Intra- and Extra-articular Features of Temporomandibular Joint Ankylosis in the Cat (Felis catus)

Abstract

Temporomandibular joint (TMJ) ankylosis is an uncommon clinical entity in human and veterinary medicine. However, the condition is severely debilitating and is life-limiting if not treated. This study sought to characterize the intra-and extra-articular features of naturally occurring TMJ ankylosis in cats. TMJs from clientowned cats (n ¼ 5) that underwent bilateral TMJ gap arthroplasty were examined and compared with TMJs from healthy, age-matched feline cadavers (n ¼ 2) by cone-beam computed tomography (CBCT), microcomputed tomography (mCT) and histologically. Features of bilateral intra-and extra-articular ankylosis compounded by degenerative joint lesions were identified radiographically and histologically in all affected cats. Features of TMJ 'true' ankylosis included variable intracapsular fibro-osseous bridging, degeneration of the disc and the articular surfaces, narrowing of the joint space and flattening of the condylar process of the mandible. Extra-articular features of TMJ ankylosis included periarticular bone formation and fibroosseous bridging between the mandible, zygomatic arch and coronoid process. In addition, subchondral bone loss or sclerosis, irregular and altered joint contours and irregularly increased density of the medullary bone characterized the degenerative changes of the osseous components of the TMJ. Complex radiological and histological features of both ankylosis and pseudoankylosis were identified that clinically manifested in complete inability to open the mouth.

Temporomandibular Joint Gap Arthroplasty in Cats

“…TMJ ankylosis is defined as fibrous or bony fusion of the mandibular head of the condylar process and the mandibular fossa of the squamous part of the temporal bone. Ankylosis can be further defined as intraarticular, extraarticular, or a combination of both (4,6,9). Intraarticular ankylosis involves destruction of the fibrocartilaginous disc, narrowing of the joint space, and flattening of the mandibular head (9).…”

“…Ankylosis can be further defined as intraarticular, extraarticular, or a combination of both (4,6,9). Intraarticular ankylosis involves destruction of the fibrocartilaginous disc, narrowing of the joint space, and flattening of the mandibular head (9). Extraarticular ankylosis occurs due to encapsulation of the joint or structures near the joint (i.e., the zygomatic arch and coronoid process of the mandible) with little or no involvement within the joint (5,9).…”

“…Intraarticular ankylosis involves destruction of the fibrocartilaginous disc, narrowing of the joint space, and flattening of the mandibular head (9). Extraarticular ankylosis occurs due to encapsulation of the joint or structures near the joint (i.e., the zygomatic arch and coronoid process of the mandible) with little or no involvement within the joint (5,9). Extraarticular ankylosis may be termed "pseudoankylosis" due to mechanical obstruction or fusion of bones surrounding the joint (4,6).…”

“…Extraarticular ankylosis may be termed "pseudoankylosis" due to mechanical obstruction or fusion of bones surrounding the joint (4,6). Often times, severe cases have a combination of intraarticular and extraarticular ankylosis (9).…”

Feline skull injuries: treatment goals and recommended approaches

“…In addition, the articular cartilage of the temporomandibular joint (TMJ) is not made of hyaline cartilage but a fundamentally different fibrocartilaginous tissue, with a fibrocartilaginous disc separating the joint into two non-communicating compartments. 4,5…”