Return to physical activity and change in body mass index after hypoallergenic medial mobile-bearing unicompartmental knee arthroplasty

BACKGROUND: The primary purpose of the present prospective study was to consecutively analyse the outcomes of the return to sports activity of patients with positive patch tests undergoing a medial mobile-bearing titanium niobium nitride (TiNbN) unicompartmental knee arthroplasty (UKA). The secondary purpose was to ascertain if a higher grade of physical activity leads to a reduction in the body mass index (BMI) of the patients. MATERIAL AND METHODS: Forty-one patients with positive skin patch tests were included in this prospective study. The clinical evaluation consisted of the University of California, Los Angeles (UCLA) activity scale and the High-Activity Arthroplasty Score (HAAS). Each patient was evaluated the day before surgery (T(0)), after 12.37 ± 0.70 months (T(1)), and on the day of the final follow-up, after 67.03 ± 18.2 months (T(2)). Furthermore, the BMI of each patient was analysed before surgery and during the final follow-up. RESULTS: The UCLA and HAAS mean preoperative values ranged from 3.68 ± 1.1.7 and 6.15 ± 0.76 to 6.1 ± 0.76 and 10.34 ± 1.3, respectively, at T(1) (p < 0.0001) and to the final values of 6.34 ± 0.62 and 11.0 ± 8.9, respectively, at T(2) (UCLA: T(2) versus T(1): p = 0.132; T(2) versus T(0): p < 0.0001; HAAS: T(2) versus T(1): p = 0.0027; T(2) versus T(0): p < 0.001). BMI ranged from a preoperative value of 27.97 ± 3.63 to a final value of 26.84 ± 3.11 (p < 0.0001). The only differences within the subgroups concerned patients with BMI ≥ 28, showing a superior HAAS at each follow-up (p < 0.05). A positive correlation was found between BMI and HAAS at T(0) and T(2) (p < 0.05). CONCLUSIONS: This is the first study to evaluate the rate of the return to sports activities and change in BMI following hypoallergenic UKA. The majority of patients reduced their weight following UKA and improved their physical activity, showing outcomes that were comparable to the standard cobalt–chrome (CoCr) prostheses, regardless of gender, age, BMI and implant size. LEVEL OF EVIDENCE: IV – Prospective Cohort Study. Trial registration researchregistry5978—Research Registry www.researchregistry.com SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s10195-021-00598-4.