Introduction <p>Despite the growing use of unicompartmental knee arthroplasty (UKA), no prior systematic review has focused exclusively on stair ascent and descent biomechanics. This review addressed this gap by synthesizing spatiotemporal, kinematics, and kinetics outcomes compared to healthy individuals and between operated and contralateral limbs.</p> Materials and methods <p>Five databases, including Medline, Embase, CINAHL, Web of Science, and Ergonomics Abstracts were searched until February 2025. Studies were screened based on title and abstract, followed by a full text reading conducted by two authors following inclusion and exclusion criteria. The risk of bias was assessed using ROBINS-I tool. Main outcomes included spatiotemporal, kinematics and kinetics outcomes compared to healthy individuals or contralateral limb.</p> Results <p>A total of 7 studies were included. All the included studies evaluated stair ascent, descent or both. A total of 92 patients operated with UKA, and 58 healthy individuals were included. Medial unicompartmental knee arthroplasty does not appear to fully restore normal knee function in terms of knee flexion amplitude compared to healthy individuals during stair ascent. Moreover, UKA patients appeared to decrease stride velocity and increase contact time compared to healthy individuals during both stair ascent and descent.</p> Conclusions <p>Due to the limited quality of included studies, definitive conclusions could not be drawn. However, patients following UKA exhibit altered stair negotiation mechanics with persistent asymmetry compared to healthy controls. This highlights the need for future longitudinal research on stair negotiation following UKA, including assessment of muscle activation and a focus on mobile-bearing UKA.</p> Level of evidence <p>Level III, systematic review.</p>