*2.2. Histopathological Grading*

The IFP histopathological grading was evaluated in 23 ACL IFP and 25 OA IFP (Table 1). It was not possible to perform the histological analysis in 3 ACL samples due to the small volume of the biopsies. Lymphocytic infiltration was substantially absent in all ACL IFP (grade 0) except for one, which was graded as 1. On the contrary, lymphocytic infiltration was present in the majority of OA IFP: 28% of the OA IFP was graded as 1 and 52% as 2. Lymphocytic infiltration was found to be statistically different between the two groups (*p* < 0.0001). Vascularity was increased in OA IFP (median 30.6; 42.9–30.6) compared to ACL IFP (median 8.9; 17.5–7.2) (*p* < 0.0001).



ACL = anterior cruciate ligament; OA = osteoarthritis. Data are expressed as number (%) or median (IQR).
