Mechanical properties of various suture materials and placement patterns tested with surrogate in vitro model constructs simulating laryngeal advancement tie-forward procedures in horses

Enhancing prosthesis stability at the cricoid cartilage in equine laryngoplasty using 3-D-printed laryngeal clamps: An ex vivo model study

OBJECTIVE

To assess a three-dimensional (3-D)-printed laryngeal clamp (LC) designed to enhance the anchoring of laryngeal prostheses at the cricoid cartilage.

STUDY DESIGN

Ex vivo biomechanical study.

SAMPLE POPULATION

A total of 22 equine larynges.

METHODS

Two experimental groups included larynges with standard prosthetic laryngoplasty (PL; n = 10) and larynges with prosthetic laryngoplasty modified with laryngeal clamps (PLLC; n = 10). All constructs underwent 3000 cycles of tension loading and a single tension to failure. Recorded biomechanical parameters included maximum load, actuator displacement, and construct failure. Finite element analysis (FEA) was performed on one PL and one PLLC construct.

RESULTS

The maximum load at single tension to failure was 183.7 ± 46.8 N for the PL construct and 292.7 ± 82.3 N for the PLLC construct (p = .003). Actuator displacement at 30 N was 1.7 ± 0.5 mm and 2.7 ± 0.7 mm for the PL and PLLC constructs, respectively (p = .011). The cause of PL constructs failure was mostly tearing through the cartilage whereas the PLLC constructs failed through fracture of the cricoid cartilage (p = .000). FEA revealed an 11-fold reduction in the maximum equivalent plastic strain, a four-fold reduction in maximum compressive stress, and a two-fold increase in the volume of engaged cartilage in PLLC constructs.

CONCLUSION

The PLLC constructs demonstrated superior performance in biomechanical testing and FEA compared to standard PL constructs.

CLINICAL SIGNIFICANCE

The use of 3-D-printed laryngeal clamps may enhance the outcomes of laryngoplasty in horses. In vivo studies are necessary to determine the feasibility of performing laryngoplasty using the laryngeal clamp in horses.

Laryngeal tie-forward in standing sedated horses

OBJECTIVES

To investigate the feasibility and describe the clinical experience of performing laryngeal tie-forward (LTF) in standing horses unaffected (experimental) and affected (clinical) by intermittent dorsal displacement of the soft palate (iDDSP).

STUDY DESIGN

Experimental study and case series.

ANIMALS

Five normal experimental controls and five client owned horses affected by iDDSP.

METHODS

Standing LTF was performed and evaluated in five experimental horses and five clinical cases diagnosed with iDDSP. Standing LTF was performed under endoscopic guidance with horses sedated and the surgical site desensitized with local anesthetic solution. Short term outcome was assessed using radiography, resting and (in clinical cases) dynamic upper respiratory tract (URT) endoscopy.

RESULTS

Standing LTF was well tolerated and completed in all horses. Radiographic assessment demonstrated that compared to preoperatively, the basihyoid bone and thyrohyoid-thyroid articulation were positioned dorsally (9.6 mm, p = .006 and 20.4 mm, p = .007, respectively) at 2 days postoperatively. During repeat dynamic URT endoscopy at 48 hours postoperatively, 3/5 horses showed resolution of iDDSP and 2/5 marked improvement. One horse experienced brief iDDSP associated with neck flexion which corrected after swallowing. The second achieved a greater speed and total distance prior to iDDSP.

CONCLUSIONS

Standing LTF did not incur any major peri- or postoperative complications. The laryngohyoid apparatus was repositioned dorsally and in a small case series had a similar surgical effect on laryngeal position.

CLINICAL SIGNIFICANCE

Standing LTF is feasible, mitigates the risk of general anesthesia related complications and reduces cost.

Ex-vivo Mechanical Testing of Novel Laryngeal Clamps Used for Laryngeal Advancement Constructs

Rostral laryngeal advancement, also known as laryngeal tie-forward, is used to treat horses for intermittent dorsal displacement of the soft palate and has a morbidity rate of about 6%. We hypothesized that a novel laryngeal clamp would prevent morbidity associated with the sutures tearing through the thyroid cartilage. Larynges (n = 35 horses) were used for ex vivo testing. For uniaxial testing, 15 equine larynges were tested in one of three laryngeal tie-forward constructs [standard laryngeal tie-forward; modified laryngeal tie-forward using a suture-button; and modified laryngeal tie-forward using a laryngeal clamp]. For biaxial testing, 20 larynges were tested in one of two treatment groups: laryngeal tie-forward and laryngeal tie-forward using a laryngeal clamp. Constructs were tested in single cycle-to-failure. Statistical analyses were performed using ANOVA for uniaxial testing and t-tests for biaxial testing. The laryngeal tie-forward using a laryngeal clamp construct was superior to laryngeal tie-forward and laryngeal tie-forward using a suture-button constructs in resistance to pullout in uniaxial testing. The laryngeal tie-forward using a laryngeal clamp presented a significantly different method of failure than the standard laryngeal tie-forward in the biaxial testing. Failure modes for each construct were primarily by suture failure at the clamp (laryngeal tie-forward using a laryngeal clamp), suture pullout through the thyroid cartilage, or, less commonly, tearing of the cricothyroid ligament (laryngeal tie-forward). In uniaxial testing, the laryngeal tie-forward using a laryngeal clamp failed most commonly due to tearing of the cricothyroid ligament, whereas the standard laryngeal tie-forward and the laryngeal tie-forward using a suture-button failed due to the tearing of the cartilage. The laryngeal clamps provided greater stiffness, load at yield, and tensile stress at yield than did the standard construct. Laryngeal clamps may offer an alternative to standard methods of anchoring the thyroid cartilage when performing the laryngeal tie-forward procedure. Further testing and clinical trials are needed to elucidate the utility of the laryngeal tie-forward using a laryngeal clamp.

In vitro mechanical evaluation of equine laryngeal tie-forward constructs prepared with different suture materials and placement patterns

OBJECTIVE

To compare the mechanical properties of laryngeal tie-forward (LTF) constructs prepared with different suture materials and suture placement patterns during single load to failure testing.

SAMPLE

Larynges harvested from 50 horse cadavers and 5 intact horse cadavers.

PROCEDURES

In vitro LTF constructs were created by a standard technique with polyester sutures, a standard technique with polyethylene sutures, a modified technique with metallic implants and polyester sutures, a modified technique with metallic implants and polyethylene sutures, or a modified tie-off technique with polyester sutures (10 of each type of construct). Mechanical properties including maximal load (N) at failure and failure mode were compared among constructs. Also, maximal loads at failure of the in vitro LTF constructs were compared with the loads exerted on the sutures tightened to achieve rostral laryngeal advancement in intact cadavers.

RESULTS

Constructs prepared by a standard technique with polyethylene sutures had a significantly higher pull out strength than those prepared by a modified technique with metallic implants and either polyester or polyethylene sutures. For constructs prepared by a standard technique with polyethylene sutures or similarly placed polyester sutures, maximal load at failure did not differ but the failure mode did differ significantly. The load to failure for all in vitro constructs was higher than the maximal load measured during a range of motion test in intact horse cadavers.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that LTF procedures can be performed in live horses with any of the suture materials and techniques tested.