Remodeling Pattern of the Medial Tibial Metaphysis after a Cementless Unicondylar Knee Replacement; a Radiological Study.

Objective: Unicondylar knee arthroplasty (UKA) is a surgical procedure primarily used for the resurfacing of the medial compartment and many studies have previously analyzed the changes taking place on the surrounding osseous tissues after the procedure. The purpose of this study is to investigate the effects of bone strain in the medial tibial metaphysis after a cementless unicondylar replacement. Methods: Patients treated with a cementless UKA between March 2015 and March 2019 was selected for this study. Inclusion criteria were a minimum of 1 and a maximum of 2 years follow-up and presence of standard radiographs of the operated knee at yearly intervals. A total of 109 patients were included in the study. Two lines at a distance of 5 and 7 cm from the lateral tibial eminence were horizontally drawn and the medial cortical thickness and the total cortical distance were measured. A cortex-to-metaphysis (CTM) ratio was established. The increase of density in the metaphysis was analyzed though the "reactive triangle" phenomenon. We initially hypothesized that some degree of increase in sclerosis would be detected in the medial tibial metaphysis and that the increase would be greater in patients with an implant underhanging, since more cancellous bone would come under strain. Results: The CTM ratio showed a decreasing pattern during the 1st post-operative year for all measured levels. An increase in density at the metaphyseal area just below the keel was observed in 58% of patients during the 1st post-operative year and in 80% during the 2nd year. The increase in the density was correlated with the absence of coronal overhanging. Patients with coronal overhanging of the tibial implant showed an increase in CTM ratio. Conclusion: Increased strain after a unicondylar procedure leads to cortical and cancellous bone changes in the proximal tibial metaphysis. These changes depend on the presence or absence of coronal overhanging. [ABSTRACT FROM AUTHOR]