Orthopedic surgery researchers at Washington University School of Medicine in St. Louis have identified yet another reason not to smoke. Studying rotator cuff injury in rats, the research team found exposure to nicotine delays tendon-to-bone healing, suggesting this could cause failure of rotator cuff repair following surgery in human patients.
Smoking is implicated in a host of physical problems, from cardiovascular disease to lung disorders. Many of us probably don’t think about smoking’s effects on orthopedic conditions, but several studies have shown that nicotine interferes with healing of bone fractures and also inhibits bone fusion processes — many spine surgeons, for example, won’t do certain operations on people who smoke because of the risk of failure. But little is known about the effects of cigarettes on tendon and ligament healing.
There also are some gaps in medical knowledge about the prevalence of rotator cuff injuries. The rotator cuff is a group of four muscles and their tendons in the shoulder that provide rotation, elevate the arm and stabilize the shoulder joint. Rotator cuff tears involve one or more of the tendons. The injuries are more common as people age and more common in the dominant arm. The true incidence of the injuries is hard to determine because between 5 percent and 40 percent of people who may have a torn rotator cuff have no accompanying shoulder pain.
What surgeons do know is that rotator cuff repairs can fail in the days and weeks after surgery. Some studies have reported short- to intermediate-term recurrence rates from 30 percent to 90 percent, depending on the size of the tear, chronic nature of the injury and the age of the patient, among other factors.
During the first six weeks after surgery, tissue may be vulnerable to re-injury. Those early weeks are a time when there’s a lot of tissue healing and remodeling occurring.
This study, published in the Journal of Bone and Joint Surgery in 2006, was the first to evaluate the effects of nicotine on rotator cuff repair, found that when rats were exposed to nicotine following rotator cuff repair, inflammation persisted for a longer time in the shoulder joint. That’s detrimental to healing. The researchers also noted that there was less cellular proliferation in the rats’ surgically repaired shoulders and decreased collagen production, leading to inferior healing.
When you have an injury and a repair, new cells come in and start to facilitate healing. When the new cells arrive, they make proteins such as collagen to form the junction between tendon and bone. In the rats exposed to nicotine, there was lower cellular proliferation.
The rats also made less type-I collagen and had different biomechanical properties in their shoulders following rotator cuff repair. Measuring properties called maximum stress and maximum force, the researchers found that shoulder joints in the nicotine-exposed rats were weaker.
Those changes were most apparent at earlier time points, and shoulder strength tended to equalize between the two groups about 8 weeks after surgery. But certainly, the tissue was weaker early on and more vulnerable to re-injury.
The study also may underestimate the harmful effects of smoking because rats tend to be better healers than humans and because they were exposed to nicotine for only a few weeks following surgery, whereas people may smoke for many years before surgery, as well as continue smoking following rotator cuff repair.
Based on this study there is now enough evidence to state that nicotine has a negative impact on healing in tendons as well as in bone.
Nicotine and cigarette smoking inhibit the formation of new blood vessels, and basically, all healing and all repair processes are aided by the formation of new blood vessels that bring in new cells. That process is assisted by increases in blood supply that may not happen as efficiently in smokers.
Galatz LM, Silva MJ, Rothermich SY, Zaegel MA, Havlioglu N, Thomopoulos S. Nicotine delays tendon-to-bone healing in a rat shoulder model. The Journal of Bone & Joint Surgery 2006 Sept;88:2027-2034.
Thanks,
JTM, MD