Pain pumps created a totally new and untested way of using well known local anesthetics. Because local anesthetics historically were only administered by a single shot injection they were limited in how long they could provide pain relief. Even the longest acting local anesthetics could not provide pain relief for more than 3-4 hours after injection. The pain pump created a mechanism by which the local anesthetic could be continuously infused into the body thereby extending the period of pain relief from hours to days. The manufacturers touted the advantages of controlling pain in this manner rather than oral pain medication, including better pain control, no risk of addiction to narcotics, fewer return visits to hospital for pain issues.
The pain pump manufacturers performed no safety studies to determine if it was safe to continuously infuse a local anesthetic into different parts of the human body for 24 hours or more. The manufacturers of the local anesthetics lacked any information on this use as well because they were not aware until much later that this new manner of delivering the drug to the patient had been developed. There was nothing in the warnings or labeling of the local anesthetic to alert patients or physicians that it might not be well suited to continuous infusion.
It is now known that when local anesthetics are continuously infused into joints for more than 48 hours the articular cartilage is killed. The destruction is permanent, and dead cartilage sloughs off over time resulting in increasing pain and loss of range of motion for the patient. In most patients there is no cartilage left within a year to 18 months of the initial exposure to the local anesthetic. The mechanism of injury is simple. Cartilage is made up of a matrix of cells shaped like a honeycomb. In the center of honeycomb compartment there is a cell called a chondrocyte. The chondrocyte is the life center of the cartilage; it nourishes and maintains the matrix.