Structural and functional restitution ad integrum is the final objective of reconstructive bone surgery. Bone grafting is widely used for bone reconstruction. Iliac crest and tibial tuberosity are among the most frequent donor sites for cortical and cancellous bone harvest. The procedure is traumatic and potentially associated with donor site morbidity and difficult bone regeneration. Thus, any treatment modality which reduces donor site morbidity would be beneficial. Bone tissue engineering plays a major role. Application of biodegradable polymeric bone substitutes, particularly a biomaterial based on polyurethane (PU sponge), might be an excellent alternative.

Achieving a good surgical approach and technique after iliac and tibial bone defects creation and reconstruction with different bone substitutes.

24 adult female sheep, 3-4 years old and average 40-50 kg/b.w, randomly distributed by four groups. Group 1 (control): empty defect (no membrane surrounding); Group 2: defects covered with a biodegradable, microporous, thermoplastic (70ºC), poly (L/DL-lactide) 80/20 membrane (no bone substitute). Group 3: defects implanted with a biodegradable polyurethane bone substitute of composition A (composite of polyurethane + nanosize hydroxyapatite, biolized with lecithine), covered with the microporous membrane previously described. Group 4: defects implanted with a polyurethane bone substitute of composition B (composite of polyurethane + nanosize hydroxyapatite, with incorporated cell stimulating agent). Membrane fixation with 2.0 AO titanium screws. All the experiments were done according to the International Standard Organization document ISO 10993-2 (Animal Experimentation). Under general anaesthesia and aseptic conditions, two types of defects were created: 1) a tibial tuberosity monocortical defect (15 x 15 mm) extended to the opposite cortex; 2) an iliac crest tricortical rectangular defect (20 x 40 mm), created with an oscillating saw. Wound closure with poliglatin 910 and silk sutures. In the ilium defect a suction drain was used for 24hs. Post-operative antibiotheraty (Ceporex® (cephalexine 8 days) and pain control Vetalgin® (metamizol 4 days).Intravital bone labelling: calcein green s.c. (5mg/Kg b.w), 8th and 10th weeks; xylenol orange s.c. (90mg/Kg b.w), 20th and 22nd.

Harvest of the specimens at 26th week, under general anaesthesia. Qualitative and quantitative evaluation: 1) teleradiography; 2) contact radiography; 3) Quantitative Computerized Tomography; 4) histomorphology with light microscopy (Giemsa-Eosin) and fluorescent microscopy (calcein green and xylenol orange), and histomorphometry; 5) Indian ink (intra-arterial) per mortem, for vascular evaluation; 6) EDAX analysis, for evaluation of the relative amount of calcium and phosphorus contained in the regenerated bone.

Introduction

SURGICAL ALTERNATIVES TO REDUCE DONOR SITE IATROGENIC BONE MORBIDITY ASSOCIATED TO BONE GRAFT HARVEST. SURGICAL ALTERNATIVES TO REDUCE DONOR SITE IATROGENIC BONE MORBIDITY ASSOCIATED TO BONE GRAFT HARVEST. A SHEEP MODELA SHEEP MODEL. . Preliminar report.Preliminar report. Authors: P Coelho (2,4), C Lavrador(1,4) , R Mascarenhas(1,3,4)J Leitão(2,4), K Gorna (5), S Gogolewski(5)

1.Departamento de Sanidade Animal e Vegetal, University of Évora, Portugal 2.School of Dentistry, University of Lisbon, Portugal3.National Zootechnical Station, Santarém, Portugal4.Biomedical Technologic Institute, Lisbon, Portugal

5.AO Research Institute, Davos, Switzerland

Methods

Gogolewski S, Gorna K, Rahn B, Wieling R, Biodegradable polyurethane cancellous bone substitute promotes bone regeneration in the iliac crest defects, 27th Society for Biomaterials Annual Meeting, Saint Paul, MN, USA, April 25-29, 2001 (Transactions 24, 573, 2001).

Gorna K, Polowinski S, Gogolewski S, Syntheses and Characterization of Biodegradable Poly (-caprolactone urethanes). I. The Effect of the Polyol Molecular Weight, the Catalyst and the Chain Extender on Molecular and Physical Characteristics, J Polym Sci., A: Polym Chem, 40 (1), 156-170, 2002

Gogolewski S, Gorna K, Turner AS, Regeneration of bicortical defects in the iliac crest of estrogen deficient sheep using new biodegradable polyurethane cancellous bone graft substitutes. A pilot study, 48th Annual Meeting, Orthopaedic Research Society, Dallas, TX, USA, February 10-13, 2002.

The surgical technique proved to be adequate. The post operative period didn’t show significant mobility problems. 3 animals had local infections in the ilium region. Two of them were successfully treated with local and systemic antibiotic and one of them rejected the membrane and the PU sponge (animal replaced). Bone heeling is actually under evaluation: macroradiographs and CT Scans were done and histological slides are now being processed.

This project appears as a natural continuation of previous projects directed to the study of bone substitutes for the treatment of critical size bone defects. If the resorbable 3-D polyurethane scaffolds facilitate healing of critical-size skeletal defects, such implants could be used as a bone substitute. The fact The bone substitute is radiolucent, would be additional advantages.

Discussion and Conclusions

References

Results

Aims

Fig 3. Tibial bone defect Fig 4. Macroradiograph of the tibial bone defect with PU sponge

Fig 1. Iliac crest bone defect covered with polylactide membrane Fig 2. Macroradiograph of the Iliac crest

bone defect with PU sponge

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Fig 5. CT Scan of the tibial bone defect with PU sponge composition A, covered with the membrane fixed with titanium screws (three-dimensional view)