Periosteal augmentation of allograft bone and its effect on implant fixation - an experimental study on 12 dogs()

Abstract

Purpose: Periosteum provides essential cellular and biological components necessary for fracture healing and bone repair. We hypothesized that augmenting allograft bone by adding fragmented autologous periosteum would improve fixation of grafted implants.

Methods: In each of twelve dogs, we implanted two unloaded cylindrical (10 mm x 6 mm) titanium implants into the distal femur. The implants were surrounded by a 2.5-mm gap into which morselized allograft bone with or without addition of fragmented autologous periosteum was impacted. After four weeks, the animals were euthanized and the implants were evaluated by histomorphometric analysis and mechanical push-out test.

Results: Although less new bone was found on the implant surface and increased volume of fibrous tissue was present in the gap around the implant, no difference was found between treatment groups regarding the mechanical parameters. Increased new bone formation was observed in the immediate vicinity of the periosteum fragments within the bone graft.

Conclusion: The method for periosteal augmentation used in this study did not alter the mechanical fixation although osseointegration was impaired. The observed activity of new bone formation at the boundary of the periosteum fragments may indicate maintained bone stimulating properties of the transplanted cambium layer. Augmenting the bone graft by smaller fragments of periosteum, isolated cambium layer tissue or cultured periosteal cells could be studied in the future.

Keywords: Allograft bone; autologous; implant fixation; morselized; osseointegration; periosteum..

Fig. (1)

Gap-implant in distal femur. Radiograph taken post mortem. The implant with dimensions is shown.

Fig. (2)

Left: Periosteum harvest from the anterior medial surface of the proximal tibia. Right: Enlarged picture of the fragmented periosteum.

Fig. (3)

Mechanical testing. Left: Push-out test performed with the 3.5 mm thick specimen placed on metal support jig. In the corner, a picture of the implant/bone specimen after the implant has been pushed from the bone, demonstrating in-substance bone failure mode. Displacement velocity 5 mm/min. Right: Load (N) displacement (mm) curve enables calculation of ultimate shear strength (MPa), apparent shear stiffness (MPa/mm), and total energy absorption (KJ/m²)

Fig. (4)

Histology: Representative histologic sections of the control group (A: Allograft) and the intervention group (B: Allograft + periosteum). The sections are from two implants inserted in the same animal. Left side (allograft only): A-1: Overview of implant and bone graft; A-2: Thin fibrous tissue membrane in contact with implant; A-3: Allograft bone chip with ongrowth of new bone in contact with implant. Right side (Allograft + periosteum): B-1: Overview of implant and bone graft. Large island of fibrous tissue is seen in the gap with activity of new bone formation in its vicinity. B-2: Allograft bone chip with ongrowth of new bone in contact with implant; B-3: Magnification of the island revealing solid fibrous tissue. A = Implant, B = New bone, C = Allograft bone, D = Marrow space, E = Fibrous tissue. (Stain, toluidine blue; magnification, x28 (A-1 and B-1), x230 (A-2, A-3, B-2 and B-3).

Fig. (5)

Mechanical testing - Scatter plots showing results from mechanical push-out test. Ultimate shear stiffness, apparent shear strength, and total energy absorption; n(control) = 12, n(periosteum) = 12; [mean (95% CI)].