Temporomandibular joint osteoarthritis (TMJ‑OA) is characterized by progressive loss of articular cartilage and remodeling of subchondral bone in the mandibular condyle. The TMJ is lined by fibrocartilage rather than hyaline cartilage, making repair biology and mechanical behavior distinct from other diarthrodial joints. Preclinical models that replicate the anatomical, biomechanical, and physiological features of the human TMJ are needed to evaluate implantable regenerative therapies before clinical translation. Small animal models offer mechanistic insight but have limitations in joint size, cartilage thickness, and loading that restrict translational evaluation of human‑scale biomaterials and surgical approaches. Large animals, including pigs, sheep, and goats, better approximate human TMJ dimensions and loads; among these, goats offer practical advantages in surgical accessibility and procurement of skeletally mature animals.
The study aimed to establish a reproducible large‑animal model of osteochondral defects (OCDs) in the goat mandibular condyle suited to test regenerative strategies targeting the osteochondral interface in TMJ‑OA. Specifically, the authors compared a novel retrograde tunnel defect with a conventional anterograde superior defect to determine healing outcomes, degeneration of adjacent fibrocartilage, and relative procedural advantages for future regenerative studies.
Skeletally mature goats were used to create critically sized OCDs in the TMJ condyle. Two defect geometries were produced surgically: a tunnel defect drilled retrograde from the posterior condylar cortex to the articular surface, and a superior defect drilled anterograde from the articular surface into the subchondral bone. The tunnel configuration was designed to minimize disruption of the articular disc attachments and reduce manipulation of the joint while permitting larger defects. The superior approach represents the commonly used method in previous caprine TMJ OCD work.
Defects and joint structures were monitored with in vivo computed tomography (CT) imaging and evaluated by histological analysis at defined postoperative time points. Histology included assessment of defect filling, bone remodeling, and the state of the adjacent articular fibrocartilage. Degenerative changes in the cartilage were graded using a modified OARSI (Osteoarthritis Research Society International) scale appropriate for the TMJ fibrocartilaginous surface.
Both defect types behaved as critically sized OCDs: at up to 60 days after surgery neither the subchondral bone nor the overlying articular cartilage showed complete regeneration. Imaging and histology demonstrated incomplete subchondral bone healing. The defect sites were predominantly occupied by fibrous tissue throughout the lesion, while woven bone formation was confined to the peripheral regions of the defects. No evidence of restoration of normal zonal cartilage architecture or hyaline‑like cartilage repair was observed within the follow‑up interval reported.
The articular fibrocartilage adjacent to both defect types showed signs of arthritic degeneration as measured by the modified OARSI scoring. Observed changes included loss of the normal zonal structure of the condylar surface—specifically disruption or loss of the fibrous, transition, and cartilaginous layers—consistent with OA‑like degeneration. These degenerative features support the model’s capacity to reproduce pathological changes relevant to TMJ‑OA.
Healing outcomes were similar between the two defect geometries: both exhibited impaired bone repair, fibrous filling, peripheral woven bone, and adjacent cartilage degeneration. The tunnel defect produced comparable OA‑like changes while offering procedural differences relevant to experimental design. The authors note that the tunnel approach can create larger defects and achieves similar pathological endpoints without extensive manipulation of intra‑articular structures.
The tunnel defect is presented as favorable for future regenerative research because it preserves disc attachments and minimizes direct surgical disturbance of the TMJ. These features reduce operative handling of intra‑articular tissues and may simplify implantation of regenerative constructs, particularly larger or more complex biomaterials. Given the similar impaired healing and OA‑like degeneration produced by both approaches, the tunnel model provides a practical, translationally relevant platform for testing osteochondral repair strategies in a caprine TMJ.
Reported findings reflect assessments up to 60 days post‑surgery; longer time points were not described in the source and therefore longer‑term outcomes and potential delayed repair were not reported. Specific procedural details, sample sizes, statistical comparisons, and potential perioperative complications beyond the histological and imaging outcomes were not restated here beyond what the source presented. As with any animal model, anatomical and functional differences between goat and human TMJs should be considered when extrapolating to clinical application.
This work establishes a reproducible caprine OCD model in the TMJ condyle that yields critically sized lesions with incomplete subchondral bone healing, fibrous defect filling, peripheral woven bone, and OA‑like degeneration of adjacent fibrocartilage within 60 days. The tunnel defect offers practical surgical advantages—disc preservation and reduced joint manipulation—while producing comparable pathological outcomes to the superior defect, making it a recommended approach for studies of implant‑based osteochondral regeneration. Overall, the model provides a practical preclinical platform for evaluating candidate regenerative therapies aimed at condylar repair in TMJ‑OA.