Uptake of 99mTc- radiolabeled chondroitin sulfate (99mTcCS) in osteoarthritis (OA). Correlation with degree of cartilage degeneration using SPECT and X-ray technics.

Objectives Since a specific radiotracer for imaging of OA is not established yet we investigated uptake of chondrotropic 99mTcCS in dogs suffering from OA and in healthy controls (C).

Methods We used CS (Chondrosulf, IBSA, Lugano, Switzerland) labeled with 99mTc (10-20 MBq/kg bw) by tin method. For in-vivo studies dogs (n=15, castrated males, 4-10 years, 15-51 kg bw) were used. 6 healthy C and 9 with clinical and radiological signs of OA in carpal, elbow and tarsal joints were examined. The tracer was injected i.v. into external cephalic vein. We evaluated uptake in OA joints and correlated it with OA grade I-III according to a radiological scoring. The uptake was monitored at 2, 4 ,6 and 24h using a planar gamma camera (Diacam, MiE GmbH, Germany). For whole body scintigraphy animals were under general anaesthesia, for planar under sedation only.

Results Median target (joint) to background (mid antebrachium or mid lower leg) ratio (T/B) in OA joints after 4, 6, and 24 h was 2.13, 2.08, and 2.41, (n=9) versus 1.54, 1.31, and 1.02 in C (n=6) which was significantly higher (p= 0.04, 0.001 and 0.028). Target to background ratio (soft tissue) (T/S) was 1.42, 2.38, and 1.91 in OA versus 0.98, 1.58 and 0.89 in C joints which was significantly higher at 6 and 24 h (p= 0.004, and 0.008). Uptake in contralateral OA joints using T/B and T/S versus C was also significantly higher (p= 0.0035, p=0.0052). In all OA joints we found a significant positive correlation (r=0.8, n =19) between grade of disease (I-III) and T/B. When matching radiographic (X ray) changes in OA joints (grade II and III) we found also a maximal uptake of 99mTcCS at the specific anatomical site of highest cartilage degeneration.

Conclusions 99mTcCS could be a suitable specific radiotracer in imaging OA. Furthermore, we have shown that it is possible to differentiate cartilage degeneration in OA. As next step, we will start in vivo evaluation in human OA patients.