Histopathology and computed tomography of age-associated degeneration of the equine temporohyoid joint.

The research study aims to understand the age-related degenerative changes in horse’s temporohyoid joint. It suggests that such changes might be the basis of temporohyoid osteoarthropathy, rather than infectious causes.

Research Objective

• The cause of Temporohyoid Osteoarthropathy (THO) in horses has remained indefinite. This study’s primary goal is to explore the histopathology of the temporohyoid joint, primarily in aged horses, and juxtapose the joint’s appearance with readings taken through Computed Tomography (CT) and peripheral quantitative CT (pQCT).

Methodology

• pQCT scans of the temporohyoid joints were accomplished from 31 horses, bilaterally. The age of these horses ranged from 1 to 44 years, and all of them were post mortem.
• Images obtained from these scans were sent for grading to two observers who were unaware of the specifics of the images – a process called ‘blinding’. They were graded for the presence of osteophytes, the irregularity of the joint surface, and mineralisation.
• Eight of these heads had priorly undergone CT scans, and the images procured were graded similarly for the shape and density of the proximal stylohyoid bones, bone proliferation around the joint, tympanohyoid cartilage mineralisation and the relationship of the petrous temporal bone to the stylohyoid bone.
• Post this procedure, 16 temporohyoid joints were evaluated histologically.

Results

• The findings of the study highlight a significant association between the severity of joint degeneration and age.
• The changes observed with age include the development of a club shape by the proximal stylohyoid bone, rounding of the synostosis with the petrous temporal bone, and extension of osteophytes from the petrous temporal bone to envelope the stylohyoid head and bridge the joint.
• However, no evidence of osteomyelitis within the petrous temporal bone, stylohyoid bone, or tympanohyoid cartilage was found in any horse.

Conclusions

• The research offers substantial evidence that an increase in the severity of degenerative changes in the horse’s temporohyoid joint is related to age. Furthermore, it suggests that similar changes are often found bilaterally.
• The changes noted resemble, albeit less severe, the alterations reported in horses with THO, implying that degenerative causes, rather than infectious ones, might underpin the aetiology of THO.
• The researchers conclude that future research should focus on examining the histopathology of clinical THO cases.