Association of Skin and Cartilage Variables with Composite Graft Healing in a Rabbit Model

Importance: Composite grafting in nasal reconstruction involves transplanting auricular chondrocutaneous grafts, but the optimal design of these grafts is unknown. Objectives: To investigate the ideal ratio of skin to cartilage as well as study the importance of the perichondrial attachment for graft survival. Design, Setting, and Participants: A New England white rabbit model was used in this study, performed at the Laboratory for Animal Research at University of Kansas Medical Center from January 25 to March 18, 2016. Four varying designs of chondrocutaneous auricular grafts were transplanted to dorsal back defects, with a total of 10 grafts per treatment arm completed. The following 4 chondrocutaneous circular grafts were designed: group A, 1.5-cm diameter graft of equal skin to cartilage ratio; group B, 2.0-cm diameter skin and 1.5-cm diameter cartilage; group C, 1.5-cm diameter skin and 2.0-cm diameter cartilage; and group D, 1.5-cm diameter skin and cartilage separated and placed back together in a layered fashion. Grafts were observed until postoperative day 21, harvested, and evaluated with visual observation as well as histopathologic assessment. Main Outcomes and Measures: Visually graded areas of survival were marked by 2 blinded academic facial plastic surgeons and calculated for approximate survival. Hematoxylin-eosin-stained, paraffin-embedded 5-μm slides were evaluated for overall survival rate, rate of cartilage necrosis, and mean vessel density per high-power field. In both cases, observers were blinded as to the study group. Results: Visual assessments of the 5 female rabbits showed significant agreement between surgeons and consistency, with a Spearman coefficient of 0.84 and an intraclass correlation of 0.98. Group D (skin and cartilage separation) was visually graded to have significantly decreased mean survival (45.4%; 95% CI, 23.3%-67.4%) compared with group A (mean survival, 97.4%; 95% CI, 94.8%-99.9%; P <.001), group B (mean survival, 87.6%; 95% CI, 69.9%-100%; P =.004), and group C (mean survival, 82.1%; 95% CI, 66.0%-98.1%; P =.008). Histopathologic assessment revealed that group D again showed significantly inferior overall survival, increased cartilage necrosis, and decreased mean vessel density compared with group A. Group C additionally showed significantly decreased cartilage survival compared with group A (65% vs 0%; P <.001) and group B (65% vs 35%; P =.02). Conclusions and Relevance: These results represent preliminary evidence that the attachment of skin to perichondrium in a composite graft plays an important role for graft survival. Clinicians performing nasal reconstruction with chondrocutaneous composite grafts should consider preserving attachments at this junction to improve graft survival. Levels of Evidence: NA.