Goat temporomandibular joint osteochondral defects for future regenerative studies of osteoarthritis-like degeneration.

Temporomandibular joint osteoarthritis (TMJ-OA) is a type of temporomandibular disorder (TMD) characterized by structural changes in the joint due to the gradual degeneration and loss of articular cartilage, as well as remodeling of the underlying bone. The complexity of these structural and functional changes underscores the importance of evaluating regenerative therapies in large- animal models that closely mimic human joint physiology prior to clinical translation. Considering that TMJ cartilage consists of fibrocartilage, dissimilar from hyaline cartilage found in other diarthrodial joints, and that osteochondral defects (OCDs) are reproducible injuries for developing regenerative therapies for osteoarthritis (OA), this study aimed to establish a suitable large-animal model of OCD in the TMJ condyle of goats. We surgically generated and compared two types of OCDs, a novel tunnel defect drilled retrograde from the posterior aspect of the condyle to the articular surface and a superior defect drilled anterograde. Live computed tomography (CT) and histological assessment showed that the defects were critically sized, with incomplete subchondral bone healing and no cartilage regeneration up to 60 days post-surgery. All defects were filled with fibrous tissue throughout and woven bone at the periphery. The articular fibrocartilage surrounding both defect types displayed signs of arthritic degeneration per the modified OARSI scale, including the loss of the zonal structure (fibrous, transition, and cartilaginous layers). Given similar impaired healing, the tunnel OCD is favorable to preserve the disc attachments and minimize surgical manipulation of the TMJ while creating larger defects and OA-like degeneration in the goat. In summary, this study presents a practical preclinical goat model for evaluating future regenerative therapies targeting TMJ-OA.