Incorporation of perforated and demineralized cortical bone allografts. Part I: radiographic and histologic evaluation.

Massive cortical bone allografts have been found to incorporate slowly into host bone. They are subject to complications such as nonunion, fatigue fracture and infection. In an attempt to improve osteoinduction in cortical bone allografts, laser perforated and partially demineralized cortical bone allografts were orthotopically transplanted into the sheep tibia. In this model, mid-shaft tibial bone allografts from out-bred sheep donor animals were prepared by partial demineralization and drilling of 0.33-mm diameter holes with a pulsed, 2.94-microm wavelength Erbium:Yttrium-Aluminum-Garnet laser. Recipient animals of the same out-bred strain were divided into three groups of eight according to the type of cortical allograft used: group 1, fresh-frozen, no treatment; group 2, laser hole grid; and group 3, laser hole grid and partial demineralization. Plain films were taken in two standard views at monthly intervals. Incorporation was evaluated at nine months postoperatively. Longitudinal radiographic data was correlated to a histologic and morphometric evaluation of each bone graft. Computer tomography was used for the latter analysis. Results showed that untreated allografts, although surrounded by a periosteal bone cuff, were poorly incorporated. Partial demineralization lead to excessive resorption of allografts, but little new bone formation. Laser perforation and partial demineralization induced complete incorporation of allografts into the host bone. Based on the results of the radiographic, histologic and morphometric evaluation, the development of laser-perforated and partially demineralized bone allografts was proposed for clinical use.

Incorporation of perforated and demineralized cortical bone allografts. Part II: A mechanical and histologic evaluation.

Laser perforated and partially demineralized cortical bone allografts were orthotopically transplanted into sheep tibiae. This paper reports results of the mechanical testing of the transplanted bones, which was done at nine months postoperatively. Animals were divided into three groups of eight according to the type of cortical allograft used: group 1, no treatment; group 2, laser hole grid; and group 3, laser hole grid and partial demineralization. Thus, changes in flexural rigidity of 24 transplanted whole tibiae were investigated. Starting in the anterior direction at the tibial tuberosity, the flexural rigidity was determined using a nondestructive 4-point bending test. The elliptical distribution of the flexural rigidity was compared to the untreated contralateral control bone of each animal. Mechanical parameters were defined as percentage rates for comparative analysis between groups. Flexural rigidity measurement showed that bones transplanted with untreated allografts were stiffer than contralateral control bones. Partial demineralization of allografts reduced the flexural rigidity of transplanted bones below the level of contralateral control bones. Flexural rigidities of test bones transplanted with laser perforated and partially demineralized allografts were higher than those seen in bones transplanted with partially demineralized allografts. These results were corroborated by the histologic analysis which showed that untreated allografts, although surrounded by a periosteal bone cuff that effectively increased their outer diameter. In contrast, excessive bone resorption was observed in partially demineralized allografts. Laser-perforated and partially demineralized allografts showed histologic evidence of complete incorporation into the host bone. Based on this mechanical evaluation, it was concluded that processing of cortical bone allografts by the combination of perforation and partial demineralization resulted in improved mechanical strength of the transplanted bones as compared to processing by partial demineralization alone.