LAUSR

Purpose Previous clinical studies have shown the effectiveness of bone repair using two-stage surgery called the induced membrane (IM) technique. The optimal wait before the second surgery is said to be 1 month. We have been successfully performing the IM technique while waiting an average of 6 months to carry out the second stage. We hypothesised that the IM maintains its beneficial capabilities, even at a later second stage, and that there is no relation between the speed of bone union and the wait between the first and second stage. We sought to explore the biological properties of ‘older’ IMs sampled to substantiate our clinical observations. Methods Thirty-four patients with a critical size defect were treated with the IM technique. In seven of these patients, pieces of the IM were collected 4.2–14.7 months after the first surgery. IM-derived cell phenotype and osteogenic potential were investigated using in vitro studies ( n  = 4) while IM nature and function were investigated by histology and immunohistochemistry ( n  = 3). Results The median wait before the second surgery was 5.8 months [range 1.2–14.7] and bone healing occurred at 7.6 months [range 2.5–49.9] for 26 patients. IMs aged 4.2–14.7 months contained mesenchymal stromal cells with in vitro osteogenic potential and corresponded to a multipotent tissue with osteogenic and chondrogenic capabilities contributing to osteogenesis over time. Conclusion This preliminary study suggests the IM retains its powerful osteogenic properties over time and that waiting longer between the two surgeries does not delay bone union.