Intermittent DDSP is the most common cause of upper respiratory tract obstruction in racehorses, affecting 10% to 20% of Thoroughbreds and Standardbreds.1,2 The etiopathogenesis of DDSP is not fully understood; therefore, there are numerous treatments used for the management of this condition.3 Conservative treatments include rest, systemic and local administration of anti-inflammatory medications, changes in tack, and the use of a tongue-tie.3,4 These nonsurgical treatment options have success rates of 53% to 61%.4 A throat-support device has been developed to mimic the effect of an LTF procedure (ie, surgical advancement of the larynx in a cranial direction)5; however, no reports have been published regarding the success of that device for restoration of racing performance in horses with DDSP, to the authors’ knowledge. The surgical procedures advocated for prevention or treatment of DDSP include staphylectomy, sternothyrohyoideus myectomy, sternothyroideus tenotomy, ventriculectomy, tension palatoplasty, epiglottal augmentation, and thermocautery of the soft palate.3,4 These surgical procedures have reported success rates of 35% to 70% for improvement or restoration of racing performance or capacity.6
Dysfunction of the thyrohyoideus muscles during exercise has been implicated in the pathophysiology of DDSP in horses.7 Experimental bilateral resection of the thyrohyoideus muscles in healthy horses induces intermittent DDSP during exercise.7 Replacement of the action of the thyrohyoideus muscles with prosthetic sutures by means of an LTF procedure restores nasopharyngeal stability in such horses during exercise.7 During that surgical procedure, the larynx is anchored in a more rostral and dorsal position to the basihyoid bone relative to its original position; paired sutures are placed between the thyroid cartilage of the larynx and the basihyoid bone along the orientation of the thyrohyoideus muscles.7,8 The specific mechanism by which the thyrohyoideus muscles prevent intermittent DDSP has not been determined, to the authors’ knowledge. The LTF procedure may mimic the action of the thyrohyoideus muscles and prevent ventral and caudal movement of the larynx and DDSP.8 The LTF procedure has a success rate of approximately 80% for restoration of airway function and nasopharyngeal stability in horses with intermittent DDSP.8,9
Despite widespread clinical use of the LTF procedure, no studies have been performed regarding the mechanical strength of LTF constructs. Given that the implanted sutures must withstand high mechanical forces, the LTF procedure is typically performed with No. 5 braided polyethylene sutures coated with polyester8 or No. 5 braided polyester sutures coated with polybutylate.7 Evaluation of mechanical characteristics of LTF constructs with various suture materials may help improve the procedure and assist surgeons in the selection of biomechanically suitable suture material.
Although suture failure after LTF procedures is rare,8,9 it is our experience that braided polyester sutures coated with polybutylate can break during the immediate postoperative period as a result of suddenly applied high loads during recovery from anesthesia, leading to LTF failure and the need for revision surgery. However, suture material may not be the weakest material in LTF constructs; failure can occur as a result of suture pullout from the thyroid cartilage.10–12 Consequently, the LTF surgical technique has been modified to increase the strength of the surgical constructs and decrease surgical failure.5 Moreover, another modification of the LTF surgical technique has been described10 in which metallic implants are used to increase resistance to pullout of suture from the thyroid cartilage.
An objective of the study reported here was to determine the mechanical properties and breakage sites of 2 types of sutures (No. 5 braided polyethylene sutures coated with polyester and No. 5 braided polyester sutures coated with polybutylate) in LTF surrogate constructs tested in single loading to failure in vitro; this was intended to simulate dynamic loading during anesthetic recovery in horses that have undergone LTF procedures. Another objective was to determine whether a modification of the standard LTF surgical technique would increase the tensile strength and change the breakage site of the LTF constructs for both suture materials evaluated. Non-biological LTF surrogates were used in the study to eliminate the effects of variability in tissue characteristics and viscoelastic deformation of cartilage at suture anchoring sites. We hypothesized that no differences would be detected in the strength, elongation, stiffness, or suture breakage site between LTF constructs performed with the 2 types of sutures or between constructs prepared by use of the standard and modified techniques.
Dorsal displacement of the soft palate
FiberWire, Arthrex Vet System, Arthrex Inc, Naples, Fla.
Ethibond Excel, Novartis Animal Health US Inc, East Hannover, NJ.
Instron model 880, Instron Corp, Norwood, Mass.
Phantom Miro eX4, Vision Research Inc, Wayne, NJ.
SAS, version 9.2 for Windows, SAS Institute Inc, Cary, NC.
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