The Mechanism of Action of Induced Membranes in Bone Repair

Abstract

Inducement of foreign-body granulation tissue is a relatively novel therapeutic modality in bone repair. A two-stage bone reconstruction method, known as the Masquelet technique, combines inducement of a granulation tissue membrane and subsequent bone autografting as a biphasic technique allowing reconstruction of large bone defects. In light of their already well-characterized osteogenesis-improving capabilities in animals, we performed this translational study to investigate these membranes in patients. Fourteen patients with complicated fractures and bone defects were randomly selected for this study. Biopsy samples of foreign-body-induced membranes were collected at different time points during scheduled surgical procedures. The membranes were co-cultured with mesenchymal stromal cells, and differentiation into the osteoblastic lineage was assessed by measuring alkaline phosphatase activity, aminoterminal propeptide of type-I procollagen (PINP) production, and Ca2+ concentration. Histological characteristics were evaluated with image analysis. Quantitative reverse transcription polymerase chain reaction was used to measure vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), and type-I collagen (Col-1) expression. The induced membranes were characterized histologically by maturating vascularized fibrous tissue. The vascularization was greatest in one-month-old samples and decreased to <60% in three-month-old samples. One-month-old membrane samples had the highest expression of VEGF, IL-6, and Col-1, whereas two-month-old membranes expressed <40% of the levels of the one-month-old membranes. Specific alkaline phosphatase activity, PINP production, and Ca2+ concentration were increased in co-cultures when a membrane sample was present. In cultures of one-month-old membranes, PINP production was more than two times and Ca2+ deposition was four times higher than that in cultures of two-month-old membranes. The induced membranes have osteogenesis-improving capabilities. These capabilities, however, appear to decrease over time. We speculate that the optimal time for performing second-stage surgery may be within a month after implantation of foreign material.