Are knee replacement surgery and Alzheimer’s disease linked? Our knowledge of brain injury has exploded in the past 10 years, led in large part by the recognition that sports like football and boxing can permanently injure the brain. As a result, it’s not surprising that we’re beginning to study whether some types of general anesthesia can cause brain injury. A recent study seems to demonstrate that even the lower risk spinal anesthesia that’s commonly performed for knee replacement may also result in brain injury and cognitive decline in a surprisingly large percentage of patients.
First, as I’ve blogged before, certain types of general anesthesia (where the patient is put asleep) may cause brain injury. However, spinal anesthesia is less invasive because the doctor avoids general anesthesia by numbing the spinal cord and nerves through the back. This type of anesthesia should avoid problems in the brain. Having said that, I’ve already blogged that knee replacement is such a big and invasive surgery that it’s associated with dramatic increases in heart attacks. So will using less invasive anesthesia in a big surgery spare the brain? Based on this study the answer seems to be no.
The new study looked at 125 patients who were older than 65 who were undergoing knee replacement and who had spinal anesthesia plus twilight sedation. The research team used very sophisticated monitoring of the blood flow and oxygen going to various parts of the brain. They measured their memory and cognition before and three months after surgery. A surprising 40% of patients had some sort of memory or thinking problem after the surgery! Interestingly, those with memory declines had asymmetrical blood oxygen changes during the surgery (one part of the brain got less oxygen). The authors thought that this relationship could have something to do with the memory centers of the brain getting less oxygen during surgery. Another study has shown a connection between an Alzheimer’s disease bio-marker and those patients who get the most cognitive decline after big surgeries.
So what caused these very concerning findings in otherwise healthy elderly patients? This one hits close to home as my father had a severe cognitive decline after hip surgery. In reviewing the medical literature on the topic, it looks like patients who are predisposed to Alzheimer’s disease are the ones who get the most cognitive decline after surgery. This fits with the stats above (40%), as the lifetime prevalence of this brain disease is about 1 in 3 people.
Could certain medications be causing this effect? From looking at the drugs they used for the spinal anesthesia, one stands out-Marcaine or bupivicaine. This is a known neurotoxic anesthetic that’s still in common use in pain management, orthopedics, and surgical anesthesia because it provides numbing for a long time. The American Academy of Orthopedic Surgeons has warned it’s members not to use Mracaine to numb joints as it’s also very toxic to cartilage. Could this anesthetic be the culprit or was it some other aspect of the spinal or twilight anesthesia, the post-operative pain medications, or perhaps even the surgery itself? This study’s connection between changes in surgical blood flow and post-operative memory make the case that the injury happened during the surgery.
The upshot? Knee replacement surgery is a very big procedure with big side effects and complications. The fact that 4 in 10 patients had issues with their brain functioning 3 months after surgery is very concerning.