This study evaluated the effect of a collagen type I /hyaluronate (c/h) implant combined with recombinant human growth and differentiation factor-5 (rhGDF-5) in osteochondral cartilage defects of Göttinger minipigs. In 20 Göttinger minipigs, critical size defects (6.2mm wide and 10mm deep) were created in the medial condyle of both femora. Defects were treated on one side either with the c/h implant alone (n=10) or the c/h implant + rhGDF-5 (n=10), whereas the other side was left empty as an intra-individual control. After 3 and 12 months, 5 animals from each treatment group were killed. The evaluation included macroscopic investigation, biomechanical exploration by relaxation test and semi-quantitative histological scoring using the O’Driscoll score. No macroscopic differences were found between the two treatment groups, neither could any differences be found in semi-quantitative histological scoring. Biomechanical measurement after 12 months showed a significant increase in peak stress in the c/h group compared to empty defects, however, rhGDF-5 supplementation was not found to influence the biomechanical properties compared to controls. Bony cysts were seen throughout the three treatment groups, indicating insufficient bone regeneration. In two animals treated with rhGDF-5, pronounced ossifications within the joint capsule were observed. In contrast, no ossifications were detected in the knees with empty defects or single treatment with c/h implant. In conclusion, the combination of a c/h implant plus rhGDF-5 did not result in better defect regeneration compared to c/h implants alone or even to empty defects in our minipig model. One major problem seems to be the incomplete regeneration of the bony defect when using this device. In further studies, bilayer matrices should be used to address this problem. Due to the small number of specimens in this study, it cannot be resolved whether the ossifications seen in two knees were due to the usage of rhGDF-5 or can be regarded as an independent event. Further data about growth factor interaction should be acquired in animal studies before clinical introduction can be considered.
