterior cruciate ligament (ACL) must all be critically assessed. Patients must complain of isolated knee pain to a single side of the knee with the 1-finger test (eg, ask the patient to point with 1 finger to the area of pain) (Fig. 2). In the case of a dual-sided loss of joint space or magnetic resonance imaging (MRI) evidence of grade IV Outerbridge OA, pain or discomfort, if present, going up stairs must match the side of pain in order to be considered a candidate for UKA. Complaints of pain going downstairs with narrowing on the medial side with grade IV Outerbridge OA yields excellent medial-sided UKA results. Patients with controlled inflammatory arthropathies are also good candidates, in our experience. A thorough
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