Salpingopharyngeal fistula as a treatment for guttural pouch mycosis in seven horses.

BACKGROUND: Guttural pouch mycosis (GPM) is a cause of nasal discharge, dysphagia and fatal haemorrhage in the horse. OBJECTIVES: To report the complications and success of salpingopharyngeal fistulation in horses with GPM. We hypothesised that creating a direct static opening into the guttural pouch from the pharynx would cause a regression of fungal plaques due to a change in the guttural pouch environment and that this treatment would result in resolution of infection prior to secondary complications. STUDY DESIGN: Retrospective case series. METHODS: The medical records of all horses diagnosed with GPM that were presented to New Bolton Center between the years 2006 and 2017 were examined retrospectively. Seven cases of guttural pouch mycosis treated with salpingopharyngostomy without other surgical intervention were included. Information collected included signalment, presenting complaint, which pouch was affected, size and location of the plaques, laryngeal and pharyngeal function, concurrent medical therapy, location of the fistula, surgical time, time to resolution of clinical signs, time to full resolution of the mycotic plaque, and patency of the salpingopharyngostomy site. RESULTS: Nasal discharge resolved in 10-30 days post-operatively in all cases where nasal discharge was present. The mycotic plaques showed complete resolution at time points ranging from 1 to 6 months post-operatively. No case developed epistaxis or neurological deficits post-operatively that were not present at presentation. MAIN LIMITATIONS: There were differing adjunctive treatments between cases. This technique is not appropriate for horses that have had epistaxis or are currently bleeding. CONCLUSIONS: Salpingopharyngostomy can minimise cost of treatment, be performed on an outpatient basis and provide better exposure of the infected area with few complications. This case series documents seven cases treated with this method that resolved the infection without any further complications of the mycosis.

Fifty years of recurring struggles with recurrent laryngeal neuropathy.

Recurrent laryngeal neuropathy appears to be a simple problem that should have a simple solution, yet the complexity and dynamic nature of laryngeal function is underappreciated. This review highlights the challenges and accomplishments that work towards that greater understanding of what is necessary to find a successful solution.

Analysis of conformational variations of the cricoid cartilages in Thoroughbred horses using computed tomography.

REASONS FOR PERFORMING STUDY: Loss of arytenoid abduction is a common post operative complication of laryngoplasty without a definitive cause. It has been a clinical impression during laryngoplasty surgery that there is great conformational variability along the caudal edge of the Thoroughbred cricoid cartilage that could impact post operative retention of suture position. A change in suture position would probably lead to some loss of abduction. Defining any structural variability of the cricoid would be an initial step in determining whether this variability could impact on the retention of suture position. HYPOTHESIS: Anatomical variations in the larynx of Thoroughbred horses may be detected and measured using objective analysis and computed tomography. METHODS: Larynges were harvested from 15 mature Thoroughbred horses. Helical CT scans were performed on each specimen. Three independent observers performed a series of measurements on 2D and 3D reconstruction images using digital software. Measurements included the lateral cricoid angle, the caudal cricoid prominences, the distance to the cricoid slope, the angle of the cricoarytenoid joints (CAJ), the cricoid thickness and the suture angle. Mean, standard deviation, coefficient of variation and linear regression analysis were performed among all observers and all measurements. RESULTS: Notable conformational differences were evident on the 3D reconstructions. The highest degree of variability was found in 3 measurements: the distance to the lateral cricoid slope, the lateral cricoid angle and the cricoid thickness. A larger left CAJ angle directly and significantly correlated with a larger suture angle. CONCLUSIONS: There are notable conformational differences among cricoid specimens in the Thoroughbred larynx. POTENTIAL RELEVANCE: The morphometric differences identified may impact on optimal prosthesis placement and long-term retention. Since a larger lateral cricoid angle may facilitate abduction loss secondary to a displaced and loosened suture, alternative techniques for suture placement may be of value to prevent arytenoid abduction loss.

Exercising upper respiratory videoendoscopic evaluation of 100 nonracing performance horses with abnormal respiratory noise and/or poor performance.

REASONS FOR PERFORMING STUDY: Although well documented in racehorses, there is paucity in the literature regarding the prevalence of dynamic upper airway abnormalities in nonracing performance horses. OBJECTIVE: To describe upper airway function of nonracing performance horses with abnormal respiratory noise and/or poor performance via exercising upper airway videoendoscopy. METHODS: Medical records of nonracing performance horses admitted for exercising evaluation with a chief complaint of abnormal respiratory noise and/or poor performance were reviewed. All horses had video recordings of resting and exercising upper airway endoscopy. Relationships between horse demographics, resting endoscopic findings, treadmill intensity and implementation of head and neck flexion during exercise with exercising endoscopic findings were examined. RESULTS: Dynamic upper airway obstructions were observed in 72% of examinations. Head and neck flexion was necessary to obtain a diagnosis in 21 horses. Pharyngeal wall collapse was the most prevalent upper airway abnormality, observed in 31% of the examinations. Complex abnormalities were noted in 27% of the examinations. Resting laryngeal dysfunction was significantly associated with dynamic arytenoid collapse and the odds of detecting intermittent dorsal displacement of the soft palate (DDSP) during exercise in horses with resting DDSP was only 7.7%. Exercising endoscopic observations were different from the resting observations in 54% of examinations. CONCLUSIONS: Dynamic upper airway obstructions were common in nonracing performance horses with respiratory noise and/or poor performance. Resting endoscopy was only helpful in determining exercising abnormalities with recurrent laryngeal neuropathy. POTENTIAL RELEVANCE: This study emphasises the importance of exercising endoscopic evaluation in nonracing performance horses with abnormal respiratory noise and/or poor performance for accurate assessment of dynamic upper airway function.

Branchial remnant cysts of mature and juvenile horses.

This clinical report describes 8 cases of branchial remnant cysts (BRC) in the horse. The horses presented with bimodal age distribution, with 5 cases in mature horses (age 8-21 years) and 3 in foals (age 1, 6 and 10 months). Mature cases presented for dysphagia or intermittent oesophageal obstruction (2/5), and retropharyngeal swelling (3/5), whereas respiratory stridor and visible mass were presenting complaints in the foals. Presence of a right-sided (5/8) or dorsally located (2/8) palpable retropharyngeal mass of 3-35 cm diameter was noted clinically; one left-sided mass was identified as an incidental finding at necropsy. Ultrasonography typically revealed a thick-walled cyst containing hypoechoic fluid with dependent hyperechoic masses consistent with blood clots. Radiographs and upper airway endoscopy were also consistent with a retropharyngeal mass. Fluid cytology revealed chronic haemorrhage in 6/8 cases, and squamous epithelial cells in one case. Histopathology in all cases demonstrated an epithelium-lined cyst with no smooth muscle or thyroid tissue. Two cases was subjected to euthanasia; one due to concurrent laryngeal anomalies and one due to financial constraints. The remaining 5 cases were treated via surgical excision. Post operatively, right laryngeal hemiplegia was observed in 4/5 cases. All previous reports of BRC in the horse have described juvenile individuals. Brachial remnant cyst should be considered a differential diagnosis for mature horses with masses of the throatlatch area and can be definitively diagnosed by the presence of squamous epithelium in aspirated fluid or by histopathology of the excised mass. Right recurrent laryngeal nerve damage is a common complication of surgery.

Long-term study of partial arytenoidectomy with primary mucosal closure in 76 Thoroughbred racehorses (1992-2006).

REASON FOR PERFORMING STUDY: The effectiveness and best method to perform a partial arytenoidectomy in racehorses is unclear. This study was performed to evaluate the success of and complications that can occur after a unilateral partial arytenoidectomy with primary mucosal closure in Thoroughbred racehorses. HYPOTHESIS: Partial arytenoidectomy is an effective surgical procedure to return Thoroughbred racehorses, afflicted by arytenoid chondropathy or a failed laryngoplasty, to preoperative levels of performance. METHODS: Seventy-six Thoroughbred racehorses admitted to the New Bolton Centre between 1992 and 2006 were assessed. Information was obtained from the medical records about the horse, laryngeal abnormalities, surgery and other findings during hospitalisation. Racing information was evaluated relative to those independent variables by an analysis of variance with a level of significance of P<0.05. RESULTS: Arytenoid chondropathy was the presenting complaint in 54 horses and failed laryngoplasty in 22 horses. Thirteen horses (17%) underwent a second surgery for laser excision of intralaryngeal granulation tissue at the arytenoidectomy site. Seventy-three horses were discharged from the hospital and racing outcome was evaluated. Sixty horses (82%) raced after surgery and 46 horses (63%) raced 5 or more times after surgery. The median time from surgery to the first start was 6 months. The average earnings/start was not significantly different before and after surgery. There was no association between earnings after surgery and age, gender, location of lesion, type of lesion, duration of tracheal intubation or undergoing a second surgery. CONCLUSIONS AND POTENTIAL RELEVANCE: A Thoroughbred racehorse is likely to race after a unilateral partial arytenoidectomy with primary mucosal closure and return to a preoperative level of performance.

Myosin heavy chain composition in normal and atrophic equine laryngeal muscle.

The myosin heavy chain (MHC) composition of a given muscle determines the contractile properties and, therefore, the fiber type distribution of the muscle. MHC isoform expression in the laryngeal muscle is modulated by neural input and function, and it represents the cellular level changes that occur with denervation and reinnervation of skeletal muscle. The objective of this study was to evaluate the pattern of MHC isoform expression in laryngeal muscle harvested from normal cadavers and cadavers with naturally occurring left laryngeal hemiplegia secondary to recurrent laryngeal neuropathy. Left and right thyroarytenoideus (TA) and cricoarytenoideus dorsalis (CAD) were obtained from 7 horses affected with left-sided intrinsic laryngeal muscle atrophy and from 2 normal horses. Frozen sections were evaluated histologically for degree of atrophy and fiber type composition. MHC isoform expression was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of muscle protein. Histologic atrophy was seen in all atrophic muscles and some right-sided muscles of 3 affected horses, as well as the left TA of 1 normal horse. Fiber type grouping or loss of type I muscle fibers was observed in the left-sided laryngeal muscles in all but 1 affected horse, as well as in the right muscles of 2 affected horses, and the left TA of 1 normal horse. SDS-PAGE showed 2 bands corresponding to the type I and type IIB myosin isoforms in the CAD and TA of the 2 normal horses. Affected horses demonstrated a trend toward increased expression of the type IIB isoform and decreased expression of the type I isoform in atrophic muscles. This study confirmed the presence of histologic abnormalities in grossly normal equine laryngeal muscle, and it demonstrated an increased expression of type IIB MHC with a concurrent decreased expression of type I MHC in affected muscles. Evaluation of muscle fiber changes at the cellular level under denervated and reinnervated conditions may aid in assessing future strategies for reinnervation or regeneration of atrophic laryngeal muscle.

Incomplete sagittal fracture of the talus in 11 racehorses: outcome.

REASONS FOR PERFORMING STUDY: Little information exists regarding talus fractures in the horse and there have been no previously published case series of racehorses diagnosed with incomplete sagittal fracture of the talus. OBJECTIVE: To describe the diagnosis, treatment and post injury performance of horses with incomplete sagittal fracture of the talus. METHODS: Medical records of 11 racehorses (8 Standardbreds and 3 Thoroughbreds) admitted between January 1992 and January 1999 were reviewed. Subject details, anamnesis, results of lameness examination, radiographs and nuclear scintigraphic findings were evaluated. Racing performance was assessed by comparing pre- and post injury race records. RESULTS: Nuclear scintigraphic examination, performed in 8 of the 11 horses, revealed focal increased radiopharmaceutical uptake in the proximal aspect of the affected talus. Fractures could best be seen on dorsal 10-20 degrees lateral-plantaromedial oblique radiographs; all had raced pre-injury. All horses were treated conservatively and follow-up information was available for 8 horses, of which 7 raced after injury. Performance in 3 horses was improved, in 1 it was unchanged and in 3 horses performance declined. CONCLUSIONS: Horses with incomplete fracture of the talus have a good prognosis for return to racing after conservative management. POTENTIAL RELEVANCE: Incomplete sagittal fracture of the talus should be considered as a cause of hindlimb lameness in racehorses. Further research is necessary to determine the pathophysiology of these fractures.

Effects of mild forelimb lameness on exercise performance.

Mild lameness is considered a performance-limiting problem that may escape detection until it worsens, and is considered the primary reason for reduced racing performance. The kinematics changes associated with a lame horse at the trot have been demonstrated previously, but the metabolic cost of these alterations in their gait have not been demonstrated. Six fit Thoroughbred horses with an established VO2max participated in 4 trials using a randomised cross-over design study, separated by 10-14 days. The horses were tested with one of 4 trial conditions: lead forelimb lameness (LL); off-lead forelimb lameness (OL); bilateral forelimb lameness (BL) or no lameness (NL). Lameness was induced by sole pressure from a modified shoe that resulted in a consistent slight head nod at a trot in a straight line while jogging in hand. Lameness was adjusted to provide a lameness that would be quantified as a 1-2/5 on the grading system recommended by the AAEP. Each trial consisted of 4 different levels of exercise intensity at speeds equivalent to 30, 60, 80 and 110% of an individual's speed required to elicit VO2max. Stride parameters, oxygen consumption (VO2), carbon dioxide production (VCO2), electrolytes, plasma lactate, glucose and PCV/TP were measured prior to exercise, at each exercise level and after exercise. A multiway ANOVA with repeated measures was utilised to examine possible effects of individual horse, lameness, and exercise intensity on measured parameters. Significance was set at alpha = 0.05. For horses exercising at the maximum intensity, VO2 was significantly lower for both of the single-leg lamenesses (LL or OL) when compared to NL or BL (mean +/- s.e. 165.6 +/- 2.5, 164.7 +/- 3.0, 175.8 +/- 2.4 and 170.9 +/- 2.1 ml O2/min/kg bwt, respectively). Blood lactate concentrations were not significantly different among the treatment groups. However, lactate accumulation rates computed as the change with time in lactate concentration at the highest exercise intensity were significantly higher for LL and OL than for NL and BL (7.8 +/- 03, 83 +/- 0.2, 4.1 +/- 0.2 and 4.7 +/- 0.3 mmol/min, respectively). Exercise intensity had significant effects on all of the measured parameters, but there were no other significant differences due to treatment. These results suggest that metabolic energy transduction is affected by even mild unilateral forelimb lamenesses.

The effect of recurrent laryngeal neurectomy in conjunction with laryngoplasty and unilateral ventriculocordectomy in thoroughbred racehorses.

OBJECTIVE: To investigate the effects of recurrent laryngeal neurectomy (RLN) in combination with laryngoplasty and ventriculocordectomy on the postoperative performance of Thoroughbred racehorses treated for grade III left laryngeal hemiparesis (LLH). STUDY DESIGN: Retrospective study. SAMPLE POPULATION: Fifty-five Thoroughbred racehorses. METHODS: Medical records for Thoroughbred racehorses treated surgically by laryngoplasty and laser ventriculocordectomy with or without RLN between June 1993 and December 1996 were reviewed. Outcome was evaluated subjectively by assessment of performance obtained from telephone interviews with owners and trainers, and objectively by assessment of racing performance for 3 races before and after surgery using a performance index (PI). RESULTS: Fifty-five Thoroughbred racehorses with resting endoscopic grade III LLH were treated by laryngoplasty and ventriculocordectomy either with (39 horses) or without (16 horses) RLN. For RLN horses, respondents for 38 horses believed performance was improved in 19 horses, unchanged in 16 horses, and decreased in 3 horses. For horses without RLN, respondents for 9 horses reported that performance was improved in 5 horses, unchanged in 2 horses, and decreased in 2 horses. PI scores were improved in 18 RLN horses and in 6 horses without RLN; there was no statistical difference in outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Use of RLN in combination with laryngoplasty and ventriculocordectomy for treatment of grade III LLH may not improve postoperative racing performance.

Clinical experiences with axial deviation of the aryepiglottic folds in 52 racehorses.

OBJECTIVE: To describe the clinical findings in 52 racehorses with axial deviation of the aryepiglottic folds (ADAF) and to report outcome in 33 of these horses after either rest or transendoscopic laser excision of aryepiglottic fold tissue. STUDY DESIGN: Retrospective study. ANIMAL OR SAMPLE POPULATION: Racehorses admitted for high-speed treadmill (HST) evaluation of poor performance. METHODS: Medical records and videotapes of resting and exercising videoendoscopic examinations were reviewed. Racing performance records and owner or trainer interviews, at least 1 year after HST examination, were used to compare results after either surgical management or rest in 33 horses with ADAF and no other upper-airway abnormalities. RESULTS: ADAF occurred in 6% of horses evaluated for poor performance. No breed or gender predisposition existed, but horses with ADAF were younger than the overall population evaluated on the HST. Of 52 horses with ADAF, 19 horses had at least one other upper-airway abnormality. There was no apparent association between ADAF and other causes of dynamic upper-respiratory obstruction. Surgical correction was successfully performed in standing or anesthetized horses without complications. When ADAF was the only upper-airway obstruction, 75% of horses that had surgery and 50% of rested horses had objective improvement in performance. Owners and trainers also perceived greater improvement in performance in horses that had surgery. CONCLUSIONS: Whereas surgical management of ADAF is recommended, clinical experience indicated that it is not required to resolve ADAF in all horses. However, owners and trainers of horses that had surgery were more satisfied with outcome than those with horses managed conservatively. CLINICAL RELEVANCE: Diagnosis of ADAF can only be made by videoendoscopic evaluation during high-speed exercise. Transendoscopic laser excision of the collapsing portion of the aryepiglottic folds can be performed safely in standing horses and results in resolution of airway obstruction and rapid return to training.

Causes of poor performance of horses during training, racing, or showing: 348 cases (1992-1996).

OBJECTIVE: To determine results for horses undergoing a high-speed treadmill examination, including videoendoscopy of the pharynx and larynx before and during exercise, echocardiography before and after exercise, and electrocardiography before, during, and after exercise, because of poor performance. DESIGN: Retrospective study. ANIMALS: 348 horses. RESULTS: A definitive diagnosis was obtained for 256 (73.5%) horses. One hundred forty-eight horses had dynamic obstruction of the airway during exercise, 33 had clinically important cardiac arrhythmias alone, 22 had a combination of dynamic airway obstruction and clinically important cardiac arrhythmias, 19 had poor cardiac fractional shortening immediately after exercise, 10 had exertional rhabdomyolyis, 15 had clinically apparent lameness, and 9 had other disorders. Thirty-nine of the horses with dynamic obstruction of the airway during exercise had multiple airway abnormalities. Fifty-three horses also had subclinical myopathy CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that a complete evaluation, including a high-speed treadmill examination, should be conducted in horses with poor performance, regardless or whether horses do or do not have a history of abnormal respiratory noises and particularly if the horses have grade-II or -III left laryngeal hemiplegia.

Cytologic examination of specimens obtained by means of tracheal washes performed before and after high-speed treadmill exercise in horses with a history of poor performance.

OBJECTIVE: To evaluate results of cytologic examination of specimens obtained by means of tracheal washes (TW) in 42 horses with a history of poor performance. DESIGN: Cross-sectional case series. ANIMALS: 42 horses with a history of poor performance. PROCEDURE: A TW was performed via endoscopy before and after horses exercised on a high-speed treadmill, and specimens were evaluated microscopically and graded. RESULTS: Ten (24%) horses were considered to be clinically normal before and after exercise. Pulmonary hemorrhage was diagnosed in 8 (19%) horses. One horse had evidence of exercise-induced pulmonary hemorrhage (EIPH) before exercise and pulmonary hemorrhage and allergic or inflammatory airway disease (IAD) after exercise. Five (12%) horses had IAD, and 1 had IAD and pulmonary hemorrhage after exercise. Seven (17%) horses had evidence of EIPH and IAD in both specimens. Four (10%) horses with EIPH had an increase in the proportion of hemosiderophages in the specimen obtained after exercise. Specimens obtained before exercise in 6 (14%) horses were not representative of the respiratory tract and could not be compared with specimens obtained after exercise. CLINICAL IMPLICATIONS: Interpretation of TW specimens obtained before and after exercise differed for only 5 of 36 (14%) horses. Specimens obtained after exercise were more likely to reveal airway disease. All specimens obtained after exercise adequately represented the respiratory tract, whereas 6 specimens obtained before exercise did not. Specimens obtained after exercise contained more airway secretions and had less cytologic evidence of pharyngeal contamination. Therefore, we recommend that TW samples be obtained after exercise in horses.

Effect of high-intensity exercise on arterial blood gas tensions and upper airway and cardiac function in clinically normal quarter horses and horses heterozygous and homozygous for hyperkalemic periodic paralysis.

OBJECTIVE: To determine the effect of exercise on arterial blood gas tensions and upper airway and cardiac function in clinically normal Quarter Horses and horses heterozygous and homozygous for hyperkalemic periodic paralysis (HYPP). ANIMALS AND PROCEDURE: 5 clinically normal Quarter Horses, and 5 heterozygous and 2 homozygous HYPP-affected horses were examined before, during, and after exercise on a high-speed treadmill. Arterial blood gas tensions, ECG, and echocardiogram were obtained prior to exercise. Upper airway endoscopy, collection of arterial blood samples, and continuous electrocardiography were performed during a high-intensity stepwise exercise test. An ECG was obtained within 1-minute after completion of the final step. RESULTS: None of the horses homozygous or heterozygous for HYPP had signs of weakness or muscle fasciculations before, during, or after exercise. Horses homozygous for HYPP had intermittent laryngospasm, dynamic pharyngeal collapse, and appreciable hypoxemia, hypercapnia, and ventricular premature contractions during exercise. Heterozygous and clinically normal horses did not have any abnormalities. Potassium concentration increased significantly above the baseline reference range during exercise in all groups of horses. CONCLUSIONS: Horses homozygous for HYPP had laryngospasm and dynamic pharyngeal collapse associated with exercise, most likely secondary to increase in potassium concentration. Upper airway dysfunction is the most likely cause of hypoxemia and hypercapnia. Cardiac arrhythmias were most likely caused by a combination of hypoxemia and hyperkalemia.

Videoendoscopic assessment of dynamic laryngeal function during exercise in horses with grade-III left laryngeal hemiparesis at rest: 26 cases (1992-1995).

OBJECTIVE: To evaluate laryngeal function by means of videoendoscopy during high-speed treadmill exercise in racehorses with grade-III left laryngeal hemiparesis at rest and to determine outcome of treatment. DESIGN: Retrospective study. ANIMALS: 26 racehorses. PROCEDURE: Videoendoscopy of the larynx was performed while horses were at rest and exercising on a treadmill. Horses were classified as having grade-IIIA, -IIIB, or -IIIC laryngeal hemiparesis on the basis of the degree of arytenoid cartilage abduction maintained during exercise. Postoperative racing performance was determined by evaluating race records and conducting telephone surveys. RESULTS: 20 (77%) horses had grade-IIIC laryngeal hemiparesis (i.e., severe dynamic laryngeal collapse during exercise). Eighteen underwent surgery, and racing performance was improved in 9. Five (19%) horses had grade-IIIB laryngeal hemiparesis (i.e., left arytenoid cartilage and vocal fold were maintained in an incompletely abducted position during exercise). Four underwent surgery, and racing performance was improved in 1. One (4%) horse had grade-IIIA laryngeal hemiparesis (i.e., full abduction of arytenoid cartilage during exercise); surgery was not performed. CLINICAL IMPLICATIONS: Videoendoscopy is useful in determining dynamic laryngeal function in racehorses with grade-III laryngeal hemiparesis at rest.

Testing methods for exercise intolerance in horses.

The many testing methods available and the increasing sophistication of diagnostic equipment have enhanced greatly our capabilities to diagnose causes of exercise intolerance in the equine athlete during the last several years. High-speed treadmill examination has become the focus of this form of evaluation. Not all clinicians perform or have access to high-speed treadmill examinations. Testing methods that require the use of the high-speed treadmill, as well as methods that do not, are discussed.

Stress protection afforded by a cast on plate fixation of the distal forelimb in the horse in vitro.

Six forelimb specimens from three adult horses had the fetlock joint fused by application of a dorsal plate and by a screw placed in lag fashion through the metacarpus to each proximal sesamoid bone. Five specimens were instrumented on the central dorsal surface of the plate with a single rosette strain gage, and the plate of the sixth specimen was instrumented with four longitudinally oriented single-axis strain gages. The specimens were loaded axially in compression to 4,000 N in a cast (test 1), in a cast with a heel block (test 2), and uncast (test 3). The principal angle of strain in all specimens, in all tests, closely approximated the vertical axis at loads < 1,000 N. The principal angle in uncast specimens was significantly different at loads > 1,000 N than the cast specimens (P < .05). At loads > 3,000 N, the principal angle in test 3 closely approximated the horizontal axis, indicating a change from tension to compression on the dorsal surface of the plate, whereas the principal angle of the cast specimens was unchanged. Specimens in a cast (tests 1 and 2) suffered less surface deformation than did uncast specimens (test 3). Therefore, the cast changed the direction and extent of bending at the point of fixation, and thereby decreased the deformation of the plate. This effect would lead to greater fatigue life of the implant in the cast specimens compared with the uncast specimens.