Abstract
After damage to the spinal cord, some of the most frequent and severe complications are due to the neurogenic bladder and bowel, in spite of a variety of methods of management.
Bladder and bowel emptying is usually impaired, but electrical stimulation of nerves surviving after spinal cord injury can produce controlled contraction of muscle, including the smooth muscle of the bladder and lower bowel, and this can be used to produce safe and effective bladder emptying on demand without catheters. It can also aid emptying of the bowel and reduce constipation. Hyper-reflexia of the bladder and lower bowel after spinal cord injury can produce reflex incontinence of urine and stool, and while this can sometimes be reduced by neuromodulation, it can be more predictably reduced by rhizotomy of the sacral sensory roots, while preserving the motor roots for stimulation. This combination of electrical stimulation and rhizotomy has restored bladder and bowel emptying and continence to several thousand patients, with reduced complications and improved quality of life over many years.
Keywords
1. Introduction
Bladder and bowel complications cause some of the most prevalent and persistent problems after damage to the spinal cord from trauma or disease. These complications used to be responsible for as much as 50% of the mortality following spinal cord injury, and while the mortality is now much reduced, these complications still cause much morbidity, social and economic costs. Impaired emptying of the bladder leads to chronic and recurrent urinary tract infection and stones. Impaired continence has not only significant social consequences but also contributes to skin damage and pressure ulcers and has substantial economic costs for supplies to manage it. This is in spite of a variety of medical and surgical methods used to manage the neurogenic bladder and bowel. Surveys of patients with chronic spinal cord injury show they desire restoration of bladder and bowel function very highly, typically prioritizing it over walking.
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2. Pathophysiology of the neurogenic bladder and bowel
Normal bladder function requires involvement of the frontal cortex and other parts of the brain to sense fullness of the bladder via sacral sensory nerves and ascending spinal tracts, and to decide on appropriate times and methods for emptying. A person can then alternate between continence and micturition. This alternation is co-ordinated by the pontine micturition centre which communicates via the spinal cord with the sacral segments innervating the bladder, sphincters and pelvic floor. For continence, the bladder is relaxed and there is sufficient tone or contraction of the urethral sphincters to retain urine at low pressure. For micturition, the bladder contracts and the urethral sphincters relax to allow most or all of the urine to be expelled at safe pressures. Bowel continence and emptying are analogous but happen over a longer timescale.
A complete spinal cord injury between the pons and the sacral segments interrupts the ascending and descending tracts, resulting in inability to sense bladder fullness or emptying, and inability of the pons to co-ordinate contraction and relaxation of the bladder and sphincters.
If the sacral segments and their peripheral nerves are preserved after a suprasacral spinal cord injury, the loss of inhibition by the descending tracts in the spinal cord results in hyper-reflexia of the bladder and/or sphincters. Hyper-reflexia of the bladder can cause reflex incontinence; hyper-reflexia of the sphincters can hinder or prevent the flow of urine, causing retention or incomplete voiding, which predisposes to urine infection and stones. If both the bladder and sphincter are hyper-reflexic, and co-contract, this can cause dangerously high pressures in the bladder, leading to hypertrophy of the bladder muscle and diverticula, which further predispose to infection and stones. The high bladder pressures can hinder flow of urine into the bladder from the ureters and cause reflux of urine up the ureters, spreading infection to the kidneys, and causing hydro-ureter and hydro-nephrosis with associated kidney stones. Acute and chronic pyelonephritis can cause serious systemic infection and the kidney damage can cause renal failure, requiring renal dialysis or resulting in death.
If the sacral segments and/or their peripheral nerves are damaged by an injury to the conus medullaris or the cauda equina, the bladder and/or sphincters may be denervated and areflexic. In this case the bladder may fill to abnormally large volumes without reflex contraction, and then overflow. Chronic retention of urine may also lead to urine infection and stones in this situation. Absence of tone or contraction of the sphincters can lead to stress incontinence.
In a similar manner, supra-sacral spinal cord injury can result in loss of voluntary control and hyper-reflexia of the anal sphincter and impaired emptying of the bowel; hyper-reflexia of the rectum can cause reflex incontinence of stool. This is sometimes called an “upper motor neuron bowel”. Damage to the conus medullaris or cauda equina can cause reduced reflex activity of the lower bowel from the splenic flexure to the rectum, resulting in profound constipation; denervation of the anal sphincter can cause stress incontinence of stool. This is sometimes called a “lower motor neuron bowel”.
3. Goals of management of the neurogenic bladder and bowel
The goal of management of the neurogenic bladder and bowel is ideally to restore both continence and emptying in safe and socially appropriate ways. Unfortunately, most of the methods currently available aim to restore one of these functions but are unable completely to restore both.
After supra-sacral spinal cord injuries, the hyper-reflexia of the bladder can sometimes be managed by anticholinergic or related medicines to reduce the contraction of the smooth muscle. Unfortunately, these medicines also have side effects on other smooth muscle and glands in the body, such as the bowel, aggravating constipation, and the salivary glands, causing a dry mouth. These side effects often lead to patients discontinuing the medicines. The reduction of bladder contraction also impairs micturition, requiring the patient to use other methods for bladder emptying, such as intermittent self catheterization. If this is not feasible, patients sometimes revert to using an indwelling urethral catheter.
As an alternative to medication, surgical methods are sometimes used to reduce hyper-reflexia of the bladder. These include various techniques for augmentation of the bladder, often using bowel tissue. Sometimes the bladder is diverted to an opening on the abdominal wall to which a urine collection bag can be attached. It is sometimes possible to create a continent stoma on the abdominal wall, through which the person can perform intermittent catheterization, which can be easier than self-catheterization vis the urethra, particularly in females.
After sacral spinal cord injuries, dribbling of urine and stress incontinence can sometimes be managed by attachment of a condom and legbag in male patients, provided the condom can be attached securely. In females this is not an option, and they may be able to be managed by an indwelling urethral catheter. However, in the long term this may lead to stretching or erosion of the bladder neck, and the resulting severe stress incontinence may require surgical closure of the bladder neck and diversion of the urine to a stoma on the abdominal wall.
Management of bowel function usually requires a combination of a diet with adequate fibre or roughage, oral medicines for stool softening, laxatives to improve peristalsis, and stimulant or lubricant suppositories to promote emptying, sometimes aided by digital stimulation of the rectum and manual evacuation of stool. If bowel management is particularly troublesome, quality of life can sometimes be improved by colostomy.
4. Principles of electrical stimulation of the neurogenic bladder and bowel
After supra-sacral spinal cord injuries, the surviving sacral nerves to the bladder, lower bowel and sphincters and pelvic floor can be stimulated electrically to produce contraction on demand of these muscles. In the sacral nerves or sacral anterior (motor) roots, the efferent axons to the bladder are mingled with the efferent nerves to the external urethral sphincter, and stimulation of these nerves or roots can produce co-contraction of both the bladder and the sphincter, which would normally be undesirable. However, it was shown by Brindley that intermittent bursts of stimulation could produce sustained contraction of the smooth muscle of the bladder, which is slow to contract and relax, with intermittent contraction of the striated muscle of the external urethral sphincter, which contracts and relaxes rapidly.
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During the intermittent relaxation of the sphincter, the sustained bladder pressure can produce voiding, in an intermittent pattern known as “post-stimulus voiding”. The pressure in the bladder can be regulated by adjustment of the stimulation, and this pattern of voiding has now been shown to be both safe and effective for bladder emptying. A similar intermittent pattern of stimulation, spread over a longer period because the bowel responds more slowly, can produce post-stimulus defaecation. The fact that the bowel responds more slowly usually makes it possible to produce micturition without defaecation.If the sacral segments or nerves are damaged by injuries to the conus medullaris or cauda equina, they are usually unresponsive to electrical stimulation which is currently not an option for bladder and bowel management after such injuries.
While bladder and bowel emptying can be produced by electrical stimulation, hyper-reflexia of the bladder and bowel can still cause reflex incontinence which may need to be addressed. Frequently this has been done by carrying out surgical rhizotomy of the sacral posterior nerve roots. This abolishes the reflex bladder contractions, but the preserved sacral anterior nerve roots can still be stimulated to produce emptying. This combination of stimulation and rhizotomy can therefore often improve both emptying and continence, the dual functions required of the bladder and bowel.
5. Surgical implantation of electrodes and stimulator and rhizotomy of the sacral posterior roots
Long term stimulation of the sacral nerves or anterior roots can be achieved by implanting on them electrodes that are connected by subcutaneous wires to a stimulator implanted under the skin of the front of the body. This stimulator has no batteries but is powered and controlled by radio transmission from a battery-powered external controller operated by the patient.
The sacral anterior roots can be separated from the posterior roots most clearly in the intradural space. This requires opening of the dura over the cauda equina, and identifying the anterior and posterior roots by intra-operative electrical stimulation while monitoring bladder pressure. Stimulation of the appropriate anterior roots (usually S3 and S4, and sometimes S2) at about 30Hz can produce bladder contraction, while stimulation of the posterior roots should not do so, though it may produce rises in blood pressure which should be monitored by the anaesthetist. Electrodes can then be implanted on the anterior roots intradurally.
The posterior roots can be cut at the same time via this approach. An alternative approach is to cut the posterior roots at the level of the conus medullaris, where they enter the posterior surface of the lower inch of the spinal cord and can more easily be identified anatomically. This approach requires an additional laminectomy at the thoracolumbar junction, which is sometimes complicated by the presence of internal fixation, and can potentially lead to later instability of the spine at that level.
An alternative surgical procedure is to implant electrodes extradurally on the sacral nerves, which are more robust as they have a fibrous covering. This covering makes it more difficult to separate sensory from motor axons in this location, and there is more risk of damage to the motor axons, though the separation can be done with care and good training.
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More often, extradural electrodes are implanted on the intact sacral nerves, containing both motor and sensory axons, and a sensory rhizotomy is done via one of the intradural approaches described above.Post-operatively, the function of the stimulator can be checked by measuring bladder pressures using urodynamic equipment, and adjusted to produce appropriate pressures, flow and residual volumes of urine. This urodynamic testing can also confirm the reduction of reflex bladder contraction by the rhizotomy, though bladder tone can take some days to decline. It is usually possible for patients to be discharged home with a working system several days after surgery.
6. Results
The results of sacral anterior root stimulation and sacral posterior rhizotomy have been reported in many publications from different countries
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, 6
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and there have also been several narrative and systematic reviews.9
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In summary, the implanted electrical stimulator is able to produce micturition on demand with low residual volumes in the great majority of patients, resulting in low rates of urinary tract infection. The ability to empty the bladder without intermittent or indwelling catheters improves quality of life and can save costs.
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Stimulation of the sacral parasympathetic nerves also improves peristalsis between the splenic flexure and the rectum, reducing constipation, and can often be programmed to improve bowel emptying, reducing the time spent in bowel emptying and the need for bowel medications.
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Posterior sacral rhizotomy greatly reduces reflex incontinence and restores low pressure storage of normal volumes of urine, reducing the risk of ureteric reflux, pyelonephritis and hydronephrosis. The ability to store normal volumes of urine without anticholinergic medication avoids the side effects of such medication, such as dry mouth and constipation. The rhizotomy also abolishes autonomic dysreflexia originating in the bladder or lower bowel, and reduces hyper-reflexia of the external urethral sphincter, facilitating micturition.
The rhizotomy has the disadvantage of abolishing reflex erection and reflex ejaculation. However, reflex erection is often not very functional after spinal cord injury, and there are now very effective ways of restoring effective erection after spinal cord injury, such as intra-cavernosal injection of vasoactive medications. Reflex ejaculation is also often not very functional after spinal cord injury, but in most patients with spinal cord injury electro-ejaculation can produce emission of semen that can be placed into the vagina to produce pregnancy.
Studies in Europe and North America of the economic consequences of this technique have shown significant advantages. The initial costs of the device and its implantation are offset by reduced annual costs of medicines, supplies and hospital visits for managing retention and incontinence and treating infection and other complications. A break-even point is defined as the point at which the initial costs are recovered by subsequent savings, after which the technique is expected to save money. A study in the Netherlands, using economic data from the national health care system, showed a break-even point at eight years.
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A study in North America by a life care planner experienced in modelling the costs of spinal cord injury showed a breakeven point at five years.18
All the patients in that study have lived much longer than five years, and it is thus expected that the procedure has saved money for their health care payers, in addition to its medical and social benefits.The combination of sacral anterior root stimulation with sacral posterior rhizotomy has thus provided several thousand patients who have had a complete spinal cord injury with much improved bladder and bowel function and reduced complications, greatly improved quality of life and has probably reduced the costs of their care.
7. Potential complications
In a few patients the surgical handling of nerve roots can cause neuropraxia, which can result in temporary unresponsiveness of the nerves to electrical stimulation. The nerves usually recover with time, but during this time it is important to avoid the bladder muscle being stretched. This can be achieved by regular intermittent catheterization or the use of an indwelling catheter until the nerves recover.
When intradural electrodes are used, there have been instances of leakage of cerebrospinal fluid along the wires to collect in the subcutaneous pocket containing the stimulator. This usually subsides spontaneously, and is now minimized by the use of a grommet glued to the wires and sutured to the dura.
Over many years, the wires connecting the stimulator with the electrodes can break, particularly in highly active patients, and they can usually be repaired with a subcutaneous procedure. If the stimulator develops a fault, which is rare, it can usually be replaced in a subcutaneous procedure.
Infection of the implant is rare, and can be minimized by careful pre-operative skin cleansing. If the subcutaneous pocket containing the stimulator becomes infected, it is sometimes possible to cut the wires and remove the stimulator, leaving the electrodes in place to be reconnected to a new stimulator when the infection has been treated. However, if the electrodes become infected the entire implant needs to be removed. It may be possible to replace intradural electrodes with extradural electrodes, and vice versa.
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8. Prospects for the future
The surgery is best performed in specialized spinal cord injury centres where teams including spinal surgeons, urologists and rehabilitation specialists can see sufficient numbers of patients to develop the expertise and teamwork required. It is best for such implant centres to work with a network of referral centres who can collaborate to make the technique known, screen patients, identify potentially suitable candidates and perform initial evaluation such as urodynamics to confirm that sacral parasympathetic innervation is intact by demonstrating the presence of reflex bladder contractions. Such contractions should produce a rise in bladder pressure of at least 35 cm water in a female and 50 cm water in a male. After referral of patients to an implant centre for surgery, the referral centres can continue to collaborate in follow-up of patients.
This technique has mainly been used in Britain and Europe, Australasia and North and South America. However, the growth of comprehensive rehabilitation and lifelong care of spinal cord injury patients in other countries raises the possibility of it being made available to such patients much more widely.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References
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Article info
Publication history
Published online: February 21, 2023
Accepted:
February 21,
2023
Received:
January 9,
2023
Footnotes
☆For publication in 2023 in a special issue on Spinal injuries of the Journal of Clinical Orthopaedics and Trauma, published by Elsevier on behalf of the Delhi Orthopaedic Association.
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© 2023
