The effect of cyanoacrylate on knot elongation in three sutures used for prosthetic laryngoplasty in the horse.

OBJECTIVE: This study investigated the elongation following cyclic loading on square knots of 5 USP multifilament long-chain ultra-high molecular weight polyethylene core (UHMWPE), 2 mm woven UHMWPE tape, and 5 USP braided polyester, with and without cyanoacrylate glue. STUDY DESIGN: Experimental study. SAMPLE POPULATION: n = 4. METHODS: Three conditions (suture without knot, suture with knot, suture with knot + cyanoacrylate) were evaluated for each suture material on a mechanical test stand by measuring the increased length of the construct after cycling from 25 to 50N for 1000 repetitions at 20 mm/second. Knot elongation was determined by subtracting the length of the control suture from the suture with knot or suture with knot + cyanoacrylate. The data were analyzed with a linear regression model with robust estimation of variance. Post-hoc analysis determined the model adjusted differences (square knot vs. cyanoacrylate) as a difference from control. t-tests were conducted to identify the significant findings. RESULTS: Total elongation of polyester (6.2-7.8 mm) was greater than multifilament UHMWPE (3.4-6.4 mm) and UHMWPE tape (2-3.7 mm) for all conditions. Polyester had the lowest knot elongation (1.6 mm) and the addition of cyanoacrylate decreased knot elongation for polyester by 1 mm. CONCLUSIONS: Polyester had the most total construct elongation followed by multifilament UHMWPE and UHMWPE tape. Polyester showed the least knot elongation and cyanoacrylate decreased this knot elongation. CLINICAL SIGNIFICANCE: Total construct and knot elongation should be considered as contributing factors to loss of arytenoid abduction following prosthetic laryngoplasty when using polyester, multifilament UHMWPE, or UHMWPE tape. Addition of cyanoacrylate to polyester knots should be explored to limit elongation.

Variations in the application of equine prosthetic laryngoplasty: A survey of 128 equine surgeons.

OBJECTIVE: To document variations in the application of equine prosthetic laryngoplasty among equine surgeons. STUDY DESIGN: Cross-sectional survey. SAMPLE POPULATION: Six hundred and seventy-eight equine surgeons performing prosthetic laryngoplasty. METHODS: An online questionnaire was sent to equine surgeons, including diplomates of the American College of Veterinary Surgeons and European College of Veterinary Surgeons. Questions focused on participant profile, surgical technique, antimicrobial therapy, and concurrent procedures. Descriptive statistical analysis was performed on the survey output. RESULTS: Complete responses were received from 128/678 individuals, mostly from experienced surgeons. Most participants used 2 prostheses (106/128, 82.8%) and a single loop was the most common method used to anchor the prosthesis in the cricoid (95/128, 74.2%) and arytenoid (125/128, 97.7%) cartilages. Use of general anesthesia was common, although 46/128 (35.9%) participants now performed most laryngoplasty surgery with standing sedation. The material used as a prosthesis varied among surgeons, although participants typically aimed to achieve grade 2 intraoperative arytenoid abduction. Participants most commonly administered perioperative systemic antimicrobial therapy for 1-3 days (57/128, 44.5%) and 48/128 (37.5%) used local antimicrobial therapy. CONCLUSION: Most surgeons performed laryngoplasty with 2 prostheses, a single loop construct at the muscular process of the arytenoid cartilage and systemic antimicrobial therapy. There was variation in the preferred method of surgical restraint, prosthesis material selection, and use of local antimicrobial therapy. CLINICAL SIGNIFICANCE: Long-established techniques remain popular in clinical practice despite evidence that variations offer advantages, particularly in relation to biomechanics. Other factors are also likely to influence technique selection in a clinical context.

The effect of repeated freezing and thawing on the suture pull-out strength in equine arytenoid and cricoid cartilages.

OBJECTIVE: To assess the effect of repeated freezing and thawing on the suture pull-out strength in arytenoid and cricoid cartilages subjected to the laryngoplasty (LP) procedure. STUDY DESIGN: Ex vivo experimental study. SAMPLE POPULATION: Ten grossly normal equine cadaveric larynges. METHODS: Bilateral LP constructs were created using a standard LP technique. One hemilarynx was randomly allocated to the single freeze and thaw group and the other allocated to the repeated freeze and thaw (3 complete cycles) group. The suture ends of each LP construct were attached to a load frame and subjected to monotonic loading until construct failure. Mean load (N) and displacement (mm) at LP construct failure were compared between groups. RESULTS: All LP constructs failed by suture pull through the arytenoid cartilage. The mean load at failure was similar between groups (118.9 ± 25.5 N in the single freeze and thaw group and 113.4 ± 20.5 N in the repeated freeze and thaw group, P = .62). The mean displacement at failure was similar between groups (54.4 ± 15.1 mm in the single freeze and thaw group and 54.4 ± 15.4 mm in the repeated freeze and thaw group, P = .99). CONCLUSION: Repeated freezing and thawing did not affect the suture pullout strength of the arytenoid and cricoid cartilages. CLINICAL SIGNIFICANCE: Laryngeal specimens that have been subjected to repeated freezing and thawing can be utilized in the experimental evaluation of LP procedures because there is no alteration of the suture pull-out strength of the relevant cartilages.

Influence of unilateral and bilateral vocal cordectomy on airflow across cadaveric equine larynges at different Rakestraw grades of arytenoid abduction.

OBJECTIVE: To assess the effect of vocal cordectomy on airflow across equine larynges at different Rakestraw grades of arytenoid abduction using a unidirectional airflow model. STUDY DESIGN: Ex vivo, repeated measures. SAMPLE POPULATION: Twenty cadaveric equine larynges. METHODS: The right arytenoid cartilage was maximally abducted in all larynges. Each larynx was assigned a Rakestraw grade A or B, and the left arytenoid was abducted accordingly. Each larynx was tested under 3 conditions: intact, left vocal cordectomy (LVC), and bilateral vocal cordectomy (BVC). Translaryngeal pressure and airflow were measured, and digital video footage was obtained. Translaryngeal impedance (TLI) was calculated, and the arytenoid left-to-right quotient angle (LRQ) and rima glottis cross-sectional area (CSA) were measured from standardized still images. RESULTS: Vocal cordectomy reduced TLI by 14.5% in LVC in comparison with intact larynges at Rakestraw grade B (P = .014). In Rakestraw grade A position, neither unilateral nor bilateral vocal cordectomy had any effect on TLI. Regardless of Rakestraw allocation, both LVC and BVC increased CSA in comparison with intact larynges (P < .005), with BVC larynges experiencing a greater effect than LVC (P < .0001). CONCLUSION: Using a unilateral airflow model, LVC improved TLI in larynges where arytenoid position approximated Rakestraw grade B. However, when the arytenoid position approximated Rakestraw grade A, there was no effect on TLI following LVC or BVC. CLINICAL SIGNIFICANCE: Surgeons considering a vocal cordectomy should take into account the degree of arytenoid abduction before performing the procedure, as it may not be warranted from a TLI point of view.

Ex vivo biomechanical evaluation of polyester and polyblend suture techniques to perform equine laryngoplasty.

OBJECTIVE: To validate the use of a polyblend tape suture in equine laryngoplasty (PL). STUDY DESIGN: Experimental study. ANIMALS: Thirty-two cadaveric larynges. METHODS: Each larynx was randomly assigned to 1 of 4 groups: PL with polyblend tape suture (TigerTape), without (TT) or with a cannula (TTC) in the muscular process of the arytenoid cartilage, and PL with polyester suture (Ethibond), without (EB) or with a cannula (EBC). Construct stiffness, total migration, creep, and drift values were measured after 3000 cycles. The specimens were then loaded to failure to assess their residual properties: load at failure, total energy, displacement, and 2 stiffness coefficients. RESULTS: After cyclic testing, the total migration and creep were lower in TTC (6.36 ± 1.20 mm; 1.35 ± 0.38 mm/s) than in EB (11.12 ± 4.20 mm; 3.39 ± 2.68 mm/s) and in the TT constructs (11.26 ± 1.49 mm; 3.20 ± 0.54 mm/s); however, no difference was found with EBC (9.19 ± 3.18 mm; 2.14 ± 0.99). A correlation was found between total migration and creep (R = .85). The TTC constructs failed at higher loads (129.51 ± 33.84 N) than EB (93.16 ± 18.21 N) and EBC (81.72 ± 13.26 N) whereas the EB and EBC constructs were less stiff than TT and TTC (P < .001). CONCLUSION: Biomechanical properties were generally superior for the TTC constructs tested under cyclical loading. The TT and TTC constructs failed at a higher load than EB and EBC constructs. The cannula in TTC and EBC reduced the failure at the muscular process. CLINICAL SIGNIFICANCE: These results provide evidence to support the in vivo evaluation of the polyblend tape suture with or without a cannula in the muscular process for laryngoplasty in horses.

Evaluation of the airway mechanics of modified toggle laryngoplasty constructs using a vacuum chamber airflow model.

OBJECTIVE: To evaluate the airway mechanics of modified toggle LP constructs in an airflow chamber model and compare these to the airway mechanics of standard LP constructs. STUDY DESIGN: Ex-vivo experimental study. SAMPLE POPULATION: Fifty-one equine cadaveric larynges. METHODS: Bilateral LP constructs were performed using a modified toggle (n = 23) or a standard (n = 21) LP technique. Constructs were tested in an airflow model before and after cyclic loading which was designed to mimic postoperative swallowing. The cross-sectional area (CSA), peak translaryngeal airflow (L/s), and impedance (cmH2 0/L/s) were determined and compared between LP constructs before and after cycling. RESULTS: The mean CSA of the rima glottidis of the modified toggle LP constructs was 15.2 ± 2.6 cm2 before and 14.7 ± 2.6 cm2 after cyclic loading, and the mean CSA of the rima glottidis of the standard LP constructs was 16.4 ± 2.9 cm2 before and 15.7 ± 2.8 cm2 after cyclic loading. The modified toggle LP constructs had similar peak translaryngeal impedance before and after cyclic loading (p = .13); however, the standard LP constructs had higher peak translaryngeal impedance after cyclic loading (p = .02). CONCLUSION: The modified toggle and standard LP constructs had comparable airway mechanics in an ex-vivo model. CLINICAL SIGNIFICANCE: Further investigation is warranted to determine the extent to which the modified toggle LP technique restores normal airway function in horses with RLN.

Thyrohyoideus muscle innervation in the horse.

OBJECTIVE: To describe the innervation of the thyrohyoideus (TH) muscle and to confirm our findings with stimulation of first cervical (C1) nerve branches. STUDY DESIGN: Ex vivo phase 1 and clinical phase 2. ANIMALS: Fourteen head and neck specimens and 17 client-owned horses. METHODS: In phase 1, the cranial nerve (CN) XII and the C1 nerve were dissected with their branches in 20 dissections were performed on 14 specimens (6 left and right side and 8 only left or right) Anatomy was noted. Samples of nerve bifurcations were collected for histological confirmation of anatomical findings. First cervical nerve branches were stimulated in horses undergoing cervical nerve graft to treat laryngeal hemiplegia. RESULTS: The nerve innervating the TH muscle arose directly from the C1 nerve in 17 of 20 dissections, from an anastomotic branch between CN XII and the C1 nerve in two of 20 dissections, and from the C1 nerve and the anastomotic branch in one of 20 dissections. No direct connection between the TH muscle and CN XII was found. Histological examination revealed that the anastomosis was composed of C1 nerve fibers passing over to CN XII. First cervical stimulation resulted in TH muscle contraction in 16 of 17 horses. CONCLUSIONS: The innervation of the TH muscle originated from the C1 nerve according to dissection, histological, and conduction studies, with variation in the branching pattern. CLINICAL SIGNIFICANCE: Care should be taken to preserve the C1 nerve during prosthetic laryngoplasty. The surgical technique for C1 nerve grafts should be reconsidered in light of these findings, along with new options to treat dorsal displacement of the soft palate..

Ex vivo study of vagal branches at risk for iatrogenic injury during laryngoplasty in horses.

OBJECTIVE: To localize vagal branches within the surgical field of laryngoplasty and identify potentially hazardous surgical steps. STUDY DESIGN: Observational cadaveric study. SAMPLE POPULATION: Five equine head-neck specimens and four entire equine cadavers. METHODS: Dissection of the pharyngeal region from a surgical perspective. Neuronal structures were considered at risk if touched or if the distance to instruments was less than 5 mm. RESULTS: The branches of the pharyngeal plexus (PP) supplying the cricopharyngeal muscle (PPcr), the thyropharyngeal muscle (PPth), and the esophagus (PPes) were identified in the surgical field in nine of nine, five of nine, and one of nine specimens, respectively. The internal branch of the cranial laryngeal nerve (ibCLN) was identified within the carotid sheath in six of nine specimens. The external branch of the cranial laryngeal nerve (ebCLN) was identified close to the septum of the caudal constrictors in nine of nine specimens. The blade of the tissue retractor compressed the ibCLN in six of six, the ebCLN in four of six, the PPcr in six of six, the PPth in two of three, and the PPes in two of two specimens in which the respective nerves were identified after further dissection. Surgical exploration of the dorsolateral aspect of the pharynx and the incision of the septum of the caudal constrictors harmed the ebCLN in nine of nine, PPcr in seven of nine, and PPth in four of eight specimens. CONCLUSION: Several vagal branches were located in the surgical field and must be considered at risk because of their location. CLINICAL SIGNIFICANCE: Use of the tissue retractor, dissection over the pharynx, and dissection of the septum of the caudal constrictors involve a risk to damage vagal branches.

Management of postoperative dysphagia after prosthetic laryngoplasty or arytenoidectomy.

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

Partial arytenoidectomy in 14 standing horses (2013-2017).

OBJECTIVE: To report our experience with partial arytenoidectomy in sedated standing horses. STUDY DESIGN: Retrospective study. ANIMALS: Fourteen client-owned adult horses. METHODS: The medical records (2013-2017) of horses treated with unilateral partial arytenoidectomy while standing and sedated were reviewed. Demographics, endoscopic findings, previous treatments, and outcome after surgery were investigated and recorded. RESULTS: Thirteen horses had unilateral left-sided recurrent laryngeal neuropathy (RLN) and 1 horse had bilateral RLN. Five horses had a previous failed prosthetic laryngoplasty. Left-sided partial arytenoidectomy without mucosal closure was successfully completed in all horses under sedation and local anesthesia. Report of long-term outcome was obtained via telephone conversations for 12 horses, of which 9 also had an endoscopic reevaluation performed; 3 horses had granulomas at the surgical site, of which 2 eventually required a permanent tracheostomy. Nine horses returned to athletic use without respiratory noise, 2 horses returned to athletic use with noise during exercise that was reduced compared with preoperative levels, and 1 horse continued to be used as a broodmare. CONCLUSION: Partial arytenoidectomy in standing horses was achieved with adequate sedation and local anesthesia. CLINICAL SIGNIFICANCE: Partial arytenoidectomy on standing sedated horses could be considered as an alternative to eliminate the risks associated with general anesthesia.

Epiglottopexy for the treatment of epiglottic retroversion in 2 horses.

OBJECTIVE: To report an epiglottopexy technique for the treatment of epiglottic retroversion (ER) in 2 horses. STUDY DESIGN: Case report. ANIMALS: A 2-year-old thoroughbred gelding and a 6-year-old standardbred gelding, both with ER. METHODS: Epiglottic retroversion was diagnosed via exercising endoscopic examination in both horses. Epiglottopexy technique was performed in both cases. RESULTS: Both horses returned to previous racing class within 1 year after surgery. Repeat exercising endoscopy of 1 horse 6 months postoperatively revealed resolution of the ER. CONCLUSION: Epiglottopexy should be considered for treatment of ER in the equine athlete. CLINICAL SIGNIFICANCE: Previously reported surgical techniques for ER in the equine athlete have not resulted in horses returning to previous performance level. The technique reported here resulted in both horses achieving athletic status.

Evaluation of a prototype dynamic laryngoplasty system in vitro with an equine vacuum airflow system.

OBJECTIVE: To evaluate a prototype dynamic laryngoplasty system (DLPS) in a static airflow model. STUDY DESIGN: Experimental. SAMPLE POPULATION: Ten equine larynges. METHODS: The right arytenoid was fixed in abduction in all specimens. A left-sided laryngoplasty was performed with No. 2 Fiberwire and a FASTakII anchor. Each larynx was tested in a static airflow model. The system was adjusted to a flow rate of 55 L/s and prelaryngeal pressure of 12 mm Hg prior to testing in maximal arytenoid abduction. In phase 1, the left suture was loosened, shortened, and tested in 3-mm steps from 0 to 30 mm. In phase 2, the suture was tied with the DLPS in position at a target left-to-right quotient angle (LRQ) of 0.5. The DLPS was activated to target psi of 0, 25, and 50 for testing. Translaryngeal impedance (TLI), LRQ, cross-sectional areas (CSA), and resultant change in LRQ and CSA between, before, and during airflow testing were calculated. RESULTS: In phase 1, TLI was reduced by suture shortening up to 6 mm (P = .001) but not by additional shortening (P > .05). In phase 2, activation of the DLPS reduced the TLI from 0 psi (0.43 ± 0.08 mm Hg/L/s) to 25 psi (0.16 ± 0.04 mm Hg/L/s, P < .001), but no further reduction was detected at maximal psi (P = .10). CONCLUSION: Activation of the DLPS effectively reduced TLI. CLINICAL SIGNIFICANCE: These results justify further investigation of the DLPS to assess its clinical applicability.

Outcomes of horses treated with removal of a laryngoplasty prosthesis.

OBJECTIVE: To determine the proportion of horses treated by laryngoplasty prosthesis removal (LPR) for complications associated with prosthetic laryngoplasty (LP), the reason for LPR, and the outcome of horses undergoing LPR to manage iatrogenic coughing/dysphagia. STUDY DESIGN: Retrospective study. SAMPLE POPULATION: Client-owned horses treated with LP (n = 1202) and LPR (n = 58). METHODS: Clinical case records were reviewed to determine the number of horses treated with LP and LPR by the same surgeon. Historical, clinical, endoscopic, and surgical data were extracted for those horses undergoing LPR. Long-term outcome was assessed by questionnaire. RESULTS: The proportion of horses treated with LP and subsequently treated with LPR by the same surgeon was 3.5% (42/1202). Coughing/dysphagia was the reason for LPR in 90% (52/58) of horses. Sufficient follow-up to determine outcome in horses undergoing LPR for coughing/dysphagia was available in 32 horses. Arytenoid abduction grade at the time of LPR did not influence clinical response (P = .416). Presenting clinical signs resolved after LPR in 21 of 32 (66%) horses, and 24 of 32 (75%) horses returned to exercise. CONCLUSION: Coughing/dysphagia was the most common reason for LPR. Clinical signs improved in most horses after LPR. CLINICAL SIGNIFICANCE: Laryngoplasty prosthesis removal can be a useful treatment option for horses affected with unmanageable coughing/dysphagia caused by LP.

Ex vivo investigation of the effect of the transverse arytenoid ligament on abduction of the arytenoid cartilage when performing equine laryngoplasty.

Aims: To investigate the effect of the transverse arytenoid ligament (TAL) on abduction of the arytenoid cartilage when performing laryngoplasty. Methods: Modified prosthetic laryngoplasty was performed on right and left sides of 13 cadaver larynges. Increasing force was sequentially applied to the left arytenoid cartilage at 3 N intervals from 0-24 N, when the force on the right arytenoid cartilage was either 0 or 24 N, before and after TAL transection. Digital photographs of the rostral aspect of the larynx were used to determine the left arytenoid abduction angles for these given force combinations and results compared before and after TAL transection. Longitudinal and transverse sections of the TAL from seven other equine larynges were also examined histologically. Results: Increasing force on the left arytenoid cartilage from 0-24 N produced a progressive increase in the angle of the left arytenoid cartilage (p < 0.001) and increasing force on the right arytenoid cartilage from 0-24 N reduced the angle of the left arytenoid cartilage (p < 0.001). Following transection of the TAL the mean angle of the left arytenoid increased from 36.7 (95% CI = 30.5-42.8)° to 38.4 (95% CI = 32.3-44.5)°. Histological examination showed that the TAL was not a discrete ligament between the arytenoid cartilages but was formed by the convergence of the ligament and the left and right arytenoideus transversus muscles. Conclusions: Transection of the TAL in ex vivo equine larynges enabled greater abduction of the left arytenoid cartilage for a given force. These results indicate that TAL transection in conjunction with prosthetic laryngoplasty may have value, but the efficacy and safety of TAL transection under load in vivo, and in horses clinically affected with recurrent laryngeal neuropathy must be evaluated. Abbreviations: Fmax: Force needed to maximally abduct the left or right arytenoid; TAL: Transverse arytenoid ligament.

Ultrasonographic findings post laryngoplasty in the horse.

Laryngoplasty is commonly used to treat laryngeal hemiplegia in Thoroughbred racehorses. Evaluation of the success of the laryngoplasty is traditionally determined using endoscopy. Laryngeal ultrasonography and normal ultrasonographic appearance have been reported in the standing horse, but post-laryngoplasty and ventriculectomy ultrasonographic evaluation has limited literature coverage. A prospective case series of 10 Thoroughbred racehorses with left laryngeal hemiplegia was examined ultrasonographically and endoscopically prior to 3-10 days, 30-50 days, and 6-12 months after laryngoplasty and ventriculectomy. Anatomical structures and Plica vocalis movements were described and measurements and gradings analyzed by repeated means analysis of variance (P < .05). Postsurgical ultrasonographic visualization of Ventriculus laryngis entrances was possible. The distance between Plica vocalis in exhalation was significantly larger than that during inhalation (P < .05). Pre- and postsurgical caudal Basihyoideum and rostral Cartilago thyroidea depth was significantly different in some instances (P < .05). No significant differences in the Muscularis cricoarytenoideus lateralis measurements were found. Complications in the extra-luminal structures were found in seven horses including soft tissue swelling, seroma, and hematoma. A luminal Plica vocalis abscess and Plica vocalis granuloma were also detected ultrasonographically. Ultrasonography can be used to evaluate the post-laryngoplasty horse for assessing the success of the procedure, monitoring healing, and detecting complications.

In vitro evaluation of the effect of a prototype dynamic laryngoplasty system on arytenoid abduction.

OBJECTIVE: To determine the effect of a prototype dynamic laryngoplasty system (DLPS) on arytenoid abduction. STUDY DESIGN: In vitro experimental. STUDY POPULATION: Ten equine larynges. METHODS: Dissected larynges were mounted, and the right arytenoid was maximally abducted for testing. A left-sided laryngoplasty (LP) was performed by using a strand of No. 2 FiberWire and a FASTakII anchor. Phase 1 involved tightening the suture, without the DLPS device in place, in 1-mm increments and acquiring a digital image of the rima glottidis at each increment. Phase 2 involved tying the suture with the DLPS in place at a left to right quotient (LRQ) of 0.7. Digital images were subsequently taken at 3 stages of DLPS activation (0, 25, and 50 or maximal psi) and analysed to calculate LRQ. RESULTS: All tests were completed for 9 larynges. In phase 1, a total shortening of 25.89 ± 1.27 mm was possible, which increased the LRQ from 0.59 ± 0.02 to 1.07 ± 0.12. In phase 2, activation of the DLPS increased the LRQ from 0.70 ± 0.05 to 0.97 ± 0.09. This change in LRQ equated to 18.7 mm of shortening on the basis of phase 1 results. The maximum psi of the DLPS achieved was 37.33 ± 5.96. CONCLUSION: The DLPS increased the degree of arytenoid abduction in vitro. This change in LRQ equated to 18.7 mm of shortening of the LP suture based on phase 1 results. CLINICAL IMPACT: These results support further evaluation of the DLPS to determine the effect of changes in DLPS on airway resistance.

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

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

In vitro comparison of 3 techniques of prosthesis attachment to the muscular process of the equine arytenoid cartilage.

OBJECTIVE: To determine the degree and ease of arytenoid abduction achieved with abaxial placement of a FASTak II suture anchor compared to 2 suture patterns with different directions of insertion-caudomedial to craniolateral and medial to lateral. STUDY DESIGN: Ex vivo experimental. STUDY POPULATION: Cadaveric larynges from 10 Standardbred racehorses. METHODS: Each larynx was sequentially instrumented with all 3 arytenoid suture attachment in random order: (1) abaxial placement of a FASTak II suture, (2) caudomedial to craniolateral suture, and (3) medial to lateral suture placement. Each construct was abducted at 5N increments from 0 to 25N and the left to right quotient angle ratio (LRQ) measured from digital pictures acquired at each sequential increment. RESULTS: Arytenoid abduction (higher LRQ) was greater with FASTak II construct than either of the suture patterns. The largest difference occurred at 5N. Approximately 50% less force was required to achieve an LRQ of 1.0 with the FASTak II anchor compared to the suture patterns. No difference was detected between the 2 suture constructs throughout the study. CONCLUSION: Use of the FASTak II suture anchor improved arytenoid abduction compared to 2 suture patterns and minimized the suture loads required to achieve maximum arytenoid abduction. CLINICAL RELEVANCE: Use of the FASTak II anchor may decrease the suture load required to achieve arytenoid abduction in clinical cases. This may reduce the load placed on the laryngoplasty, thereby, minimizing postoperative loss of abduction.

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

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

Ex Vivo Mechanical Evaluation of a Sternal ZipFix(®) Implant for Prosthetic Laryngoplasty in Horses.

OBJECTIVE: To evaluate the properties of a ZipFix(®) (ZipFix) implant in equine laryngeal cartilages. STUDY DESIGN: Ex vivo biomechanical study. SAMPLE POPULATION: Equine arytenoid (n=36) and cricoid cartilages (n=18). METHODS: Suture bites were placed in arytenoid or cricoid cartilages using a ZipFix(®) implant or a single strand of USP 5 braided polyester (TiCron™), and arytenoid and cricoid cartilages were separately subjected to single load to failure (25 N preload) or cyclic loading for 1,000 cycles, followed by single load to failure. Load, distraction, and stiffness were recorded. RESULTS: Four arytenoid-ZipFix cartilages fractured on implant placement. Under single load, arytenoid-ZipFix (n=9) failed at a greater mean load (359.01 ± 57.98 N) than arytenoid-Ticron (159.11 ± 22.98 N; n=12; P<.001). Arytenoid-ZipFix stiffness (31.32 ± 4.26 N/mm) was significantly greater than arytenoid-Ticron (13.18 ± 2.60 N/mm; P<.001). Cricoid-ZipFix stiffness (20.83 ± 3.37 N/mm) was significantly greater than cricoid-Ticron (13.6 ± 3.82 N/mm; n=6; P=.006). Under cyclic load, arytenoid-ZipFix distraction (2.53 ± 0.63 mm; n=5) was significantly less than arytenoid-Ticron (5.06 ± 1.37 mm; n=6, P=.006). After cyclic load, arytenoid-ZipFix failure load (295.16 ± 54.95 N) was significantly greater than arytenoid-Ticron (127.69 ± 32.67 N; P=.002). Arytenoid-ZipFix stiffness (35.59 ± 1.58 N/mm) was significantly greater than arytenoid-Ticron (24.10 ± 6.85 N/mm; P=.019). CONCLUSION: In arytenoid cartilages, the sternal ZipFix(®) implant was significantly stronger and stiffer compared to a single strand of Ticron. During placement of the ZipFix(®) implant, frequent arytenoid cartilage failure occurred before testing, suggesting the implant is not suitable for clinical application.