Abrasion Assessment of Staple Line Reinforcement Materials in the Thorax of a Canine

Michael Soltz, PhD, Ludovic Boure, DVM, Clayton Ramey, DVM, Elizabeth Contini, BS, Dwight Bronson, MS, Tim Ebner, BS, Gerald Hodgkinson, PhD. Covidien.

AIM The goals of this project were to develop a surgical animal model to assess the abrasiveness of buttressed and non-buttressed staple lines in the thorax of a canine and utilize the model to test two buttress materials.

METHODS The model was developed in stages utilizing acute surgical planning and a pilot chronic survival study to assess the potential for buttress materials to cause abrasions to the pleura or surrounding tissue in the thorax. Surgically, the procedure for acute, pilot, and pivotal studies was similar, with buttress and non-buttressed control staple lines deployed on the apex and surface of the lung lobes. Figure 1 illustrates the various locations of each staple line site. In total, five individual staple line sites were created per hemi-thorax, each consisting of either crossed or single staple lines. Staple lines with buttress materials and non-buttressed controls were randomly assigned to each animal with one treatment group per hemi-thorax.  

In the pilot study, n=20 to 30 staple line sites per buttress material were surgically placed in ten canines.  Staple line contact with and movement against the pleura was verified by ultrasound on Day 2 post surgery, and an in life thoracoscopic abrasion assessment was conducted on all animals on Day 3 post surgery.  Animals were euthanized on Day 7, 10, and 14 post surgery, and assessed again for abrasions at necropsy.  In the pivotal study, n=50 staple line sites per buttress material were surgically placed in 12 canines.  All animals were euthanized at Day 7 post surgery and assessed at necropsy for abrasions.  For both the pilot and pivotal studies, staple lines were assessed intra-operatively for air leaks and scored against an ordinal scale.  Post surgically, all animals were observed for abnormal clinical signs. Post mortem staple line examination included gross assessment of the each thorax, and severity of abrasions of staple line reinforcement material against the pleura or surrounding tissue per an ordinal scale developed in acute studies. Finally, abrasion scores for two buttress materials were used to power the pivotal study. Statistical comparisons were done using Kruskal-Wallis (α=0.05).

RESULTS The surgical procedure was well tolerated by all animals. No intraoperative air leaks from the staple lines were observed, and no post-operative complications were observed.  Abrasion scores were very mild on average for both non-buttressed and buttressed staple lines.  For the pilot, abrasion severity did not increase beyond Day 3 as evidenced by no difference being found between Day 3 thoracoscopy scores and Day 7, 10 and 14 necropsy scores (p=0.585, p=0.326 and p=0.508 respectively). Likewise, abrasion scores from necropsy Day 7, 10 and 14 were no different (p=0.176). For the pivotal study, a difference in abrasion scores was observed between buttress materials (p=0.0016).

CONCLUSIONS The model was sufficiently sensitive to detect differences in the abrasiveness of two buttress materials in the thorax. Abrasion scores were mild for both buttress materials, and observed differences in abrasion scores between the two materials were not of clinical significance.

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