• Riccardo D'Ambrosi, Matteo Buda, Alessandro Nuara, Ilaria Mariani, Michele Scelsi, Federico Valli, Nicola Ursino, and Michael Tobias Hirschmann.
• IRCCS Istituto Ortopedico Galeazzi, Via Galeazzi 4, 20161, Milan, Italy. riccardo.dambrosi@hotmail.it.
• Arch Orthop Trauma Surg. 2022 Nov 1; 142 (11): 3449-3460.

PurposeThe purpose of this study was to determine the changes in patellar heights by comparing standardised pre- and post-operative radiographs in a consecutive series of patients undergoing unicompartmental knee arthroplasty (UKA) with two different approaches and implant designs [fixed bearing (FB) vs mobile bearing (MB)] and to correlate the patellar heights with clinical outcomes.MethodsOne hundred and seventy-two UKA patients were prospectively enrolled in the study. 75 patients underwent a minimally invasive FB medial UKA (referred to hereinafter as the 'FB group'); 97 patients were treated with a minimally invasive MB medial UKA. The pre-operative and mid-term (1-year) post-operative patellar heights and clinical scores of these groups of patients were compared using the Insall-Salvati (IS) and Caton-Deschamps (CD) indices and the Oxford Knee Score (OKS).ResultsNo differences were found between the two groups either with regard to the pre-operative data (p > 0.05) or between pre- and post-operative radiographic scores at the time of each follow-up (p > 0.05). Both the groups reported a significant clinical improvement (p<0.05) as did all the sub-groups (p < 0.05). In the MB group, a higher CD index in females was found at the final follow-up stage (p = 0.043) and a higher pre-operative CD index was found in patients with BMI ≥ 28 (p = 0.040). A statistically negative correlation was found between the pre-operative OKS and pre-operative IS index (rho=- 0.165; p=0.031).ConclusionsBoth FB and MB arthroplastys with different surgical approaches did not change the patellar height regardless of the age, gender and BMI at short-medium-term follow-up. The post-operative patellar height seems not to be correlated with the clinical outcomes. A higher pre-operative IS index was correlated with knee pain and function.Level Of EvidenceLevel II-prospective comparative study.Study RegistrationResearchregistry6433- www.researchregistry.com .© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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