Arthroscopic Anatomy of the Equine Temporomandibular Joint

OBJECTIVE: To develop an arthroscopic approach to, and describe the arthroscopic anatomy of, the equine temporomandibular joint (TMJ). STUDY DESIGN: Cadaveric study, after which the technique was tested in horses. ANIMALS OR SAMPLE POPULATION: Ten cadaveric equine heads and 5 normal horses (age, 5-13 years; weight, 425-545 kg). METHODS: Specimens or horses were positioned in right lateral recumbency. After fluid distention of the TMJ, arthroscopic portals were made in the dorsal compartment over the most prominent portion of the joint outpouching (caudodorsal approach) and in rostral and intermediate locations. The joint was explored and photographed. Positional changes in the mandible were made to determine if observation of the joint could be improved. Instrument portals were created to assess the feasibility of surgical arthroscopy. Cadaveric heads were dissected to assess iatrogenic damage, whereas experimental horses were observed for postoperative complications for 30 days. RESULTS: A caudodorsal arthroscopic approach provided the best evaluation of the dorsal compartment of the TMJ. The approach allowed observation of the rostral and caudal synovial pouches and the lateral aspect of the joint including the articular disc. Examination of the medial aspect of the joint was limited to the most rostral and caudal aspects. Access to the lateral aspect of the ventral compartment of the TMJ was precluded by the position of the transverse facial artery and vein. In specimens, iatrogenic damage was minimal and limited to the articular fibrocartilage, articular disc, and penetration of the parotid salivary gland. If the latter also occurred in horses, no adverse effects were noted. In horses, mild fluid extravasation occurred and resolved within 1 day. All horses ate normally after surgery but had periarticular swelling and mild pain upon palpation of the TMJ for 2 days. CONCLUSIONS: A caudodorsal arthroscopic approach to the TMJ allowed adequate observation of the lateral aspect of the dorsal compartment of the joint. Access to the ventral compartment was precluded by the location of the transverse facial artery and vein. CLINICAL RELEVANCE: Conditions affecting the lateral and caudal aspects of the dorsal compartment of the TMJ should be visible by arthroscopy.     

Arthroscopic Approaches and Intraarticular Anatomy of the Equine Elbow

Periarticular anatomy and techniques for arthroscopic access to the equine elbow were studied in six joints from cadavers. Caudomedial and craniolateral approaches were evaluated subsequently in 11 anesthetized horses. The caudomedial approach was made between the flexor carpi radialis and flexor carpi ulnaris muscle bellies. Most of the caudal articular surfaces of the humeral condyles, the caudal perimeter of the radius, and the trochlear notch and portions of the anconeal process of the ulna could be identified. The voluminous caudal joint capsule cul-de-sac proximal to the anconeal process was readily entered. A 70 degree arthroscope allowed examination of more of the joint recesses and articular surfaces of the olecranon fossa than a 25 degree arthroscope. A second portal for intraarticular instrument manipulation was made caudal and slightly proximal to the arthroscope entry. Entry more proximal than the level of the radiohumeral articulation carried significant risk of damage to the ulnar nerve and collateral ulnar artery and vein. For examination of the cranial regions of the elbow, a craniolateral portal was established cranial to the lateral collateral ligament. An instrument portal was made through the muscle bellies of the extensor carpi radialis or common digital extensor muscles. The cranial articular surfaces of the humeral condyles were readily exposed by extension of the elbow. The weight-bearing articular surface of the radius could not be seen. Eight horses were euthanatized without recovery from anesthesia and the elbows were dissected for examination. Three horses were allowed to recover from anesthesia and were euthanatized on days 3, 30, and 60.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anatomy and Anaesthesia of the Equine External Ear Canal

Anaesthesia of the external ear canal (external acoustic meatus) is usually performed by blocking both the great and internal auricular nerves by regional infiltration. However, exact landmarks for blocking the internal auricular nerve to accomplish effective anaesthesia have not been described yet. In this study, detailed anatomical dissection of the equine external ear canal and its nerve supply was carried out on fifteen cadaver heads. Tissue samples of the dissected nerves were taken from two cadaver heads processed and were evaluated microscopically. Prior to the dissection, the region of interest was evaluated ultrasonographically, and injection of a local anaesthetic was simulated with an injection of methylene blue on ten cadaver heads. The tympanic membranes of three cadaver heads were obtained by microdissection and processed for microscopic evaluation. The entrance point of the internal auricular nerve, which is a branch of the facial nerve, into the ear canal is formed by the styloid process of the auricular cartilage. Using ultrasound, the styloid process presented as a thin hyperechoic line 2.17–2.97 cm deep, based on the skin surface. Landmarks for performing a complete and reliable anaesthesia of the external ear canal were established, and the simulated anaesthesia with methylene blue injection was evaluated as successful in all ten cases. Additionally, the histological composition of the equine tympanic membrane is described and illustrated.     

The Macroscopic Vascular Anatomy of the Equine Ethmoidal Area

The vascular anatomy of the ethmoidal area in six normal horses and two normal ponies was studied using vascularcorrosion casts. The major arterial supply to the ethmoidal area sterns from an intracranial source. The internal and external ethmoidal arteries anastomose on the rostral intracranial surface of the cribriform plate to form the arterial ethmoidal rete which arborizes and passes through the perforations of the cribriform plate to supply the ethmoid labyrinth. A minor arterial supply to the ventral portion of the ethmoid labyrinth sterns from a small caudal nasal branch of the sphenopalatine artery. Multiple parallel venules drain the ethmoid labyrinth rostrally to its apex then join the venous drainage from the surrounding sinuses.     

Tenoscopic Anatomy of the Equine Carpal Flexor Synovial Sheath

Objective —To describe the tenoscopic anatomy of the carpal sheath of the flexor tendons (carpal sheath) viewed from a lateral approach.
Study Design —Tenoscopic observation of structures within the carpal sheath subsequently confirmed by dissection.
Animals or Sample Population—12 equine cadaveric forelimbs.
Methods —The limbs were positioned lateral side up with the carpus slightly flexed. After distention of the carpal sheath, a portal for the arthroscope was made approximately 3 cm proximal to the distal radial physis and 2.5 cm caudal to the radius between the tendons of the ulnaris lateralis and lateral digital extensor muscles.
Results —A lateral tenoscopic approach was adequate to identify all structures within the carpal sheath. From proximal to distal, structures identified using this approach were the radial head of the deep digital flexor muscle, accessory ligament of the tendon of the superficial digital flexor muscle, distal radial physis, tendons of the superficial and deep digital flexor muscles, accessory carpal bone, antebrachiocarpal and middle carpal joints, and vincula of the tendon of the deep digital flexor muscle.
Conclusions —A lateral tenoscopic approach offered an easy, repeatable entry into the carpal sheath and allowed good observation of all structures within the sheath except for the medial borders of the tendons of the deep and superficial digital flexor muscles.
Clinical Relevance —Applications of a lateral tenoscopic approach to the carpal sheath include diagnostic procedures, lavage and synovial resection for septic tenosynovitis, desmotomy of the accessory ligament of the tendon of the superficial digital flexor muscle for flexural deformity or tendinitis, and removal of osteochondromas from the distal radial metaphysis.     

Computed Tomographic Features of Choanal Atresia in a Friesian Foal

A 3-week-old Friesian colt with a history of respiratory distress since birth was presented to our facility. Results after an endoscopy showed obstruction of the right nasal passage to the nasopharynx. Computed tomography was performed to further characterize this unilateral blockage. The images demonstrated a complete membranous obstruction of the ventral meatus, along with deviation of the vomer bone toward the left side of the nasal cavity. The diagnosis of unilateral choanal atresia was confirmed. This report is the first to describe computed tomographic features of choanal atresia in a foal.     

Arthroscopic Surgical Approaches and Intraarticular Anatomy of the Equine Shoulder Joint

Arthroscopic approaches to the scapulohumeral joint were developed in four clinically normal, live horses (5 limbs) to determine their usefulness for evaluation and potential surgical treatment of intraarticular lesions. The articular surface of the entire glenoid, cranial humeral head (medial and lateral) and caudolateral humeral head, as well as the synovial membrane, could be closely examined from an arthroscopic portal cranial to the infraspinatus tendon. The caudomedial humeral head could be examined partially. Cranial and caudal instrument portals allowed good surgical access to the entire glenoid and the majority of the humeral head (except caudomedial in adult, heavily muscled horses). The described arthroscopic and instrument portals allowed access to the areas frequently affected with osteochondritis dissecans (OCD). Potential difficulties with this technique include problems establishing triangulation, extravasation of fluids, and inability to reach potential lesions on the caudomedial humeral head with conventional equipment in heavily muscled horses.     

Computed Tomographic Lymphography of the Thoracic Duct by Mesenteric Lymph Node Injection

Objective— To document a novel technique to image the thoracic duct and its tributaries by contrast enhanced computed tomography (CT) lymphography.
Study Design— Clinical report.
Animals— Dogs (n=6) idiopathic chylothorax.
Methods— Ultrasonography was used to guide percutaneous injection of intestinal lymph nodes with nonionic iodinated contrast medium for preoperative CT lymphography of the thoracic duct in 6 dogs with chylothorax. Thoracic CT images were acquired immediately after contrast medium injection. All dogs had subtotal pericardectomy and thoracic duct ligation. Postoperative thoracic duct lymphography was performed in 3 dogs. Superficial cervical lymph node lymphography was performed in 2 dogs to determine cervical lymphatic contribution to thoracic effusions.
Results— Preoperative thoracic duct lymphography using this technique was successful in delineating the cisterna chyli, thoracic duct, and associated lymphatic vessels in all dogs. Immediate postoperative lymphography performed in 2 dogs revealed successful duct ligation in 1 dog and persistent lymphatic leakage in the other. A 1-month postoperative thoracic duct lymphogram performed in 1 dog revealed unsuccessful ligation or recannulation of 1 of 3 redundant vessels seen preoperatively.
Conclusion— Percutaneous CT lymphography results in excellent detection of the thoracic duct and abnormal thoracic duct drainage patterns both pre- and postoperatively. The contribution of superficial cervical lymph node drainage to reoccurrence of effusions can be evaluated.
Clinical Relevance— Percutaneous CT lymphography using ultrasound-guided contrast medium injection should be considered as an alternative to conventional open abdominal approaches to radiographic or CT lymphography.     

Comparison of Computed Tomographic and Radiographic Popliteal Lymphangiography in Normal Dogs

Objective: To (1) describe computed tomographic (CT) popliteal lymphangiography; (2) compare the number of thoracic duct (TD) branches detected by CT and by radiography after popliteal lymphangiography; and (3) to compare the number of branches detected after left and right popliteal lymphangiography. Study Design: Experimental study. Animals: Adult dogs (n=6). Methods: A randomly selected popliteal lymph node was percutaneously injected with 12 mL iodinated contrast medium through a 25‐g butterfly catheter over 4–5 minutes. Lateral and ventrodorsal (VD) thoracic radiograph projections and thoracic CT were performed. The procedure was repeated using the contralateral lymph node after a 48–72 hours washout period. Results: One dog had TD branches visible on CT but not on radiographs. A significantly greater number of TD branches were observed with CT popliteal lymphangiography compared with lateral and VD radiographic popliteal lymphangiography (P=.003 and P<.001, respectively). The number of visible TD branches observed between the 6th thoracic and 1st lumbar vertebrae were not significantly different in these dogs (P=.146). A significant difference in number of TD branches observed was not found after left or right popliteal lymph node injection (P=.097). Conclusions: CT popliteal lymphangiography consistently identified a greater number of TD branches when compared with radiographic popliteal lymphangiography. Injection of either popliteal lymph node resulted in the same number of TD branches being observed.