Biomechanical evaluation of double-strand (looped) and single-strand polyamide multifilament suture: influence of knot and suture size.

Abstract

Flexor tendon repair in zone II remains a vexing problem. Repair techniques have been developed to strengthen and optimize the number of core strands crossing a repair. A polyamide looped suture doubles the number of core strands for every needle path. This simplifies repairs, but the knot remains a potential weakness. The purpose of our study was to create a biomechanical model used to evaluate the bulky knot of a looped suture as it may be weaker, resulting in greater deformation. Using machined steel rods to hold our suture constructs, we compared four different knot configurations using looped and non-looped sutures in 3-0 and 4-0 varieties using a four-core strand technique. The constructs were tested under increased cyclic loading recording both forces applied and suture construct lengthening ("clinical gapping") and ultimate breaking strength. During continuous periods of cyclic loading, we measured permanent deformation and ultimate breaking strength. Permanent deformation results when there is no recoverable change after force removal defined as a permanent rod separation (or gapping) of 2mm. Four-strand 3-0 and 4-0 looped sutures failed at 39.9 and 27.1N faring worse than a four-strand non-looped suture which reached a rod separation of 2mm at 60.7 and 41.3N. The ultimate breaking strength demonstrated absolute failure (construct rupture) with the 3-0 looped suture breaking at the knot at 50.3N and the non-looped suture at 61.5N. For the 4-0 suture, these values were 32.4 and 41.76N. Within the constraints of this model, a looped suture fared worse than a non-looped suture especially when comparing 4-0 and 3-0 sutures. However, two-knot 3-0 looped suture constructs did resist the force generally accepted as occurring with early non-resistive tendon motion protocols, while two-knot 4-0 looped suture constructs did not. This paper provides a description of a model to evaluate various suture materials and knot strengths in isolation of the tendon itself. This allowed us to evaluate mechanical differences between looped and non-looped sutures for polyamide, which are commonly used in flexor tendon repair. These differences between sutures may impact choices for a suture type selected for these repairs.