Experimental research on the change of subchondral bone microstructure in early stage of mouse osteoarthritis

Objective To establish a mouse model of osteoarthritis (OA) and study the bone microarchitecture and bone metabolism of tibial subchondral bone in early stage of OA. Methods The mouse model of post-traumatic osteoarthritis (PTOA) with anterior cruciate ligament (ACLT) was established by using c57 mice. The Sham operation group served as the control group. All mice were fed with conventional diet. All mice were sacrificed after 4 weeks. The degeneration of knee joint was observed by HE staining and Safranin O-Fast Green staining. The number of osteoclasts was counted by TRAP staining. Micro CT was used to analyze the quantitative parameters of the microstructure of tibia subchondral bone in mice. Serum levels of bone resorption biomarker CTX I and cartilage degeneration marker CTX II were determined. Results After ACLT 4 weeks, the average score of OARSI in ACLT group was 3.2, which was higher than that in Sham group, and the joint degeneration occurred in mice, presenting the pathological characteristics of early OA. Compared with the sham operation phase, the total subchondral bone volume (TV) of ACLT group was 4.72 mm3, increased by 13.6%; the bone trabecular resolution (Tb.Sp) was 0.130 and 0.154 mm, respectively, and the ACLT group also increased by 18.8%; the bone volume/tissue volume (BV/TV) was 0.470 and 0.294, respectively, and the ACLT group decreased by 48.9%; the bone trabecular thickness (Tb.Th) was 0.162 and 0.083 mm groups, ACLT decreased by 37.5%. Trap staining showed that the number of osteoclasts per unit volume in ACLT group was 72, which was significantly higher than that in sham operation group. The CTX I of mice in the sham operated ACLT group and sham operated group were 20.9 ng/ml and 18.29 ng/ml, with an increase of 48.9% in the ACLT group; the CTX II of mice in the ACLT group and sham operated group were 35.5 ng/ml and 28.6 ng/ml, with an increase of 24.1% in the ACLT group. Conclusion ACLT Mouse model can successfully construct early OA, which confirms the early loss of osteochondral bone and the pathological changes of osteoclast activation in OA, and provides a new specific target for the treatment of OA. Key words: Anterior cruciate ligament; Osteoarthritis; Cartilage, articular; Osteoclasts