Overview of Spinal Cord Stimulation
Spinal cord stimulation is a technique that utilizes electrical pulses around the spinal cord to help manage pain. This approach initially involved the use of these electrical pulses in a space encasement within the spinal column. But nowadays, this method typically involves placing leads or wires in the epidural space – the region between the spinal cord and the protective encasement of the spinal column.
This principle works similarly to other types of neurostimulation like deep brain simulation and peripheral nerve stimulation. These methods involve stimulating parts of the central nervous system (the brain and spinal cord) and the peripheral nervous system (nerves outside the brain and spinal cord), respectively.
The creation of these methods aimed to address a concept known as the “gate control theory” of pain proposed by Melzack and Wall. According to this theory, the pain signals that are generated in the peripheral parts (like limbs) of the body, carried by certain types of small nerve fibers, can be interrupted by the stimulation of larger nerve fibers. This interruption happens because these different types of nerve fibers meet at common junctions in specific areas of the spinal cord.
In simple words, by stimulating sensory nerves related to touch and vibrations, we can “shut the door” on the pain signals traveling upwards towards the brain.
Our body’s pain system is quite complex, with several types of neurons (nerve cells) playing a role. These neurons can either activate or lessen the sensitivity of pain receptors known as nociceptors. Some of these receptors pick up harmful levels of temperature, chemical or mechanical signals and relay this information to neurons located in the spinal cord, which in turn transmit these signals to complex neural networks in the brain. The various components of this system work together to create our perception of pain and how we react to it.
Although the gate control theory was a major influence in the development of spinal cord stimulation, our current understanding suggests that the actual mechanisms might be different, particularly when this technique is used for different types of pain, like nerve-related pain versus pain due to inadequate oxygen supply to tissues. In nerve-related pain, research suggests that spinal cord stimulation works by changing local levels of certain neurotransmitters – chemicals that enable communication between nerve cells. In pain due to inadequate oxygen supply, it’s thought that the method helps by modifying sympathetic nervous system’s activity to improve the balance of oxygen supply and demand.
Anatomy and Physiology of Spinal Cord Stimulation
To insert a spinal cord stimulator, a special needle is used to access a space in your spine known as the epidural space. So, it is important to understand the parts of the spine that are involved in this process.
Your spine is made up of individual bones called vertebrae. Each vertebra has a body at the front and an arch at the back which branches into two side sections. These side sections connect to two flatter parts at the back, a long, center spine-like shape, and two smaller spines sticking out sideways. The space between two neighboring vertebra is called foramine. In a human body, there are 7 vertebrae in your neck (cervical), 12 in your middle (thoracic), 5 lower down (lumbar) and then 5 fused or fixed ones which make up your sacrum and coccyx or tailbone.
After the needle goes through the skin and a fatty layer underneath, it will reach a set of ligaments (bands of strong, flexible tissue), including a specific one which connects the neighboring vertebrae, called the supraspinal ligament. After this, the needle encounters an another ligament called the interspinous ligament and finally, an especially thick one known as the ligamentum flavum. There are also two other ligaments at the front of the spine that connect the bodies of the neighboring vertebrae.
The spinal cord is wrapped in three layers: the dura mater (the outer layer), the arachnoid mater, and the pia mater (the inner layer lying directly on the spinal cord). The spinal cord starts from the brain and goes down to the L1 level in adults, where it tapers or narrows down. Below this level, the spinal nerves become long and run parallel, forming an area known as the cauda equina, which is the preferred location for the insertion of the epidural needle.
The blood supply to the spinal cord comes from the neck in the cervical spine and from arteries between the ribs and in the lower back in the thoracic and lumbar spine. These arteries meet up with other blood vessels of the spinal cord to form a network. There are two sets of branches, one supplies the spinal cord’s nerve roots at the front and the other at the back. In the sensory part of the spinal cord, these arteries safeguard this area from low blood supply. However, a single artery, the largest one known as the artery of Adamkiewicz, supplies the lower two-thirds of the spinal cord. An improperly performed epidural can damage this artery and possibly causing paralysis in both lower limbs.
The spinal cord’s veins drain into a network that enters into the spinal canal. These veins then discharge into a main vein that eventually flows into a large vein leading back to the heart. This vein network is particularly important in people with a mass or increased pressure in the belly pressing on the big vein as this can cause a backup of blood into the epidural space, increasing the risk of accidentally piercing the veins with the epidural needle.
Why do People Need Spinal Cord Stimulation
Choosing the right patient for a treatment method known as neurostimulation can often be challenging. Many different patient characteristics can have a big influence on how well the treatment works. Some of these factors can be social and might not seem directly related to the patient’s medical condition at first.
An implantable device, such as used in neurostimulation, requires ongoing care and maintenance. This includes regular check-ups, possible adjustments to the device’s settings, taking care of the area where the device was implanted, and sometimes recharging the device without wires. This means that the patient will need to play an active role in their treatment and take responsibility for managing their ongoing pain.
Aside from social aspects, a patient is more likely to have a positive outcome from the therapy if they have a condition known as complex regional pain syndrome (CRPS). And, if a patient responds well to a treatment called a sympathetic nerve block, they may also do well with stimulation therapy. There is strong scientific evidence that neurostimulation works well for people who have not found relief from other treatments for failed back surgery syndrome (pain arising after back surgery), peripheral ischemia (poor blood supply to the limbs), peripheral neuropathy (damaged or diseased nerves), and angina pectoris (chest pain or discomfort). Furthermore, the use of neurostimulation on a part of the spinal cord – the dorsal column – has proven effective for many types of nerve and radicular (pain that radiates along the nerve) pain syndromes. This method is particularly helpful for those whose pain is not controlled by medicines, physical therapy, psychotherapy, chiropractic care, and other treatments.
Interestingly, factors like a patient’s age, how long they’ve had the pain, the intensity of the pain, and whether the pain is on one or both sides of the body, don’t seem to make a big difference to the success of neurostimulation therapy.
When a Person Should Avoid Spinal Cord Stimulation
The existing research on Spinal Cord Stimulation (SCS) therapy, a method to treat nerve pain, mostly consists of smaller, directed studies or studies that look back at past results. Because of this, there are only a few clear guidelines about when this treatment should not be used.
Like other optional surgeries, there are some standard reasons why SCS might not be a good choice. These include:
* Infections at the spots where surgery would be done.
* Unusual body structure at the spots where surgery would be done, which might make safe placement an issue.
* Illness that affects the whole body and isn’t under control.
* A bleeding condition that isn’t under control.
If a patient is on blood thinners, they are usually asked to stop taking them before the surgery, following ASRA guidelines. But if a life-threatening clotting disease or a recent heart surgery means blood thinners can’t be stopped, the surgery should also be halted.
One study by Eijs and his team observed 36 patients with Complex Regional Pain Syndrome (CRPS), a chronic pain condition. They noted that mechanical allodynia, where even a light touch causes pain, may be a reason not to use SCS therapy. In the study, patients with mechanical allodynia had only a 31% reduction in pain as compared to an 81% reduction in patients without allodynia. Other signs that SCS may not work well include symptoms of ongoing depression, anxiety, conversion of a mental condition into physical symptoms (somatization), and poor ability to manage stress. This is why a psychological evaluation is necessary before considering a patient for an SCS device. It’s important to note, however, that a thought pattern of exaggerating how bad a situation will be (called catastrophizing) does not affect SCS therapy negatively.
Patients with pain resulting from an amputated limb (stump or phantom-limb pain) or paraplegic pain don’t seem to get benefits from SCS therapy.
Equipment used for Spinal Cord Stimulation
A spinal cord stimulator is a device made up of three main parts. The first part is electrodes or leads, which can have different shapes such as cylindrical or paddle shapes. The second part is the implantable pulse generator or, simply put, batteries, which supply power to the device. The third part is the charging and programming equipment that includes a remote control.
Various companies manufacture these devices. Still, three companies mainly dominate the market that focuses on modifying nerve activity, otherwise known as the neuromodulation market.
All these companies produce devices with rechargeable batteries that last up to 10 years. This feature allows patients to use higher power levels without draining the battery quickly. It also increases the options for reprogramming the device and reduces the need for frequent replacements.
Another point to note is that each of these battery-operated devices has a different level of compatibility with MRI imaging, a common type of body scan. If the patient may need MRI scans in the future, it’s important to consider how well each device can work with MRI before choosing one.
Who is needed to perform Spinal Cord Stimulation?
The medical team involved in your treatment has different roles to ensure you receive the best care. Here is how they contribute:
The main operating doctor, also known as the provider, is the one who performs the actual procedure. They have been highly trained and certified to put in a Spinal Cord Stimulation (SCS) device (this provides relief to chronic pains). This doctor has also discussed thoroughly with you about the advantages, risks, and alternatives related to this procedure.
The anesthesia provider is another key person involved in the procedure. This specialist ensures that you are comfortable and safe during the procedure by managing your sedation (medicine to make you relaxed and less aware). They also know the steps of the procedure and are ready to respond swiftly if needed.
The circulating nurse is an expert in this type of surgical procedure who keeps track of all the necessary equipment and also ensures your safety throughout your stay in the surgery room and during your transfer.
A radiology technician is involved as well. This person is trained to understand the body’s anatomy and how to capture images using medical equipment for the procedure. They also help in ensuring the area is sterilised properly during the operation.
The surgical technician also plays an essential role. They are familiar with all the surgical tools needed and the steps of the procedure. They also help to maintain a clean and sterile environment, keeping track of things like needles and sponges to ensure patient safety.
Last, but not least, we have the device representative. This person is an expert in the SCS device being used. They help the operating doctor with any device-related queries and provide additional information about how the device works to alleviate your pain.
Preparing for Spinal Cord Stimulation
The doctor may first consider referring a patient to a pain specialist to evaluate if they might benefit from a treatment called neuromodulation, particularly if quicker, basic treatments have not improved their condition. This treatment can help adjust the way nerves transmit signals about pain to the brain.
Aspart of the decision process, a psychological evaluation may be suggested. Certain active or untreated mental health disorders could affect the success rate of the treatment. So, a patient would need to get a ‘thumbs-up’ from a mental health professional to make sure they’re a good fit for the procedure.
Next, the doctor could ask for an image, typically an MRI scan, of the area around the spinal cord. It helps the doctor to “see” the area and plan how to proceed with the procedure in a way that best matches the patient’s pain patterns.
Then, a temporary pain relief device (lead) could be implanted to see if it’s beneficial. Its connected to an external device that runs the trial system. The patient would continue with the trial device if they experience a reduction of at least half of their pain or an improvement of at least 50% in their functionality.
If the trial proves satisfactory for the patient, doctors will then proceed with the full procedure. This procedure includes the reimplantation of one or more devices (leads) and the full pain control device (IPG).
How is Spinal Cord Stimulation performed
Spinal cord stimulation (SCS) is a procedure often used to relieve chronic pain and is viewed as one of the more complex procedures in pain management. The overall process of SCS implantation comes in two stages: the trial stage and the permanent implantation stage. The same equipment is used for both stages, but the techniques used differ somewhat.
The trial stage allows patients to experience the SCS device and see how well it works for their specific type of pain. This stage usually lasts around ten days. If the patient experiences major pain relief, shows an increase in their activity levels, or needs less medication during this time, the trial is considered a success. They can then have a permanent SCS operation scheduled.
The trial and the permanent SCS implantation are both done in an operating room, with the patient under sedation. Patients are told to thoroughly clean their bodies with chlorhexidine before these operations to reduce the risk of infection. The sterilized operation area on the back is covered with sterilized towels and sheath. A special needle (epidural needle) is used to place a wire (lead) into the spinal canal under radiological guidance. This lead, once accurately placed, delivers electric current to the spinal cord, which helps block pain signals.
There are two types of SCS trials: a percutaneous lead trial, which is the most common, and a permanent lead trial. The percutaneous lead trial has the lead sutured to the skin and connected to an external device, which is programmed before and after the operation. This trial strategy usually reduces the risk of infection and postoperative discomfort, even though, if successful, it means a return to the operating room for permanent lead placement.
A permanent lead trial entails making a cut in the skin and inserting and securing the lead directly into the spinal cord tissue. This is then connected to a device that is secured within the body. This method also ensures that the lead remains in the same location if successful and tends to be more cost-effective.
Permanent placement can be via a broad, flat introducer device or through an incision that allows the paddle to enter the spinal canal. The latter approach is typically performed by a neurosurgeon.
If a permanent lead trial was successful, the part that connected the lead to the external device is cut off and discarded. A new part is then attached to the lead and the implanted pulse generator (IPG – the electronic device that generates stimulating pulses). If the percutaneous trial were successful, the IPG would be inserted into a pocket under the skin, and the lead directly connected to it. After the procedure, the incision is covered with a sterile dressing and monitored.
The placement of the device in the body is often selected for the patient’s comfort and accessibility. This way, the patients can easily reach the device for reprogramming or recharging as needed.
Possible Complications of Spinal Cord Stimulation
Spinal cord stimulation, a type of treatment that uses electrical currents to treat chronic pain, can sometimes cause complications. These could range from minor issues like tingling sensation not reaching the right spots, to serious ones like infection, internal bleeding around the spinal cord, nerve damage, paralysis, and even death. Thankfully, the serious issues are extremely rare.
Doctors minimize the risk of infection by maintaining sterile conditions during the procedure. They also minimize the risk of nerve injury and paralysis by using a technique known as fluoroscopy, which creates a continuous live image of the patient’s spine, during the procedure. Risks from anesthesia, such as oversedation and airway blockage, as well as extreme allergic reactions, can be managed and reduced by licensed anesthesia professionals.
The most common serious problem is infection. Over the years, thanks to a combination of better techniques, strict quality control procedures, and the use of antibiotics during surgery, the rate of infection has fallen to around 3%-5%. Most of these infections are caused by a type of bacteria called Staphylococcus, which is responsible for about 18% of cases. The most common spot for infection is the site of the implanted pulse generator, a small device that delivers the electrical pulses, accounting for 54% of cases. Usually, if an infection occurs, the entire stimulation system needs to be removed, except when the infection is only on the skin.
The most frequent problem overall is movement or damage to the leads, which are wires that deliver the electric current. This issue can be reduced by instructing patients to avoid bending, lifting, and twisting movements for one to two months after the procedure. This allows time for the leads to be secured in the right place by the body’s natural healing process. The technology of leads and the devices used to secure them is improving, further reducing this risk. However, it’s worth noting that stiffer types of leads, known as “paddle” leads, are twice as likely to break as percutaneous leads, which are inserted through the skin.
What Else Should I Know About Spinal Cord Stimulation?
Spinal cord stimulation (SCS) therapy is a way to manage chronic pain and involves sending electrical signals to the spinal cord. In the US, it’s mainly used for people who still have severe back pain even after surgery. In Europe, it’s typically used for problems related to poor blood flow in the arms and legs.
Clinical recommendations for SCS therapy differ based on the condition:
1. For people with chronic pains after back surgery (known as “failed back surgery syndrome” or FBSS), SCS has top-level recommendations based on research and expert opinion. Studies have found that it can reduce long-term pain, improve physical ability, and boost quality of life, among other benefits. In one research, 47% of patients with FBSS experienced significant pain relief with SCS therapy compared to 12% who had a repeat back surgery.
2. For complex regional pain syndrome (CRPS), a chronic pain condition affecting a limb, SCS is also suggested as it enhances the effect, reduces pain, and improves quality of life. Even though some scientists believe it should have a top-level recommendation, more high-quality studies are needed to support this.
3. For angina pectoris, a type of chest pain caused by reduced blood flow to the heart, SCS therapy is highly recommended. Studies have shown that it can decrease painful angina attacks and increase exercise capacity.
4. For peripheral ischemia, a condition in which blood flow to the limbs is restricted, SCS therapy is recommended as it can reduce the risk of amputation and improve the quality of life.
In all these cases, it’s important to remember that treatment options might vary. It’s good practice to speak with your health care professional about available treatment options and potential risks and benefits.
