Histologic assessment of age-related changes in the temporomandibular joints of horses

Abstract

OBJECTIVE To describe histologic changes in the temporomandibular joints (TMJs) of horses of various ages. SAMPLE 22 TMJs from cadavers of 11 horses. PROCEDURES Horses were categorized into 3 age groups (group 1, 2 to 10 years old [n = 3]; group 2, 11 to 20 years old [3]; and group 3, > 20 years old [5]). Each TMJ was sectioned into 5-mm slices, preserved in formalin, decalcified in formic acid, and routinely processed for histologic analysis. Joints were systematically assessed by use of previously described methods. Multilevel mixed-effects models were used to examine the data. RESULTS The number of changes was significantly fewer and degree of changes was significantly less within the TMJs of group 1 horses, compared with those of group 3 horses. Comparison among groups revealed that the combination of temporal and mandibular scores for group 1 was significantly lower than for groups 2 or 3. Disk score did not differ significantly between groups 1 and 2, but disk scores of groups 1 and 2 were significantly lower than the disk score of group 3. CONCLUSIONS AND CLINICAL RELEVANCE The assessed lesions were associated with osteoarthritis, and they accumulated in the TMJs as horses aged. In the absence of signs of pain manifested as changes in mastication, behavior, or performance, it would be difficult to determine the point at which accrued pathological changes represented the onset of clinically important osteoarthritis of the TMJs.

Developmental orthopaedic disease and early osteoarthritis of the temporomandibular joint in a 15‐month‐old Quarter Horse filly

“…The hyaline cartilage contained many hypertrophied chondrocytes and relatively small foci of necrosis. The deep layers of the hyaline cartilage were undergoing endochondral ossification, as expected in a horse less than 2 years old (Smyth et al, 2019). There was a relatively large depression in the lateral aspect of the articular surface of the mandibular condyle which varied in thickness (Fig 4d).…”

“…Multiple osteochondral fragmentswithin the depression of the articular surface of the mandibular condyle and the The intra-articular disc contained at least one focus of chondro-osseous metaplasia and three foci of woven and lamellar trabecular bone, which is commonly found in the intra-articular disc of much older horses (Smyth et al, 2019).…”

“…The intra‐articular disc contained at least one focus of chondro‐osseous metaplasia and three foci of woven and lamellar trabecular bone, which is commonly found in the intra‐articular disc of much older horses (Smyth et al., 2019).…”

Animal Models of Temporomandibular Joint Osteoarthritis: Classification and Selection

“…Therefore, such models are often referred to as naturally occurring models. Studies have shown that STR/Ort ( Kumagai et al, 2015 ; Yamashita-Futani et al, 2021 ), STR/IN ( Dreessen and Halata, 1990 ), SAMP8 ( Ishizuka et al, 2014 ), C57BL/6S ( Fukuoka et al, 1993 ), C57BL/6J ( Cui et al, 2020 ), C57BL/6NCrSlc ( Ukita et al, 2020 ), ICR ( Silbermann and Livne, 1979 ; Livne and Silbermann, 1986 ) mice, Dunkin-Hartley guinea pigs ( Wu et al, 2016 ), and horses ( Smyth et al, 2019 ) all manifest OA-like lesions with increasing age, among which multiple subtypes of SAM mice can develop OA-like lesions in TMJ ( Chen et al, 1989 ) ( Table 5 ). Yamashita-Futani et al (2021) found in STR/Ort mice that the production of elastin-digested peptides was related to the upregulation of pro-inflammatory mediators, such as IL-6 and MMP-12.…”

Equine Models of Temporomandibular Joint Osteoarthritis: A Review of Feasibility, Biomarkers, and Molecular Signaling

“…Osteoarthritis (OA) stands out as the most prevalent degenerative disease affecting the temporomandibular joint (TMJ), manifesting spontaneously in humans [ 1 ] and various animal species, such as mice [ 2 , 3 ], guinea pigs [ 4 ], and horses [ 5 , 6 , 7 , 8 , 9 , 10 ]. TMJ OA is characterized as a chronic disease marked by degenerative alterations in cartilage, accompanied by reparative processes in the surrounding tissues [ 1 , 11 , 12 , 13 , 14 ].…”