Magnetic resonance imaging of the rabbit knee: detection of cartilage proteoglycan degradation.

Intra-articular (i.a.) injection of papain causes a reversible loss of proteoglycan in intact rabbit knees. Twelve rabbits were scanned with magnetic resonance imaging (MRI) at 0, 24, 48 and 72 hours after 5 units of papain i.a. in a 1.5 Tesla Signa with a three inch surface coil using spin echo sequence. Total cartilage thickness in proton density images was 1.08 +/- 0.09 mm prior to papain injection. The magnetic resonance images showed a reduction in articular cartilage thickness in papain-treated rabbit femurs at 24 hours to 0.69 +/- 0.18 mm and partial restoration by 72 hours to 0.77 +/- 0.21 mm.