Right knee joints were injected with 1 U papain solution and left knee joints served as internal controls. After 3 days, patellae with surrounding tissue were isolated and transferred to RPMI medium supplemented with solRII (10 μg/ml). MMP-3 and -13 RT-PCR products were quantified using PicoGreen. GAPDH levels were used to correct for the amount of template used. For left and papain-injected knee joints the mRNA levels of the nontreated patellae were stated as 100%. Each PCR was performed in triplicate and results were averaged. Results were analyzed via a Student t test. Shown is the mean ± SD.