Mechanics of the linea alba and suture-based wound closure
Citation:Gerard M. Cooney, 'Mechanics of the linea alba and suture-based wound closure', [thesis], Trinity College (Dublin, Ireland). Department of Mechanical and Manufacturing Engineering, 2016
Cooney, Gerard_PhD Thesis.pdf (PDF) 28.77Mb
Over the past thirty years, there has been a dramatic change in the methodology of abdominal surgery. The introduction of digitalisation, miniaturisation, improved optics, novel imaging techniques and computerised information systems in the operating theatre in the form of minimally invasive laparoscopic surgery have greatly reduced risk to the patient and the length of time required to complete the surgery. However, there are still medical situations that require the more invasive laparotomy surgery and it is estimated that the same number of people (two million for each laparoscopic and laparotomy surgeries) undergo the procedure in the USA each year. Unfortunately, despite the medical advances in recent years, incisional hernia can form post-operatively, having a prevalence of approximately 1-5% for laparoscopic surgery and as high as 20% for open laparotomies. There are claims that the risk of incisional hernia is related to the quality of wound closure. This thesis therefore aims to develop a novel wound closure method that will reduce the risk of incisional hernia occurring. The design of a novel wound closure method requires a fundamental understanding of the mechanical properties of the tissue involved. To achieve this, the tensile mechanical characterisation of the porcine and human linea alba, as determined by uniaxial and equi-load biaxial testing using image-based strain measurement methods is presented due to the limited data available in the literature and which use less accurate methods of stretch measurement. Significant anisotropy was observed in the tissue of both species with deformation heavily biased in the longitudinal direction under equal application of load. It was found that the response of porcine linea alba to uniaxial and biaxial loading is similar to that of human linea alba, permitting the use of a porcine model for investigations into wound closure methodology. Additionally, a finite element model of the uniaxial experiments quantified the effect of clamping and tissue dimensions (which are suboptimal for tensile testing) on the porcine uniaxial results. A correction factor was produced that was used to scale the porcine uniaxial data to account for the effects of clamping. These results provide an improved assessment of the mechanical properties of the porcine and human linea alba to help further an understanding of wound closure. The suture pullout characteristics of both porcine and human linea alba are investigated to ascertain an optimal placement of sutures for surgical wound closure. This is performed again in response to the very limited data available in the literature. It was found that the relationship between pullout force of the suture, bite separation and bite depth is quadratic and characterises low separation and high depth as optimal parameters. Of the parameters used in the study, it was found that resistance to pullout could be improved by as much as 290%. Both human and porcine tissue were observed to exhibit the same behaviour, again corroborating the use of a porcine model for investigations into wound closure methodology. Orientation of suture application was also found to significantly affect the magnitude of suture pullout. Suture styles applied longitudinally across a transverse defect were observed to be more beneficial and it was concluded that it could especially reduce the risk of laparoscopic incisional hernia. Since the abdomen is itself a pressurised vessel, it is generally described as being subjected to multi-axial loading; not solely in the direction of the abdominal muscles aponeurotic processes. To more adequately describe the effect that suture-based wound closure has on the apposition of the linea alba laparotomy defect, it is necessary to create an environment that adequately reflects an in-vivo standpoint. To this end, deformation tests on porcine linea alba (intact abdominal wall) with a suture-closed laparotomy incision were performed on a surrogate abdominal rig. This was done in order to more accurately ascertain the optimum bite depth and bite separation of a continuous suture to be used to close a laparotomy defect through quantitative measurement of wound apposition. The conclusions proved to be the same as that of uniaxial suture pullout, validating uniaxial pullout as a reliable source. Theoretical and experimental evaluation of suture pullout was also investigated in order to predict the pressure of suture pullout beyond what is capable of the surrogate rig. However, the theoretical model tended to under-predict the experimental results due to the types of assumptions used. In conclusion, a detailed understanding of the mechanics of the linea alba and suture-based wound closure has been developed and used to improve upon clinical methodologies and could potentially reduce the risk of post-operative complications. Two clinical recommendations were developed and accepted by a surgical consultant. A suture bite depth of 16mm and a bite separation of 5mm is advised for laparotomy closure and transverse incisions closed using longitudinal applications of suture are advised for laparoscopic closure to help minimise the risk of incisional hernia.
Author: Cooney, Gerard M.
Advisor:Simms, Ciaran K.
Publisher:Trinity College (Dublin, Ireland). Department of Mechanical and Manufacturing Engineering
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Type of material:thesis
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