Effect of Bone Morphogenetic Protein on Experimental Carapace Defects in Turtles
Anecdotal reports suggest that bone morphogenetic protein (BMP) may be useful for treating chelonian shell defects, but controlled studies are lacking. Under general anesthesia, 2-cm-diameter, full-thickness carapace defects were created bilaterally in the second costal scute of 12 red-eared slider turtles (Trachemys scripta elegans). Defects were managed for 10 days by using negative pressure wound therapy, followed by bandages. Three weeks postoperatively, one defect on each turtle was injected with 0.1 mg of recombinant human BMP-2 carried in bovine type 1 collagen, whereas the contralateral defect was injected with only collagen. Four turtles were euthanized at each of three time points (2, 4, and 12 wk posttreatment). Defects were evaluated by gross appearance, computed tomography, and histology. No difference was noted between the treated and untreated defects. Nonetheless, histologic assessment provided novel characterization of the progression of chelonian shell healing under controlled conditions. Examination indicated that margins of exposed carapace bone underwent osteonecrosis. Re-epithelialization and osteoclastic activity undermined necrotic bone, which was eventually sloughed. Inflammation of the deep wound bed, including the pericoelomic membrane, resolved with completion of re-epithelialization and was associated with the transition of granulation tissue into mature fibrous connective tissue. Osteoid and woven bone formed along remodeled margins and began to bridge the wound along its deep surface within this fibrous connective tissue. Although this study did not demonstrate BMP efficacy, the surgical model described here may be useful for future studies of chelonian shell repair and healing, including studies that evaluate alternative formulations of BMP.Abstract
(A) Circular masonry bit used to create the carapace osteotomy site in red-eared slider turtles (Trachemys scripta elegans). (B) Osteotomy in progress with saline irrigation. (C) Completed osteotomy incision before bone excision. (D) Completed bilateral osteotomy immediately postoperatively.
Red-eared slider turtle (Trachemys scripta elegans) after carapace osteotomy. Rubber stoppers have been affixed over the site to allow for negative pressure wound therapy.
Representative carapace osteotomy sites of red-eared slider turtles (Trachemys scripta elegans). (A) Ten days postoperatively. (B) Three weeks postoperatively. (C) Protective mesh has been applied after injection of bone morphogenetic protein (BMP). (D) Two weeks post-BMP (5 wk postoperatively). (E) Four weeks post-BMP (7 wk postoperatively). (F) Twelve weeks post-BMP (15 wk postoperatively).
Transverse computed tomography images of carapace osteotomy sites of red-eared slider turtles (Trachemys scripta elegans). Bone morphogenetic protein (BMP)–treated images are on the right; carrier-only images are on the left. (A and B) Two weeks post-BMP. (C and D) Four weeks post-BMP. (E and F) Twelve weeks post-BMP. Focal darker regions are artifactual.
Transverse computed tomography images of carapace osteotomy sites of red-eared slider turtles (Trachemys scripta elegans). (A) Two weeks post–bone morphogenetic protein (BMP), showing margin of bone necrosis (white arrow). (B) Twelve weeks post-BMP showing persistence on necrotic bone margin, with limited boney ingrowth emanating from the bone at the defect margins (white arrows). Focal darker regions are artifactual.
Histologic images of the margins of carapace osteotomy sites of red-eared slider turtles (Trachemys scripta elegans). (A–C) Two weeks post-BMP. (D–F) Four weeks post-BMP. (G–I) Twelve weeks post-BMP. In all images, the wound defect is oriented to the left and the healing wound margin is on the right. Features shown are necrotic bone (NB), re-epithelialization (RE), osteoclastic activity (OC), osteoblast formation (OB), osteoid formation (OS), and woven bone formation (WB). Images in (C), (F), and (I) are nondecalcified sections stained with Goldner's trichrome; all other slides are stained with H&E. Magnifications are × 20 for the first row (scale bar, 0.9 mm) and × 200 for the second and third rows (scale bar, 100 μm).
Histologic images of the margins of carapace osteotomy sites of red-eared slider turtles (Trachemys scripta elegans). These sections are of soft tissues comprising the deep wound margin collected at 2, 4, and 12 wk postwounding. (A) At 2 weeks, the wound bed is covered by a row of multinucleated giant cells (MN) underlying heterophilic exudate (HE). There is residual hemorrhage (H) within the granulation tissue. (B) By 4 wk, the hemorrhage and inflammation have resolved and wound bed is re-epithelialized (RE) covering residual granulation tissue containing numerous small blood vessels (BV). (C) At 12 wk, there is reduced vascularity, the re-epithelialized surface is covered by epithelium with thick stratum corneum (SC), and mature collagen bundles (C) have formed. Nondecalcified sections stained with Goldner's trichrome (× 100 magnification). Scale bar, 150 μm.
