Page 259 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

234 CHAPTER 1

VetBooks.ir it is unclear whether disease of the joint caused the 1.443
dental changes or vica versa.
Pain or dysfunction of one or both TMJs inter-
feres with the normal movements of the mandibles,
which are vital for prehension and mastication of
food. Over time the abnormal dental wear will
lead inexorably to pronounced tooth abnormalities,
which may further interfere with feeding. The mas-
seter muscle atrophy seen with TMJ disease may be
due to reduced movement of the mandibles or from
damage to the mandibular branch of the trigeminal
nerve medial to the temporal condyle. Head shaking,
head tilts and behavioural changes have also been
attributed to TMJ disease.

Clinical presentation
Disease of the TMJ is often diagnosed only at an
advanced stage. Affected horses show marked prob-
lems when feeding (slow feeding, quidding, food
pouching in cheeks), masseter muscle atrophy and
weight loss despite a good appetite. Dental abnor- Fig. 1.443 Cross-sectional CT image of bilateral
malities and soft-tissue trauma may be identi- osseous changes to the mandibular condyles of the
fied on careful oral examination using a mirror or temporomandibular joint.
oral endoscope. When the mandibles are passively
manipulated there may be a reduced range of move-
ment and possibly resentment by the horse. Where widening and a mixed pattern of periarticular lysis
there is sepsis of the TMJ there may also be pain on and sclerosis. Unfortunately, radiographic exami-
direct palpation of the joint capsule. Luxation of the nation is limited to the lateral aspect of the joints
joint is caused by trauma and there may be concomi- and more central and medial lesions are likely to be
tant signs (wounds, fractures, draining tract). overlooked. Transcutaneous ultrasonography allows
examination of the meniscus, joint capsule, support-
Differential diagnosis ing ligaments and the articular cartilage. However,
It is possible to overlook a TMJ abnormality as as with radiography, the examination is limited to
affected horses have obvious dental abnormalities the lateral aspect of the joint.
that may be thought to account for the clinical signs. Nuclear scintigraphy, used in conjunction with
Dysphagia can be caused by oesophageal obstruc- radiography, may be useful in the diagnosis of osseous
tion (choke), retropharyngeal masses, mandibular abnormalities associated with the joint. CT exami-
or maxillary fractures, guttural pouch disorders, nation, however, provides identification of disease
equine protozoal encephalitis, botulism and other throughout the entire joint capsule, some of which may
neurological conditions. easily be missed by conventional imaging modalities
(Fig. 1.443). MRI also provides a three-dimensional
Diagnosis examination of the joint and offers a more detailed
Radiography may allow identification of bone prolif- examination of the soft- tissue structures than CT,
eration and focal bone lysis associated with OA, and a but at present requires a general anaesthetic and is less
number of specific oblique views have been described commonly available. Diagnostic local anaesthesia of
to reduce superimposition of adjacent structures. one, or both, of the joint compartments may also be
Septic arthritis, as elsewhere, appears more aggres- useful in patients showing signs of quidding or pain
sive radiographically than OA, with joint space on manipulation of the mandible.