Background: Healing of segmental diaphyseal bone defects in animals can be enhanced by covering the defects with resorbable polylactide membranes. Based on the results of bone healing in defects 10 mm long in the rabbit radii, it was suggested that the membrane prevents muscle and soft tissue from invading the defect and maintains osteogenic cells and osteogenic substances within the space covered with membrane, thus promoting new bone formation. However, for bone defects larger than a critical size, bone healing did not occur when covered with polylactide membrane.

Objectives: To investigate and compare bone regeneration with resorbable polylactide membrane and polylactide sponge in a 20 mm bone defect in rabbit radii. The material used was polylactide (L/DL) 80/20/1.

To determine and compare the biomechanical strength of the bone fixation construct with reinforcement by membrane and sponge of such bone defect which were rendered unstable by ulnar osteotomy.

Material & method: 20 mm long diaphyseal segmental defects were made in the left radii of adult New Zealand rabbits. Transverse ulnar osteotomies were made at mid-shaft to make the forearm unstable. The rabbits were divided into 4 groups. In group 1, no fixation of the bone were performed and the limbs were immobilized in a plaster for 8 weeks. In group 2, the bone defects were fixed with 1.5 AO miniplate, with 2 screws on each side of the defect. In group 3, the bone defects were fixed similarly and polylactide membranes were used to cover up the bony defect. In group 4, the bone defects were fixed similarly to group 2 and the defects were bridged by sponge of 20 mm long, 3.5 mm in diameter. In group 5, the bone defects were bridged by sponge similar to group 4 and were also covered by polylactide membrane and similar internal fixation were performed.

Results: In group 1, there was bone healing bridging the bone ends. However, there was marked shortening of the limbs and all the limbs were deformed.

In group 2, there were bone formation at the ends of both proximal bone stumps and distal bone stumps. There was no bone bridging the defect.

In group 3,4, there were bone formation across the defect. There was more bone formation in group 4, i.e. the defects were bridged by sponge.

Conclusion: Polylactide membrane and sponge promote bone regeneration in 20 mm both defects in the rabbit radii model. There was more bone formation when sponged were employed.