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.

Laryngeal reinnervation using the spinal accessory nerve: Electromyographic study of the sternomandibularis muscle.

BACKGROUND: Selective laryngeal reinnervation using the first and second cervical nerve (C1C2) is a treatment option for recurrent laryngeal neuropathy that aims to restore the function of the cricoarytenoideus dorsalis (CAD) muscle. Despite the technique's satisfying success rate, it has several limitations. These triggered the search for another potential donor nerve that could reduce CAD muscle fatigue and shorten rehabilitation. The ventral branch of the spinal accessory nerve, providing motor innervation to the sternomandibularis (SM) muscle, was identified as a potentially well-adapted nerve. OBJECTIVES: To gather normative data from SM muscle activity induced by physiological spinal accessory nerve stimulation at rest and during exercise, and to determine SM muscle activity and fibre type recruitment relative to posture, gait and respiratory cycle. STUDY DESIGN: Clinical observational study. METHODS: Surface electromyography (EMG) of the SM muscle was performed in nine horses: trained warmbloods, Thoroughbreds and Standardbreds. Signals were recorded in different feeding postures and at exercise, which included standardised treadmill exercise tests, lungeing and ridden work. RESULTS: Timing of the SM muscle contraction coincided with inspiration at gallop. Intra-individual mean SM muscle activity increased with exercising speed (four times higher in Thoroughbreds at gallop than walk and seven times higher in Standardbreds at high-speed trot than walk). Moreover, the SM muscle was strongly activated at rest when the horse was grazing (seven times more than when it was eating out of a hay net or stable feeder). Frequency domain analysis revealed a predominant type I muscle fibre recruitment during feeding and at exercise (type I muscle fibre activity was at least 2.5 times higher than type II muscle fibre activity). MAIN LIMITATIONS: Lack of reference data on equine EMG. CONCLUSIONS: This study confirmed the potentially advantageous properties of the spinal accessory nerve for laryngeal reinnervation.

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.

Equine Nasal Endoscopy: Treating Bullae Disease and Sinus Disease.

The nasal conchal bullae (dorsal and ventral) are separate, air-filled structures within their respective dorsal and ventral nasal conchae. Computed tomography scans have assisted with the increasing diagnosis of empyema of the nasal conchae. This condition is usually associated with dental or sinus disease. Drainage of affected bullae is considered critical for resolution of clinical signs. The ventral conchal bullae can be easily viewed with a standard 10 mm diameter flexible endoscopy via the middle nasal meatus. This approach can also be used for fenestration of the bullae, using a diode laser, equine laryngeal forceps, or bipolar vessel sealing device.

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.

Functional electrical stimulation following nerve injury in a large animal model.

INTRODUCTION: Controversy exists over the effects of functional electrical stimulation (FES) on reinnervation. We hypothesized that intramuscular FES would not delay reinnervation after recurrent laryngeal nerve (RLn) axonotmesis. METHODS: RLn cryo-injury and electrode implantation in ipsilateral posterior cricoarytenoid muscle (PCA) were performed in horses. PCA was stimulated for 20 weeks in eight animals; seven served as controls. Reinnervation was monitored through muscle response to hypercapnia, electrical stimulation and exercise. Ultimately, muscle fiber type proportions and minimum fiber diameters, and RLn axon number and degree of myelination were determined. RESULTS: Laryngeal function returned to normal in both groups within 22 weeks. FES improved muscle strength and geometry, and induced increased type I:II fiber proportion (p = 0.038) in the stimulated PCA. FES showed no deleterious effects on reinnervation. DISCUSSION: Intramuscular electrical stimulation did not delay PCA reinnervation after axonotmesis. FES can represent a supportive treatment to promote laryngeal functional recovery after RLn injury. Muscle Nerve 59:717-725, 2019.

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.

Rhodococcus equi Joint Sepsis and Osteomyelitis Is Associated With a Grave Prognosis in Foals.

The most common pathologic manifestation of Rhodococcus equi, a gram-positive, facultative intracellular bacterium, is pyogranulomatous pneumonia in foals and weanlings. Hematogenous spread of bacteria may subsequently occur, resulting in joint sepsis, osteomyelitis, or subcutaneous abscessation. Medical records from horses presenting to the Cornell University Equine Hospital from 1998 to 2018 were reviewed for cases diagnosed with R. equi joint and/or bone infection, and information about case progression and outcome were analyzed. We hypothesized that, despite advances in diagnostic imaging, antimicrobials and antimicrobial delivery methods, the prognosis for R. equi joint sepsis and osteomyelitis remains grave for athletic activity and poor for survival. The 12 cases that met the review criteria had a mortality rate of 84% (10/12), with one case lost to follow up after discharge and one case discharged with a grave prognosis for athleticism.

Anatomy of the vestibulum esophagi and surgical implications during prosthetic laryngoplasty in horses.

OBJECTIVE: To describe the anatomy of the entry to the equine esophagus (vestibulum esophagi) and to assess the risk of penetrating its adventitia and/or lumen during laryngoplasty. STUDY DESIGN: Ex vivo cadaveric study. SAMPLE POPULATION: Five isolated equine larynges and 39 equine head and neck specimens. METHODS: The anatomy of the vestibulum esophagi was studied by dissection of 5 cadaver specimens. Then, a bilateral laryngoplasty was performed, including 5 suture placements through the muscular processes, caudal, rostral, and sagittal, with straight and curved needles. Two of the 3 surgeons performing the implantations were unaware of the goals of the study. Suture positions and iatrogenic trauma to the lumen and/or adventitia of the vestibulum esophagi were identified during dissection of the specimens. Risk factors for penetrating the adventitia were evaluated with a multivariate regression model. RESULTS: The vestibulum esophagi spans between both wings of the thyroid cartilage over the entire width of the larynx, covering the rostral spine (arcuate crest) of the arytenoid cartilages. It is covered by the thyropharyngeus and cricopharyngeus muscles. Masked surgeons were associated with a significantly higher number of adventitia penetrations (72%) compared to the nonmasked surgeon (9%). The lumen of the vestibulum esophagi was penetrated in 4.6% of suture placements and only by the 2 masked surgeons. CONCLUSION: Penetration of the adventitia was more common when surgeons were unaware of the anatomical extent of the vestibulum esophagi. CLINICAL SIGNIFICANCE: Anatomical knowledge of the extent of the vestibulum esophagi reduces the risk of penetrating its lumen or adventitia during suture placement on the muscular process of the arytenoid cartilage.

Ex vivo biomechanical stability of 5 cricoid-suture constructs for equine laryngoplasty.

OBJECTIVE: To determine the biomechanical properties of 5 suture constructs in the equine cricoid under cyclic loading and load to failure testing. STUDY DESIGN: Ex vivo study. SAMPLES: Seventy-five equine cadaver larynges. METHODS: Each larynx was implanted with 1 of 5 cricoid-suture constructs. The standard laryngoplasty, where a suture is passed once through the cricoid, including its caudal edge, was used in 2 constructs: 1 with 5 USP Ethibond (ES) and 1 with 2 mm Fibertape (FS). In the third construct, the 2 mm Fibertape was passed twice through the cricoid including its caudal edge (Double Loop-DL). Constructs 4 and 5 used 2 mm Fibertape in a U-shaped loop passed through the cricoid but excluding its caudal edge. One construct was supported with a metallic button (MB) on the caudo-ventral aspect of the cricoid while the other included only the U-shaped loop (U). Constructs were subjected to cyclic loading and to single cycle to failure. Reduction of the left-to-right arytenoid angle quotient (LRQ), suture migration, and load at failure were compared. RESULTS: LRQ reduction after cyclic loading was lower in MB and U than ES constructs. During cyclic loading, suture migration was reduced in MB, U, and DL compared to ES constructs. Mean load at failure was lower in FS and U than in ES constructs. CONCLUSION: Loss of abduction after equine laryngoplasty may be reduced and pullout forces increased by applying a MB construct in the cricoid cartilage. In vivo testing is required to verify these results.

Feasibility, repeatability, and safety of ultrasound-guided stimulation of the first cervical nerve at the alar foramen in horses.

OBJECTIVE To develop and assess the feasibility, repeatability, and safety of an ultrasound-guided technique to stimulate the first cervical nerve (FCN) at the level of the alar foramen of the atlas of horses. ANIMALS 4 equine cadavers and 6 clinically normal Standardbreds. PROCEDURES In each cadaver, the FCN pathway was determined by dissection, and any anastomosis between the first and second cervical nerves was identified. Subsequently, each of 6 live horses underwent a bilateral ultrasound-guided stimulation of the FCN at the alar foramen 3 times at 3-week intervals. After each procedure, horses were examined daily for 5 days. RESULTS In each cadaver, the FCN passed through the alar foramen; a communicating branch between the FCN and the accessory nerve and anastomoses between the ventral branches of the FCN and second cervical nerve were identified. The anastomoses were located in the upper third of the FCN pathway between the wing of the atlas and the nerve's entry in the omohyoideus muscle. Successful ultrasound-guided electrical stimulation was confirmed by twitching of the ipsilateral omohyoideus muscle in all 6 live horses; this finding was observed bilaterally during each of the 3 experimental sessions. No complications developed at the site of stimulation. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that ultrasound-guided stimulation of the FCN at the alar foramen appears to be a safe and straightforward procedure in horses. The procedure may have potential for use in horses with naturally occurring recurrent laryngeal neuropathy to assess reinnervation after FCN transplantation or nerve-muscle pedicle implantation in the cricoarytenoideus dorsalis muscle.

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.

Ultrasonography detects early laryngeal muscle atrophy in an equine neurectomy model.

INTRODUCTION: A unilateral neurectomy model was used to study the relationship between histologic and ultrasonographic tissue characteristics during muscle atrophy over time. METHODS: This investigation was an in vivo experimental study in an equine model (n = 28). Mean pixel intensity of ultrasonographic images was measured, a muscle appearance grade was assigned weekly, and muscles were harvested from 4 to 32 weeks. Minimum fiber diameter, fiber density per unit area, percent collagen, percent fat, and fiber type profile were measured from muscle cryosections and correlated with the ultrasonographic parameters. RESULTS: A significant relationship was identified between collagen content, minimum fiber diameter, and ultrasonographic muscle appearance by as early as 8 weeks. There was no apparent association between fat content of muscle and the ultrasonographic appearance of atrophy before 28 weeks. CONCLUSIONS: Early muscle atrophy before fatty infiltration is detectable with ultrasound. The effect of muscle collagen content on echointensity may be mediated by reduced fiber diameter.

Effects of Functional Electrical Stimulation on Denervated Laryngeal Muscle in a Large Animal Model.

Bilateral vocal fold paralysis (BVCP) is a life-threatening condition that follows injury to the Recurrent Laryngeal nerve (RLn) and denervation of the intrinsic laryngeal musculature. Functional electrical stimulation (FES) enables restoration and control of a wide variety of motor functions impaired by lower motor neuron lesions. Here we evaluate the effects of FES on the sole arytenoid abductor, the posterior cricoarytenoid (PCA) muscle in a large animal model of RLn injury. Ten horses were instrumented with two quadripolar intramuscular electrodes in the left PCA muscle. Following a 12-week denervation period, the PCA was stimulated using a once-daily training session for 8 weeks in seven animals. Three animals were used as unstimulated controls. Denervation produced a significant increase in rheobase (P < 0.001). Electrical stimulation produced a 30% increase in fiber diameter in comparison with the unstimulated control group (33.9 ± 2.6 µm FES+, 23.6 ± 4.2 µm FES-, P = 0.04). A trend toward a decrease in the proportion of type 1 (slow) fibers and an increase in type 2a (fast) fibers was also observed. Despite these changes, improvement in PCA function at rest was not observed. These data suggest that electrical stimulation using a relatively conservative set of stimulation parameters can reverse the muscle fiber atrophy produced by complete denervation while avoiding a shift to a slow (type 1) fiber type.

Ultrasonographic detection of early atrophy of the intrinsic laryngeal muscles of horses.

OBJECTIVE: To describe the ultrasonographic changes in the cricoarytenoideus dorsalis (CAD) and cricoarytenoideus lateralis (CAL) muscles of horses before and at various times during the 32 weeks after unilateral neurectomy of the right recurrent laryngeal nerve. ANIMALS: 28 healthy Standardbreds. PROCEDURES: For each horse, the appearance of the CAD and CAL muscles on the right (neurectomized) and left (control) sides was serially monitored ultrasonographically by percutaneous (CAD and CAL) and transesophageal (CAD) approaches. The ultrasonographic images were assessed to determine the mean pixel intensity, muscle thickness, and appearance grade, and comparisons were made between the muscles of the neurectomized and control sides. RESULTS: The muscle appearance grade and mean pixel intensity for the CAL and CAD muscles on the neurectomized side were significantly increased by 2 and 4 weeks, respectively, after the neurectomy. The transesophageal approach enhanced the ultrasonographic visibility of the CAD muscle and allowed us to detect a significant decrease in the thickness of the CAD muscle on the neurectomized side over time, compared with thickness of the CAD muscle on the control side. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested ultrasonography can be used to successfully assess the CAL and CAD muscles of horses. A qualitative grading scheme was sufficient for successful detection and monitoring of muscle atrophy and reduced the need for image standardization. The transesophageal approach described for assessment of the CAD muscle warrants further investigation.

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.