» Effect of Pain Pump on Joint Cartilage
Effect of Pain Pump on Joint Cartilage

Injections into joints of anesthetics (numbing agents) and pain relieving medications have been used for a long time. They were considered "safe" based on clinical research in the mid-1980s. The use of single injection anesthetics such as lidocaine and bupivacaine gradually expanded to include modern day use of pain pumps.

A pain pump delivers a continuous, steady low-dose of anesthetic to the joint. With maximum pain control (for example after joint replacement surgery), patients are able to reduce the amount of narcotics used with each surgical episode. With less pain, they are able to get up, move, and enter into a rehab program sooner. And that is a huge benefit of pain pumps.

Locally injected medications do have some systemic effects (e.g., heart attack, depression, seizures) but these are rare. There is new evidence that delivery of anesthetics into joints may have some local toxic effects previously unrecognized.

Scientists are taking a new and fresh look at this potential problem. In this report, surgeons from the University of California - San Francisco provide an update on current findings related to toxic effects of local anesthetics on joint cartilage.

Basic science studies have shown that numbing agents (bupivacaine, lidocaine, ropivacaine) do indeed kill cartilage cells called chondrocytes. Even brief exposure can decrease cell metabolism and cause cellular disruption. The end result is chondrocyte breakdown and self-destruction. This effect of anesthetics on cartilage cells is called chondrotoxicity.

Further study showed scientists that once the thin protective layer of cartilage is destroyed, the number of dead cells increases. More time and further exposure to anesthetic agents are the two main risk factors for chondrotoxicity. And they found that the damage to chondrocytes after contact with anesthetics is permanent. The chondrocytes do not regenerate or replace themselves.

With this new information about the potential destructive effect of local anesthetics, the next area of concern was pain pumps with their more continuous exposure. It turns out that damage done by pain pumps after surgery is similar to changes seen with early osteoarthritis.

The last and final step in new research was a search for the reason why anesthetics delivered by pain pumps cause joint cartilage destruction. Current theories include chemical effects, pH (acid-base balance), and preservatives in the solution used to deliver the agents. There may also be an effect of anesthetics on potassium and calcium that damages the cartilage cell DNA. There's enough destruction to turn on cell apoptosis (the cell's suicide cycle).

In summary, the use of postoperative pain pumps is getting a second look. Whereas the joint can quickly clear the effects of a single (local) injection of anesthetics, there isn't a similar ability with continuous exposure. The use of anesthetics delivered by pain pump may be something to be reconsidered if not discouraged or even discontinued.

The authors who reviewed this new information suggest further study is needed in this area. There is a need to verify these findings and to uncover any long-term effects of pain pumps on joints.

Reference: Samantha L. Piper, MD, et al. Effects of Local Anesthetics on Articular Cartilage. In The American Journal of Sports Medicine. October 2011. Vol. 39. No. 10. Pp. 2245-2453.