Effects of a bisphosphonate on bone histomorphometry and dynamics in the canine cruciate deficiency model of osteoarthritis

Abstract

Objective: To examine the effect of the bisphosphonate NE- 10035 on bone histomorphometry and bone dynamics in dogs after transection of the anterior cruciate ligament (ACL), and to determine, in a placebo controlled trial, whether treatment modified the severity of pathologic changes of osteoarthritis (OA) in the unstable joint.

Methods: Ten adult male mongrel dogs underwent ipsilateral ACL transection. Five dogs then received daily subcutaneous injections of NE-10035 on 5 days per week for 12 weeks beginning the day after surgery. The other 5 dogs served as concurrent OA controls and received subcutaneous injections of saline on the same schedule. At sacrifice, 12 weeks after ACL transection, the articular cartilage and synovium of both knees of each dog were evaluated grossly and histologically and the water content and uronic acid concentration of the articular cartilage was determined. Fifteen days before sacrifice, each dog was injected with the fluorochrome label calcein. The injection regimen was repeated 10 days after the initial date. At sacrifice, static and dynamic variables of bone formation were assessed and bone resorption was quantified.

Results: In the OA knee of the control group, bone formation and resorption were markedly increased. NE-10035 markedly reduced both formation and resorption of cancellous subchondral bone, but had no effect on osteophyte formation or pathologic changes of OA in the articular cartilage, which were mild in both treatment groups. Water content of the OA cartilage was increased by about 8% in both treatment groups. However, among the controls, the mean uronic acid concentration of the OA cartilage was increased by about 30% in comparison with values for the contralateral knee, while in the NE-10035 treatment group the mean uronic acid concentration of OA knee cartilage was about 15% lower in the active treatment group than in cartilage from the contralateral knee (p = 0.003 for the difference in OA knee uronic acid concentration between the 2 treatment groups, relative to that in the contralateral knee).

Conclusion: The antiresorptive agent employed in this study effectively reduced turnover of subchondral bone in the OA joint, consistent with the coupling of bone formation to bone resorption at that site. Nonetheless, over the 12 week period of the study it had no effect on osteophyte formation, in which bone formation occurs via enchondral ossification and is not linked to bone resorption, and, despite the clear inhibition of bone turnover in the OA knee of the active treatment group, did not affect the severity of cartilage changes of OA. It should be noted, however, that although treatment with this antiresorptive agent did not affect the level of chondropathy, the cartilage changes in both treatment groups were relatively mild and the sample size relatively small. Additional studies with a larger number of animals and a longer period of observation (to increase the severity of pathology) are warranted to determine whether the inhibition of bone turnover and the decrease in proteoglycan concentration that resulted from therapy will affect articular cartilage degeneration in the OA joint.