Induced membranes—summary
Introduction
The implantation of a methylmethacrylate bone cement spacer into the area of a bone defect has been noted to result in the creation, or induction, of a pseudosynovial membrane around the methylmethacrylate spacer. This so-called induced membrane is created as a result of the body′s reaction to a foreign body. Specifically, methylmethacrylate appears to incite a foreign body response from the surrounding soft-tissue envelope that subsequently generates a membrane to encapsulate the methylmethacrylate. Unlike the response seen with textured implants, the smooth methylmethacrylate spacer results in rare villous hyperplasia and hardly excites any histological reactions to foreign material. Recent clinical and basic science research has shown that the induced membrane may have several substantial advantages for the management of bone defects, particularly those that occured secondary to trauma or infection. These advantages can be divided into three different categories: mechanical, histological, and biochemical.
Mechanical
The initial role of the methylmethacrylate spacer is to physically occupy the defect created by the resection or traumatic loss of bone in a limb. This provides a space, or pocket, available for later bone grafting by eliminating fibrous tissue ingrowth into the region of the bone defect. Once the bone graft has been placed into the space previously occupied by the methylmethacrylate, the membrane can be sutured closed over the top of the graft. The obvious advantage of this procedure is that it maintains the graft in the position the surgeon intended it to be in, preventing displacement.
Histological
Similar to the membrane found at the bone-cement interface of a total hip replacement, the induced membrane demonstrates a synovial-like epithelium with few inflammatory cells. The membrane tissue is composed of numerous elongated fibroblast-like cells embedded within a collagenous matrix. The collagen fibers appear to be arranged parallel to the long axis of the bone. Most importantly, the membrane is a highly vascularized tissue with the vessels running perpendicular to the long axis of the bone toward the defect. This increased vascularity provides significant blood supply to the bone graft after implantation. Using different staining techniques, it has also been shown to possess a large amount of osteoblast activity.
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