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

Long-Term Outcome of Horses Undergoing Unilateral Mandibular Condylectomy and Meniscectomy for Temporomandibular Joint Disease

Background

There are no reports describing the long-term outcome of sport horses undergoing unilateral mandibular condylectomy with meniscectomy (UMC) for treatment for severe temporomandibular joint (TMJ) disease (TMD). Whether horses undergoing UMC require a specialized diet, can return to riding with a bit, or return to intended function after surgery is unknown.

Objective

To determine the long-term outcome of horses undergoing UMC for treatment of severe TMD.

Study Design

A multi-institutional, retrospective study.

Methods

Medical records obtained from seven equine referral hospitals of horses with severe TMD that underwent UMC were reviewed. Details regarding the presenting complaints, results of clinical examination, findings of diagnostic imaging, surgical technique, and outcome (including long-term follow-up with an owner questionnaire) were recorded.

Results

Eleven horses fit the inclusion criteria. Three had severe idiopathic osteoarthritis, and eight had confirmed septic osteoarthritis of the TMJ. The most common post-operative complications were drainage and peri-incisional swelling (n = 5). One horse developed a hematoma at the surgical site because the facial artery was inadvertently transected during the approach, causing the condylectomy to be postponed. All horses were discharged alive from the hospital, and 10 returned to their previous or intended use. All had complete resolution of clinical signs of TMD. One mare was retired from athletic use due to her genetic value as a broodmare. One horse was euthanized 2 years after UMC due to progressively worsening of clinical signs of temporohyoid osteoarthropathy (THO), which were not present before surgery. When available, owner satisfaction of the results of the procedure was excellent.

Main Limitations

Sample size; multiple institutions; owner bias.

Conclusions

Unilateral mandibular condylectomy should not be considered a salvage procedure. Horses treated for severe TMD by UMC can return to their previous or intended level of athletic performance and do not require a specialized diet.

The Equine Temporomandibular Joint: Comparisons Between Standard and Needle Arthroscopic Examination of Cadaver Specimens and Standing Horses

Background

Definitive diagnosis of equine temporomandibular joint osteoarthritis (TMJ-OA) may require advanced diagnostic imaging. Arthroscopy is a modern, minimally invasive, diagnostic, and treatment modality. Standing arthroscopic treatment of joint disease is a relatively recent advance in equine surgery, despite which there are few published comparisons between the available arthroscopic systems.

Objective

To compare and contrast two arthroscopic systems for assessing the equine temporomandibular joint compartments in cadavers and standing horses.

Study design

Experimental study.

Methods

Phase I involved the assessment of the discotemporal joint (DTJ) and discomandibular (DMJ) joint compartments of both temporomandibular joints (TMJ) of 14 cadaveric equine heads using a caudally placed arthroscopy portal. Joints were initially examined using the needle arthroscope and the results compared to the findings of examination using a 2.5 mm 30° arthroscope system (standard). Three healthy horses were subsequently examined to determine the validity of the procedure in live animals in Phase II.

Results

Needle and standard arthroscopy, in combination with mandibular manipulation, allowed evaluation of the caudal aspects of both joint compartments of the TMJ in Phase I. However, the extreme margins of the joint were more commonly visualized using standard arthroscopy. Live horses in phase II were restrained in stocks and both the rostral and caudal aspects of the DTJ and DMJ compartments of both TMJs were examined successfully understanding sedation and local analgesia. The use of a modified Guenther speculum allowed the mandible to be manipulated and offset, which facilitated a complete examination of the joint compartments. Despite adverse behavior encountered during the procedure in one horse, no surgical complications ensued.

Main Limitations

Not blinded-bias; learning curve.

Conclusions

The needle arthroscope system is a relatively inexpensive diagnostic tool, which can be used to evaluate the TMJ in the absence of advanced diagnostic imaging such as computed tomography or magnetic resonance imaging. However, if arthroscopic treatment is required after advanced imaging and pre-operative diagnosis, superior image quality and ease of manipulation may favor the use of the standard equipment.

The Frequency of Communication Between the Synovial Compartments of the Equine Temporomandibular Joint: A Contrast-Enhanced Computed Tomographic Assessment

Background: There is conflicting evidence regarding communication between the two compartments of the equine temporomandibular joint (TMJ). Understanding the inter-relationship between TMJ compartments is critical for diagnostic and clinical management purposes. Objective: To determine the frequency of communication between the discotemporal joint (DTJ) and the discomandibular joint (DMJ) of the equine TMJ in horses free of overt disease. Study Design: A randomized, blinded, controlled cadaveric study. Methods: Equine cadaver heads (n = 20), with no reported history of potential TMJ disease, were collected and stored frozen until use. Horses were randomized to the treatment group, such that Group A horses (n = 10) underwent arthrocentesis of the left DTJ and the right DMJ compartments, while Group B (n = 10) underwent arthrocentesis of the left DMJ and the right DTJ compartments of the TMJ, for a total of 40 joints. Computed tomography (CT) imaging was performed before, and after, intra-articular injection of contrast media in each head. Two observers, blinded to the treatment group, independently interpreted CT images. Results: Communication between synovial compartments occurred in the left TMJ of two horses. Arthroscopic evaluation revealed that both horses had a perforation of the intra-articular disc in the region of the caudomedial fibrous expansion. Mild anterior displacement of the abnormal disc in the joint of one horse was demonstrated using magnetic resonance imaging (MRI). Main Limitations: Sample size, the use of owner provided animals' history, and frozen specimens. Conclusions: No physiological communication was present between the DTJ and the DMJ in the equine TMJ of the cases studied, regardless of which compartment underwent arthrocentesis. Two joints had pathological communications. These results suggest that diagnostic, and medical, treatment of intra-articular disease may be most effective when both joint compartments are injected. Furthermore, this study illustrates the value of contrast enhancement while imaging the equine TMJ.

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

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.