C3AR1 and obesity due to melanocortin 4 receptor deficiency: Although we have not seen any differences in this cross-sectional study in the percentage of adipocytes in the DSST after ACL injury and MT, the role of obesity has clearly been documented in the development of PTOA, for adipocytes do express C3aR1 and C5aR1 on their surface; in addition, as the BMI in this study patients is in the higher range, we don’t rule out that adipocytes also generate complement factor D (a.k.a. adipsin), especially as lipodystrophic mice do not develop spontaneous or PTOA (49–52).