Equine laryngoplasty: Effects of three anchoring techniques in the muscular process and three positions for suture implantation in the cricoid cartilage.

OBJECTIVE: To compare the effects of three anchoring techniques in the muscular process and three positions of laryngoplasty suture implantation in the cricoid cartilage on abduction of the arytenoid cartilage and interaction with the cricoarytenoid dorsalis (CAD) muscle compartments. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Twenty-two cadaveric equine larynges. METHODS: Three implantation techniques were assessed in the left muscular process. They were the use of a titanium corkscrew (CS), a standard caudal passage using a Jamshidi needle (JCa), and a standard cranial passage using a Jamshidi needle (JCr). Each was assessed in combination with three caudal locations in the cricoid cartilage (right, left, and left lateral). Each suture combination was tightened to submaximal abduction (Dixon grade 2). Force on the suture, degree of larynx caudal rotation, and CAD muscle indentation were evaluated. RESULTS: The force required for optimal arytenoid cartilage abduction was lower (p < .01) for constructs involving a CS (7.45 ± 4 N). The CS also resulted in lower (p < .01) CAD muscle indentation (2.01 ± 1.25 mm) and less larynx rotation (9 ± 3.87°; adjusted p < .05). CONCLUSION: When inserted into the muscular process at the CAD tendon insertion point, the biomechanical properties of the CS reduced the force required for optimal arytenoid cartilage abduction. The CS also minimized interference with the CAD muscle compartments and reduced caudal displacement of the left arytenoid cartilage when it was under suture tension. CLINICAL SIGNIFICANCE: The CS implantation avoided larynx deformation and muscle interaction, offering the possibility to combine a nerve graft and laryngoplasty as a treatment for recurrent laryngeal neuropathy.

Decreasing polymethyl methacrylate bone cement concentration extends working and setting times in vitro.

OBJECTIVE: To determine setting and temperature properties of diluted polymethyl methacrylate (PMMA) bone cement in vitro to assess utility for vocal fold augmentation in horses. SAMPLES: 4 dilutions of PMMA equivalent to volumes of 15 mL, 20 mL, 25 mL, and 30 mL PMMA powder (PMMAp) in 10 mL solvent. METHODS: For each volume PMMAp, setting times (tset), peak temperatures (Tmax), and times to peak temperature (tmax) were determined using a temperature data logger in a 4-mL volume of PMMA. Injectability was assessed in vitro by documenting the force required to inject 0.2 mL PMMA through an 18-gauge 3.5-inch spinal needle attached to a 6-mL syringe at 1-minute intervals. Working time (twork) was calculated from a linear regression of injectability. RESULTS: Peak temperatures increased with increasing volume of PMMAp: 56 °C, 86 °C, 99 °C, and 101 °C. Times for tset, twork, and tmax were inversely proportional to PMMA concentrations, resulting in tset of 23, 21, 17, and 14 minutes; twork of 22.75, 12.25, 7, and 4 minutes; and tmax of 28, 24, 19, and 16 minutes, respectively, for 15, 20, 25, and 30 mL PMMAp. Pairwise comparisons for all analyses were significant apart from Tmax for 25 and 30 mL PMMAp (P = .96) and twork for 20 and 25 mL PMMAp (P = .06). CLINICAL RELEVANCE: Decreasing the concentration of PMMA bone cement resulted in longer working times and setting times; however, peak temperatures did not differ between the 2 strongest concentrations. Further research is warranted to quantify diluted PMMA properties for in vivo use for vocal fold augmentation in horses.

An Exploratory Study into the Implantation of Arytenoid Cartilage Scaffold in the Horse.

Respiratory function in the horse can be severely compromised by arytenoid chondritis, or arytenoid chondropathy, a pathologic condition leading to deformity and dysfunction of the affected cartilage. Current treatment in cases unresponsive to medical management is removal of the cartilage, which can improve the airway obstruction, but predisposes the patient to other complications like tracheal penetration of oropharyngeal content and dynamic collapse of the now unsupported soft tissue lateral to the cartilage. A tissue engineering approach to reconstructing the arytenoid cartilage would represent a significant advantage in the management of arytenoid chondritis. In this study, we explored if decellularized matrix could potentially be incorporated into the high motion environment of the arytenoid cartilages of horses. Equine arytenoid cartilages were decellularized and a portion of the resultant acellular scaffolds was implanted in a full-thickness defect created in the arytenoids of eight horses. The implantation was performed bilaterally in each horse, with one side randomly selected to receive an implant seeded with autologous bone marrow-derived nucleated cells (BMNCs). Arytenoids structure and function were monitored up to 4 months. In vivo assessments included laryngeal ultrasound, and laryngeal endoscopy at rest and during exercise on a high-speed treadmill. Histologic evaluation of the arytenoids was performed postmortem. Implantation of the cartilaginous graft had no adverse effect on laryngeal respiratory function or swallowing, despite induction of a transient granuloma on the medial aspect of the arytenoids. Ultrasonographic monitoring detected a postoperative increase in the thickness and cross-sectional area of the arytenoid body that receded faster in the arytenoids not seeded with BMNCs. The explanted tissue showed epithelialization of the mucosal surface, integration of the implant into the native arytenoid, with minimal adverse cellular reaction. Remodeling of the scaffold material was evident by 2 months after implantation. Preseeding the scaffold with BMNCs increased the rate of scaffold degradation and incorporation. Replacement of arytenoid portion with a tissue-engineered cartilaginous graft preseeded with BMNCs is surgically feasible in the horse, is well tolerated, and results in appropriate integration within the native tissue, also preventing laryngeal tissue collapse during exercise.

Clinical and Pathological Features in Horses With Advanced Arytenoid Chondritis.

Equine arytenoid chondritis causes airway obstruction and abnormal upper airway noise due to a space-occupying lesion(s) and decreased abduction. Our objective was to compare clinical scores and ultrasonographic findings with gross and microscopic lesions of naturally occurring arytenoid chondritis, in order to guide surgical treatment. Seventeen naturally affected horses with advanced/severe chronic arytenoid chondritis and 4 control arytenoid cartilages were evaluated after partial arytenoidectomy. Cartilages were sectioned caudal to the corniculate process and the body of each arytenoid was measured. We assessed total gross area (TA), percentage of viable cartilage (VC), percentage of viable cartilage on the lateral wall, and medial expansion. Retrospectively, the gross lesions were used to suggest 2 preferred surgical management (SM) groups: those requiring partial arytenoidectomy and those amendable to focal medial resection (a conservative SM). TA of horses with arytenoid chondritis was significantly larger than controls (P = .005), due to a layered lesion composed of cavitation, granulation tissue, fibrosis, inflammation, hemorrhage, and edema, with relatively equal medial and lateral expansion that distorted the geometry of the affected cartilage. The increased TA paralleled the presence of immature cartilage with disorganized primitive mesenchymal cells. TA and SM were positively correlated (P = .01). All cases showed varying degrees of cartilage degeneration or necrosis, more severe medially; those appearing amenable to focal medial resection arytenoid group had significantly more viable cartilage on the lateral wall (P = .02). The gross and histopathologic findings suggest a new surgical approach-focal medial resection-that may save the lateral wall of the arytenoid.

Management of postoperative dysphagia after prosthetic laryngoplasty or arytenoidectomy.

OBJECTIVE: To evaluate the efficacy of various treatments for dysphagia after laryngeal surgery. STUDY DESIGN: Retrospective. ANIMALS: Horses treated for dysphagia after laryngeal surgery. METHODS: Medical records of horses treated for dysphagia after prosthetic laryngoplasty (PLP) or partial arytenoidectomy (PA) were reviewed. Signalment, prior surgery, preoperative videoendoscopic diagnosis, and surgical treatments were recorded. Short- and long-term follow-up were obtained. Chi-square and logistical regression were performed to correlate independent variables and outcomes. RESULTS: Forty-four percent of horses with prior PLP and 88% of horses with prior PA had persistent resting dorsal displacement of the soft palate (DDSP). Vocal fold augmentation (VFA) as a single treatment was most commonly performed (n = 22), followed by laryngoplasty removal (LPR; n = 1). Fifteen horses received a combination of treatments: VFA (n = 15), LPR (n = 4), laryngeal tie-forward (LTF; n = 2), and esophageal release (n = 1). Short-term clinical outcomes were reported; 80% of horses treated with VFA (n = 35) had resolution of dysphagia, and 20% were improved. Among the 33 horses available to long-term follow-up, 31 (94%) returned to some level of work, and DDSP during work was reportedly resolved in 23 of 25 horses. CONCLUSION: Vocal fold augmentation resulted in resolution of symptoms relating to dysphagia in 81% of horses. Twenty percent of horses treated with LPR had sustained resolution of dysphagia. A combination of LPR, VFA, LTF was performed in 18% of horses. CLINICAL SIGNIFICANCE: Treatment options directed at altering laryngeal geometry and/or position of the larynx were successful in resolving 86% of dysphagia in horses previously regarded as very difficult to treat.

Transendoscopic correction of epiglottic entrapment with a silicone-covered laser guide and diode laser in 29 horses.

OBJECTIVE: To describe the use of a silicone-covered laser guide and diode laser for surgical correction of epiglottic entrapment and report postoperative outcomes in horses with epiglottic entrapment. STUDY DESIGN: Retrospective case series. ANIMALS: Thoroughbred and standardbred racehorses (n = 29) with epiglottic entrapment. METHODS: A silicone-covered laser guide was placed endoscopically to direct the diode laser cutting action during transection of the entrapping subepiglottic membrane and to act as a physical barrier between the membrane and the epiglottic cartilage. Postoperative complications and trainer satisfaction were recorded via use of a follow-up questionnaire. Race records were reviewed to determine return to racing and detect differences in the number of starts, wins, or earnings before and after surgery. RESULTS: The entrapping membrane was successfully released in all horses. Mild postoperative complications such as swelling of the surgical site (12 horses) and coughing or mild nasal discharge (5 horses) were recorded during the first few days after surgery. Ninety-six percent of trainers were satisfied with the outcome of the procedure; 93% of horses returned to racing. CONCLUSION: Laser guide-assisted transection of the subepiglottic membrane corrected epiglottic entrapment in standing horses. CLINICAL SIGNIFICANCE: Ease of surgical technique, mild postoperative complications, and a good prognosis to return to racing make this a suitable alternative to the traditional laser procedure.

Investigation into pathophysiology of naturally occurring palatal instability and intermittent dorsal displacement of the soft palate (DDSP) in racehorses: Thyro-hyoid muscles fatigue during exercise.

Exercise induced intermittent dorsal displacement of the soft palate (DDSP) is a common cause of airway obstruction and poor performance in racehorses. The definite etiology is still unclear, but through an experimental model, a role in the development of this condition was identified in the dysfunction of the thyro-hyoid muscles. The present study aimed to elucidate the nature of this dysfunction by investigating the spontaneous response to exercise of the thyro-hyoid muscles in racehorses with naturally occurring DDSP. Intramuscular electrodes were implanted in the thyro-hyoid muscles of nine racehorses, and connected to a telemetric unit for electromyographic monitoring implanted subcutaneously. The horses were recruited based on upper airway function evaluated through wireless endoscopy during exercise. Five horses, with normal function, were used as control; four horses were diagnosed as DDSP-affected horses based on repeated episodes of intermittent dorsal displacement of the soft palate. The electromyographic activity of the thyro-hyoid muscles recorded during incremental exercise tests on a high-speed treadmill was analyzed to measure the mean electrical activity and the median frequency of the power spectrum, thereafter subjected to wavelet decomposition. The affected horses had palatal instability with displacement on repeated exams prior to surgical implantation. Although palatal instability persisted after surgery, only two of these horses displaced the palate after instrumentation. The electromyographic traces from this group of four horses showed, at highest exercise intensity, a decrease in mean electrical activity and median power frequency, with progressive decrease in the contribution of the high frequency wavelets, consistent with development of thyro-hyoid muscle fatigue. The results of this study identified fatigue as the main factor leading to exercise induced palatal instability and DDSP in a group of racehorses. Further studies are required to evaluate the fiber type composition and metabolic characteristics of the thyro-hyoid muscles that could predispose to fatigue.

Return to racing after surgical management of third carpal bone slab fractures in thoroughbred and standardbred racehorses.

OBJECTIVE: To determine the prognosis for racing of horses surgically treated for slab fractures of the third carpal bone (C3). STUDY DESIGN: Retrospective case study. ANIMALS: Horses (n = 125) surgically treated for C3 slab fractures. METHODS: Medical records of horses surgically treated for dorsal or sagittal C3 fractures were reviewed for age, sex, breed, limb, fracture type, degree of cartilage damage, and surgical treatment. Radiographs were evaluated to determine fracture depth, width, and displacement. Osteophytes, C3 lysis, and fragmentation were scored. Racing performance was obtained from online databases. Univariable and multivariable analyses were used to determine associations between independent variables and outcomes. RESULTS: Fifty-four (43%) horses raced postoperatively. Among thoroughbreds, 35% (30/86) with dorsal fractures and 63% (17/27) with sagittal fractures raced postoperatively. Among standardbreds, 77% (10/13) with dorsal fractures and 0% (0/2) with sagittal fractures raced postoperatively. Fracture displacement, C3 lysis, and cartilage damage affected the likelihood of racing postoperatively. Placement of 3.5-mm screws vs 4.5-mm screws and the placement of fewer screws were associated with improved likelihood of racing. CONCLUSION: The prognosis for postoperative racing of thoroughbreds with dorsal C3 fractures was less favorable than that previously reported. Concurrent joint pathology, such as cartilage damage at time of surgery, affected the ability of the horse to race postoperatively. CLINICAL SIGNIFICANCE: Although internal fixation of C3 slab fractures is required to restore joint congruity, return to racing should be expected in only 42% of thoroughbreds and 67% of standardbreds.

Asymmetric recurrent laryngeal nerve conduction velocities and dorsal cricoarytenoid muscle electromyographic characteristics in clinically normal horses.

The dorsal cricoarytenoid (DCA) muscles, are a fundamental component of the athletic horse's respiratory system: as the sole abductors of the airways, they maintain the size of the rima glottis which is essential for enabling maximal air intake during intense exercise. Dysfunction of the DCA muscle leads to arytenoid collapse during exercise, resulting in poor performance. An electrodiagnostic study including electromyography of the dorsal cricoarytenoid muscles and conduction velocity testing of the innervating recurrent laryngeal nerves (RLn) was conducted in horses with normal laryngeal function. We detected reduced nerve conduction velocity of the left RLn, compared to the right, and pathologic spontaneous activity (PSA) of myoelectrical activity within the left DCA muscle in half of this horse population and the horses with the slowest nerve conduction velocities. The findings in this group of horses are consistent with left sided demyelination and axonal loss, consistent with Recurrent Laryngeal Neuropathy (RLN), a highly prevalent degenerative disorder of the RLn in horses that predominantly affects the left side. The detection of electromyographic changes compatible with RLN in clinically unaffected horses is consistent with previous studies that identified "subclinical" subjects, presenting normal laryngeal function despite neuropathologic changes within nerve and muscle confirmed histologically.

Transnasal, Endoscopically Guided Skull-Based Surgery by Pharyngotomy for Mass Removal from the Sphenopalatine Sinus in a Horse.

OBJECTIVE: To report a transnasal, endoscopically guided ventral surgical approach for accessing the cranial and caudal segments of the sphenopalatine sinus for mass removal in a horse. STUDY DESIGN: Case report. ANIMAL: Adult horse with acute onset blindness referable to a soft tissue mass within the sphenopalatine sinus. CLINICAL REPORT: A 7-year-old Warmblood gelding presented with a history of running into a fence and falling. No neurologic signs were identified at initial examination but acute blindness was noted 3 weeks later. On computed tomography (CT) the sphenopalatine sinus was filled with a large homogeneous mass with poor contrast enhancement that extended dorsally with thinning to the dorsal cortex of the sphenoid bone, just rostral to the entrance of the optic canals into the cranial cavity. Surgical access to the sphenopalatine sinus was achieved using a transnasal, endoscopically guided ventral pharyngotomy approach and the mass lesion was removed. A presumptive diagnosis of chondroma was made based on histopathology. The horse recovered well from surgery, and although it has not regained vision as of 6.5 years postoperatively, the disease has not progressed. CONCLUSION: Transnasal, endoscopically-guided ventral surgical access to the sphenopalatine sinus is possible in horses and may improve access in horses with disease extending caudally beyond the palatine portion of the sinus. Use of smaller diameter or specialized instruments, such as various endoscopic bone cutting instruments, and CT image guidance may improve sinus access by this route.

Laryngoplasty in standing horses.

OBJECTIVE: To describe the clinical experience with standing laryngoplasty in a series of horses mostly nonracing. STUDY DESIGN: Case series. ANIMALS: Seventy-one client-owned horses. METHODS: Medical records (April 2008-February 2014) of horses treated by standing laryngoplasty for abnormal respiratory noise and or poor performance were reviewed. Horses were included if they had a diagnosis of idiopathic right or left recurrent laryngeal neuropathy confirmed by videoendoscopy. All horses underwent a unilateral laryngoplasty with a unilateral or bilateral ventriculectomy or ventriculocordectomy. Follow-up endoscopy was performed in all horses within 24 hours postoperative, in 24 horses at 2-weeks, and in 65 horses at 6 weeks. Late follow-up was obtained from the trainer, owner, or referring veterinarian by telephone. RESULTS: Laryngoplasty was performed under endoscopic guidance with the horses sedated, and the surgical site was desensitized with local anesthetic solution. Laryngoplasty was completed in all horses and was well tolerated. No hyperabduction was observed. Two horses developed incisional swelling that resolved with drainage only. Late follow-up reported satisfactory improvement in respiration in all but 3 horses. CONCLUSIONS: Laryngoplasty performed with the horse standing avoids risks associated with general anesthesia and recovery and yields comparable results in nonracing horses, to laryngoplasty performed with the horse anesthetized. This technique reduces cost and allows accurate intraoperative adjustment of the degree of arytenoid abduction.

Computed tomography-guided tissue engineering of upper airway cartilage.

Normal laryngeal function has a large impact on quality of life, and dysfunction can be life threatening. In general, airway obstructions arise from a reduction in neuromuscular function or a decrease in mechanical stiffness of the structures of the upper airway. These reductions decrease the ability of the airway to resist inspiratory or expiratory pressures, causing laryngeal collapse. We propose to restore airway patency through methods that replace damaged tissue and improve the stiffness of airway structures. A number of recent studies have utilized image-guided approaches to create cell-seeded constructs that reproduce the shape and size of the tissue of interest with high geometric fidelity. The objective of the present study was to establish a tissue engineering approach to the creation of viable constructs that approximate the shape and size of equine airway structures, in particular the epiglottis. Computed tomography images were used to create three-dimensional computer models of the cartilaginous structures of the larynx. Anatomically shaped injection molds were created from the three-dimensional models and were seeded with bovine auricular chondrocytes that were suspended within alginate before static culture. Constructs were then cultured for approximately 4 weeks post-seeding and evaluated for biochemical content, biomechanical properties, and histologic architecture. Results showed that the three-dimensional molded constructs had the approximate size and shape of the equine epiglottis and that it is possible to seed such constructs while maintaining 75%+ cell viability. Extracellular matrix content was observed to increase with time in culture and was accompanied by an increase in the mechanical stiffness of the construct. If successful, such an approach may represent a significant improvement on the currently available treatments for damaged airway cartilage and may provide clinical options for replacement of damaged tissue during treatment of obstructive airway disease.

Regenerative medicine approach to reconstruction of the equine upper airway.

Airway obstruction is a common cause of poor performance in horses. Structural abnormalities (insufficient length, rigidity) can be a cause for the obstruction. Currently, there are a few effective clinical options for reconstruction of the equine larynx. A regenerative medicine approach to reconstruction may provide the capability to stabilize laryngeal structures and to encourage restoration of site-appropriate, functional, and host-derived tissue. The purpose of this study was the histopathological evaluation of (1) decellularization of equine (horse) laryngeal cartilages (epiglottis and arytenoids); (2) the host response to decellularized laryngeal cartilages implanted subcutaneously in a donkey model as a test of biocompatibility; and (3) the use of decellularized laryngeal cartilages in a clinically relevant pilot study in the horse larynx. Equine laryngeal cartilages were found to be sufficiently decellularized and were subsequently implanted subcutaneously in donkeys to test biocompatibility. After 4 weeks, the implanted cartilage was harvested. In the subcutaneous model, the samples did not elicit a rejection or foreign body type reaction and were judged suitable for implantation in a clinically relevant equine model. Implants were placed in the upper airway (arytenoids and epiglottis) of one horse. At 4 weeks, the implants were observed to remodel rapidly and were replaced by dense connective tissue with signs of new hyaline cartilage formation in the arytenoids and by connective tissue containing glandular structures and an epithelial covering in the epiglottis. The results of the present study demonstrate the feasibility of a scaffold-based regenerative medicine approach to reconstruction of the equine upper airway; however, further studies investigating long-term integration, formation of new cartilage, and mechanical properties are needed.

Equine laryngoplasty sutures undergo increased loading during coughing and swallowing.

OBJECTIVES: To report (1) the force required on a single laryngoplasty suture to achieve optimal abduction of the left arytenoid cartilage, (2) peak forces experienced by the suture during induced swallowing and coughing, and during 24-hour resting activity in a stall, and (3) peak forces during induced swallowing and coughing after left recurrent laryngeal nerve blockade. STUDY DESIGN: Experimental study. ANIMALS: Horses (n=8). METHODS: Each laryngoplasty suture was instrumented with an E-type buckle force transducer to measure the force required for optimal intraoperative left arytenoid cartilage abduction. This was correlated with abduction observed postoperatively. Change in suture force from baseline was measured during induced coughing and swallowing, and during normal stall activity. RESULTS: Optimal intraoperative arytenoid abduction was achieved with a mean (±SD) force of 27.6±7.5 N. During saline-induced swallowing and coughing mean force on the suture increased by 19.0±5.6 N (n=233 measurements; 7 horses) and 12.1±3.6 N (n=31; 4 horses), respectively. Sutures underwent increased loading a mean of 1152 times in 24 hours. No change in suture force was observed with respiratory rhythm. CONCLUSION: Swallowing increases laryngoplasty suture force to a greater extent than coughing.

A technique for laser-facilitated equine pastern arthrodesis using parallel screws inserted in lag fashion.

OBJECTIVE: To report a technique for laser-facilitated, minimally invasive proximal interphalangeal joint (PIJ) arthrodesis in horses. STUDY DESIGN: Case series. ANIMALS: Horses (n=6); 5 thoracic and 2 pelvic limb PIJ. METHODS: PIJ osteoarthritis (OA) diagnosis was confirmed by radiography. A diode laser was used to apply 2000 J of energy to the joint followed by insertion of 3 parallel 5.5 mm screws in lag fashion through stab incisions to achieve PIJ arthrodesis. After anesthetic recovery, limbs were maintained in bandages (n=2) or bandage casts (5) for 3 weeks. Horses were allowed exercise or turnout by 3 months. RESULTS: Three horses (4 limbs) were sound throughout follow-up (6-18 months). One horse remained lame the 1st month, another had mild lameness at pasture at 6 weeks, and another had persistent low-grade lameness and delayed joint fusion (1 year). Within 6 months, 5 horses were sound, 4 had radiographic evidence of successful joint fusion, and 5 had returned to intended use. CONCLUSION: Diode laser-facilitated, 3 parallel screw arthrodesis for PIJ OA costs less and is associated with less pain compared with standard, open PIJ arthrodesis using 3 parallel screws inserted in lag fashion. CLINICAL RELEVANCE: In horses with advanced PIJ OA, this technique appears to be a viable alternative for PIJ arthrodesis. Further study including characterization of the effects of the laser, ideal case selection indications, and optimal laser dose is indicated before this technique is recommended for routine PIJ arthrodesis.

Role of the hypoglossal nerve in equine nasopharyngeal stability.

The equine upper airway is highly adapted to provide the extremely high oxygen demand associated with strenuous aerobic exercise in this species. The tongue musculature, innervated by the hypoglossal nerve, plays an important role in airway stability in humans who also have a highly adapted upper airway to allow speech. The role of the hypoglossal nerve in stabilizing the equine upper airway has not been established. Isolated tongues from eight mature horses were dissected to determine the distal anatomy and branching of the equine hypoglossal nerve. Using this information, a peripheral nerve location technique was used to perform bilateral block of the common trunk of the hypoglossal nerve in 10 horses. Each horse was subjected to two trials with bilateral hypoglossal nerve block and two control trials (unblocked). Upper airway stability at exercise was determined using videoendoscopy and measurement of tracheal and pharyngeal pressure. Three main nerve branches were identified, medial and lateral branches and a discrete branch that innervated the geniohyoid muscle alone. Bilateral hypoglossal block induced nasopharyngeal instability in 10/19 trials, and none of the control trials (0/18) resulted in instability (P<0.001). Mean treadmill speed (+/-SD) at the onset of instability was 10.8+/-2.5 m/s. Following its onset, nasopharyngeal instability persisted until the end of the treadmill test. This instability, induced by hypoglossal nerve block, produced an expiratory obstruction similar to that seen in a naturally occurring equine disease (dorsal displacement of the soft palate, DDSP) with reduced inspiratory and expiratory pharyngeal pressure and increased expiratory tracheal pressure. These data suggest that stability of the equine upper airway at exercise may be mediated through the hypoglossal nerve. Naturally occurring DDSP in the horse shares a number of anatomic similarities with obstructive sleep apnea. Study of species with extreme respiratory adaptation, such as the horse, may provide insight into respiratory functioning in humans.

A technique for internal fixation of scapulohumeral luxation using scapulohumeral tension sutures in three alpacas and one miniature steer.

OBJECTIVE: To report a technique for open reduction and internal fixation of scapulohumeral joint luxation in large animals, and outcome. STUDY DESIGN: Clinical case reports. ANIMALS: Mature alpacas (n=3) and immature miniature steer (1). METHODS: Shoulder joint luxation was diagnosed by physical examination and confirmed by radiography. Open reduction was performed with internal fixation using lateral tension band sutures. RESULTS: Animals maintained shoulder joint reduction and were sound with radiographically normal shoulder joints (n=2) and normal range of motion without appreciable gait abnormalities (4) at follow-up 8-36 months later. CONCLUSIONS: In contrast to previous reports of open reduction with internal fixation of shoulder joint luxation in large animals, open reduction and use of lateral scapulohumeral tension sutures resulted in functionally normal shoulder joints. CLINICAL RELEVANCE: Stabilization of the shoulder joint with lateral scapulohumeral tension sutures after open reduction is effective, technically simple, and should be considered in large animal species weighing <100 kg.

In vitro model for testing novel implants for equine laryngoplasty.

OBJECTIVE: To develop an in vitro laryngeal model to mimic airflow and pressures experienced by horses at maximal exercise with which to test laryngoplasty techniques. STUDY DESIGN: Randomized complete block. SAMPLE POPULATION: Cadaveric equine larynges (n=10). METHODS: Equine larynges were collected at necropsy and a bilateral prosthetic laryngoplasty suture was placed with #5 Fiberwire suture to achieve bilateral maximal arytenoid abduction. Each larynx was positioned in a flow chamber and subjected to static flow and dynamic flow cycling at 2 Hz. Tracheal pressure and flow, and pressure within the flow chamber were recorded at a sampling frequency of 500 Hz. Data obtained were compared with the published physiologic values for horses exercising at maximal exercise. RESULTS: Under static flow conditions, the testing system produced inspiratory tracheal pressures (mean+/-SEM) of -33.0+/-0.98 mm Hg at a flow of 54.48+/-1.8 L/s. Pressure in the flow chamber was -8.1+/-2.2 mm Hg producing a translaryngeal impedance of 0.56+/-0.15 mm Hg/L/s. Under dynamic conditions, cycling flow and pressure were reproduced at a frequency of 2 Hz, the peak inspiratory (mean+/-SEM) pharyngeal and tracheal pressures across all larynges were -8.85+/-2.5 and -35.54+/-1.6 mm Hg, respectively. Peak inspiratory flow was 51.65+/-2.3 L/s and impedance was 0.57+/-0.06 mm Hg/L/s. CONCLUSIONS: The model produced inspiratory pressures similar to those in horses at maximal exercise when airflows experienced at exercise were used. CLINICAL RELEVANCE: This model will allow testing of multiple novel techniques and may facilitate development of improved techniques for prosthetic laryngoplasty.

Arthroscopic removal of palmar/plantar osteochondral fragments from the proximal interphalangeal joint in four horses.

OBJECTIVE: To describe anatomic considerations and arthroscopic technique in horses for arthroscopic removal of palmar/plantar osteochondral fragments from the proximal interphalangeal (PIP) joint. STUDY DESIGN: Retrospective study. ANIMALS: Adult horses (n=4) with osteochondral fragments of the palmar/plantar PIP joint. METHODS: Arthroscopic removal of palmar/plantar osteochondral fragments within the PIP joint was performed with horses in dorsal recumbency under general anesthesia. Medical records of affected horses were reviewed to determine history; physical, lameness, and radiological findings; surgical technique; complications and outcome. RESULTS: Two horses had lameness localized to the PIP joint. Two other horses had lameness suspected, but not confirmed to the pastern region. One of these horses had a history of intermittent lameness, but was not lame on admission. All horses had radiographic evidence of palmar/plantar osteochondral fragmentation within the PIP joint. Fragmentation was located abaxially in 2 horses in the hind limb and axially in 2 horses in the left forelimb. Osteochondral fragments were successfully removed via a palmar/plantar arthroscopic approach in all horses. Three horses returned to previous levels of athletic performance; 1 horse was used for trail riding instead of reining. CONCLUSIONS: Arthroscopy of the palmar/plantar pouch of the PIP joint allowed limited assessment of the joint and removal of osteochondral fragments. CLINICAL RELEVANCE: Arthroscopy of the palmar/plantar PIP joint pouch for assessment and removal of osteochondral fragments is possible and should be considered when lameness is localized to this joint.

Septic epiglottic chondritis with abscessation in 2 young Thoroughbred racehorses.

Septic epiglottic chondritis with abscessation diagnosed in 2 Thoroughbred racehorses. Infected cartilage removed videoendoscopically followed by systemic antibiotics. The infectious process was successfully controlled, but permanent dorsal displacement of the soft palate (DDSP) with a shortened, deformed epiglottic cartilage developed. Surgery for the DDSP using bilateral partial sternothyroidectomy or laryngeal tie-forward failed.