Anatomy of the equine temporomandibular joint: study by gross dissection, vascular injection and section

Morphological description of the temporomandibular joint ligaments in domestic pigs

The temporomandibular joint (TMJ) ligaments play crucial roles in its function or dysfunction. The objective of this study was to describe the macro and microscopic morphology of these ligaments in domestic pigs, aiming to: (1) expand knowledge about the species; (2) provide anatomical references for advancing veterinary therapy and utilizing pigs as animal models in craniofacial research. Heads of young Sus scrofa domesticus were dissected to identify TMJ ligaments. Fragments of these ligaments were collected and processed for subsequent histological analysis with Haematoxylin and eosin staining. The results were qualitatively described. Pigs exhibited a TMJ reinforced by three individualized capsular ligaments: a lateral ligament, attaching to the ventral margin of the zygomatic process of the temporal bone and the lateral margin of the mandibular neck; a caudomedial ligament, attaching to the retroarticular process of the squamous part of the temporal bone and the caudomedial margin of the mandibular neck and a caudolateral ligament, attaching to the ventral margin of the base of the zygomatic process of the temporal bone and the caudal margin of the mandibular neck. The lateral ligament exhibited a greater constitution of dense irregular connective tissue, while the caudomedial and caudolateral ligaments showed a greater constitution of dense regular connective tissue. It is concluded that the TMJ of pigs presents one more ligament than horses, cattle, dogs, cats and what has been described for pigs themselves. We believe these results may contribute to the improvement of veterinary clinical and surgical therapy overall, as well as provide essential morphological information for a better interpretation and application of interspecies results in craniofacial research using pigs as an experimental model, as in the case of humans.

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 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.

Standing Arthroscopic Treatment of Temporomandibular Joint Sepsis in a Horse

A 15-year-old Thoroughbred gelding was presented for investigation of fever, right temporomandibular region swelling, and progressive pain when opening the mouth. Right temporomandibular joint (TMJ) sepsis was diagnosed based on synovial fluid analysis, sonographic imaging, and standing robotic cone-beam computed tomography. Concurrent otitis media and temporohyoid osteoarthropathy (THO) were also noted. The horse was treated with arthroscopic debridement and lavage during standing sedation followed by local and systemic antimicrobial therapy. There were no complications associated with the surgical procedure and the gelding's clinical signs resolved. Arthroscopy of the TMJ can be accomplished in the standing horse and should be considered when arthroscopic exploration or debridement of this joint is indicated. This is also the first case report of concurrent otitis media, TMJ sepsis, and THO; due to their close anatomic relationship, it is possible that septic otitis media could lead to pathology in the TMJ and temporohyoid joint, as described in humans.

Arthroscopic approach and intra-articular anatomy of the equine discomandibular joint compartment of the temporomandibular joint

OBJECTIVE

To develop an arthroscopic approach to the discomandibular joint (DMJ), the ventral compartment of the temporomandibular joint (TMJ) of the horse.

STUDY DESIGN

Experimental study.

SAMPLE POPULATION

Nine cadaveric equine heads and two live horses.

METHODS

A 2.5-mm 30° arthroscope was used to explore the DMJ after joint distension. The first portal was created caudally, allowing placement of a rostral portal under visual guidance. Nasotracheal intubation of the live horses allowed mandibular manipulation, which is required for complete visualization of the joint.

RESULTS

A novel injection technique allowed consistent arthrocentesis of the DMJ. The joint could be completely explored by using both portals and manipulation of the mandible. Variations in the medial joint capsule were observed between horses along with a cyst of the mandibular condyle in one horse. The only complication consisted of damage to the parotid salivary gland, which occurred in three cadaver heads. No communication was found between the joint compartments of the TMJ.

CONCLUSION

Correct portal placement and intraoperative manipulation of the mandible were critical and allowed complete exploration and debridement of the DMJ.

CLINICAL SIGNIFICANCE

Determining the independence of the TMJ joint compartments has clinical ramifications for the diagnosis and treatment of clinical disorders. Most TMJ pathology, notwithstanding sepsis, is identified within the DMJ. Arthroscopic exploration of the DMJ is possible and may help manage these conditions.

Ultrasound-guided arthrocentesis of the temporomandibular joint in healthy adult horses is equivalent to blind arthrocentesis

Equine temporomandibular joint (TMJ) diseases are increasingly recognized as a problem for the well-being and performance of horses. Diagnosis is confounded by overlap of clinical signs associated with pathology of the oral cavity, poll, and cervical vertebrae. Arthrocentesis for intra-articular analgesia, sampling of synovial fluid, and medication is needed for diagnostic and therapeutic purposes. Ultrasound features of the normal TMJ and a blind arthrocentesis technique have been described, but a systematic approach to ultrasound-guided (USG) arthrocentesis has not been reported. Ultrasound guidance allows visualization of the TMJ that may prove beneficial in cases when pathology, abnormal anatomy, or clinician inexperience make blind arthrocentesis difficult. We hypothesized that USG arthrocentesis would result in fewer needle repositions than blind arthrocentesis. We also aimed to assess synovial fluid parameters for normal equine TMJs. A prospective randomized method comparison with crossover experimental design compared the number of needle positionings required for accurate injection of the TMJ using each technique. Arthrocentesis technique and operator experience were tested using cadavers and two operators. Injection success was confirmed using CT. The radiologist then applied both techniques in normal live horses. No statistically significant difference was noted between arthrocentesis techniques or operators (P > .05). No complications were observed in live horses following either technique. Synovial fluid parameters were largely within the normal range expected for other synovial joints. Either blind or USG arthrocentesis of the equine TMJ can be performed with minimal prior operator experience. Ultrasound-guided arthrocentesis is an alternative method and can be considered in cases with altered anatomy.

E12 technique: Conventional epoxy resin sheet plastination

Epoxy plastination techniques were developed to obtain thin transparent body slices with high anatomical detail. This is facilitated because the plastinated tissue is transparent and the topography of the anatomical structures well preserved. For this reason, thin epoxy slices are currently used for research purposes in both macroscopic and microscopic studies. The protocol for the conventional epoxy technique (E12) follows the main steps of plastination-specimen preparation, dehydration, impregnation and curing/casting. Preparation begins with selection of the specimen, followed by freezing and slicing. Either fresh or fixed (embalmed) tissue is suitable for epoxy plastination, while slice thickness is kept between 1.5 and 3 mm. Impregnation mixture is made of epoxy E12 resin plus E1 hardener (100 ppw; 28 ppw). This mixture is reactive and temperature sensitive, and for this reason, total impregnation time under vacuum at room laboratory temperature should not last for more than 20-24 hr. Casting of impregnated slices is done in either flat chambers or by the so-called sandwich method in either fresh mixture or the one used for impregnation. Curing is completed at 40°C to allow a complete polymerization of the epoxy-mixture. After curing, slices can be photographed, scanned or used for anatomical study under screen negatoscope, magnification glass or fluorescent microscope. Based on epoxy sheet plastination, many anatomical papers have recent observations of and/or clarification of anatomical concepts in different areas of medical expertice.

Cheek teeth apical infection in cattle: Diagnosis, surgical extraction, and prognosis

OBJECTIVE

To report the clinical presentation, treatment, and outcome of cattle undergoing surgical extraction of apically infected cheek teeth (CT).

STUDY DESIGN

Short case series.

ANIMALS

Nine adult cattle.

METHODS

Medical records were searched for cattle having a diagnosis of apical infection of CT that were treated with surgical extraction between 2005 and 2017. Data retrieved included clinical examination, ancillary tests, surgical procedure, and outcomes.

RESULTS

The main presenting complaints were mandibular swelling and decreased appetite and milk production. In total, 7 mandibular and 3 maxillary CT were extracted, 7 molars and 3 premolars that were distributed more frequently on the left dental arcades (n = 7 CT). Two cattle had no visible external lesions. Radiograph images revealed that lucency surrounded all affected tooth roots. Mandibular teeth were removed by lateral buccotomy with removal of alveolar bone plate or retrograde repulsion, and maxillary teeth were removed by repulsion through a maxillary sinus flap. Most common bacterial isolates consisted of anaerobic bacteria (6/11 isolates) and Truperella pyogenes (3/11 isolates). The most common complications included inability to remove the tooth intact (n = 4 cattle) and surgical site infection (n = 5). All cattle remained in their herd after treatment.

CONCLUSION

Surgical extraction of CT was achieved in all 9 cattle. The postoperative morbidity was high but without long-term consequences on animal productivity.

CLINICAL SIGNIFICANCE

Surgical extraction of CT is a successful treatment for apical infection in cattle.

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

It has been assumed that dental conditions cause disorders of the equine temporomandibular joint (TMJ), due to biomechanical overload or aberrant loading. However, the incidence of published TMJ disorders in horses is low and this leads to the question whether the equine TMJ is adapted well to its biomechanical requirements or is able to remodel its articular surfaces in response to modified loading conditions. The aim of this study was to determine the histological characteristics of healthy equine TMJs. The tissue components of the articular surfaces of 10 TMJs obtained from horses without any clinical history of dental or TMJ disorders were analysed. Apart from the mandibular fossa of the temporal bone, the osseous aspects of the TMJ exhibited a uniform zoning pattern. The articular surfaces were composed of three tissue layers: (1) a superficial cell-rich dense connective tissue layer; (2) a middle fibrocartilage layer; and (3) a deep hyaline-like cartilage layer. The articular disc was composed of an inner core of fibrocartilage and hyaline-like cartilage meshwork covered with both cell-rich dense connective tissue and fibrocartilage at its dorsal and ventral aspects. In contrast, the mandibular fossa was only covered by a dense connective tissue, frequently supplemented by a synovial membrane, suggesting low biomechanical stress. Glycosaminoglycans, which are indicative of compressive loads, were predominantly present within the rostral part of the articular tubercle and the retroarticular process, the dorsal part of articular disc and the entire mandibular head, but were absent within the mandibular fossa. The results of this study suggest the presence of different biomechanical demands in the dorsal and ventral compartment of the equine TMJ.

Functional anatomy of the equine temporomandibular joint: Collagen fiber texture of the articular surfaces

In the last decade, the equine masticatory apparatus has received much attention. Numerous studies have emphasized the importance of the temporomandibular joint (TMJ) in the functional process of mastication. However, ultrastructural and histological data providing a basis for biomechanical and histopathological considerations are not available. The aim of the present study was to analyze the architecture of the collagen fiber apparatus in the articular surfaces of the equine TMJ to reveal typical morphological features indicating biomechanical adaptions. Therefore, the collagen fiber alignment was visualized using the split-line technique in 16 adult warmblood horses without any history of TMJ disorders. Within the central two-thirds of the articular surfaces of the articular tubercle, the articular disc and the mandibular head, split-lines ran in a correspondent rostrocaudal direction. In the lateral and medial aspects of these articular surfaces, the split-line pattern varied, displaying curved arrangements in the articular disc and punctual split-lines in the bony components. Mediolateral orientated split-lines were found in the rostral and caudal border of the articular disc and in the mandibular fossa. The complex movements during the equine chewing cycle are likely assigned to different areas of the TMJ. The split-line pattern of the equine TMJ is indicative of a relative movement of the joint components in a preferential rostrocaudal direction which is consigned to the central aspects of the TMJ. The lateral and medial aspects of the articular surfaces provide split-line patterns that indicate movements particularly around a dorsoventral axis.

COMPUTED TOMOGRAPHIC APPEARANCE OF THE TEMPOROMANDIBULAR JOINT IN 1018 ASYMPTOMATIC HORSES: A MULTI-INSTITUTION STUDY

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.

The effect of acute unilateral inflammation of the equine temporomandibular joint on the kinematics of mastication

REASONS FOR PERFORMING STUDY

Diseases of the temporomandibular joint (TMJ) are well reported in man and some domestic animals other than the horse. The pathophysiology of equine TMJ disease and the effects of disease on the kinematics of mastication are unknown.

OBJECTIVES

To determine whether transient unilateral inflammation of the equine TMJ results in alterations in the masticatory cycle.

STUDY DESIGN

An experimental controlled study utilising 6 horses of various ages with normal dentition.

METHODS

Each horse was equipped with an optical motion tracking (kinematic) system. Horses were observed chewing grass hay over 3 min intervals. Regardless of the initial side of the power stroke in the masticatory cycle, lipopolysaccharide (LPS) was injected in the left TMJ in each horse and the horses were reassessed after 6 h.

RESULTS

Four horses developed effusion of the injected TMJs; 2 of these also began quidding. All horses injected on the original side of the power stroke switched sides while the 2 injected on the contralateral side did not. All horses developed reduced vertical pitch (vertical opening) of the mandible. Overall, rostrocaudal movement of the mandible did not change; however, the timing of this movement relative to the phase of the masticatory cycle did. Injection with LPS did not affect the amount of lateral movement of the mandible.

CONCLUSIONS

Injection of LPS into the TMJ significantly altered the masticatory cycle compared with baseline values representing avoidance behaviour due to inflammation of the joint, despite which the horses continued to eat using the contralateral mandible. Lipopolysaccharide administration also led to quidding and a loss of feed efficiency (in some individuals).

Anatomy of the temporomandibular joint in the cat: a study by microdissection, cryosection and vascular injection

The minute anatomy of the temporomandibular joint (TMJ) is of great clinical relevance in cats owing to a high number of lesions involving this articulation. However, the precise anatomy is poorly documented in textbooks and scientific articles. The aim of this study was to describe, in detail, the TMJ anatomy and its relationship with other adjacent anatomical structures in the cat. Different anatomical preparations, including vascular and articular injection, microdissection, cryosection and plastination, were performed in 12 cadaveric cats. All TMJ anatomical structures were identified and described in detail. A thorough understanding of the TMJ anatomy is essential to understand the clinical signs associated with TMJ disorders, to locate lesions precisely and to accurately interpret the results in all diagnostic imaging techniques.

Computed tomography and magnetic resonance imaging features of the temporomandibular joint in two normal camels

Computed tomography (CT) and magnetic resonance (MR) image features of the temporomandibular joint (TMJ) and associated structures in two mature dromedary camels were obtained with a third-generation equipment CT and a superconducting magnet RM at 1.5 Tesla. Images were acquired in sagittal and transverse planes. Medical imaging processing with imaging software was applied to obtain postprocessing CT and MR images. Relevant anatomic structures were identified and labelled. The resulting images provided excellent anatomic detail of the TMJ and associated structures. Annotated CT and MR images from this study are intended as an anatomical reference useful in the interpretation for clinical CT and MR imaging studies of the TMJ of the dromedary camels.

In search of clinical truths: equine and comparative studies of anatomy

The importance of correlating anatomical studies with diagnostic and therapeutic approaches in practice has long been recognised. Such studies in the horse have, until recently, lagged behind this discipline in human medicine and surgery. Clinical techniques by which this correlation is achieved include radiography, ultrasound, computed tomography and magnetic resonance imaging. This review presents published literature on the subject and, in addition, describes the part played by plastination, a recently developed technique for the preservation of biological specimens. In this, tissue fluids and part of the lipids are replaced by certain polymers yielding specimens that can be handled without gloves, do not smell or decay, and even retain microscopic properties of the original sample. The technique has proved to be a useful tool to correct previously presented anatomical descriptions and is one now favoured by human surgeons. Studies of the horse employing this technique include those of the temporomandibular joint and tarsus. The aim of the review is to stimulate further correlations of anatomical structure and equine medical and surgical procedures, thereby advancing knowledge and understanding in practice and teaching.

Temporomandibular joint ankylosis caused by chondroid hyperplasia from the callus of condylar neck fracture

A patient who complained of difficulty in opening his mouth after condylar neck fracture 1 year ago presented typical features of temporomandibular joint ankylosis in clinical and radiologic examinations. To demonstrate a possible pathogenesis of temporomandibular joint ankylosis after condylar neck fracture, the fractured condylar portion removed was examined by histologic and immunohistochemical stainings. Interpositional gap arthroplasty was performed by removing the inferomesially displaced fractured condyle, and reconstruction with subcutaneous dermis to the previous vertical height was performed immediately. The fractured condylar portion was almost intact with slight erosion of the condylar cartilage. In the hematoxylin and eosin and Masson trichrome stainings, an extensive chondroid hyperplasia with abundant hyaline cartilage was shown in the removed condylar portion. There were also hyperplastic features of the synovial membrane, which were abnormally distributed throughout the chondroid tissues. In the immunohistochemical stainings of proliferating cell nuclear antigen (PCNA) and bone morphogenetic protein (BMP)-2 and BMP-4, the chondroid tissues were conspicuously hyperplastic and strongly positive for BMP-4 but sparse for BMP-2. From these results, we think that the hyperplastic chondroid tissue was derived from the callus of the primary fractured site of the condylar neck and propose that the chondroid tissue could proliferate continuously because of synovial tissue support from around the temporomandibular joint, resulting in temporomandibular joint ankylosis. This pathogenesis is quite different from those of other diaphyseal fracture of long bones.

Comparison of mandibular motion in horses chewing hay and pellets

REASONS FOR PERFORMING STUDY

Previous studies have suggested that temporomandibular joint (TMJ) kinematics depend on the type of food being masticated, but accurate measurements of TMJ motion in horses chewing different feeds have not been published.

HYPOTHESIS

The temporomandibular joint has a larger range of motion when horses chew hay compared to pellets.

METHODS

An optical motion capture system was used to track skin markers on the skull and mandible of 7 horses as they chewed hay and pellets. A virtual marker was created on the midline between the mandibles at the level of the 4th premolar teeth to represent the overall motion of the mandible relative to the skull during the chewing cycle.

RESULTS

Frequency of the chewing cycles was lower for hay than for pellets. Excursions of the virtual mandibular marker were significantly larger in all 3 directions when chewing hay compared to pellets. The mean velocity of the virtual mandibular marker during the chewing cycle was the same when chewing the 2 feeds.

CONCLUSIONS

The range of mediolateral displacement of the mandible was sufficient to give full occlusal contact of the upper and lower dental arcades when chewing hay but not when chewing pellets.

POTENTIAL RELEVANCE

These findings support the suggestion that horses receiving a diet high in concentrate feeds may require more frequent dental prophylactic examinations and treatments to avoid the development of dental irregularities associated with smaller mandibular excursions during chewing.

ULTRASONOGRAPHIC ANATOMY OF THE TEMPOROMANDIBULAR JOINT IN HEALTHY PURE-BRED SPANISH HORSES

The objective was to describe the normal ultrasonographic appearance of the soft tissue and bony structures of the temporomandibular joint in Pure-Bred Spanish horses using frozen and plastinated sections performed as anatomical references. The temporomandibular joint of five healthy Pure-Bred Spanish horses and the head specimens from 12 Pure-Bred Spanish cadavers that were subjected to euthanasia for reasons other than temporomandibular joint problems were studied sonographically and anatomically. An 11 MHz linear-array transducer was used to obtain longitudinal ultrasonographic images of the temporomandibular joint from rostral, lateral, and caudal approaches. For anatomic study, a gross dissection was performed on six temporomandibular joints. The other six head specimens were first frozen at -30 degrees C for 48h and then, at -70 degrees C for a week. Three millimeter thick anatomic sections were collected in the same plane as the sonographic planes. These sections were plastinated, photographed, and compared with the corresponding ultrasonographic images. The articular surfaces, the articular cartilage, the disc, the intra-articular fat tissue, the joint capsule, and other structures were clearly visualized sonographically. Structures identified on the ultrasonographic images were in accordance with those identified on the corresponding anatomic sections. We confirmed the appearance of structures of the equine temporomandibular joint that have been described previously but we also identified the caudal fibrous expansion of the disc, the caudal compartment of the dorsal synovial pouch, and the lateral ligament. Our results define a reference that will aid in sonographic evaluation of the equine temporomandibular joint region.