Understanding the mechanics of closure is key to optimal midurethral sling technique
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Understanding the mechanics of closure is key to optimal midurethral sling technique Peter Petros 1 Received: 13 August 2020 / Accepted: 3 September 2020 # The International Urogynecological Association 2020
Abstract The animal experiments and prototype midurethral sling operations demonstrated that the sling provided new collagen to reinforce weak pubourethral ligaments (PUL). The now strengthened PULs were able to restore the contractile power of the 3 oppositely-acting directional closure forces. By contraction, these three forces exponentially altered the intraurethral resistance to flow when they closed the urethra to sustain continence. Relaxation of the forward force allowed the two posterior forces to uninhibitedly open the posterior urethral wall just prior to detrusor contraction, to facilitate evacuation of urine. The aim of this work is to examine the mechanics of the component anatomical structures which contribute to these functions, to analyse how subtle details impact on the actual surgical technique of the midurethral sling operations to optimize success, contribute to complications and how to prevent and fix them. Keywords Midurethral sling . Urethral resistance . Obstructive micturition . Posterior fornix syndrome . Tethered vagina syndrome
Introduction There are compelling reasons for understanding the anatomy of bladder closure and evacuation. The aim of performing the midurethral sling (MUS) is to repair the closure mechanisms of the bladder so the urethra can be closed on effort instead of opening; the mechanism of evacuation also needs to be known, as this impacts on the main complication of MUS, urinary retention; both mechanisms impact on how the sling itself restores continence and when it does not. Despite the MUS being the most studied operation in the history of surgery with animal studies and prototypes extending from 1986 to 1996 [1–8], more than 1000 MUS surgical papers, 10,000,000 operations, it has been my experience that very few surgeons who perform the MUS have ever studied the anatomical mechanisms on which the MUS was based. Yet these very mechanisms, closure and evacuation, their component muscles, ligaments, tissues, constitute the very core of normal function, pathogenesis, the surgery itself and
* Peter Petros [email protected] 1
School of Mechanical and Chemical Engineering University of Western Australia, Crawley, Australia
complications of MUS surgery. The aim of this work is to revisit these mechanisms, how they explain pathogenesis, how the MUS works, why immediate post-op retention occurs, how to prevent and manage it; how surgery can unbalance these mechanisms to cause de novo symptoms such as pain, urge, nocturia, urinary retention, often months or years later and how to fix them. The development of the MUS began in 1986 with an observation: mechanical support of the pubourethral ligament (PUL) at its origin immediately behind the pubic symphysis, controlled urine loss, but not always entirely; where there was some prolapse of the distal vag
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