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Biomechanical Integrity in Craniofacial Surgery: Calvarial Reconstruction in Favorable and Infected Defects with Bone Morphogenetic Protein 2
Zoe M. MacIsaac, MD, Sarah E. Henderson, BS, James Cray, PhD, Gregory M. Cooper, PhD, Alejandro J. Almarza, PhD, Joseph E. Losee, MD
University of Pittsburgh
2012-02-15
Presenter: Zoe MacIsaac
Affidavit:
The material in this abstract has not been published in any scientific journal nor has it been previously presented at a major meeting. This is original work of the research fellow.
Director Name: Joseph Losee, MD
Author Category: Student
Presentation Category: Basic Science Research
Abstract Category: Craniomaxillofacial
How does this presentation meet the established conference educational objectives?
Craniofacial defects pose a longstanding problem for plastic and reconstructive surgeons. Although the current gold standard, autologous graft, may be employed, this introduces donor site morbidity and other complications such as graft loss, while implant-based approaches introduce risk of extrusion and increased risk of infection. rhBMP-2 has shown to reliably provide near-complete radiographic coverage for calvarial defects, but the biomechanical properties of this bone have not been tested. Here we will address this deficiency in the literature, reporting a new measure of the clinical potential of rhBMP-2 regenerated calvarial bone.
How will your presentation be used by practicing physicians in the audience?
The audience will evaluate the efficacy of BMP-2 therapy for bone regeneration in both favorable calvarial wounds and in those complicated by infection, as well as consider the current measures being utilized to determine the clinical potential of bone-regenerative therapies.
OBJECTIVES
Recombinant human bone morphogenetic protein-2 (rhBMP-2) has been shown to be a promising therapeutic modality in inducing near complete radiographic coverage in calvarial defects, but its true potential to produce mechanically sound coverage has yet to be established.
METHODS
12-week old New Zealand white rabbits underwent subtotal calvariectomy. Reconstructions were performed with rhBMP-2 on an absorbable collagen sponge (rhBMP-2/ACS)
Groups:
1.) Favorable: Immediate reconstruction (n=5)
2.) Infected: Bone flaps were inoculated with Staphylococcus aureus. Following 2 weeks, infected wounds/bone flaps were debrided, followed by 2-weeks antibiotic and 4-weeks additional recovery. Final debridement/reconstruction was then performed (n=4)
3.) Native calvarial bone (n=17)
Measured outcomes included biomechanical analysis at 6 weeks. For biomechanical testing, an unconfined compression test was performed on standard-sized sections. Samples were tested at a strain rate of 0.1mm/min to 20% of initial height, followed a 1-hour relaxation, then compression to 1800N. Load and displacements were recorded and normalized into stress and strain. The stress at 20% strain, relaxation stress, and the final strain from crushing to 1800N were compared using a 1-way ANOVA.
RESULTS
Native bone values were significantly higher (p<0.05) when compared to both reconstructed groups for the following (average ± standard deviation, outliers omitted): Stress at 20% (Native 3.57±0.57MPa, Favorable 0.22±0.13MPa, Infected 0.40±0.29MPa), relaxation stress (Native 1.9±1.47MPa, Favorable 0.11±0.06MPa, Infected 0.25±0.17MPa) and final strain (Native 0.56±0.07, Favorable 0.81±0.02, Infected 0.74±0.11).
CONCLUSIONS
Despite providing radiographic coverage, the capacity of the BMP-2-based bone to resist trauma remains suboptimal in both favorable and post-infectious reconstructions after 6 weeks.
