In the recent study by Wang et al (1), the authors concluded that after anterior cruciate ligament transection (ACLT), changes in subchondral bone begin early and simultaneously with cartilage degradation and that oral glucosamine hydrochloride has a protective effect (1). They based this conclusion on distal femur and proximal tibia bone mineral density measured by dual x-ray absorptiometry (DXA) and on subchondral bone measurements obtained using subchondral trabecular bone turnover testing and histomorphometric techniques. Nonetheless, at least partial bone loss due to immobilization after surgery cannot be ruled out. Also, a favorable effect of glucosamine could have been due to its analgesic properties, facilitating activity, rather than to a direct effect on bone subchondral turnover (2,3).
DXA measurements at other anatomic sites, such as the lumbar spine or the whole femur or tibia, would have helped to exclude the possibility of juxtaarticular bone loss due to immobilization. We have demonstrated (in an experimental model of osteoporosis in rabbits) that bone loss develops to different degrees according to the region analyzed (4,5). We therefore suggest that the authors should have performed DXA at different anatomic regions, and should have obtained sequential measurements.
Wang and colleagues pointed out that cartilage ulcerations were more marked on the caudal (posterior) tibial articular surface. They imputed this finding to biomechanical alterations caused by the instability induced by ACLT. We have described the same findings in experimental rabbit models of osteoarthritis induced either by partial medial meniscectomy or by partial medial meniscectomy plus ACLT (5,6). Although the severity of cartilage deterioration increased when ACLT was performed in addition to meniscectomy, abnormalities followed the same anatomic distribution, being more intense in the posterior articular tibial surface. Since partial medial meniscectomy does not cause gross joint instability, we hypothesized that this distribution of abnormalities on the articular surface is due mainly to the particular biomechanical characteristics of the gait of the rabbit, an animal that usually stands and walks with the knee in a semiflexed position, and not to biomechanical instability secondary to ACL insufficiency.