A new in vivo model for testing cartilage grafts and biomaterials: the 'rabbit pinna punch-hole' model

In this study an animal model was developed for evaluation of the feasibili ty of cartilage grafts. In the cartilage of the external ear of the rabbit multiple holes, 6 mm in diameter, were punched, leaving the adherent skin i ntact. Different experimental groups were evaluated. First, the punch-hole model was validated under various conditions to study spontaneous or perich ondrial initiated regeneration of the cartilage defect. When both cartilage and perichondrium was excised no spontaneous repair of the cartilage defec t was observed. When perichondrium is present, variable patch-like closure of the punch hole was found. As 'golden standard' a punched out piece of ca rtilage was reimplanted directly. This condition showed adequate closure of the punch hole, however, no perfect integration of graft and surrounding c artilage was observed. Secondly, to evaluate the 'punch-hole model' a bioma terial, trabecular demineralized bovine bone matrix (DBM), was implanted an d tested as a scaffold for tissue engineering techniques in vivo and in vit ro. Direct implantation of DBM did not lead to any cartilage formation to c lose the defect. In vivo engineered cartilage, generated by enveloping DBM in perichondrium for 3 weeks, could adequately close the punch hole. When D BM was seeded with isolated chondrocytes in vitro before implantation in th e defect, a highly fragmented graft, with some islets of viable cells was s een. To promote an efficient and reliable evaluation of cartilage grafts a semi-quantitative grading system was developed. Items such as quality, quan tity and integrity of the cartilage graft were included in a histomorpholog ical grading system to provide information about the properties of a specif ic cartilage graft. To validate the grading system, all conditions were sco red by two independent observers. An excellent reliability (R = 0.96) was s een between the observers. In summary, the rabbit pinna punch-hole model is a reliable and efficient method for first evaluation of cartilage grafts. The results can be easily analyzed using a semi-quantitative grading system . (C) 2001 Elsevier Science Ltd. All rights reserved.