Histological characteristics of induced membranes in subcutaneous, intramuscular sites and bone defect.

BACKGROUND

The induced membrane technique was proposed as a treatment of large segmental bone defects. The influence of the surrounding tissues on its characteristics remains unknown. It is therefore not known which kind of plastic surgery procedure (muscular or facio-cutaneous flap) would optimize bone osteointegration within a bone defect reconstructed using the induced-membrane technique.

HYPOTHESIS: We hypothesized that membrane characteristics could be influenced by the soft-tissue environment either subcutaneous or muscular.

OBJECTIVE

To evaluate the histological characteristics of poly-methylmethacrylate (PMMA) induced membranes in intramuscular, subcutaneous and bony environment (radius defects) at 2 steps: spacer implantation; secondary bone graft and its subsequent osteintegration after spacer removal.

METHODS

PMMA-induced membranes were obtained in the three sites of 15 rabbits. Subsequent new bone formation was studied in the same environments in 24 other rabbits. Six weeks after the initial implantation, PMMA spacers were replaced with iliac autografts. Animals were euthanized at 2, 4, and 8 weeks postoperatively. Tissue samples were harvested and stained with hematoxylin and eosin. The histological characteristics of the membrane (thickness and microvessel density) and the newly-formed bone (cortical thickness) were quantitatively analyzed.

RESULTS

The membranes in the subcutaneous sites developed quicker, were thicker and had the lowest microvessel density (P<0.01). The membranes in the intramuscular sites developed later and were thinner (P<0.01). The membranes in the osseous defects had the greatest microvessel density (P<0.01). After bone grafting, induced membranes became thinner and their microvessel density decreased substantially, but maintained better in osseous site. The newly-formed bone that developed in the radius defects, had the thickest cortices (P<0.01).

CONCLUSIONS

The evolution of membranes induced in the intramuscular and subcutaneous environments was close to that of the bone defect model, although bone formation appeared weaker.