Eggshell membrane as a biodegradable bone regeneration inhibitor.

The efficiency of chicken eggshell membranes combined with a minimally invasive small osteotomy procedure of the ulna to accomplish an efficient release of the radius so that it can continue to grow in an unstressed manner was tested in rabbits. Eggshell membranes were extracted from chicken eggs, rinsed, dried and sterilized with ethylene oxide for 24 h. For reactivity testing, four separate subcutaneous pockets were created in 10 rats in the paravertebral region by blunt dissection and eggshell membranes were implanted in two of them. After 1-16 weeks, the implants were retrieved with the surrounding soft tissues and submitted to histological examination. Subsequently, 10 rabbits were anaesthetized and a complete 0.5 mm wide osteotomy was performed in both the right and the left distal ulna. A piece of eggshell membranes was interposed in the osteotomy site of one ulna. The opposite osteotomized ulna was left as a negative control. The rabbits were injected with oxytetracycline at the time of surgery and this was repeated every 7 days for labelling new bone formation. After 1-16 weeks, ulnar osteotomized regions were histologically examined. After histological, fluorescence microscopy and radiological evaluation, we demonstrate here for the first time that eggshell membranes as interpositional material in rabbit osteotomized ulnar experiments acted as an active barrier against bone bridging. The degradation of the eggshell membrane, due to host reaction, appeared sufficiently late to cause the desirable delay of bone healing that is compatible with the time needed for a corrective response.