The intervertebral disc is an important structure, which helps provide flexibility to our spine. It is comprised of a strong outer layer, the annulus, which is rather like a radial tire, and an inner gel, the nucleus, which acts as a sort of shock absorber or cushion between the bones of the spine. With injury or age, these discs can become damaged, causing low back pain. One of the reasons we lose height as we age is that the intervertebral discs lose their water and with that, their height.
The idea behind a pump is that the spinal cord is involved in sorting out all of the information, which we get from the outside world, particularly with regards to such sensations as hot or cold, pressure or cutting. The function of this sorting process is to present important information to the brain and not to present information that is not important, such as the fact that we have pressure on our feet while we walk.
As a part of processing all of this information, the spinal cord has receptors on it for multiple medications, such as narcotics. By selectively applying small amounts of narcotics (or other medications) to the spinal cord, it is possible to get the desired effect, such as pain relief, without the undesired side effects, such as nausea, vomiting, or sedation.
To apply narcotics in this way, we generally use an implantable pump, which has a reservoir to store the medication and a pump to regulate how fast it gets released from the reservoir. The pump is usually programmable, so that we can adjust the rate of the pump. The pump is attached to tubing, which releases the medication into the cerebral spinal fluid, the fluid that surrounds, buffers and nourishes the spinal cord. Once in the CSF, the medication binds to the receptors on the spinal cord.
Prior to placing a pump, you are given a trial of medications. These trials can be inpatient or at home, done overnight or last several days. During the trial, we will usually give you just a narcotic, although we may occasionally add other medications.
If you have good relief of your pain with minimal side effects, then we can proceed with the permanent placement of a pump. This placement is a surgical procedure and involves making a pocket under the skin, usually in your abdomen, for the pump and then making a small incision in your back for the placement and tunneling of the subarachnoid catheter. You can expect to be sore for up to two weeks, just as you would after any surgery. You will be provided pain medication and antibiotics.
Pumps do require some maintenance. The reservoir does need to be refilled; we like to do so about every three months, but sometimes, it must be refilled sooner. Pumps can have problems. Although we follow a technique to minimize the incidence of catheter fracture, kinking, or dislodgement, all of these things can occur. Accordingly, it may be necessary to repair the pump. Since we are refilling the pump, it is possible for an infection to occur, whether because of a refill or simply because the pump is there and presents a site for infection. Finally, the battery for the pump, like the battery for a stimulator, will not last forever and the device will need to be changed. Usually, the battery lasts about 5 years.