[Experimental study on the causes of spontaneous osteogenesis of Masquelet technique induced membrane].

Objective: To investigate the causes of spontaneous osteogenesis of Masquelet technique induced membrane.

Methods: Forty-two male Sprague-Dawley rats aged 7-9 weeks were selected to establish a critical-sized bone defect of the right middle femur model. Then the rats were randomly divided into 4 groups, with 12 rats in groups A-C and 6 rats in group D. The bone defects in groups A-C were filled with vancomycin-loaded polymethyl methacrylate bone cement spacers. Then the Kirschner wires were used for intramedullary fixation in groups A and B, and the bone cement was used to connect the bone cement spacers and the bone ends in group B. The steel plate was used to fixation in group C. The bone defect in group D was only fixed with steel plate as a blank control group. The general condition was observed after operation. At 5 weeks after operation, 6 rats in groups A-C were selected for STRO-1 immunohistochemical staining to observe the content of mesenchyme stem cells (MSCs) in the induced membrane (STRO-1 ⁺ cells). At 12 weeks after operation, the remaining rats in groups A-D were taken for X-ray observation, gross observation, and histological observation (HE, safranin O-green staining) to observe the spontaneous osteogenesis of the membrane.

Results: All rats in the 4 groups survived until the completion of the experiment. At 5 weeks after operation, the immunohistochemical staining showed that group B was negative, while the contents of MSCs in the induced membrane in groups A and C were 14.20%±1.92% and 5.00%±0.71%, respectively, with a significant difference ( P<0.05). At 12 weeks after operation, group A showed that the new bone formed at the osteotomy site and growth towards the center of the bone defect, with an average length of 3.1 mm on one side; and the presence of bone, cartilage lesions, fibers, and a small amount of neovascularization were observed in the induced membrane. Group C only had a small amount of new bone at the osteotomy site, and a small amount of neovascularization in the induced membrane. Groups B and D did not have any new bone, but bone resorption or atrophy at the osteotomy site.

Conclusion: Although the Masquelet technique induced membrane has osteogenesis, the key factor for the spontaneous osteogenesis is the bone marrow overflow from the bone marrow cavity providing MSCs. The spontaneous osteogenesis of the induced membrane belongs to endochondral ossification.