• View in gallery
    Figure 1—

    Photographic images depicting the technique used to create a modified laryngoplasty construct in an equine cadaver larynx. A—Image of the left side of a specimen with the 2.7-mm drill bit positioned before drilling through the muscular process and base of the muscular process of the arytenoid cartilage. B—Image of the dorsal aspect of the same specimen as in panel A with the drill bit fully inserted through the muscular process of the arytenoid cartilage. C—Image of the left arytenoid cartilage with a 12-mm titanium button used as a toggle that is secured at the base of the muscular process of the arytenoid cartilage.

  • View in gallery
    Figure 2—

    Photographic images of the lateral (A) and dorsal (B) aspects of a laryngeal specimen during monotonic loading for testing of the standard laryngoplasty construct. Notice the surgeon's throw on the laryngoplasty suture and attachment of the ends of the suture to the clamps of the load frame.

  • View in gallery
    Figure 3—

    Photographic image of a laryngeal specimen before cyclic loading. The rostral aspect of the larynx is at the bottom of the image, and the muscular processes of the arytenoid cartilages are indicated (asterisks). Notice the stainless steel E-type buckle load transducer placed on the suture of the standard laryngoplasty construct on the left side of the larynx and the modified laryngoplasty construct on the right side.

  • View in gallery
    Figure 4—

    Mean ± SD maximal load at failure during monotonic testing of the modified laryngoplasty constructs (n = 20) and standard laryngoplasty constructs (21). *Value differs significantly (P < 0.001) from the value for the standard laryngoplasty constructs.

  • View in gallery
    Figure 5—

    Kaplan-Meier survival curve for cyclic testing of 20 modified laryngoplasty constructs (dashed line) and 20 standard laryngoplasty constructs (solid line) by use of grade 3 arytenoid abduction (Dixon grading system10) as the end event. Survival rate for the standard laryngoplasty constructs over 10,000 cycles was significantly (P < 0.001) less, compared with the survival rate for the modified laryngoplasty constructs.

  • View in gallery
    Figure 6—

    Bar graph of the grades of arytenoid cartilage abduction (Dixon grading system10) after cyclic loading (10,000 cycles) for the 20 modified laryngoplasty constructs (black bars) and 20 standard laryngoplasty constructs (gray bars).

  • 1. Brakenhoff JE, Holcombe SJ, Hauptman JG, et al. The prevalence of laryngeal disease in a large population of competition draft horses. Vet Surg 2006;35:579583.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. Sweeney CR, Maxson AD, Soma LR. Endoscopic findings in the upper respiratory tract of 678 Thoroughbred racehorses. J Am Vet Med Assoc 1991;198:10371038.

    • Search Google Scholar
    • Export Citation
  • 3. Dixon PM, McGorum BC, Railton DI, et al. Laryngeal paralysis: a study of 375 cases in a mixed-breed population of horses. Equine Vet J 2001;33:452458.

    • Search Google Scholar
    • Export Citation
  • 4. Cahill JI, Goulden BE. Equine laryngeal hemiplegia. Part I. A light microscopic study of peripheral nerves. N Z Vet J 1986;34:161169.

  • 5. Fulton IC, Anderson BH, Stick JA, et al. Larynx. In: Auer J, Stick J, eds. Equine surgery. 4th ed. St Louis: Elsevier Saunders, 2012;592623.

    • Search Google Scholar
    • Export Citation
  • 6. Christley RM, Hodgson DR, Evans DL, et al. Cardiorespiratory responses to exercise in horses with different grades of idiopathic laryngeal hemiplegia. Equine Vet J 1997;29:610.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Shappell KK, Derksen FJ, Stick JA, et al. Effects of ventriculectomy, prosthetic laryngoplasty, and exercise on upper airway function in horses with induced left laryngeal hemiplegia. Am J Vet Res 1988;49:17601765.

    • Search Google Scholar
    • Export Citation
  • 8. Derksen FJ, Stick JA, Scott EA, et al. Effect of laryngeal hemiplegia and laryngoplasty on airway flow mechanics in exercising horses. Am J Vet Res 1986;47:1620.

    • Search Google Scholar
    • Export Citation
  • 9. Marks D, Mackay-Smith MP, Cushing LS, et al. Use of a prosthetic device for surgical correction of laryngeal hemiplegia in horses. J Am Vet Med Assoc 1970;157:157163.

    • Search Google Scholar
    • Export Citation
  • 10. Dixon RM, McGorum BC, Railton DI, et al. Long-term survey of laryngoplasty and ventriculocordectomy in an older, mixed-breed population of 200 horses. Part 1: maintenance of surgical arytenoid abduction and complications of surgery. Equine Vet J 2003;35:389396.

    • Search Google Scholar
    • Export Citation
  • 11. Radcliffe CH, Woodie JB, Hackett R P, et al. A comparison of laryngoplasty and modified partial arytenoidectomy as treatments for laryngeal hemiplegia in exercising horses. Vet Surg 2006;35:643652.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12. Witte TH, Cheetham J, Soderholm LV, et al. Equine laryngoplasty sutures undergo increased loading during coughing and swallowing. Vet Surg 2010;39:949956.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Schumacher J, Wilson AM, Pardoe C, et al. In vitro evaluation of a novel prosthesis for laryngoplasty of horses with recurrent laryngeal neuropathy. Equine Vet J 2000;32:4346.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14. Parente EJ, Birks EK, Habecker P. A modified laryngoplasty approach promoting ankylosis of the cricoarytenoid joint. Vet Surg 2011;40:204210.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15. Aceto H, Parente EJ. Using quarterly earnings to assess racing performance in 70 Thoroughbreds after modified laryngoplasty for treatment of recurrent laryngeal neuropathy. Vet Surg 2012;41:689695.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16. Froydenlund TJ, Dixon PM. A review of equine laryngoplasty complications. Equine Vet Educ 2014;26:98106.

  • 17. Ahern BJ, Boston RC, Parente EJ. In vitro mechanical testing of an alternate laryngoplasty system (ALPS) for horses. Vet Surg 2012;41:918923.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18. Witte TH, Cheetham J, Rawlinson JJ, et al. A transducer for measuring force on surgical sutures. Can J Vet Res 2010;74:299304.

  • 19. Perkins JD, Meighan H, Windley Z, et al. In vitro effect of ventriculocordectomy before laryngoplasty on abduction of the equine arytenoid cartilage. Vet Surg 2011;40:305310.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20. Barnett TP, O'Leary JM, Parkin TD, et al. Long-term exercising video-endoscopic examination of the upper airway following laryngoplasty surgery: a prospective cross-sectional study of 41 horses. Equine Vet J 2013;45:593597.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21. Ahern BJ, Parente EJ. Surgical complications of the equine upper respiratory tract. Vet Clin North Am Equine Pract 2008;24:465484.

  • 22. Barakzai SZ, Boden LA, Dixon PM. Postoperative race performance is not correlated with degree of surgical abduction after laryngoplasty in National Hunt Thoroughbred racehorses. Vet Surg 2009;38:934940.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23. Strand E, Martin GS, Haynes PF, et al. Career racing performance in Thoroughbreds treated with prosthetic laryngoplasty for laryngeal neuropathy: 52 cases (1981–1989). J Am Vet Med Assoc 2000;217:16891696.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24. Barakzai SZ, Boden LA, Dixon PM. Race performance after laryngoplasty and ventriculocordectomy in National Hunt racehorses. Vet Surg 2009;38:941945.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25. Hawkins JF, Tulleners EP, Ross MW, et al. Laryngoplasty with or without ventriculectomy for treatment of left laryngeal hemiplegia in 230 racehorses. Vet Surg 1997;26:484491.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26. Kraus BM, Parente EJ, Tulleners EP. Laryngoplasty with ventriculectomy or ventriculocordectomy in 104 draft horses (1992–2000). Vet Surg 2003;32:530538.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27. McClellan NR, Santschi EM, Hurcombe SD, et al. An ex vivo model to evaluate the effect of cyclical adductory forces on maintenance of arytenoid abduction after prosthetic laryngoplasty performed with and without mechanical arytenoid abduction. Vet Surg 2014;43:598605.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28. Lechartier A, Rossignol F, Brandenberger O, et al. Mechanical comparison of 3 anchoring techniques in the muscular process for laryngoplasty in the equine larynx. Vet Surg 2015;44:333340.

    • Crossref
    • Search Google Scholar
    • Export Citation

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Biomechanical evaluation of modified laryngoplasty by use of a toggle technique for stabilization of arytenoid cartilage in specimens obtained from equine cadavers

Erica J. SecorDepartment of Clinical Veterinary Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802.

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Santiago D. Gutierrez-NibeyroDepartment of Clinical Veterinary Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802.

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Gavin P. HornIllinois Fire Service Institute, University of Illinois, Champaign, IL 61820.

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Abstract

OBJECTIVE To biomechanically compare modified and standard laryngoplasty constructs in monotonic load to failure and cyclic loading.

SAMPLES 41 equine cadaveric larynges.

PROCEDURES Laryngoplasty constructs were created by use of a standard technique on one side and a modified technique (with a toggle to anchor suture to the arytenoid cartilage) on the other side. For monotonic loading, laryngoplasty constructs were prepared and suture ends attached to a load frame; constructs then were loaded until mechanical failure. Mean load at failure and failure modes were compared between constructs. For cyclic loading, arytenoid cartilages were maximally abducted and constructs were circumferentially loaded for 10,000 cycles. Loss of arytenoid abduction was evaluated every 500 cycles with a subjective grading scale and objective change in rima glottidis cross-sectional area.

RESULTS In monotonic loading, modified laryngoplasty constructs failed at a significantly higher mean ± SD load (191 ± 29 N) than did standard laryngoplasty constructs (91 ± 44 N). None of the modified laryngoplasty constructs failed by suture pull-through of the muscular process of the arytenoid cartilage, whereas most of the standard laryngoplasty constructs failed in that manner. In cyclic testing, 11 of 20 standard laryngoplasty constructs failed or achieved Dixon grade 3 abduction, whereas 0 of 20 modified laryngoplasty constructs failed. Modified laryngoplasty constructs lost significantly less rima glottidis cross-sectional area in circumferential testing, compared with loss for standard laryngoplasty constructs.

CONCLUSIONS AND CLINICAL RELEVANCE The modified laryngoplasty technique was biomechanically superior to the standard laryngoplasty technique in this ex vivo study.

Abstract

OBJECTIVE To biomechanically compare modified and standard laryngoplasty constructs in monotonic load to failure and cyclic loading.

SAMPLES 41 equine cadaveric larynges.

PROCEDURES Laryngoplasty constructs were created by use of a standard technique on one side and a modified technique (with a toggle to anchor suture to the arytenoid cartilage) on the other side. For monotonic loading, laryngoplasty constructs were prepared and suture ends attached to a load frame; constructs then were loaded until mechanical failure. Mean load at failure and failure modes were compared between constructs. For cyclic loading, arytenoid cartilages were maximally abducted and constructs were circumferentially loaded for 10,000 cycles. Loss of arytenoid abduction was evaluated every 500 cycles with a subjective grading scale and objective change in rima glottidis cross-sectional area.

RESULTS In monotonic loading, modified laryngoplasty constructs failed at a significantly higher mean ± SD load (191 ± 29 N) than did standard laryngoplasty constructs (91 ± 44 N). None of the modified laryngoplasty constructs failed by suture pull-through of the muscular process of the arytenoid cartilage, whereas most of the standard laryngoplasty constructs failed in that manner. In cyclic testing, 11 of 20 standard laryngoplasty constructs failed or achieved Dixon grade 3 abduction, whereas 0 of 20 modified laryngoplasty constructs failed. Modified laryngoplasty constructs lost significantly less rima glottidis cross-sectional area in circumferential testing, compared with loss for standard laryngoplasty constructs.

CONCLUSIONS AND CLINICAL RELEVANCE The modified laryngoplasty technique was biomechanically superior to the standard laryngoplasty technique in this ex vivo study.

Recurrent laryngeal neuropathy is a common cause for poor performance in horses throughout the world.1–3 Recurrent laryngeal neuropathy is a progressive demyelinating disease of the recurrent laryngeal nerve that leads to atrophy and paresis or paralysis of the ipsilateral cricoarytenoideus dorsalis muscle.4,5 Neurogenic atrophy of the cricoarytenoideus dorsalis muscle results in dyspnea, respiratory noise, hypoventilation, severe hypoxia, hypercapnia, hyperlactatemia, and exercise intolerance.6–8

Prosthetic laryngoplasty with ipsilateral vocal cordectomy or ventriculectomy is considered the treatment of choice in horses with RLN.5 The standard laryngoplasty technique involves placing a prosthetic suture between the caudal border of the cricoid cartilage and muscular process of the arytenoid cartilage to stabilize the arytenoid cartilage in almost full abduction and restore airway diameter and airflow.5,8,9 However, postoperative loss of arytenoid abduction with subsequent reduction of the rima glottidis cross-sectional area is a recognized postoperative complication,10,11 which is often attributed to partial or complete suture pull-through or to breakage of the muscular process of the arytenoid cartilage.10,12 It has been suggested that failure of the prosthesis to maintain adequate arytenoid abduction is attributable to the load exerted on the prosthetic sutures during coughing and swallowing.12 The recorded load exerted on the laryngoplasty suture during coughing and swallowing is 45 to 55 N,12 which is similar to the mean ± SD load (56 ± 13 N) reported for ex vivo laryngoplasty constructs that failed as a result of suture pull-through of the muscular process of the arytenoid cartilage.13

Facilitated ankylosis of the cricoarytenoid joint is potentially an effective treatment14,15; however, loss of arytenoid abduction can still occur in the early postoperative period before ankylosis is complete. Therefore, a highly stable laryngoplasty prosthesis that can resist loading throughout the period of ankylosis is required to consistently achieve adequate and persistent arytenoid cartilage abduction and reliably restore function of the nasopharynx in horses with RLN. It has been suggested16 that suture placement deeper into the muscular process of the arytenoid cartilage would prevent loss of arytenoid abduction. However, suture placement in the standard manner farther rostral may result in a reduced mechanical advantage for fully abducting the arytenoid cartilage.16 A modified laryngoplasty technique that involves use of a suture button to act as a toggle and secure the suture material to the base of the muscular process of the arytenoid cartilage would incorporate a much larger portion of the arytenoid cartilage; this modification theoretically would reduce suture pull-through of the muscular process of the arytenoid cartilage and progressive postoperative loss of arytenoid abduction in horses with RLN that undergo laryngoplasty.

The objective of the study reported here was to compare biomechanical properties of modified and standard laryngoplasty constructs in both monotonic and cyclic loading by use of an ex vivo method. We hypothesized that modified laryngoplasty constructs would have a higher load at failure in monotonic loading than would standard laryngoplasty constructs and that modified laryngoplasty constructs would have a reduced rate of failure attributable to suture pull-through of the arytenoid cartilage. In addition, we hypothesized that modified laryngoplasty constructs would maintain a greater rima glottidis cross-sectional area in cyclic testing than would standard laryngoplasty constructs, as determined by both subjective and objective evaluations.

Materials and Methods

Sample

Forty-two larynges that were grossly visibly normal were collected from cadavers of euthanized horses. Horses were euthanized for reasons unrelated to the study reported here. Larynges were collected within 4 hours after horses were euthanized, wrapped in gauze soaked in saline (0.9% NaCl) solution, and stored at −20°C until used in the study. Specimens were thawed for 16 hours at room temperature (20°C) prior to testing.13,17 Review of the study protocol by the University of Illinois Institutional Animal Care and Use Committee was deemed unnecessary because the study was performed on specimens obtained from cadavers of horses euthanized for reasons unrelated to the study.

Construct preparation

Specimens and laryngoplasty technique (standard or modified) were assigned by use of a randomization method (coin toss) to a testing method (monotonic or cyclic loading) and side (right and left hemilarynx), respectively. The cricoarytenoideus dorsalis muscles were removed bilaterally to facilitate the investigators' ability to see the muscular process and thus ensure similar suture placement for all constructs. Also, a 2- to 3-cm incision was made on the cricoarytenoid joint capsule bilaterally prior to suture placement to expose the articular surface, which mimicked the clinical scenario for surgeons who routinely induce ankylosis of that joint.14

Laryngoplasties were performed by use of a standard technique on one side and a modified technique on the other side; all laryngoplasties were performed by the same investigator (EJS). Standard laryngoplasty constructs were created by use of a previously described technique.5 A No. 5 (braided polyethylene covered with polyester) suturea was passed through the cricoid cartilage at a point approximately 2 cm rostral to the caudal rim and 1 cm abaxial to the dorsal ridge of the cartilage. For placement in the arytenoid cartilage, the suture was passed through the muscular process in a caudomedial to rostrolateral direction and incorporated the cartilage to a depth of approximately 1.5 cm. Modified laryngoplasty constructs were prepared by placing a No. 5 suture through the caudodorsal part of the cricoid cartilage, as described for the standard laryngoplasty, and through the muscular process and base of the muscular process of the right and left arytenoid cartilages. For the modified laryngoplasty, the suture was threaded through the holes of a commercially available 12-mm titanium buttonb and a 10-mm-long tube custom made from a teat cannula.c The dorsal aspect of the muscular process was flattened with a No. 10 scalpel blade, and then a vertical hole was drilled by use of a 2.7-mm drill bit through the center of the muscular process toward the base of the muscular process of the arytenoid cartilage. The drill bit was aimed toward the base of the arytenoid cartilage to maximize the amount of the arytenoid cartilage to be incorporated. Placing the toggle in the right position was easily performed, even though the toggle was located under nondissected soft tissues, and appropriate placement was confirmed by dissection of each specimen after testing was completed. Once the hole was drilled through the arytenoid cartilage, the prosthesis was passed through it, and the suture was pulled tight to lock the toggle on the base of the muscular process of the arytenoid cartilage (Figure 1). The custom-made tube then was inserted into the drill tract to provide additional strength to the cartilage.

Figure 1—
Figure 1—

Photographic images depicting the technique used to create a modified laryngoplasty construct in an equine cadaver larynx. A—Image of the left side of a specimen with the 2.7-mm drill bit positioned before drilling through the muscular process and base of the muscular process of the arytenoid cartilage. B—Image of the dorsal aspect of the same specimen as in panel A with the drill bit fully inserted through the muscular process of the arytenoid cartilage. C—Image of the left arytenoid cartilage with a 12-mm titanium button used as a toggle that is secured at the base of the muscular process of the arytenoid cartilage.

Citation: American Journal of Veterinary Research 79, 2; 10.2460/ajvr.79.2.226

Mechanical testing

Forty-two laryngoplasty constructs in larynges obtained from 21 equine cadavers were tested in monotonic loading until failure, which was designed to mimic acute loading of the suture during tightening at the time of surgery. Laryngoplasty sutures were passed through the arytenoid and cricoid cartilages and tied with a single surgeon's throw. Ends of the prosthetic suture were secured to the stationary load cell and servohydraulic actuator of a load framed (Figure 2); constructs then were loaded at a rate of 100 mm/min until construct failure. Data were sampled at 200 Hz, and the load at failure was recorded. Mode of failure (suture pull-through or fracture of the muscular process, suture pull-through or fracture of the cricoid cartilage, or suture breakage) was determined after failure of each construct.

Figure 2—
Figure 2—

Photographic images of the lateral (A) and dorsal (B) aspects of a laryngeal specimen during monotonic loading for testing of the standard laryngoplasty construct. Notice the surgeon's throw on the laryngoplasty suture and attachment of the ends of the suture to the clamps of the load frame.

Citation: American Journal of Veterinary Research 79, 2; 10.2460/ajvr.79.2.226

Twenty larynges with both types of laryngoplasty construct were tested in cyclic circumferential loading, which was designed to mimic forces exerted on the laryngoplasty sutures as a result of swallowing and coughing. Both laryngoplasty constructs were created in each specimen to allow for simultaneous testing. Sutures were tied with a single surgeon's throw followed by 5 square knots, with the arytenoid cartilages fully abducted to achieve grade 1 arytenoid abduction (in accordance with the Dixon grading system10). Each larynx was placed in a plastic cradle, and a 2.5-cm-wide nylon strap was wrapped around the larynx and cradle. Width of the nylon strap was chosen to fully cover and engage the muscular process. The apex of the muscular process was centered under the nylon strap, and the strap was then secured to the center at the cradle to allow balanced load actuation. Ends of the strap were secured to the load cell and actuator of a servohydraulic load framed to create circumferential loading of the larynx.

An E-type buckle load transducer was used to determine loading conditions for the nylon strap that resulted in appropriate loading of laryngoplasty constructs. The E-type buckle load transducer was custom built with specifications similar to those of another suture load transducer.18 In addition, the load transducer was calibrated with a No. 5 suturea prior to use. The load transducer was then placed on the suture of the standard laryngoplasty construct of 3 specimens to determine the load-frame displacement needed to result in a maximal suture load of 40 to 45 N during cycling, which was chosen to mimic maximal postoperative loading of laryngoplasty sutures during swallowing (Figure 3).12 A 25-mm displacement of the strap ends in the load frame resulted in a load of 40 to 45 N on the prosthetic suture. Larynges were loaded cyclically at 3 Hz for 10,000 cycles; photographs were obtained before loading and every 500 cycles throughout the cyclic testing period.

Figure 3—
Figure 3—

Photographic image of a laryngeal specimen before cyclic loading. The rostral aspect of the larynx is at the bottom of the image, and the muscular processes of the arytenoid cartilages are indicated (asterisks). Notice the stainless steel E-type buckle load transducer placed on the suture of the standard laryngoplasty construct on the left side of the larynx and the modified laryngoplasty construct on the right side.

Citation: American Journal of Veterinary Research 79, 2; 10.2460/ajvr.79.2.226

Posttesting assessment

Photographs of the specimens obtained every 500 cycles were randomly ordered (random number generator) and graded to evaluate loss of abduction by use of a postoperative arytenoid abduction grading system.10 All grades were assigned by a surgeon (SDG-N) who was unaware of the type of construct and number of loading cycles. Additionally, the rima glottidis cross-sectional area of each hemilarynx was measured with commercial imaging softwaree; image size was calibrated by use of the length of the left corniculate process. Hemilarynx cross-sectional areas were measured as described elsewhere.19

Statistical analysis

Normality of continuous data was evaluated by use of the Kolmogorov-Smirnov test, kurtosis, and Q-Q plots. Maximal load at failure during monotonic testing was normally distributed and evaluated with an independent sample t test. Load at failure was expressed as mean ± SD. A χ2 test that involved use of adjusted residuals (with adjusted residuals ≥ 2 or ≤ 2 determined to contribute to significance) was used to compare modes of failure during monotonic testing. For cyclic testing, subjective grading scores for loss of abduction were compared between laryngoplasty constructs by use of Kaplan-Meier survival analysis. A grade ≥ 3 for postoperative arytenoid abduction (by use of the Dixon grading system10) was considered surgical failure.20 Additionally, data for hemilarynx cross-sectional area were logarithmically transformed to allow for parametric testing and then evaluated with a repeated-measures ANOVA with a Bonferroni post hoc correction. Values of P ≤ 0.05 were considered significant. All statistical analyses were performed with a commercially available statistical software package.f

Results

Monotonic load to failure

Testing of one of the modified laryngoplasty constructs resulted in fracture of the cricoid cartilage through the contralateral needle hole of the previously tested standard laryngoplasty construct. Data for that modified laryngoplasty construct were not included in the statistical analysis; thus, data were available for 41 laryngoplasty constructs. Modified laryngoplasty constructs failed at a significantly (P < 0.001) higher mean ± SD load than did standard laryngoplasty constructs (191 ± 29 N and 91 ± 44 N, respectively; Figure 4). Nineteen constructs prepared with the standard laryngoplasty technique failed as a result of suture pull-through of the muscular process of arytenoid cartilage, and the remaining 2 standard laryngoplasty constructs failed as a result of suture pull-through of the cricoid cartilage. For the modified laryngoplasty technique, 12 constructs failed as a result of suture pull-through of the cricoid cartilage, and for the remaining 8 modified laryngoplasty constructs, the suture slipped from the load-frame clamp. Standard laryngoplasty constructs failed significantly (P < 0.001) more often as a result of suture pull-through of the muscular process than did modified laryngoplasty constructs.

Figure 4—
Figure 4—

Mean ± SD maximal load at failure during monotonic testing of the modified laryngoplasty constructs (n = 20) and standard laryngoplasty constructs (21). *Value differs significantly (P < 0.001) from the value for the standard laryngoplasty constructs.

Citation: American Journal of Veterinary Research 79, 2; 10.2460/ajvr.79.2.226

Cyclic loading

All laryngoplasty constructs were grade 1 prior to cyclic testing, and cyclic circumferential loading for 10,000 cycles was successfully completed for all 20 larynges subjected to testing. Modified laryngoplasty constructs had a significantly (P < 0.001) greater survival rate over 10,000 cycles than did standard laryngoplasty constructs (Figure 5). We found that 11 of 20 standard laryngoplasty constructs lost abduction (grade 3 arytenoid abduction), whereas 0 of 20 modified laryngoplasty constructs lost abduction (grade 3 arytenoid abduction; Figure 6). In addition, modified laryngoplasty constructs lost significantly (P < 0.001) less cross-sectional area over 10,000 cycles, compared with the loss for standard laryngoplasty constructs. Standard laryngoplasty constructs lost a median of 63% (interquartile range, 12.6% to 80.4%) of the original cross-sectional area over 10,000 cycles, compared with a median loss of 13% (interquartile range, 4.0% to 25.6%) for the modified laryngoplasty constructs.

Figure 5—
Figure 5—

Kaplan-Meier survival curve for cyclic testing of 20 modified laryngoplasty constructs (dashed line) and 20 standard laryngoplasty constructs (solid line) by use of grade 3 arytenoid abduction (Dixon grading system10) as the end event. Survival rate for the standard laryngoplasty constructs over 10,000 cycles was significantly (P < 0.001) less, compared with the survival rate for the modified laryngoplasty constructs.

Citation: American Journal of Veterinary Research 79, 2; 10.2460/ajvr.79.2.226

Figure 6—
Figure 6—

Bar graph of the grades of arytenoid cartilage abduction (Dixon grading system10) after cyclic loading (10,000 cycles) for the 20 modified laryngoplasty constructs (black bars) and 20 standard laryngoplasty constructs (gray bars).

Citation: American Journal of Veterinary Research 79, 2; 10.2460/ajvr.79.2.226

Discussion

In the present study, a prosthetic laryngoplasty construct that incorporated a toggle technique to anchor the suture material to the arytenoid cartilage was biomechanically superior to the standard laryngoplasty construct with regard to results of monotonic loading and cyclic circumferential loading of the larynges, both of which mimicked forces that would be exerted on the sutures in vivo. The proposed modified laryngoplasty construct involved use of a toggle to secure the suture material to the base of the muscular process of the arytenoid cartilage. We believe that incorporation of more surface area of the arytenoid cartilage with this modification would reduce the incidence of suture pull-through from the muscular process of the cartilage and progressive postoperative loss of arytenoid abduction in horses with RLN that undergo laryngoplasty. This modification also provided a mechanical advantage to the laryngoplasty construct by lengthening the lever arm of the prosthetic suture that acted around the cricoarytenoid joint, which allowed more complete and efficient arytenoid abduction. The modified laryngoplasty technique was performed in several equine cadavers by the authors; the technique was simple to perform. The surgical approach for the modified laryngoplasty construct was similar to the approach described for the standard laryngoplasty construct; this included a similar size of the surgical incision. Once the muscular process was exposed by transecting the insertion of all the bellies of the cricoarytenoideus dorsalis muscle, the lateral cricoarytenoid capsule was incised to expose the articular surface. This step was followed by rotating the arytenoid cartilage laterally and drilling through the cartilage such that the drill was directed toward the base of the muscular process with the drill bit oriented in a vertical direction.

Gradual postoperative loss of arytenoid abduction is the most common complication following prosthetic laryngoplasty, with up to 90% of horses losing at least 1 grade (Dixon arytenoid abduction grading system) after surgery.10,21,22 This loss of abduction may partially explain the reason for only fair success rates of standard laryngoplasty constructs, particularly in racehorse populations.10,23–25 Surgeons often attempt to create more abduction of the cartilage than is needed in an effort to combat the inevitable loss of abduction in the weeks after surgery.16 Horses with greater abduction at the time of surgery have a more substantial loss of abduction during the postoperative period, which somewhat negates the benefit of achieving additional abduction at the time of surgery.22 In addition, this method of planning for loss minimizes the ability of a surgeon to customize the degree of abduction for each patient. However, by incorporating a larger portion of the arytenoid cartilage and eliminating the risk of suture pull-through of the muscular process or breakage of the muscular process, the modified laryngoplasty construct described here was superior for resisting cyclic fatigue, compared with results for the standard laryngoplasty construct. By minimizing cyclic fatigue, modified laryngoplasty constructs may help to reduce much of the speculation regarding prediction of long-term arytenoid abduction in horses undergoing laryngoplasty for the treatment of RLN.

We believe that both monotonic tensile and cyclic circumferential loading of the specimens used in the present study mimicked the in vivo forces placed on prosthetic sutures at the time of surgery and during the postoperative period. Acute, complete loss of abduction as a result of cartilage failure occurs most frequently in the first week after surgery in up to 10% to 15% of horses undergoing laryngoplasty.10,12,23–26 However, this type of failure may also occur at the time of surgery during tightening and tying of prosthetic sutures, which would require placement of a prosthesis more rostral or ventral in the arytenoid cartilage that would lead to poor arytenoid abduction.16 Monotonic testing used in the present study was designed to mimic acute loading of the prosthetic sutures, such as may occur at the time of surgery or during recovery. Unfortunately, the methods used did not allow for testing of knot security, which could have impacted results of the monotonic testing. Cyclic loading of laryngoplasty sutures has been attributed to swallowing during the postoperative period.12 Pharyngeal constrictor muscles are located circumferentially around the larynx of horses and likely contribute to repeated loading of the arytenoid cartilage and larynx, with each swallow resulting in a total load of 40 to 45 N on laryngoplasty sutures.12 Cyclic loading used in the study reported here was designed to mimic circumferential loading of the larynx, rather than a single point of loading of the arytenoid cartilage or suture, as has been described for similar testing.27,28 Many details about pharyngeal constrictor loading of the larynx, specifically the arytenoid cartilage, are unknown; therefore, the present constructs were designed as a best approximation with the current body of knowledge. However, we acknowledge that the design of the laryngoplasty constructs may not have accurately represented in vivo forces applied by the pharyngeal constrictor muscles.

Numerous limitations arise when attempting to apply results for ex vivo studies to in vivo situations. The modified laryngoplasty technique could be easily performed and did not appear to require a substantially greater amount of time to perform; however, this was not objectively determined. The ability to perform the technique in a live patient is certainly a concern when testing a new surgical procedure on isolated cadaveric specimens. To address this concern, the modified laryngoplasty technique should be performed in both cadavers and live patients. Once a surgeon is comfortable with the technique, it can be easily performed in clinical situations. Although novel mechanical loading methods were developed and used to more closely mimic in vivo conditions as part of the study reported here, ex vivo results often do not fully replicate clinical scenarios. However, biomechanical superiority of the modified laryngoplasty construct in the present study was enough to likely provide a substantial benefit over the standard laryngoplasty construct in clinical patients. Further studies involving follow-up monitoring of the modified laryngoplasty technique in live horses are needed to evaluate the long-term stability and strength of the construct.

On the basis of results of the present study, the proposed modified laryngoplasty construct appeared to be biomechanically superior to the standard laryngoplasty construct during both monotonic load to failure and cyclic loading over 10,000 cycles. Further studies conducted to evaluate the long-term maintenance of arytenoid cartilage in horses are warranted. Ultimately, use of the modified laryngoplasty construct may help to combat the common postoperative complication of gradual loss of abduction that is frequently evident in horses that undergo laryngoplasty.

Acknowledgments

This manuscript represents a portion of a thesis submitted by Dr. Secor to the Department of Clinical Veterinary Medicine of the University of Illinois as partial fulfillment of the requirements for a Master of Science degree.

Supported by the Morris Animal Foundation (grant No. D16EQ-828) and Arthrex Inc.

Presented in abstract form at the 2016 American College of Veterinary Surgeons Surgery Summit, Seattle, October 2016.

The authors thank Dr. Thomas Witte for assistance in construction of the load transducer and Dr. Mark Mitchell for statistical assistance.

ABBREVIATIONS

RLN

Recurrent laryngeal neuropathy

Footnotes

a.

Fiberwire, Arthrex Inc, Naples, Fla.

b.

RetroButton, Arthrex Inc, Naples, Fla.

c.

Udder infusion cannula, Jorgensen Labs, Loveland, Colo.

d.

Instron 880, Instron Co, Norwood, Mass.

e.

Image J, version 1.50b, National Institutes of Health, Bethesda, Md. Available at: imagej.nih.gov/ij. Accessed Feb 21, 2016.

f.

SPSS Statistics for Windows, version 23.0, IBM Corp, Armonk, N Y.

References

  • 1. Brakenhoff JE, Holcombe SJ, Hauptman JG, et al. The prevalence of laryngeal disease in a large population of competition draft horses. Vet Surg 2006;35:579583.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 2. Sweeney CR, Maxson AD, Soma LR. Endoscopic findings in the upper respiratory tract of 678 Thoroughbred racehorses. J Am Vet Med Assoc 1991;198:10371038.

    • Search Google Scholar
    • Export Citation
  • 3. Dixon PM, McGorum BC, Railton DI, et al. Laryngeal paralysis: a study of 375 cases in a mixed-breed population of horses. Equine Vet J 2001;33:452458.

    • Search Google Scholar
    • Export Citation
  • 4. Cahill JI, Goulden BE. Equine laryngeal hemiplegia. Part I. A light microscopic study of peripheral nerves. N Z Vet J 1986;34:161169.

  • 5. Fulton IC, Anderson BH, Stick JA, et al. Larynx. In: Auer J, Stick J, eds. Equine surgery. 4th ed. St Louis: Elsevier Saunders, 2012;592623.

    • Search Google Scholar
    • Export Citation
  • 6. Christley RM, Hodgson DR, Evans DL, et al. Cardiorespiratory responses to exercise in horses with different grades of idiopathic laryngeal hemiplegia. Equine Vet J 1997;29:610.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 7. Shappell KK, Derksen FJ, Stick JA, et al. Effects of ventriculectomy, prosthetic laryngoplasty, and exercise on upper airway function in horses with induced left laryngeal hemiplegia. Am J Vet Res 1988;49:17601765.

    • Search Google Scholar
    • Export Citation
  • 8. Derksen FJ, Stick JA, Scott EA, et al. Effect of laryngeal hemiplegia and laryngoplasty on airway flow mechanics in exercising horses. Am J Vet Res 1986;47:1620.

    • Search Google Scholar
    • Export Citation
  • 9. Marks D, Mackay-Smith MP, Cushing LS, et al. Use of a prosthetic device for surgical correction of laryngeal hemiplegia in horses. J Am Vet Med Assoc 1970;157:157163.

    • Search Google Scholar
    • Export Citation
  • 10. Dixon RM, McGorum BC, Railton DI, et al. Long-term survey of laryngoplasty and ventriculocordectomy in an older, mixed-breed population of 200 horses. Part 1: maintenance of surgical arytenoid abduction and complications of surgery. Equine Vet J 2003;35:389396.

    • Search Google Scholar
    • Export Citation
  • 11. Radcliffe CH, Woodie JB, Hackett R P, et al. A comparison of laryngoplasty and modified partial arytenoidectomy as treatments for laryngeal hemiplegia in exercising horses. Vet Surg 2006;35:643652.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 12. Witte TH, Cheetham J, Soderholm LV, et al. Equine laryngoplasty sutures undergo increased loading during coughing and swallowing. Vet Surg 2010;39:949956.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 13. Schumacher J, Wilson AM, Pardoe C, et al. In vitro evaluation of a novel prosthesis for laryngoplasty of horses with recurrent laryngeal neuropathy. Equine Vet J 2000;32:4346.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 14. Parente EJ, Birks EK, Habecker P. A modified laryngoplasty approach promoting ankylosis of the cricoarytenoid joint. Vet Surg 2011;40:204210.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 15. Aceto H, Parente EJ. Using quarterly earnings to assess racing performance in 70 Thoroughbreds after modified laryngoplasty for treatment of recurrent laryngeal neuropathy. Vet Surg 2012;41:689695.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 16. Froydenlund TJ, Dixon PM. A review of equine laryngoplasty complications. Equine Vet Educ 2014;26:98106.

  • 17. Ahern BJ, Boston RC, Parente EJ. In vitro mechanical testing of an alternate laryngoplasty system (ALPS) for horses. Vet Surg 2012;41:918923.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 18. Witte TH, Cheetham J, Rawlinson JJ, et al. A transducer for measuring force on surgical sutures. Can J Vet Res 2010;74:299304.

  • 19. Perkins JD, Meighan H, Windley Z, et al. In vitro effect of ventriculocordectomy before laryngoplasty on abduction of the equine arytenoid cartilage. Vet Surg 2011;40:305310.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 20. Barnett TP, O'Leary JM, Parkin TD, et al. Long-term exercising video-endoscopic examination of the upper airway following laryngoplasty surgery: a prospective cross-sectional study of 41 horses. Equine Vet J 2013;45:593597.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 21. Ahern BJ, Parente EJ. Surgical complications of the equine upper respiratory tract. Vet Clin North Am Equine Pract 2008;24:465484.

  • 22. Barakzai SZ, Boden LA, Dixon PM. Postoperative race performance is not correlated with degree of surgical abduction after laryngoplasty in National Hunt Thoroughbred racehorses. Vet Surg 2009;38:934940.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 23. Strand E, Martin GS, Haynes PF, et al. Career racing performance in Thoroughbreds treated with prosthetic laryngoplasty for laryngeal neuropathy: 52 cases (1981–1989). J Am Vet Med Assoc 2000;217:16891696.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 24. Barakzai SZ, Boden LA, Dixon PM. Race performance after laryngoplasty and ventriculocordectomy in National Hunt racehorses. Vet Surg 2009;38:941945.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 25. Hawkins JF, Tulleners EP, Ross MW, et al. Laryngoplasty with or without ventriculectomy for treatment of left laryngeal hemiplegia in 230 racehorses. Vet Surg 1997;26:484491.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 26. Kraus BM, Parente EJ, Tulleners EP. Laryngoplasty with ventriculectomy or ventriculocordectomy in 104 draft horses (1992–2000). Vet Surg 2003;32:530538.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 27. McClellan NR, Santschi EM, Hurcombe SD, et al. An ex vivo model to evaluate the effect of cyclical adductory forces on maintenance of arytenoid abduction after prosthetic laryngoplasty performed with and without mechanical arytenoid abduction. Vet Surg 2014;43:598605.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • 28. Lechartier A, Rossignol F, Brandenberger O, et al. Mechanical comparison of 3 anchoring techniques in the muscular process for laryngoplasty in the equine larynx. Vet Surg 2015;44:333340.

    • Crossref
    • Search Google Scholar
    • Export Citation

Contributor Notes

Address correspondence to Dr. Gutierrez-Nibeyro (sgn@illinois.edu).