3D kinematics of the interphalangeal joints in the forelimb of walking and trotting horses

The objective was to measure 3D rotations of the distal (DIP) and proximal (PIP) interphalangeal joints at walk and trot. 3D trajectories of markers fixed to the proximal phalanx, middle phalanx and the hoof wall of the right forelimb of four sound horses were recorded at 120 Hz. Joint kinematics were calculated in terms of anatomically-based joint coordinate systems between the bone segments. Ranges of motion were similar at walk and trot. Values for the DIP joint were: flexion/extension: 46 ± 3° at walk, 47 ± 4° at trot; internal/ external rotation: 5 ± 1° at walk, 6 ± 3° at trot; and adduction/abduction: 5 ± 2° at walk, 5 ± 3° at trot. Within each gait, kinematic profiles at the DIP joint were similar between horses with the exception of adduction/abduction during breakover, which may vary depending on the direction of hoof rotation over the toe. Knowledge of the types and amounts of motion at the DIP joint will be useful in understanding the aetiology and treatment of injuries to the soft tissues, which are being recognized more frequently through the use of sensitive imaging techniques. Ranges of motion for the PIP joint were: flexion/extension: 13 ± 4° at walk, 14 ± 4° at trot; adduction/abduction: 3 ± 1° at walk, 3 ± 1° at trot; and internal/external rotation: 3 ± 1° at walk, 4 ± 1° at trot. The PIP joint made a significant contribution to flexion/extension of the digit. During surgical arthrodesis, the angle of fusion may be important since loss of PIP joint extension in late stance is likely to be accommodated by increased extension of the DIP joint.

Ultrasound-guided biopsy of the cricoarytenoideus lateralis muscle: technique and safety in horses

REASONS FOR PERFORMING STUDY

Current diagnosis of recurrent laryngeal neuropathy (RLN) depends upon disease recognition in the clinically affected horse. Biopsy of the intrinsic laryngeal muscles may provide a method to identify the changes in fibre-type composition that occur in RLN before clinical signs become apparent.

OBJECTIVE

To develop an ultrasound-guided biopsy technique of the left cricoarytenoideus lateralis muscle (CALM) and evaluate its efficacy and safety in vivo.

STUDY DESIGN

A longitudinal descriptive study.

METHODS

Six standing horses underwent ultrasound-guided biopsy of the left CALM. Frozen muscle cores were obtained with a breast biopsy tool. Serial endoscopic, ultrasonographic and physical examinations before and for 8 weeks after the biopsy were assessed for iatrogenic trauma. Histologies of representative muscle core cross-sections were analysed for the total number of muscle fibres obtained with each biopsy.

RESULTS

There were no immediate complications of the procedure and the left CALM was harvested in all instances. Biopsy samples had an average weight of 0.043 g (range = 0.023-0.077 g) and contained 3418 fibres in cross-section (range = 711-7143). Laryngeal endoscopic grade did not change significantly between prebiopsy and the end of the 8 week follow-up. The left CALM had significantly greater echogenicity than the right throughout the study (P<0.001), but there was no difference between the prebiopsy CALM echogenicity and that at completion of the study.

CONCLUSIONS

Ultrasound-guided biopsy of the left CALM is safe and well tolerated, providing a minimally invasive method to obtain muscle from healthy horses. This new technique may be applicable in research and clinical settings.

Stifle extension results in differential tensile forces developing between abaxial and axial components of the cranial meniscotibial ligament of the equine medial meniscus: a mechanistic explanation for meniscal tear patterns

REASON FOR PERFORMING THE STUDY

To identify potential functional-anatomical characteristics of the cranial horn attachment of the medial meniscus (MM) that may help explain the pathogenesis of the common tear patterns that have been reported.

HYPOTHESIS

Full extension of the stifle generates a significant increase in tensile forces within the cranial meniscotibial ligament (CrMTL) of the MM, which may predispose this structure to injury.

METHODS

The effect of femorotibial angle (160°, 150°, 140° and 130°) on tensile forces in the axial and abaxial components of the CrMTL was examined in 6 mature cadaver stifles using an implantable force probe. Three additional specimens were used to examine the histological structure of the CrMTL and its connection to the cranial horn of the MM.

RESULTS

Full extension of the stifle (160°) resulted in a significantly greater tensile force in the abaxial component of the CrMTL when compared with the axial component (P = 0.001). The tensile force in the abaxial component of the CrMTL increased significantly between 150° and 160° of stifle extension (P = 0.011). The CrMTL appears to be comprised of 2 functional components, which become more visually distinct as the stifle is extended. Histologically, these components are separated by a cleft of highly vascularised, less organised connective tissue, which becomes less prominent at the junction of the ligament and the cranial horn of the MM.

CONCLUSION

A 4-fold difference in the tensile forces in the 2 functional components of the CrMTL of the MM was observed with full extension of the stifle.

POTENTIAL RELEVANCE

The functional anatomy of the CrMTL may place this region at greater risk of injury during hyperextension of the stifle and, therefore, may provide a mechanistic rationale for the commonly reported meniscal tear patterns in the horse.

Cervical vertebral canal endoscopy in the horse: intra- and post operative observations

REASONS FOR PERFORMING STUDY

Despite modern medical diagnostic imaging, it is not possible to identify reliably the exact location of spinal cord compression in horses with cervical vertebral stenotic myelopathy (CVSM). Vertebral canal endoscopy has been successfully used in man and a technique for cervical vertebral canal endoscopy (CVCE) has been described in equine cadavers.

OBJECTIVE

To determine the feasibility and safety of CVCE in healthy mature horses.

METHODS

Six healthy mature horses were anaesthetised. A flexible videoendoscope was subsequently introduced via the atlanto-occipital space into the epidural space (epiduroscopy, Horses 1-3) or the subarachnoid space (myeloscopy, Horses 4-6) and advanced to the 8th cervical nerve. Neurological examinations were performed after surgery and lumbosacral cerebrospinal fluid (CSF) analysed in horses that had undergone myeloscopy.

RESULTS

All procedures were completed successfully and all horses recovered from anaesthesia. Anatomical structures in the epidural space (including the dura mater, nerve roots, fat and blood vessels) and subarachnoid space (including the spinal cord, blood vessels, arachnoid trabeculations, nerve roots and the external branch of the accessory nerve) were identified. During epiduroscopy, a significant increase in mean arterial pressure was recognised, when repeated injections of electrolyte solution into the epidural space were performed. In one horse of the myeloscopy group, subarachnoid haemorrhage and air occurred, resulting in transient post operative ataxia and muscle fasciculations. No complications during or after myeloscopy were observed in the other horses. CSF analysis indicated mild inflammation on Day 7 with values approaching normal 21 days after surgery.

CONCLUSIONS

Endoscopic examination of the epidural and subarachnoid space from the atlanto-occipital space to the 8th cervical nerve is possible and can be safely performed in healthy horses.

POTENTIAL RELEVANCE

Cervical vertebral canal endoscopy might allow accurate identification of the compression site in horses with CVSM and aid diagnosis of other lesions within the cervical vertebral canal.

Meniscal translocation and deformation throughout the range of motion of the equine stifle joint: an in vitro cadaveric study

REASON FOR PERFORMING STUDY

By study of the translocation and deformation of equine menisci throughout the range of motion, it may be possible to identify potential mechanical factors in the pathogenesis of injury to the cranial horn of the medial meniscus.

OBJECTIVE

To quantitatively document meniscal translocation and deformation using radiographic and MR imaging, and to evaluate for potential variation between the medial and lateral menisci.

METHODS

Radiographic markers were embedded in the periphery of the menisci in 6 cadaver stifles. Proximal-distal radiographs were taken at 15° intervals ranging from full flexion (30°) to full extension (160°). Magnetic resonance imaging sequences of 3 additional cadaver stifles were obtained in axial and sagittal planes at the predetermined stifle angles.

RESULTS

A significantly greater overall mean cranial-caudal translocation (1.6 times) of the lateral meniscus relative to the medial was seen from full extension to full flexion (P = 0.002). The cranial horn of the medial meniscus was the least mobile of the 4 horns, yet a significant cranial displacement relative to the cranial horn of the lateral meniscus was seen in the terminal 10° of extension. MRI images revealed a significantly greater axial compressive strain in the cranial horn of the medial meniscus relative to the cranial horn of the lateral meniscus in the terminal 10° of extension (P = 0.017).

CONCLUSION

The equine menisci exhibit a cranial-caudal translocation over the tibia throughout the range of motion. While the cranial horn of the medial meniscus is the least mobile of the 4 horns, it undergoes significant cranial translocation and axial compression in the terminal 10° of extension.

POTENTIAL RELEVANCE

Hyperextension of the stifle may place the cranial horn of the medial meniscus at risk of injury and thus explain the higher prevalence of meniscal tears at this location.

Effect of ventriculectomy versus ventriculocordectomy on upper airway noise in draught horses with recurrent laryngeal neuropathy

REASONS FOR PERFORMING STUDY

Little is known about the efficacy of bilateral ventriculectomy (VE) or bilateral ventriculocordectomy (VCE) in draught horses.

OBJECTIVES

To compare the effect of VE and VCE on upper airway noise in draught horses with recurrent laryngeal neuropathy (RLN) by use of quantitative sound analysis techniques.

HYPOTHESIS

In competitive draught horses with grade 4 RLN, VE and VCE reduce upper airway noise during exercise, but VCE is more effective.

METHODS

Thirty competitive hitch or pulling draught horses with grade 4 RLN were evaluated for upper airway sound during exercise. Respiratory rate (RR), inspiratory (Ti) and expiratory time (Te), the ratio between Ti and Te (Ti/Te), inspiratory (Sli) and expiratory sound levels (Sle), the ratio between Sli and Sle (Sli/Sle), and peak sound intensity of the second formant (F2) were calculated. Eleven horses were treated with VE and 19 with VCE. After 90 days of voice and physical rest and 30 days of work, the horses returned for post operative upper airway sound evaluation and resting videoendoscopy.

RESULTS

VE significantly reduced Ti/Te, Sli, Sli/Sle and the sound intensity of F2. Respiratory rate, Ti, Te and Sle were unaffected by VE. VCE significantly reduced Ti/Te, Ti, Te, Sli, Sli/Sle and the sound intensity of F2, while RR and Sle were unaffected. The reduction in sound intensity of F2 following VCE was significantly greater than following VE. After VE and VCE, 7/11 (64%) and 15/18 (83%) owners, respectively, concluded that the surgery improved upper airway sound in their horses sufficiently for successful competition.

CONCLUSIONS

VE and VCE significantly reduce upper airway noise and indices of airway obstruction in draught horses with RLN, but VCE is more effective than VE. The procedures have few post operative complications.

POTENTIAL RELEVANCE

VCE is recommended as the preferred treatment for RLN in draught horses. Further studies are required to evaluate the longevity of the procedure's results.

Three-dimensional carpal kinematics of trotting horses

REASONS FOR PERFORMING STUDY

Descriptions of 3D kinematics assist in understanding joint function and dysfunction, and are an essential step toward 3D inverse dynamic analysis.

OBJECTIVES

To measure 3D carpal joint motion during trotting.

METHODS

Three-dimensional trajectories of bone-fixed markers on the radius and third metacarpus of the right forelimb of 3 healthy horses were recorded at 120 Hz using a 6-camera analysis system. Joint kinematics were calculated in terms of helical angles between the 2 segments using a spatial attitude method.

RESULTS

All horses showed carpal extension and internal rotation of the metacarpus relative to the radius as the carpus assumed the close-packed position. In late stance, the carpus began a cycle of flexion that continued through midswing, accompanied by a small cycle of internal rotation. The direction of abduction/adduction varied between horses. The predominant rotational movement was flexion/extension, which showed a range of motion of 15 +/- 6 degrees in stance and 76 +/- 13 degrees in swing.

CONCLUSIONS

Carpal motions were generally similar between horses with the exception of abduction/adduction.

POTENTIAL RELEVANCE

Knowledge of carpal joint motion should assist in understanding the pathogenesis of carpal injuries. However, it seems probable that real differences exist between individuals; therefore, further investigations of the effect of conformation on carpal motion should be performed in a much larger population of horses.

Equine thoracoscopy: normal anatomy and surgical technique

Six normal, healthy horses age 3-10 years underwent left and right thoracoscopic examination using a rigid telescope. A minimum of 30 days was allowed between procedures. Horses were restrained in stocks and sedated with a continuous detomidine infusion. After surgical preparation of the hemithorax elected for surgery, and administration of local or regional anaesthesia of the surgery sites, thoracoscopy was completed during two 15 min pneumothorax periods. During the procedures, the thoracic structures were viewed using a 57 cm, 10 mm diameter, 30 degrees rigid telescope connected to a digital camcorder to allow computer capture of digital images. The telescope was inserted into the thoracic cavity via 3 different intercostal spaces. The 8th, 10th and 12th intercostal spaces were randomly selected and used among horses. The exploration of each hemithorax started from the dorsal-caudal quadrant continued toward the cranial thorax and was completed by observing the diaphragmatic and caudal pulmonary region. Collapsed lung, aorta, oesophagus and diaphragm were viewed readily in either hemithorax. On exploration of the right hemithorax, the azygos vein, thoracic duct and pulmonary veins were also identified. Horses tolerated thoracoscopy well. Signs of discomfort, such as increased respiratory rate, coughing and decreased level of sedation, were associated with lung collapse in one horse, with pneumothorax on 2 occasions, and when the thorax was approached through the 8th intercostal space. Surgery performed via the 8th intercostal space was hindered by the rigidity of the 8th and 9th ribs, and by the presence of a greater musculature, which did not allow easy cranial and caudal movements of the telescope.

Effect of laryngoplasty on respiratory noise reduction in horses with laryngeal hemiplegia

REASONS FOR PERFORMING STUDY

Laryngoplasty is the technique of choice for treatment of laryngeal hemiplegia, with the aim of improving airway function and/or eliminating respiratory noise. However, there are no quantitative data in the literature describing the effect of laryngoplasty on upper airway noise or its relationship to upper airway mechanics in horses with laryngeal hemiplegia.

OBJECTIVES

To determine whether laryngoplasty reduces respiratory noise in exercising horses with laryngeal hemiplegia; and to establish whether the degree of upper airway obstruction can be predicted by upper airway noise, or the degree of arytenoid abduction correlated with airway obstruction and noise production.

METHODS

Six Standardbred horses with normal upper airways during maximal exercise were used. Respiratory sounds and inspiratory transupper airway pressure (Pui) were measured in all horses before and after induction of laryngeal hemiplegia and 30, 60 and 90 days after laryngoplasty. Inspiratory sound level (SL) and the sound intensity of the 3 inspiratory formants (F1, F2 and F3, respectively) were measured using a computer-based sound analysis programme. The degree of abduction was graded by endoscopic visualisation 1, 30, 60 and 90 days post operatively. Linear regression analysis was used to determine correlations between Pui, sound indices and grades of arytenoid abduction.

RESULTS

In laryngeal hemiplegia-affected horses, Pui, inspiratory SL and the sound intensity of F1, F2 and F3 were significantly increased. At 30 days following laryngoplasty, the sound intensity of F1 and Pui returned to baseline values. The sound intensities of F2, F3 and SL were significantly improved from laryngeal hemiplegia values at 30 days post operatively, but did not return to baseline at any measurement period. Sound level, F2 and F3 were significantly correlated with Pui (P<0.05), but the correlations were weak (r2 = 0.26, 035 and 0.40, respectively). Grade of abduction and F2 were positively and significantly correlated (P<0.006, r2 = 0.76). Grade of arytenoid abduction and Pui were not correlated (P = 0.12).

CONCLUSIONS

Laryngoplasty reduced inspiratory noise in laryngeal hemiplegia-affected horses by 30 days following surgery, but did not return it to baseline values. While upper airway noise and Pui were correlated, this relationship was insufficiently strong to predict Pui from noise in individual animals. The degree of arytenoid abduction was not correlated with Pui, but was positively correlated with noise production.

POTENTIAL RELEVANCE

Laryngoplasty reduces upper airway noise in horses with laryngeal hemiplegia, but is not as effective as bilateral ventriculocordectomy in this regard, although respiratory noise reduction occurs more rapidly than with bilateral ventriculocordectomy. Residual noise during exercise cannot be used as a predictor of improvement in upper airway function in individual horses following laryngoplasty. The degree of arytenoid abduction obtained following surgery does not affect upper airway flow mechanics. Interestingly, we found that the greater the arytenoid abduction, the louder the respiratory noise.

Effects of unilateral laser-assisted ventriculocordectomy in horses with laryngeal hemiplegia

REASONS FOR PERFORMING STUDY

Recent studies have evaluated surgical techniques aimed at reducing noise and improving airway function in horses with recurrent laryngeal neuropathy (RLN). These techniques require general anaesthesia and are invasive. A minimally invasive transnasal surgical technique for treatment of RLN that may be employed in the standing, sedated horse would be advantageous.

OBJECTIVE

To determine whether unilateral laser-assisted ventriculocordectomy (LVC) improves upper airway function and reduces noise during inhalation in exercising horses with laryngeal hemiplegia (LH).

METHODS

Six Standardbred horses were used; respiratory sound and inspiratory transupper airway pressure (Pui) measured before and after induction of LH, and 60, 90 and 120 days after LVC. Inspiratory sound level (SL) and the sound intensities of formants 1, 2 and 3 (Fl, F2 and F3, respectively), were measured using computer-based sound analysis programmes. In addition, upper airway endoscopy was performed at each time interval, at rest and during treadmill exercise.

RESULTS

In LH-affected horses, Pui, SL and the sound intensity of F2 and F3 were increased significantly from baseline values. At 60 days after LVC, Pui and SL had returned to baseline, and F2 and F3 values had improved partially compared to LH values. At 90 and 120 days, however, SL increased again to LH levels.

CONCLUSIONS

LVC decreases LH-associated airway obstruction by 60 days after surgery, and reduces inspiratory noise but not as effectively as bilateral ventriculocordectomy.

POTENTIAL RELEVANCE

LVC may be recommended as a treatment of LH, where reduction of upper airway obstruction and respiratory noise is desired and the owner wishes to avoid risks associated with a laryngotomy incision or general anaesthesia.

Electromyographic activity of the stylopharyngeus muscle in exercising horses

REASONS FOR PERFORMING STUDY

There is a need to understand the process which leads to failure of recruitment of the stylopharyngeus muscle in clinical cases of nasopharygeal collapse. We therefore studied the timing and intensity of stylopharyngeus muscle activity during exercise in horses.

OBJECTIVE

To measure the electromyographic (EMG) activity of the stylopharyngeus muscle in exercising horses and correlate it with the breathing pattern.

METHODS

Five horses were equipped with a bipolar fine wire electrode placed on the stylopharyngeus muscle and a pharyngeal catheter. The horses exercised on a treadmill at speeds corresponding to 50 (HRmax50), 75 and 100% of maximum heart rate, and EMG activity of the stylopharyngeus muscle and upper airway pressures were recorded. The EMG activity of the stylopharyngeus muscle was then correlated to the breathing pattern and the activity quantified and reported as a percentage of the baseline activity measured at HRmax50.

RESULTS

There was ongoing activity of the stylopharyngeus muscle throughout the breathing cycle; however, activity increased towards the end of expiration and peaked early during inspiration. Tonic activity was present during expiration. Peak, mean electrical and tonic EMG activity increased significantly (P<0.05) with exercise intensity.

CONCLUSION

The stylopharyngeus muscle has inspiratory-related activity and tonic activity that increases with speed.

POTENTIAL RELEVANCE

The stylopharyngeus muscle is one of a group of upper airway muscles that function to support and maintain the patency of the nasopharynx during inspiration. Failure of recruitment of the stylopharyngeus muscle during exercise is a potential explanation for clinical cases of dorsal pharyngeal collapse, but further work investigating the activity of the stylopharyngeus muscle in horses affected by this disease is needed.

Ventriculocordectomy reduces respiratory noise in horses with laryngeal hemiplegia

REASONS FOR PERFORMING STUDY

Show and performance horse with laryngeal hemiplegia (LH) often present for excessive respiratory noise rather than significant exercise intolerance. Therefore, the goal of surgery in these horses is to reduce respiratory noise but there are no quantitative studies evaluating the effect of any upper-airway surgery in LH-affected horses.

OBJECTIVE

To determine whether bilateral ventriculocordectomy (VC) reduces respiratory noise in exercising horses with laryngeal hemiplegia.

METHODS

Six Standardbred horses with normal upper airways were used in this study. Respiratory sounds and inspiratory trans-upper airway pressure (Pui) were measured in all horses before and after induction of LH, and 30, 90 and 120 days after VC. In horses with LH, spectrogram analysis revealed 3 inspiratory sound formants centred at approximately 400, 1700 and 3700 Hz. Inspiratory sound levels (SL) and the sound intensity of the 3 inspiratory formants (F1, F2, F3 respectively) were measured using a computer-based sound analysis programme.

RESULTS

In LH-affected horses, Pui, inspiratory SL and the sound intensity of F2 and F3 were significantly increased compared to baseline values. At 90 and 120 days after VC the sound intensities of F2 and F3 returned to baseline values. The Pui and SL, were significantly decreased compared to LH values, but remained different from baseline.

CONCLUSIONS

VC effectively reduces inspiratory noise in LH-affected horses by 90 days following surgery. Inspiratory trans-upper airway pressures are improved 30 days following VC, but do not return to baseline values.

POTENTIAL RELEVANCE

VC can be recommended as a surgical treatment of LH-affected horses if reduction of respiratory noise is the primary objective of surgery. Further studies are required to determine if variations of the surgical technique used in this study will have similar results.

Histological evaluation of the equine larynx after unilateral laser-assisted ventriculocordectomy

REASONS FOR PERFORMING STUDY

Trans-endoscopic laser surgery, such as unilateral laser-assisted ventriculocordectomy (LVC), has gained popularity in the treatment of RLN because a laryngotomy incision or general anaesthesia are not required. However, removal of the vocal fold and ventricle takes considerable laser energy and could cause collateral tissue damage, including injury to the adjacent laryngeal cartilages.

OBJECTIVES

To document the histological effects of laser surgery on laryngeal tissues in horses that have undergone LVC for the treatment of laryngeal hemiplegia (LH).

METHODS

Six horses were used: 4 with experimentally induced LH that had subsequently undergone LVC 6 months prior to euthanasia; and, 2 horses were used as controls. One of the control horses with naturally occurring LH was used to study the effect of neuropathy alone, whereas the other was subjected to euthanasia immediately following LVC to evaluate the acute effect of laser surgery. Using a band saw, each larynx was sectioned transversely at 5 mm intervals and evaluated histologically.

RESULTS

Acutely, LVC caused thermal damage to adjacent soft tissues but did not affect the histology of the laryngeal cartilages. Six months after LVC, laryngeal cartilages were histologically normal and there was squamous metaplasia of the repaired laryngeal mucosa, resulting in restitution of the mucosal integrity.

CONCLUSIONS

Using a diode laser in contact fashion at 20 W, LVC can be used to remove the laryngeal vocal fold and ventricle without causing laryngeal cartilage damage.

POTENTIAL RELEVANCE

Laryngeal chondritis is an unlikely consequence of LVC.

3D kinematics of the interphalangeal joints in the forelimb of walking and trotting horses

The objective was to measure 3D rotations of the distal (DIP) and proximal (PIP) interphalangeal joints at walk and trot. 3D trajectories of markers fixed to the proximal phalanx, middle phalanx and the hoof wall of the right forelimb of four sound horses were recorded at 120 Hz. Joint kinematics were calculated in terms of anatomically-based joint coordinate systems between the bone segments. Ranges of motion were similar at walk and trot. Values for the DIP joint were: flexion/extension: 46 +/- 3 degrees at walk, 47 +/- 4 degrees at trot; internal/external rotation: 5 +/- 1 degrees at walk, 6 +/- 3 degrees at trot; and adduction/abduction: 5 +/- 2 degrees at walk, 5 +/- 3 degrees at trot. Within each gait, kinematic profiles at the DIP joint were similar between horses with the exception of adduction/abduction during breakover, which may vary depending on the direction of hoof rotation over the toe. Knowledge of the types and amounts of motion at the DIP joint will be useful in understanding the aetiology and treatment of injuries to the soft tissues, which are being recognized more frequently through the use of sensitive imaging techniques. Ranges of motion for the PIP joint were: flexion/extension: 13 +/- 4 degrees at walk, 14 +/- 4 degrees at trot; adduction/abduction: 3 +/- 1 degrees at walk, 3 +/- 1 degrees at trot; and internal/external rotation: 3 +/- 1 degrees at walk, 4 +/- 1 degrees at trot. The PIP joint made a significant contribution to flexion/extension of the digit. During surgical arthrodesis, the angle of fusion may be important since loss of PIP joint extension in late stance is likely to be accommodated by increased extension of the DIP joint.

Three-dimensional kinematics of the tarsal joint at the trot

The tarsal joint is a common site of injury for many sport horses. Understanding the biomechanics of this complex joint begins with developing a clear picture of the kinematics during normal locomotion. This study describes the 3D kinematics of the tarsal joint by measuring the motion of the tibia and third metatarsus in 4 sound Quarter Horses with targets attached directly to the bones via steel pins. The objective was to determine if the tarsus had significant motion outside the tarsocrural joint. Two Steinmann pins were inserted into the lateral side of the right hindlimb and marker triads were fixed to the end of each pin. 3D motion of the bones was recorded as each subject trotted in hand. Three rotations were expressed using an attitude vector based on the finite helical angle method. Three translations were calculated as the motion of the tibia relative to the third metatarsus. Angular and translation data were mostly coupled with flexion angle. Internal/external rotation during stance and translations during swing showed evidence of noncoupled motion. Although the majority of tarsal motion occurs in the tarsocrural joint, there is evidence that translations and rotations occur in other locations within the tarsal joint and that some of these are related to the tarsal joint 'snapping' phenomenon. This research provides a set of reference 3D kinematics which will aid in the study of the aetiology and mechanical effects of tarsal joint lameness.

Endoscopic assessment of airway function as a predictor of racing performance in Thoroughbred yearlings: 427 cases (1997-2000)

OBJECTIVE

To compare endoscopic findings of the upper portion of the respiratory tract in Thoroughbred yearlings with their subsequent race records to determine whether subjective assessment of airway function may be used as a predictor of future racing performance.

DESIGN

Retrospective study.

ANIMALS

427 Thoroughbred yearlings.

PROCEDURES

Endoscopic examination findings were obtained from the medical records and the videoendoscopic repository of the Keeneland 1996 September yearling sales. Racing records were requested for the yearlings through the end of their 4-year-old racing season (1997-2000). Twenty-nine measures of racing performance were correlated with endoscopic findings. Subjective arytenoid cartilage movement grades were determined, using a 4-point grading scale (grade 1 = symmetrical synchronous abduction of the arytenoid cartilages; grade 4 = no substantial movement of the left arytenoid cartilage).

RESULTS

Of the 427 Thoroughbred yearlings included in this study, 364 established race records, and 63 did not. Opinions regarding suitability for purchase, meeting conditions of the sale, and the presence of epiglottic abnormalities had no significant association with racing performance. Arytenoid cartilage movement grades were significantly associated with many of the dependent variables. However, palatine abnormalities were not predictive of inferior racing performance.

CONCLUSIONS AND CLINICAL RELEVANCE

Thoroughbred yearlings with grade-1 and -2 arytenoid cartilage movements had significantly better racing performance as adults, compared with yearlings with grade-3 arytenoid cartilage movements. In contrast, epiglottic and palatine abnormalities were not predictive of inferior racing performance. Therefore, evaluation of laryngeal function, but not epiglottic or palatine abnormalities, using the 4-point grading system, should be the major factor in developing recommendations for prospective buyers.

Myofibroblasts in the accessory ligament (distal check ligament) and the deep digital flexor tendon of foals

OBJECTIVE

To demonstrate myofibroblasts in the accessory ligament of the deep digital flexor tendon (ie, distal check ligament) and deep digital flexor tendon of clinically normal foals.

SAMPLE POPULATION

Tissue specimens from 25 foals that were necropsied for reasons unrelated to this study and unrelated to musculoskeletal disease.

PROCEDURE

The distal check ligament and deep digital flexor tendon of both forelimbs were examined histologically. Myofibroblasts were identified by immunohistochemical staining specific for alpha-smooth muscle actin (alpha-SMA).

RESULTS

Most of the cells in the distal check ligament and deep digital flexor tendon of all foals stained positive for alpha-SMA.

CONCLUSION AND CLINICAL RELEVANCE

Myofibroblasts made up most of the cells in the distal check ligament and deep digital flexor tendon of clinically normal foals. These cells have contractile ability and therefore, may play a role in flexure contracture of these tendons. The ability of tetracycline to chelate calcium or decrease the expression of the contractile protein alpha-smooth muscle actin could inhibit the myofibroblasts' ability to contract, thus providing a rationale for tetracycline administration as a treatment of distal interphalangeal joint flexor deformity in foals.

Spectrum analysis of respiratory sounds in exercising horses with experimentally induced laryngeal hemiplegia or dorsal displacement of the soft palate

OBJECTIVE

To record respiratory sounds in exercising horses and determine whether spectrum analysis could be use to identify sounds specific for laryngeal hemiplegia (LH) and dorsal displacement of the soft palate (DDSP).

ANIMALS

5 Standardbred horses.

PROCEDURE

Respiratory sounds were recorded and pharyngeal pressure and stride frequency were measured while horses exercised at speeds corresponding to maximum heart rate, before and after induction of LH and DDSP.

RESULTS

When airway function was normal, expiratory sounds predominated and lasted throughout exhalation. After induction of LH, expiratory sounds were unaffected; however, all horses produced inspiratory sounds characterized by 3 frequency bands centered at approximately 0.3, 1.6, and 3.8 kHz. After induction of DDSP, inspiratory sounds were unaffected, but a broad-frequency expiratory sound, characterized by rapid periodicity (rattling) was heard throughout expiration. This sound was not consistently detected in all horses.

CONCLUSIONS AND CLINICAL RELEVANCE

The technique used to record respiratory sounds was well tolerated by the horses, easy, and inexpensive. Spectrum analysis of respiratory sounds from exercising horses after experimental induction of LH or DDSP revealed unique sound patterns. If other conditions causing airway obstruction are also associated with unique sound patterns, spectrum analysis of respiratory sounds may prove to be useful in the diagnosis of airway abnormalities in horses.

An outbreak of salmonellosis among horses at a veterinary teaching hospital

Between May 1996 and February 1997, 27 horses and a veterinary student at a veterinary teaching hospital developed apparent nosocomial Salmonella Typhimurium infection. The source of the multiple-drug resistant Salmonella Typhimurium was a neonatal foal admitted for treatment of septicemia. A high infection rate (approx 13% of hospitalized horses) coupled with a high case fatality rate (44%) for the initial 18 horses affected led to a decision to close the hospital for extensive cleaning and disinfection. Despite this effort and modification of hospital policies for infection control, 9 additional horses developed nosocomial Salmonella Typhimurium infection during the 6 months after the hospital reopened. Polymerase chain reaction testing of environmental samples was useful in identifying a potential reservoir of the organism in drains in the isolation facility. Coupled with clinical data, comparison of antimicrobial resistance patterns of Salmonella Typhimurium isolates provided a rapid initial means to support or refute nosocomial infection. Although minor changes in the genome of these isolates developed over the course of the outbreak, pulsed-field gel electrophoresis testing further supported that salmonellosis was nosocomial in all 27 horses.

Photoelastic stress analysis of strain patterns in equine hooves after four-point trimming

OBJECTIVE

To evaluate changes in strain patterns in normal equine hooves following 4-point trimming, using photoelastic stress analysis.

SAMPLE POPULATION

15 equine front limbs with normal hoof configuration.

PROCEDURE

Limbs were disarticulated at the carpometacarpal joint. Weight-bearing surfaces of each hoof were trimmed level to ensure 100% ground contact. Hoof walls were coated with a custom-made strain-sensitive plastic, and limbs were loaded to a third of body weight. Using a polariscope, strain distribution, magnitudes, and directions were evaluated in level hooves as well as before and after standardized 4-point trimming. Repeated-measures ANOVA was used to compare strain magnitudes and directions before and after trimming.

RESULTS

In leveled specimens, strain fields were symmetrically distributed above the heels and at quarter-toe junctions along a line between the middle and distal thirds of the hoof wall. After 4-point trimming, strain epicenters localized above the contact points, whereas strain magnitudes significantly increased by approximately 50%. Decreasing contact area by 50% resulted in an additional significant increase (32%) in strain magnitude. Trimming did not have a significant effect on strain orientations.

CONCLUSION AND CLINICAL RELEVANCE

This study documents that 4-point trimming results in strain concentration above the hoof contact points and that strain magnitude is dependent on contact area.

Pleuropulmonary and cardiovascular consequences of thoracoscopy performed in healthy standing horses

Six healthy, awake, and pharmacologically restrained mature horses were studied in order to define the changes in cardiopulmonary function during and after exploratory thoracoscopy and to determine the presence of postoperative complications occurring 48 hours after thoracoscopy. In a randomised 3 x 3 latin square design with 2 replications, 18 procedures were performed: 6 right (RTH) and 6 left thoracoscopies (LTH) and 6 sham procedures (STH). Prior to each procedure a physical examination and a bronchoalveolar lavage fluid analysis were performed. During thoracoscopy and sham protocols, horses were sedated with a continual drip of detomidine HCl and data were collected at 6 time intervals: T1 (baseline), T2 (10 min detomidine administration), T3 (first 15 min pneumothorax), T4 (5 min recovery from pneumothorax), T5 (second 15 min pneumothorax), and T6 (10 min recovery from the second pneumothorax and detomidine). An endoscopic thoracic examination was conducted during the 2 pneumothorax periods. An identical protocol was followed for sham procedures without surgery or pneumothorax. Data were analysed by ANOVA with time and surgical procedure as main factors. Physical examinations, thoracic radiography and ultrasound, CBC and bronchoalveolar lavage fluid analysis were performed 48 h after thoracoscopy. Heart rate, respiratory rate, and cardiac output decreased following detomidine administration. There was a trend for cardiac output to be lower during thoracoscopy. Mild systemic hypertension was associated with thoracoscopy although there was no effect on pulmonary arterial pressure. Total and pulmonary vascular resistances were increased following detomidine administration. Thoracoscopy caused a further increase in systemic and pulmonary vascular resistances especially during the second pneumothorax. Arterial O2 tension decreased following detomidine administration and was further decreased during the second pneumothorax period. PaO2 values were lower when thoracoscopy was performed on the left rather than the right hemithorax. No significant complications were found during the 48 h follow-up evaluation. A subclinical postoperative pneumothorax occurred in 2 horses, one of which had sustained a lung laceration by the trocar. Thoracoscopy performed in healthy, awake, and pharmacologically restrained horses did not have detrimental cardiopulmonary effects and did not cause postoperative complications within the first 48 h period.

Long-term outcome of horses with a slab fracture of the central or third tarsal bone treated conservatively: 25 cases (1976-1993)

OBJECTIVE

To determine clinical features of horses with a slab fracture of the central or third tarsal bone and to report outcome of horses in which treatment did not include surgery.

DESIGN

Retrospective study.

ANIMALS

25 horses (14 Standardbreds, 6 Thoroughbreds, 5 Quarter Horses).

PROCEDURE

Medical records of horses with a slab fracture of the central (n = 9) or third (16) tarsal bone were reviewed. Only horses for which treatment consisted of confinement to a stall were included in this study. Clinical features and radiographic findings were recorded and summarized. Outcome was determined for racing breeds by obtaining official lifetime race results. Outcome for Quarter Horses was determined by phone survey of the owners.

RESULTS

16 (64%) horses had a successful outcome. Ten of 14 (71%) Standardbreds and 2 of 6 Thoroughbreds returned to racing and started at least 5 races after injury. Four of 5 Quarter Horses for which follow-up information was available successfully returned to their previous activity. Sex, age, limb affected, or gait was not associated with final outcome. Percentage of racehorses with central tarsal bone fractures that had a successful outcome (2/7) was significantly less than percentage with third tarsal bone fractures that did (10/13).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that enforced rest without surgical fixation can be an effective therapeutic option for horses with a slab fracture of the central or third tarsal bone, even if athletic function is expected.

The effect of compacted cancellous bone grafting on the healing of subchondral bone defects of the medial femoral condyle in horses

OBJECTIVE

To compare the quality of second-intention healing and that of compacting sternally harvested cancellous bone into subchondral bone defects of the medial femoral condyle in horses.

STUDY DESIGN

A controlled experiment using a surgical technique that minimizes soft tissue trauma, customized for consistency among horses.

ANIMALS OR SAMPLE POPULATION

Ten horses, aged 2 to 5 years, free of hindlimb lameness and with radiographically normal stifles.

METHODS

After a 12.7-mm-diameter x 19-mm-deep defect was created into randomly selected medial femoral condyles, bone and cartilage healing was evaluated over a 6-month period in control horses (n = 5) and horses receiving a compacted cancellous bone graft (n = 5). Healing was evaluated using lameness assessment, radiographic and microradiographic interpretation, arthroscopic appearance, percent bone fill, proteoglycan content, and histology.

RESULTS

Six months after surgery, there was no significant difference between grafted and ungrafted defects with respect to lameness, radiographic score, or percent bone fill. Histologically, grafted defects were characterized by the presence of dead graft and secondary cyst formation in four defects. Ungrafted defects filled with fibrous tissue and no cyst formation were identified.

CONCLUSIONS

Grafted defects do not heal better than ungrafted defects, and lameness was not affected by surgical technique.

CLINICAL SIGNIFICANCE

Cartilage healing is similar in grafted and ungrafted defects in the equine medial femoral condyle at 6 months, suggesting that surgical debridement alone of cystic structures remains the treatment of choice.

Factors associated with prognosis for survival and athletic use in foals with septic arthritis: 93 cases (1987-1994)

OBJECTIVE

To identify factors affecting the prognosis for survival and athletic use in foals with septic arthritis.

DESIGN

Retrospective study.

ANIMALS

93 foals with septic arthritis.

PROCEDURE

Medical records were reviewed to obtain clinical findings, laboratory test results, radiographic findings, treatment method, and outcome. Race records for Thoroughbreds and Standardbreds were evaluated to determine whether foals subsequently raced and whether they raced successfully.

RESULTS

43 foals had 1 affected joint, 44 foals had multiple affected joints, and number of affected joints was not recorded for 6 foals. The femoropatellar and tarsocrural joints were most commonly affected. Osteomyelitis or degenerative joint disease were detected in 59% (46/78) of foals. Failure of passive transfer, pneumonia, and enteritis were common. Foals were treated with lavage, lavage and intra-articular administration of antibiotics, lavage and arthroscopic debridement with or without partial synovectomy, or lavage and arthrotomy to debride infected bone and systemic administration of antibiotics. Seventy-three foals survived to be discharged from hospital, and approximately a third raced. Isolation of Salmonella spp from synovial fluid was associated with an unfavorable prognosis for survival and multisystem disease was associated with an unfavorable prognosis for survival and ability to race; other variables were not significantly associated with survival and ability to race.

CONCLUSIONS AND CLINICAL RELEVANCE

With treatment, the prognosis for survival of foals with septic arthritis was favorable, whereas prognosis for ability to race was unfavorable. Multisystem disease, isolation of Salmonella spp from synovial fluid, involvement of multiple joints, and synovial fluid neutrophil count > or = 95% at admission may be of prognostic value.

Pathophysiology of dorsal displacement of the soft palate in horses

Dorsal displacement of the soft palate (DDSP) is an intermittent obstructive upper airway condition that occurs in athletic horses during high-intensity exercise. The pathogenesis of this condition is unknown, but may involve epiglottic hypoplasia, malformation, or neuromuscular dysfunction. In this paper, we report on investigations into the pathophysiology of DDSP. In 3 separate experiments, Standardbred horses were exercised on a high-speed treadmill at speeds corresponding to 50, 75 and 100% of maximum heart rate. The upper airway was evaluated by videoendoscopy and measurement of tracheal pressures. In experiment 1, we examined the effect of bilateral hypoglossal and glossopharyngeal nerve block on epiglottic function in exercising horses. This nerve block caused epiglottic retroversion and inspiratory upper airway obstruction. However, DDSP did not occur. In experiment 2, we evaluated the hypothesis that tensor veli palatini muscle dysfunction is involved in the pathogenesis of DDSP. Bilateral tensor veli palatini muscle tenectomy did not cause DDSP, but caused instability of the rostral half of the soft palate and a modest inspiratory upper airway obstruction. In experiment 3, we hypothesised that palatinus and palatopharyngeal dysfunction causes DDSP. The pharyngeal branch of the vagus nerve was blocked bilaterally in the guttural pouch. This block caused DDSP in all horses within 2-15 min after nerve block. Furthermore, DDSP created an expiratory nasopharyngeal obstruction. Because the pharyngeal branch of the vagus nerve is in close proximity to the retropharyngeal lymph node chain, we suggest that retropharyngeal lymphadenopathy may cause neural dysfunction and thereby be involved in the pathogenesis of clinical DDSP.

Influence of exogenous hyaluronan on synthesis of hyaluronan and collagenase by equine synoviocytes

OBJECTIVE

To evaluate the influence of exogenous hyaluronan (HA) on in vitro synthesis of HA and collagenase by equine synoviocytes from normal and inflamed joints.

ANIMALS

9 adult horses.

PROCEDURE

Synoviocytes for culture were taken from the middle carpal joint of 3 horses with normal joints (control) and 6 horses with osteochondral fractures (principal). Synoviocytes were propagated in monolayer cultures and were incubated with 3 commercial HA products at concentrations of 0, 200, 400, and 1,500 micrograms/ml. Newly synthesized HA was radiolabeled with [3H]glucosamine and quantified by cetylpyridinium chloride precipitation and liquid scintillation counting. The hydrodynamic size of radioactive HA was determined by high-performance liquid chromatography, and collagenase activity was evaluated by use of a quantitative radioactive collagen film assay.

RESULTS

Exogenous HA influenced neither the rate of synthesis nor the hydrodynamic size of the newly produced HA by control or principal cell cultures. Culture supernatants from abnormal synovium, exposed to 400 and 1,500 micrograms of exogenous HA/ml, contained significantly more collagenase activity than did those exposed to lower concentrations.

CONCLUSION

Although HA is thought to have beneficial effects in equine arthropathies, the principal mechanisms of action of HA do not appear to be stimulation of synthesis of HA of augmented molecular weight or marked inhibition of collagenase synthesis.

Effect of bilateral blockade of the pharyngeal branch of the vagus nerve on soft palate function in horses

OBJECTIVE

To determine the effect of bilateral blockade of the pharyngeal branch of the vagus nerve on soft palate function in horses.

ANIMALS

5 Standardbreds.

PROCEDURE

Peak tracheal inspiratory and expiratory pressures and airflow were measured while horses exercised at the speeds corresponding to 75 and 100% of the speed that resulted in maximal heart rate, with and without pharyngeal branch of the vagus nerve blockade. Respiratory frequency-to-stride frequency coupling ratio was measured by correlating foot fall measurements with respiratory frequency. The pharyngeal branch of the vagus nerve was blocked bilaterally as the nerve coursed through the auditory tube diverticulum (guttural pouch) across the longus capitus muscle.

RESULTS

Persistent, reversible dorsal displacement of the soft palate (DDSP) occurred in all horses after nerve blockade, and lasted from 1 to 3 hours; normal nasopharyngeal function returned within 3 hours. Compared with control values, peak expiratory tracheal pressure increased (P = 0.001), expiratory impedance increased (P = 0.007), and minute ventilation decreased (P = 0.04). Respiratory frequency-to-stride frequency coupling ratio decreased (P = 0.009) so that horses took 1 breath/stride without the nerve block and, approximately, 1 breath/2 strides with the block.

CONCLUSION

DDSP creates flow-limiting expiratory obstruction and may be caused by neuromuscular dysfunction involving the pharyngeal branch of the vagus nerve. It may alter performance by causing expiratory obstruction and by altering breathing strategy in horses.

CLINICAL RELEVANCE

A repeatable, reversible model of DDSP exists that allows further study of the disease. Dysfunction of the neuromuscular group, pharyngeal branch of the vagus nerve and palatinus and palatopharyngeus muscles, may be implicated in the pathogenesis of clinical DDSP.

Use of full cortical allograft to repair a metatarsal fracture in a foal

A 4-month-old Quarter Horse colt was admitted for repair of an open, comminuted fracture of the proximal portions of the diaphyses of the left second, third, and fourth metatarsal bones. Initial repair included internal fixation and cancellous bone graft. However, the third metatarsal bone became infected and failed to heal. After removal of infected portions of the bone, a 5-cm, fullthickness cortical allograft was placed in the defect. Rigid internal fixation provided stability for the allograft and remaining fracture fragments so that the horse was able to bear weight on the second and fourth metatarsal bones. The allograft was ultimately resorbed; however, appositional bone growth permitted a massive, functional metatarsal bone to form that incorporated the second, third, and fourth metatarsal bones. The colt went on to compete successfully, long term, as a show horse.

Epiglottic augmentation for treatment of dorsal displacement of the soft palate in racehorses: 59 cases (1985-1994)

OBJECTIVE

To determine whether epiglottic augmentation, in conjunction with more traditional surgical methods, would be useful in the treatment of dorsal displacement of the soft palate in racehorses.

DESIGN

Retrospective study.

ANIMALS

40 Thoroughbred and 19 Standardbred racehorses.

PROCEDURE

Polytetrafluoroethylene paste was injected submucosally on the lingual epiglottic surface of each horse. In addition, sternothyrohyoideus myectomy or sternothyroideus tenectomy and staphylectomy were performed in most horses.

RESULTS

Racing performance was improved after surgery in 29 of 40 (73%) Thoroughbreds and 10 of 19 (53%) Standardbreds. Twenty-nine (49%) horses won > or = 1 race after surgery.

CLINICAL IMPLICATIONS

Results suggest that epiglottic augmentation, in conjunction with other surgical methods, may be an effective method of treating horses with poor racing performance attributable to dorsal displacement of the soft palate.

Effects of bilateral hypoglossal and glossopharyngeal nerve blocks on epiglottic and soft palate position in exercising horses

OBJECTIVE

To determine the effect of bilateral hypoglossal and and glossopharyngeal nerve block on epiglottic and soft palate position and tracheal and pharyngeal pressures in exercising horses.

ANIMALS

5 Standardbreds.

PROCEDURE

Tracheal and pharyngeal pressures were measured in 5 Standardbreds exercising at the speed at which the horses achieved 50, 75, and 100% of maximal heart rate after bilateral hypoglossal and glossopharyngeal nerve block and without nerve block. Nerve block was achieved by injection of 1 to 2 ml of 2% mepivicaine hydrochloride between the glossopharyngeal and hypoglossal nerves, as they coursed through the medial compartment of the diverticulum of the auditory tube (guttural pouch), using videoendoscopic guidance and an injection apparatus.

RESULTS

Compared with control values, peak inspiratory tracheal pressure was significantly (P = 0.02) more negative, and peak pharyngeal inspiratory pressure was less negative (P = 0.004) after bilateral hypoglossal and glossopharyngeal nerve block. Respiratory frequency was significantly (P = 0.024) lower after nerve block, compared with control values. The epiglottis was unstable and retroflexed through the rima glottis during inspiration after bilateral hypoglossal and glossopharyngeal nerve block. Despite loss of contact between the epiglottis and the caudal free margin of the soft palate, dorsal displacement of the soft palate did not occur.

CONCLUSIONS AND CLINICAL RELEVANCE

Loss of contact of the epiglottis with the soft palate did not affect soft palate position, suggesting that when the soft palate is normal, the epiglottis does not function as a support, holding the soft palate in a ventral position. Therefore, epiglottic dysfunction is not solely responsible for intermittent dorsal displacement of the soft palate in horses, and neuromuscular dysfunction involving the hyoepiglotticus muscle, geniohyoideus muscle, or the hypoglossal nerve may cause epiglottic retroflexion in horses.

Surgical treatment of progressive ethmoidal hematoma aided by computed tomography in a foal

A progressive ethmoidal hematoma (PEH) was treated successfully in a 4-week-old Belgian filly by surgical removal, using a frontonasal bone flap. The filly had respiratory stridor, epistaxis, and facial enlargement over the left paranasal sinuses, which had progressively increased in size since birth. Computed tomographic images of the head obtained with the foal under general anesthesia were useful in determining the extent and nature of the soft-tissue mass and planning surgical intervention. On the basis of the histologic appearance of the mass, a diagnosis of PEH was made. Twelve months after surgery, the facial appearance was normal and the abnormal appearance of the ethmoid region on endoscopic evaluation was less obvious, with return of the nasal septum to a normal position. Progressive ethmoidal hematoma is uncommon and, to our knowledge, has not been reported in a neonate. Clinical signs of PEH in this foal were atypical because of the rapid enlargement of the mass, extent of facial deformity, and minimal epistaxis and interoperative hemorrhage.

Effect of bilateral tenectomy of the tensor veli palatini muscle on soft palate function in horses

OBJECTIVE

To determine the effect of bilateral tenectomy of the tensor veli palatini muscle on soft palate and nasopharyngeal function in exercising horses.

ANIMALS

5 Standardbreds.

PROCEDURE

Treadmill videoendoscopy was performed on 5 Standardbreds exercising at 50, 75, and 100% of the speed that produced maximum heart rate; tracheal and pharyngeal pressures were measured before and after surgery. Tenectomy of the tensor veli palatini muscle was performed bilaterally on each horse while under general anesthesia, using a transoral approach.

RESULTS

Peak inspiratory tracheal pressures were significantly (P = 0.016) more negative and there was a trend (P = 0.06) for peak pharyngeal inspiratory pressure to be less negative following bilateral tenectomy of the tensor veli palatini muscle, compared with preoperative values. The rostral half of the soft palate was unstable and collapsed dorsally into the nasopharynx during inspiration, causing partial obstruction of the nasopharynx. The caudal free margin of the soft palate remained ventral to the epiglottis, and dorsal displacement of the soft palate did not occur in any horse.

CONCLUSIONS

Bilateral tenectomy of the tensor veli palatini muscle did not cause dorsal displacement of the soft palate in horses while exercising at maximum heart rate, but resulted in collapse of the nasopharynx during inspiration.

CLINICAL RELEVANCE

Results of our study indicate that the tensor veli palatini muscle functions to support and dilate the nasopharynx during intense inspiratory efforts in horses by tensing the palatine aponeurosis.

Efficacy of prosthetic laryngoplasty with and without bilateral ventriculocordectomy as treatments for laryngeal hemiplegia in horses

OBJECTIVE

To evaluate the efficacy of prosthetic laryngoplasty with and without bilateral ventriculocordectomy for treatment of experimentally induced left laryngeal hemiplegia (LLH).

ANIMALS

15 adult Standardbreds.

PROCEDURE

Horses were allotted to 3 equal groups. Sham operation (group 1), prosthetic laryngoplasty (group 2), or prosthetic laryngoplasty with bilateral ventriculocordectomy (group 3) was performed after induction of LLH. Upper airway function testing was performed prior to left recurrent laryngeal neurectomy (LRLN), 14 days after LRLN, and 60 and 180 days after surgical treatment. Measurements were obtained at rest and at treadmill speeds corresponding to 75 and 100% of maximal heart rate. Videoendoscopy was performed at rest and during exercise in all horses prior to LRLN and 60 and 180 days after surgical treatment. Upper airway endoscopy was performed immediately after LRLN to document induction of grade-IV LLH. Also, horses in group 3 were endoscopically examined at 7, 14, 21, 28, and 120 days after surgical treatment to evaluate healing of the ventriculocordectomy sites.

RESULTS

When horses were at rest, significant differences were not apparent between groups at any period or between periods for any measured variable. LRLN induced airway obstruction in all horses during exercise. In sham-operated horses, this obstruction was unaffected by time. In contrast, 60 and 180 days after surgical treatment, inspiratory flow limitations induced by LRLN were reversed in horses of groups 2 and 3. There were no significant differences between the 2 treatment groups. Endoscopy revealed the left arytenoid cartilage abducted beyond the intermediate position, but not touching the pharyngeal wall in all horses with a laryngeal prosthesis. After surgical treatment, 4 group-2 horses had filling of both ventricles with air during exercise. There was moderate to marked swelling of the ventriculocordectomy sites immediately after surgery, and this swelling resolved by 7 days after surgery. The ventriculocordectomy sites looked best at 14 and 180 days.

CONCLUSIONS

60 and 180 days after prosthetic laryngoplasty, upper airway function returned to pre-LRLN values in horses with experimentally induced LLH exercising at 100% of maximal heart rate. Combining ventriculocordectomy with prosthetic laryngoplasty does not further improve upper airway function in these horses.

Effect of nasal occlusion on tracheal and pharyngeal pressures in horses

OBJECTIVE

To compare tracheal and pharyngeal inspiratory and expiratory pressures achieved during 60 seconds of nasal occlusion in standing horses with pressures achieved in horses during intense exercise.

ANIMALS

5 Standardbreds.

PROCEDURE

Tracheal and pharyngeal inspiratory and expiratory pressures were obtained from 5 horses during 60 seconds of nasal occlusion and compared with tracheal and pharyngeal pressures achieved during incremental treadmill exercise tests in which horses ran at 50, 75, and 100% of the speed that resulted in maximal heart rate (HRmax).

RESULTS

Significant difference was not detected between peak tracheal inspiratory pressure during nasal occlusion and peak tracheal inspiratory pressure at HRmax Peak pharyngeal inspiratory pressure was significantly more negative, and peak tracheal and peak pharyngeal expiratory pressures were significantly more positive during 60 seconds of nasal occlusion than those observed in horses running at HRmax.

CONCLUSION

During upper airway endoscopy in standing horses, 60-second nasal occlusion induced tracheal and pharyngeal inspiratory pressures that equaled or exceeded pressures achieved during high-intensity exercise.

CLINICAL RELEVANCE

Nasal occlusion is useful to simulate upper airway pressures achieved during high-intensity exercise.

Instrumentation and techniques in respiratory surgery

In this article, videoendoscopy in conjunction with high-speed treadmill exercise and other specialized diagnostic techniques used to measure upper airway function are reviewed as they pertain to the four most commonly diagnosed functional upper airway obstructions: (1) laryngeal hemiplegia, (2) arytenoid chondritis, (3) epiglottic entrapment, and (4) intermittent dorsal displacement of the soft palate. Using experimental and clinical findings obtained with these new instruments and diagnostic techniques, current recommendations for surgery of these obstructions are presented.

Clinical relevance of the microvasculature of the equine proximal sesamoid bone

The blood supply to the proximal sesamoid bone of the equine forelimb was examined in 18 cadaver limbs from adult horses, using x-ray computed tomography and a tissue-clearing (Spalteholz) technique. Results of the study indicated that the proximal sesamoid bones were supplied by multiple branches of the medial and lateral palmar digital arteries, which entered the proximal half of the bones on their non-articular, abaxial surface. After entering the bone, the vessels traverse dorsally, axially, and distally, arborizing into several smaller branches that appear to supply the entire bone. The major branches of these vessels reside in bony canals, the orientation and distribution of which parallel the radiographic lucencies seen in horses with sesamoiditis and correspond to the configuration of apical fracture patterns.

Consideration of anatomic and radiographic features of the caudal pouches of the femorotibial joints of horses for the purpose of arthroscopy

Development of an arthroscopic approach to the caudal pouches of the equine stifle has been necessary because cranial approaches do not allow access to articular lesions in the caudal aspect of the joint. Therefore, the anatomy of the caudal region was examined in 52 cadaver limbs by use of gross dissection (29), x-ray-computed tomography (6), fluoroscopy (8), or arthroscopy (9). Additionally, using arthroscopic techniques developed in equine cadaver limbs, 3 stifles from 2 anesthetized horses were arthroscopically explored. Fluoroscopy was used to verify needle placement for joint injection and filling patterns of each femorotibial joint. The medial femorotibial joint sac (n = 4) held a mean +/- SD 41.67 +/- 5.77 ml of injection fluid, and the lateral femorotibial joint sac (n = 4) held a mean 61.67 +/- 2.89 ml of injection fluid. Vital structures that inadvertently could be damaged during arthroscopy of the caudal pouches of the stifle included the peroneal nerve (located approx 7 cm caudal to the lateral collateral ligament), the popliteal artery and vein (situated directly between the medial and lateral femoral condyles), and the lateral femoral condyle (most often traumatized during arthroscopy). The tendon of the popliteus muscle, which is contiguous with the joint capsule of the caudal pouch of the lateral femorotibial joint, made arthroscopic exploration of this pouch particularly difficult.

Surgical treatment for epiglottic entrapment in horses: 51 cases (1981-1992)

Medical records of 51 horses with epiglottic entrapment were reviewed, and the outcome after surgical treatment was evaluated by use of results from a survey of owners and from race records. Horses with epiglottic entrapment and no additional problem (uncomplicated) of the nares, nasal passages, pharynx, or larynx (upper airway) that were treated by transoral axial division (group 1) or resection via laryngotomy (group 2), and horses with epiglottic entrapment complicated by an additional upper airway abnormality (group 3) were compared. The cost of treatment, duration of hospitalization, time to first race start after surgery, and complication rate were significantly (P < 0.05) less in horses in group 1, compared with those in horses of group 2. Owner survey indicated that a significantly greater percentage (82%) of horses in group 1 had a successful outcome after transoral axial division, compared with that (27%) of horses in group 2. Analysis of race records indicated that performance was similar between horses in groups 1 and 2, and significantly more horses with an additional upper airway lesion (group 3) failed to return to racing than did horses with uncomplicated epiglottic entrapment (groups 1 and 2). Transoral axial division of the ary-epiglottic fold is recommended as an appropriate treatment for uncomplicated epiglottic entrapment. Resection via laryngotomy should be reserved for treatment of epiglottic entrapment associated with excessively thick and scarred aryepiglottic folds and for intermittent epiglottic entrapment in horses for which surgical correction is deemed appropriate.(ABSTRACT TRUNCATED AT 250 WORDS)

Histologic and ultrastructural changes after large-colon torsion, with and without use of a specific platelet-activating factor antagonist (WEB 2086), in ponies

The role of platelet-activating factor (PAF) in mediating the colonic damage that develops after large-colon torsion was studied in 14 ponies. Morphologic changes in areas of the ascending colon and selected abdominal and thoracic viscera after 1 hour of large-colon torsion and 3 to 5 hours of reperfusion were determined, as well as the protective effects of systemic administration of a specific PAF antagonist (WEB 2086). Ponies were selected then allocated at random and in equal numbers to 2 groups that received 1 of 2 treatments prior to induction of large-colon torsion: group 1--control (saline solution), and group 2--WEB 2086 (3 mg/kg of body weight loading dose and 3 mg/kg/h for the remainder of the study). In each pony, full-thickness tissue specimens from the gastrointestinal tract--cecum, pelvic flexure, left and right ventral colon, and right dorsal colon--heart, left lung, liver, left adrenal gland, spleen, and right kidney were collected and histologically evaluated. Edema, mucosal necrosis, and neutrophil infiltration in colonic sections were graded from 0 (normal) to 3 (most severe changes). Sections of liver and lung from 3 ponies in each group, and colon from 1 pony in each group, also were examined by transmission electron microscopy to determine the presence of ultrastructural alterations. Ischemia and reperfusion induced marked changes in all sections of colon in all ponies: moderate to severe submucosal edema, moderate necrosis of the superficial epithelium and lamina propria, and necrosis of the mucosal crypt epithelium. Extravascular neutrophil accumulation was evident in all sections of colon and cecum, but not in other tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of partial arytenoidectomy as a treatment for equine laryngeal hemiplegia

The efficacy of partial arytenoidectomy was assessed in 6 Standardbred horses, with surgically induced laryngeal hemiplegia, at rest (Period A) and during exercise at speeds corresponding to maximum heart rate (Period C) and 75% of maximum heart rate (Period B). Peak expiratory and inspiratory airflow rate (PEF and PIF), and expiratory and inspiratory transupper airway pressure (PUE and PUI) were measured and expiratory and inspiratory impedance (ZE and ZI) were calculated. Simultaneously, tidal breathing flow-volume loops (TBFVL) were acquired using a respiratory function computer. Indices derived from TBFVL included airflow rates at 50 and 25% of tidal volume (EF50, IF50, EF25, and IF25) and the ratios of expiratory to inspiratory flows. Measurements were made before left recurrent laryngeal neurectomy (baseline), 2 weeks after left recurrent laryngeal neurectomy (LRLN) and 16 weeks after left partial arytenoidectomy coupled with bilateral ventriculectomy (ARYT). After LRLN, during exercise Periods B and C, Z1 and the ratio of EF50/IF50 significantly increased and PIF, IF50 and IF25 significantly decreased from baseline values. At 16 weeks after ARYT, Z1 returned to baseline values during Periods B and C. Although PIF, IF50, IF25, PEF/PIF, and EF50/IF50 returned to baseline values during Period B, these indices remained significantly different from baseline measurements during Period C. After ARYT, TBFVL shapes from horses during Period C approached that seen at the baseline evaluation. Partial arytenoidectomy improved upper airway function in exercising horses with surgically induced left laryngeal hemiplegia, although qualitative and quantitative evaluation of TBFVLs suggested that some flow limitation remains at near maximal airflow rates. These results indicate that, although the procedure does not completely restore the upper airway to normal, partial arytenoidectomy is a viable treatment option for failed laryngoplasty and arytenoid chondropathy in the horse.

Computer-assisted three-dimensional gait analysis of amphotericin-induced carpal lameness in horses

Motion of 6 clinically sound horses trotting at a speed of 4 m/s on a treadmill was captured by video cameras before and 9, 16, and 23 days after amphotericin-induced lameness to determine the quantitative variables of three-dimensional computer-assisted image analysis that objectively describe carpal lameness. Amphotericin-B was used to induce lameness, and phenylbutazone (2.2 mg/kg of body weight, PO, once) and butorphanol tartrate (0.1 mg/kg IM, q 6 h, to effect) were used to control discomfort. Four 60-Hz cameras were symmetrically placed around the treadmill to capture 6 seconds of images from retro-reflective spheres taped to the trotting horses. Images were transferred to a video-based digitizer and a computer work station, where 4 files of two-dimensional data were reduced to 1 file of three-dimensional data. The effect of lameness on motion analyzed was assessed by use of two-way ANOVA. Differences between means were assessed, using the Student-Newman-Keul's test (P < or = 0.05). Head and withers excursions, (dorsal vertical displacement of head and withers targets, respectively) during the sound forelimb support phase were increased significantly during all lameness measurement periods. Head excursion, but not withers excursion, during the lame forelimb support phase, was decreased significantly during all lameness measurement periods. Computer determinations of stride length swing phase, stance phase, forelimb abduction, and carpal and fetlock ranges of motion did not consistently characterize the lameness. It was concluded that three-dimensional computer-assisted image analysis could be used for objective lameness evaluation in horses and that head and withers excursions were the most consistent variables for assessing equine carpal lameness.

Effects of hylan on amphotericin-induced carpal lameness in equids

In this double-blind study, the effectiveness of and dose response to intra-articular administration of modified hyaluronan (hylan) was determined in an equine carpal lameness model over a 23-day period, using a computerized three-dimensional motion analysis system, synovial fluid variables, and synovial histologic examination. In 24 clinically sound horses, baseline motion data was acquired from horses trotting at 4 m/s on a high-speed treadmill. Then, to induce lameness, 25 mg of amphotericin B in 5 ml of sterile water was injected into the left middle carpal joint of each horse every other day for 3 treatments. Phenybutazone (2.2 mg/kg of body weight, PO, once) and butorphanol tartrate (0.1 mg/kg, IM, q 6 h, for 36 hours) were used to control signs of discomfort. Horses were assigned at random to 4 equal groups and received intracarpal administration of either 1, 2, 4 ml of hylan (8 mg/ml), or 2 ml of balanced electrolyte solution (control). Intracarpal administration of amphotericin B caused significant (P < or = 0.01) increase in subjective lameness grades over the 2-week evaluation period, and hylan administration did not significantly (P < or = 0.01) change the subjective lameness grade. Lameness induction caused significant (P < or = 0.01) decrease in head and withers excursions during the lame forelimb support phase and significant (P < or = 0.05) increase in head and withers excursions during the sound forelimb support phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of flow-volume loops to evaluate upper airway obstruction in exercising standardbreds

Flow-volume loops generated from 6 Standardbreds at rest and during treadmill exercise were evaluated for their use in detecting upper airway obstruction. Tidal breathing flow-volume loops (TBFVL) were obtained from horses at rest and exercising at speeds corresponding to 75% of maximal heart rate and at maximal heart rate. The TBFVL were evaluated, using a pulmonary function computer; calculated indices describing airflow rate and expiratory-to-inspiratory airflow ratio for individual loops were determined. In addition to TBFVL indices, standard variables of upper airway function also were measured: peak airflow, peak pressure, and calculated inspiratory and expiratory impedances. Measurements were recorded before left recurrent laryngeal neurectomy (LRLN; baseline) and 14 days after surgically induced left laryngeal hemiplegia. When horses were at rest, TBFVL shape and indices describing the loop were highly variable. In contrast, in exercising horses, TBFVL shape was consistent and coefficients of variation of loop indices were less during exercise than at rest. After LRLN, TBFVL from exercising horses indicated marked inspiratory airflow limitation, while the expiratory airflow curve was preserved. Peak inspiratory flow rate and inspiratory flow at 50 and 25% of tidal volume decreased, and the ratio of peak expiratory to inspiratory airflow and that of midtidal volume expiratory and inspiratory airflow rates increased significantly (P < 0.05). Inspiratory impedance also increased after LRLN. Although in resting horses TBFVL were not a useful indicator of upper airway obstruction, examination of TBFVL from exercising horses allowed objective, specific, and repeatable detection of upper airway obstruction. The technique was noninvasive, rapid, and well tolerated by horses; thus, it is a potentially valuable clinical diagnostic test.

Effect of a specific platelet-activating factor antagonist on cardiovascular and peripheral cellular responses to colonic ischemia and reperfusion in anesthetized ponies

The role of platelet-activating factor in mediating the cardiovascular and peripheral cellular responses to large-colon ischemia and reperfusion, was explored in anesthetized ponies. A specific platelet-activating factor (PAF) antagonist (WEB 2086) was administered to a group of 6 ponies, and another 6 ponies (controls) were given an equivalent volume of saline solution, prior to 1 hour of large-colon torsion. After correction of the torsion, ponies were monitored during the reperfusion period. Significant (P < 0.05) hypotension and metabolic acidosis developed in all ponies after correction of colonic torsion, cardiac index increased initially, but then decreased significantly (P < 0.05) over the study period. Mean times between correction of torsion and onset of cardiac failure and death were not different between groups. Significant (P < 0.05) thrombocytopenia developed during the reperfusion period in control ponies, but not in WEB-treated ponies. Blood leukocyte concentration in control ponies was more variable and significantly (P < 0.05) decreased immediately upon reperfusion, compared with that in WEB-treated ponies. We conclude that although the cardiovascular responses to colonic ischemia and reperfusion are not prevented by use of a specific PAF-antagonist, specific peripheral cellular responses are mediated by PAF.

Epiglottic augmentation by use of polytetrafluoroethylene to correct dorsal displacement of the soft palate in a standardbred horse

A 2-year-old 400-kg Standardbred colt with a history of exercise intolerance was determined to have dorsal displacement of the soft palate (DDSP). Standing endoscopy revealed a soft, flaccid, and hypoplastic epiglottis and arytenoid cartilages that moved symmetrically and abducted fully. Lateral laryngeal radiography was used to calculate a corrected thyroepiglottic length of 6.48 cm. Videoendoscopy during exercise on a high-speed treadmill at standardized treadmill speeds was performed weekly for 3 consecutive weeks. The soft palate dorsally displaced at each examination. A sternohyoideus/sternothyroideus myectomy was followed by 2 weeks of stall rest and 2 weeks of treadmill training. Because endoscopy during exercise at standardized treadmill speeds caused the horse to dorsally displace the soft palate once a week for 3 weeks after the myectomy, this surgery was deemed ineffective in this horse. Epiglottic augmentation was performed by injecting 7 ml of polytetrafluoroethylene into the ventral submucosal space of the epiglottis. After 21 days of stall rest and 5 weeks of pasture rest, the horse was placed on a 2-month treadmill conditioning program. Using endoscopy at standardized treadmill speeds, exercise efforts to encourage DDSP were unsuccessful, which suggested that epiglottic augmentation by use of polytetrafluoroethylene was an effective surgical treatment to correct dorsal displacement of the soft palate in this horse. It is believed that polytetrafluoroethylene increases the rigidity of the epiglottis, allowing it to maintain the ventral position of the soft palate.

Arthroscopic removal of an osteochondral fragment from the caudal pouch of the lateral femorotibial joint in a colt

An osteochondral fragment was removed from the caudal pouch of the lateral femorotibial joint in a 2-year-old Trakehner colt by use of arthroscopic surgery and a lateral approach. The approach to this aspect of the femorotibial joints was developed in another horse. The fragment was not attached and resembled an osteochondritis dissecans lesion. The intermittent lameness associated with the fragment resolved after surgical removal. A positive response to diagnostic anesthesia of the femorotibial joint in the absence of a confirmed diagnosis (following radiographic and arthroscopic evaluations of the other aspects of the stifle joint) is an indication for arthroscopic exploration of the caudal pouches of the femorotibial joints of stifles in horses.

Long-term effects of desmotomy of the accessory ligament of the deep digital flexor muscle in standardbreds: 23 cases (1979-1989)

Desmotomy of the accessory ligament of the deep digital flexor muscle (inferior check desmotomy) permitted Standardbred foals affected with flexural deformities to reach their full athletic potential. Long-term effects of inferior check desmotomy were examined in 23 Standardbreds over a 10-year period. Six of 11 foals that were treated surgically either raced 6 times and obtained a race record or were training sound (if yearlings). All 12 horses with flexural deformity that did not receive an inferior check desmotomy had an unfavorable outcome (no race record). Foals that had surgery performed at a younger age apparently had a better chance of racing or training sound because no foals treated surgically after 8 months of age had a favorable outcome and only 1 foal that was older than 5 months at the time of surgery had a favorable outcome. In 5 foals that had surgery with an unsuccessful outcome, 3 were greater than or equal to 1 year old at the time of surgery and were lame when training was started on the limb(s) with the desmotomy.

Histologic evaluation of nerve muscle pedicle graft used as a treatment for left laryngeal hemiplegia in standardbreds

A nerve muscle pedicle (NMP) graft was placed in the cricoarytenoideus dorsalis (CAD) muscle of 6 horses with induced left laryngeal hemiplegia. The NMP graft was created by use of the first cervical nerve and omohyoideus muscle. In 1 horse (control), the first cervical nerve was transected after placement of the NMP graft. One year after the surgical procedure, horses were examined endoscopically and then anesthetized. While the larynx was observed endoscopically, the first cervical nerve was stimulated. Horses were subsequently euthanatized, and the larynx was harvested. Prior to anesthesia, the endoscopic appearance of the larynx of all horses was typical of laryngeal hemiplegia. During anesthesia, stimulation of the first cervical nerve produced vigorous abduction of the left arytenoid in principal horses but not in the control horse. The right cricoarytenoideus lateralis and CAD muscles were grossly and histologically normal. Also, the left cricoarytenoideus lateralis was atrophic in all horses as was the left CAD muscle of the control horse. In contrast, the left CAD muscle harvested from principal horses had evidence of reinnervation with type 1 or type 2 fiber grouping. One year after the NMP graft procedure, horses with left laryngeal hemiplegia had reinnervation of the left CAD muscle. In another study, reinnervation was sufficient to allow normal laryngeal function during exercise. Combined, these data suggest that the NMP graft procedure is a viable technique for the treatment of left laryngeal hemiplegia in horses.

Thromboxane and prostacyclin production in ponies with colonic volvulus

Effects of 1 hour of colonic volvulus and 3 hours of reperfusion on concentrations of thromboxane (TXB2) and prostacyclin (6-keto-PGF1 alpha) in portal, pulmonary arterial, and jugular blood were determined by radioimmunoassay to assess the site of production and clearance of these eicosanoids from the circulation in 5 anesthetized ponies. Colonic volvulus had no significant effect on mean arterial pressure or TXB2 concentrations, but significantly (P less than 0.05) increased 6-keto-PGF1 alpha concentrations in all blood samples. Immediately after colonic reperfusion, all eicosanoid concentrations were significantly (P less than 0.05) increased. Then, TXB2 returned to baseline values, whereas 6-keto-PGF1 alpha concentrations remained significantly (P less than 0.05) high for the remainder of the study. Eicosanoid concentrations were significantly (P less than 0.05) greater in portal blood than in pulmonary arterial and jugular blood samples at all periods. This suggests that the splanchnic circulation is the primary site of eicosanoid production during and after colonic volvulus and the liver appears to provide most of the circulatory clearance of thromboxane and prostacyclin.