Knotless bidirectional barbed versus smooth polypropylene three-loop pulley sutures for repair of canine gastrocnemius tendon
Canine common calcaneal (Achilles) tendon injury is a well-known cause of lameness in the dog. The Achilles tendon complex is primarily composed of the gastrocnemius tendon, with smaller contributions from the superficial digital flexor tendon and the common tendon of the biceps femoris, semitendinosus and gracilis muscles. The primary goal in tendon repair is to provide strength appropriate to allow healing while minimizing gap formation. A large gap (>3 mm) in repaired tendon results in slower healing and decreased ultimate tensile strength (UTS) at 6 weeks, compared to those with a smaller gap. Barbed sutures are a relatively recent entry into the veterinary field. These sutures have found multiple applications in human medicine, including digital flexor tendon repair, as well as gastrointestinal, gynecologic, urologic and cosmetic surgeries. Recent veterinary studies demonstrate that knotless barbed sutures have supraphysiologic, and in some cases, increased load to failure compared to conventional sutures in selected soft tissue surgeries. Each barb provides a small component of the total anchoring force which cumulatively can exceed the tensile strength of the smooth monofilament sutures. The barbs increase suture-tendon interface and theoretically distribute load more evenly throughout the construct, as well as minimize the chances of suture pull-out as a mode of failure. As these sutures are processed from existing materials and result in a smaller core diameter, it is recommended to select a barbed suture 1-2 sizes larger than the appropriate smooth suture, with the expectation of at least equal tensile strength. We hypothesized that a knotless barbed polypropylene repair would have increased strength compared to a smooth knotted polypropylene repair when placed in the clinically utilized three-loop pulley (3LP) suture pattern in an in-vitro model for gastrocnemius tendon repair. Common calcaneal tendons and calcaneii were obtained as paired units from pelvic limbs of adult, sexually intact mixed breed dogs euthanized for unrelated reasons and free of gross evidence of orthopedic disease. Extraneous tissues were removed, leaving only the gastrocnemius tendon. Each bone-tendon unit was wrapped in towels moistened with saline (0.9% NaCl) solution and stored at -20⁰C until testing. The units were thawed to room temperature overnight prior to testing. Tensile testing was performed with a servohydraulic testing machine equipped with a 2 kN load cell. Constructs were positioned in the testing machine at a 135⁰ angle to mimic physiological load direction. Tendons were preloaded to 2 N, allowing precise transection 3 cm proximal to the tuber calcaneii. One of each paired unit was randomly selected to receive a 3LP repair with 2-0 USP smooth monofilament polypropylene suture while the other received 3LP repair with 1 USP bi-directional barbed monofilament polypropylene suture. Ultimate tensile strength, load to 1 mm and 3 mm gap, and mode of failure were recorded with a material testing system synchronized with digital video. This data was analyzed for normal distribution and compared with Student’s T-tests. If data was non-normally distributed, Mann-Whitney U tests were performed. Significance was set at P ≤ 0.05 for all tests. Thirty-three paired limbs were obtained from dogs weighing between 15.9-27.2 kg (average 21.8 kg, range 16.8-27 kg). Significantly higher ultimate tensile strength (p<0.001) for smooth (40.5 ± 10.6 N) compared to the barbed suture repairs (28.6 ± 7.1 N) was noted. The 1mm gap load for the barbed repair (17.2 ± 5.3 N) was significantly less (p<0.001) than the smooth repair (26.8 ± 7.1 N). The 3mm gap load for the barbed (25.3 ± 5.7 N) was also significantly lower (p<0.001) than the smooth repair (35.1 ± 9.4 N). Thirty-one (94%) out of thirty-three barbed sutures failed when the barbs reversed direction under tensile loading and the suture backed out from its initial placement. Two (6%) barbed sutures broke under tension during testing. With regards to the smooth polypropylene, 31/33 constructs failed by suture material pulling through the tendon. In these cases, the knot and suture material remained intact. The remaining two constructs failed by tendon tears proximal to the repair. The results demonstrate that the load results at each individual sample point (1 mm gap, 3 mm gap, and UTS) were significantly lower for the barbed than the smooth polypropylene repairs. The p-values for each normally distributed data set were actually an order of magnitude beyond the threshold of significance established prior to testing with our power analysis (P <0.001). Based on our results, knotless barbed polypropylene repair is not a suitable alternative to smooth knotted polypropylene repair when placed in 3LP pattern for canine gastrocnemius repair in vitro.
canine, barbed suture, polypropylene, gastrocnemius, tendon, knotless
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign