Processing of whole femoral head allografts: a method for improving clinical efficacy and safety

Femoral heads removed during primary hip replacement surgery are widely utilised as a source of allograft bone. Despite evidence that processing these grafts to remove blood and marrow elements improves both the clinical performance and safety of these allografts, many are transplanted without any processing being applied at all. The goal of this study was to investigate the efficiency of an allograft processing protocol which incorporates pasteurisation, (3 h, 56-60 degrees C) centrifugation, (1850g, 2 x 15 min, 40 degrees C) sonication, and repeated washing in warm (56-60 degrees C, 19 h) distilled, sterile water to remove blood and marrow elements from the graft. The protocol also involves applying heat treatment to the grafts which has been demonstrated to inactivate many pathogenic viruses. Following the processing procedure, the grafts are lyophilised and sterilised with ethylene oxide gas. The amount and rate of removal of 4 different components of blood and marrow from 6 whole femoral head allografts were measured. These were lipid, soluble protein, elastase and chloride ions. Lipid removal was assessed gravimetrically by solvent extraction of dried samples, soluble protein by the Bradford assay, elastase by radioimmunoassay and choride ion content by a modified commercially available colorimetric assay. Removing lipid from grafts has been shown to increase the rate of incorporation when the graft is used clinically. Elastase was studied as a marker of leukocyte removal, as evidence suggests the majority of potentially infective transmissible spongiform encephalopathy (TSE) activity resides in a sub-population of leukocytes. Soluble protein was studied as a marker of plasma removal, as a smaller amount of TSE infectivity resides here. Chloride removal was measured as this is a necessary pre-requisite to terminal sterilisation with ethylene oxide. The results showed that the protocol removed 74.5% (range: 68.0-90.8) of the lipid content, 96.4% (range: 94.8-98.4) of the soluble protein content, 97.7% (range: 97.1-100) of the elastase content and 98.8% (range: 98.0-99.2) of the chloride ion content. We have shown that processing designed to improve the clinical efficiency and safety of bone allografts can be accomplished without compromising the structural and biological properties of the graft.