Complete subchondral bone defect regeneration with a tricalcium phosphate collagen implant and osteoinductive growth factors: a randomized controlled study in Göttingen minipigs

The restoration and reconstruction of osseous defects close to the joint, constitutes a challenging field for reconstructive surgery. A dual-layer implant of β-tricalcium phosphate (TCP) and a collagens I/III scaffold was evaluated in a prospective, randomized comparison in a larger animal model. For this purpose, a standardized osteochondral defect was created in the medial facet of the patellar groove in both stifle joints of Göttingen minipigs. Critical-size osseous defects were either left empty (spontaneous healing; group 1; n = 12) or treated with the two-layer TCP collagen implant (group 2; n = 12). In group 3 (n = 12), additional growth factor mixture (GFM) was supplemented (bone morphogenetic proteins 2, 3, 4, 6, 7, and TGF-β1, 2, 3). Osseous defect regeneration was assessed at 6, 12, and 52 weeks postoperatively (n = 4). Qualitative and quantitative histomorphometric assessment of defect regeneration and bone substitute resorption was conducted by means of light microscopy, fluorescence microscopy, and microradiography. Critical-size defects did not heal spontaneously throughout follow-up (group 1: max. 21.84 ± 2.81% defect area at 52 weeks). The TCP layer of the implant significantly increased the amount of new bone formation with 29.8 ± 9.68% at 6 weeks and 40.09 ± 4.76% at 12 weeks when compared with controls. After 52 weeks, the TCP was almost fully degraded (4.35 ± 3.70%) and the defect was restored with lamellar trabecular bone (31.28 ± 5.02%). Growth factor supplementation resulted in earlier resorption of the TCP implant and faster defect regeneration. The dual-layer TCP collagen implant is suitable to restore subchondral osseous defects. Additional use of GFM increased the resorption of the TCP layer, but did not foster new bone formation.