Tension of knotted surgical sutures shows tissue specific rapid loss in a rodent model

Abstract

Background: Every surgical suture compresses the enclosed tissue with a tension that depends from the knotting force and the resistance of the tissue. The aim of this study was to identify the dynamic change of applied suture tension with regard to the tissue specific cutting reaction.

Methods: In rabbits we placed single polypropylene sutures (3/0) in skin, muscle, liver, stomach and small intestine. Six measurements for each single organ were determined by tension sensors for 60 minutes. We collected tissue specimens to analyse the connective tissue stability by measuring the collagen/protein content.

Results: We identified three phases in the process of suture loosening. The initial rapid loss of the first phase lasts only one minute. It can be regarded as cutting through damage of the tissue. The percentage of lost tension is closely related to the collagen content of the tissue (r = -0.424; p = 0.016). The second phase is characterized by a slower decrease of suture tension, reflecting a tissue specific plastic deformation. Phase 3 is characterized by a plateau representing the remaining structural stability of the tissue. The ratio of remaining tension to initial tension of phase 1 is closely related to the collagen content of the tissue (r = 0.392; p = 0.026).

Conclusions: Knotted non-elastic monofilament sutures rapidly loose tension. The initial phase of high tension may be narrowed by reduction of the surgeons' initial force of the sutures' elasticity to those of the tissue. Further studies have to confirm, whether reduced tissue compression and less local damage permits improved wound healing.

Figure 1

Used forced sensor for tension measurements developed by Applied Medical Engineering, Helmholtz Institute, RWTH Aachen, Germany.

Figure 2

Model of experiment settings showing placed suture upon sensor and involved tissue. Yellow arrows are indicating force applied to tissue by knotting.

Figure 3

Sensors placed on skin (3 sensors), stomach (2 sensors) and small intestine (3 sensors) during documentation.

Figure 4

Model of dynamic of suture tension in liver showing measured tension strength within the suture loop (solid blue), and estimate (fitted model according to formula above; solid red) for the course of tension between P₁ and P_plat, assuming a final plateau and a constant rate for declination; relation of the fitted model with the measured curve is indicated by Pearson's correlation coefficient r. P₀ = peak suture tension, P₁ = transition to the constant declining phase, P_plat = suture tension of the constant plateau (mean ± SD).

Figure 5

Model of dynamic of suture tension in skin showing measured tension strength within the suture loop (solid blue), and estimate (fitted model according to formula above; solid red) for the course of tension between P₁ and P_plat, assuming a final plateau and a constant rate for declination; relation of the fitted model with the measured curve is indicated by Pearson's correlation coefficient r. P₀ = peak suture tension, P₁ = transition to the constant declining phase, P_plat = suture tension of the constant plateau (mean ± SD).

Figure 6

Model of dynamic of suture tension in stomach showing measured tension strength within the suture loop (solid blue), and estimate (fitted model according to formula above; solid red) for the course of tension between P₁ and P_plat, assuming a final plateau and a constant rate for declination; relation of the fitted model with the measured curve is indicated by Pearson's correlation coefficient r. P₀ = peak suture tension, P₁ = transition to the constant declining phase, P_plat = suture tension of the constant plateau (mean ± SD).

Figure 7

Model of dynamic of suture tension in muscle showing measured tension strength within the suture loop (solid blue), and estimate (fitted model according to formula above; solid red) for the course of tension between P₁ and P_plat, assuming a final plateau and a constant rate for declination; relation of the fitted model with the measured curve is indicated by Pearson's correlation coefficient r. P₀ = peak suture tension, P₁ = transition to the constant declining phase, P_plat = suture tension of the constant plateau (mean ± SD).

Figure 8

Model of dynamic of suture tension in small intestine showing measured tension strength within the suture loop (solid blue), and estimate (fitted model according to formula above; solid red) for the course of tension between P₁ and P_plat, assuming a final plateau and a constant rate for declination; relation of the fitted model with the measured curve is indicated by Pearson's correlation coefficient r. P₀ = peak suture tension, P₁ = transition to the constant declining phase, P_plat = suture tension of the constant plateau (mean ± SD).