Page 40 - Advances in Biomechanics and Tissue Regeneration

34 3. DESIGN, SIMULATION, AND EXPERIMENTATION OF COLONIC STENTS

Men Women
Leukaemia Non-Hodgkin lymphoma
Kidney Liver
Non-Hodgkin lymphoma Thyroid
Oesophagus Ovary

Bladder Corpus uteri
Liver Stomach
Stomach Cervix uteri
Colorectum Lung
Prostate Colorectum
Lung Breast
50 40 30 20 10 0 0 10 20 30 40 50
ASR (W) rate per 100,000 Incidence Mortality ASR (W) rate per 100,000
FIG. 3.1 Malignant tumors with the highest ratio of incidence and mortality in the world (age-standardized rates for world standard population,
ASR(W) per 100,000 population) [13].

incidence and the fourth in mortality in the world, after lung cancer [13] (Fig. 3.1). Due to its endoluminal growth, 29%
of patients with this tumor developed intestinal obstruction [14].
Colonic occlusion is the primary reason for emergency colorectal surgery [15]. Traditional treatment of colonic
obstruction is surgery, which is usually a colon resection with primary anastomosis and is more often associated
(two-stage procedure) with bowel resection and colostomy (Hartmann’sprocedure) [16] and restoration of gastro-
intestinal continuity in a subsequent intervention. However, both possibilities are limited, especially when it comes
to elderly patients with associated serious diseases, causing high morbidity, prolonged hospitalization, and a mor-
tality rate between 5% and 11% [17]. Moreover, in many cases it is not possible to restore intestinal continuity, so
the patient is left with a permanent colostomy and consequent deterioration in their quality of life [18].
Sixty percent of patients with colorectal cancer present with a tumor in the left colon, and up to 25% have complete
or partial occlusions at the time of diagnosis [19]. As is well known, metallic self-expanding stents are an option widely
used to treat acute obstruction of the colon, either for palliation or bridging or transition to surgical intervention, thus
avoiding emergency surgery rates of morbidity and mortality greater than 30% [19]. The stent allows decompression,
complete preparation of the colon, and resection surgery in one step [20].
Colonic stenting in acute large bowel obstruction is more likely to be successful in shorter, malignant strictures with
less angulation distal to the obstruction. Longer benign strictures are less likely to be successful and may be associated
with an increased risk of perforation [21]. Although the placement of colonic stents is much less invasive, morbidity can
be high due to the complications associated with this procedure. The most common complications include perforation,
wrong positioning, migration, and reobstruction. To prevent or minimize these complications, it is necessary to make a
correct choice of stent to use [22]. Since the technical success of a stent for a particular obstructive lesion depends
mainly on its mechanical behavior, mechanical modeling is required to design the stent structure through a predictive
model as in Kim et al. [23] for braiding stents and Tzamtzis et al. [24] for an aortic valve. This will allow custom-
designed stents for each type of obstruction and patient.
Colonic stents were introduced in the early 1990s. In 1990 Dohmoto et al. [25] presented the treatment of a malig-
nant rectal obstruction with the placement of an expandable metal stent, and in 1994 Tejero et al. [26] reported two
cases of acute malignant obstruction treated successfully with the placement of a stent prior to elective surgery. In
1996 the first prototype a self-expanding colonic stent made of Nitinol was presented [27]. Since then, the field of
colorectal stent placement has evolved substantially with the introduction of new stent models and more versatile
deployment systems. Self-expandable metallic stents (SEMSs) are widely used to treat malignant colonic obstruction
[28]. They may be used both as a palliative measure and as a preoperative bridge to facilitate a one-stage surgical
resection of primary colonic tumors [29, 30]. Increasing experience in the management of colorectal cancer with
colonic stents decreases morbidity and mortality, as well as cost, in comparison with surgical intervention for acute
colonic obstruction.

I. BIOMECHANICS