The ideal indications for UKR proposed by Kozinn and Scott [
18], revised more recently by several authors, and in association with new designs and materials, have resulted in higher success rates. Careful patient selection is critical for unicompartmental knee arthroplasty if reliable results are to be achieved. The arthritis should be predominantly confined to a single compartment. No significant degenerative changes in the other (medial, lateral or PF) compartments should be present, and both cruciate ligaments should be intact. Absence of the anterior cruciate ligament (ACL) is a contraindication; the ACL makes the combined rolling and sliding at the meniscal femoral and meniscal tibial interfaces possible, which may yield near-normal joint kinematics and mechanics. The operation is also indicated in patients with osteonecrosis of the femoral condyle. Not all of the unicompartmental replacements are suitable for the lateral side because the ligaments of the lateral compartment are more elastic than those of the medial side. Malalignment of the limb should be passively correctable to neutral and not beyond. This is usually possible in patients with a varus deformity <15° or a valgus deformity <20°. The deformity of the knee should be only mild; therefore, a flexion contracture should be <15°. Unicompartmental knee arthroplasty with excision of osteophytes in the notch cannot correct moderately severe flexion contractures. Ideally, the knee can be flexed to 110°. This is important for the preparation of the femoral condyle during the operation. Recently survival rates of >90% at 10 years’ follow-up have been shown even in patients <60 years of age by Swienckowski et al. [
19]. In comparison with TKR, UKR allows use of smaller implants, shorter operative time, and preservation of both the cruciate ligaments and minimal bone resection [
20,
21]. Maintenance of the ACL and its mechanoreceptors may produce a better functional result in UKR [
22‐
24]. Knee kinematics during flexion following UKR have been shown to more closely resemble the intact knee; however, biomechanical studies of TKR have yielded results far from that of a normal knee [
22,
25]. Weale et al. [
26] documented superior functional recovery with improved performance in descending stairs and better patient satisfaction with UKR compared with TKR. In a cadaveric study, Patil et al. [
27] demonstrated normal joint biomechanics after UKR implantation in a knee. A number of prosthetic designs are now available, including both mobile and fixed tibial bearing surfaces: no statistically significant clinical advantage could be demonstrated between a fixed or mobile bearing tibial component in UKR at a mean follow-up of 5.7 years [
28], or 6.8 and 7.7 years [
29]. We have had good success in treating patients with either medial or lateral unicompartmental disease using the MIS Unicompartmental Fixed Knee System (ZUK, Zimmer® Inc., Warsaw, IN, USA; JOURNEY OXINIUM UNI, Smith & Nephew, Memphis, TN, USA). Typically, patients recover functionality of the operated knee within 40 days.