Computed Tomographic Appearance of the Temporomandibular Joint in 1018 Asymptomatic Horses: A Multi‐institution Study

Abstract

Published descriptions of nonseptic arthritis of the equine temporomandibular joint (TMJ) are rare and large studies investigating variations in the TMJ for asymptomatic horses are lacking. The objectives of this cross-sectional, retrospective, multi-institutional study were to describe anatomical variations in the TMJ detected using computed tomography (CT) in an equid population asymptomatic for TMJ disease and determine whether these variations were associated with patient signalment, reason for CT examination, or CT slice width. Medical records at eight hospitals were searched for horses that had head/neck CT scans and no clinical signs of TMJ disease. Age, breed, sex, clinical presentation, and CT slice width data were recorded. Alterations in CT contour and density of the mandibular condyles, mandibular fossae, and TMJ intra-articular discs were described for each horse. Generalized logistic regression was used to test associations between anatomical variations and horse age. A total of 1018 horses were sampled. Anatomical variations were found in TMJ CT images for 40% of horses and 29% of joints. These were dichotomous with regard to age. Horses <1 year old commonly had alterations in the shape and density of the mandibular condyle. Older horses commonly had spherical hypodensities within the mandibular condyles consistent with bone cysts; and hyperdense regions of the intra-articular disc consistent with dystrophic mineralization. Findings indicated that TMJ anatomic variations were common in CT images of younger and older horses asymptomatic for TMJ disease. Future studies are needed to more definitively characterize these CT variations using gross pathology and histopathology.

Functional anatomy of the equine temporomandibular joint: Histological characteristics of the articular surfaces and underlining tissues

“…A recent study analyzing more than 1000 equine TMJ by computed tomography has demonstrated a region of discrete linear mineralization in the articular disc (Carmalt et al, 2016), which closely resembles the lateral attractive singular point determined in the present study. Carmalt et al (2016) demonstrated that the appearance of this hyperdense zone is related to increasing age. It is likely that this age-dependent occurrence reflects the accumulation of ongoing mechanical stress, as previously demonstrated in the human TMJ (Jibiki et al, 1999).…”

“…Concomitantly, several studies have been performed to evaluate the suitability and potential relevance of advanced imaging techniques, i.e. radiography (Ebling et al, 2009), computed tomography (Rodríguez et al, 2008;Carmalt et al, 2016), ultrasonography (Rodríguez et al, 2007), magnetic resonance imaging (Rodríguez et al, 2010) and TMJ-arthroscopy (May et al, 2001;Weller et al, 2002). Besides these diagnostic and gross anatomical investigations, functional examinations of the equine masticatory movements have been performed.…”

Managing dysmastication in horses: an update

“…Fortunately, clinical diseases affecting the TMJ of horses appear relatively uncommon and in many instances the significance of TMJ lesions are hard to interpret. In a recent CT study of 1018 asymptomatic horses, anatomical variations were identified in the TMJs of 40 per cent of horses (Carmalt and others 2016). …”

Highlights of recent clinically relevant papers

“…In this multi‐institution retrospective study James Carmalt and colleagues aimed to describe anatomical variations in the temporomandibular joint (TMJ) detected using computed tomography (CT) in an equid population asymptomatic for TMJ disease and determine whether these variations were associated with patient signalment, reason for CT examination, or CT slice width .…”