Introduction

There are innumerable published studies describing the deleterious effects of smoking on the musculoskeletal system. The authors of a recent review in the Journal of the American Academy of Orthopedic Surgeons have summarized the main conclusions from the more important studies.

Different periods of time for patients to quit smoking before or after undergoing surgery have been suggested; however, there is no established standard for this. Proposed time durations vary from 1 day to 3 weeks pre-operatively, and from 5 days to 4 weeks post-operatively. Some authors encourage surgeons not to withhold elective surgery from a smoker when it is needed. Nevertheless, the weight of evidence suggests that a smoker should stop before and after surgery.

There was a fair degree of concordance among the studies examined. At least 44 articles showed smoking to be deleterious to the musculoskeletal system, while 14 showed no such association, and several showed weak associations.

Smoking has been determined to adversely affect bone mineral density, lumbar disk health, the relative risk of sustaining wrist and hip fractures, low back pain, and the dynamics of bone and wound healing.

Physiology

The effects of smoking can be divided into 2 phases: a volatile and particulate phase. The volatile phase, accounting for 95% of the cigarette smoke, provides nearly 500 different gases, including nitrogen, carbon monoxide, carbon dioxide, nor-nicotine, anatabine, and anabasine, and contains the majority of the carcinogens

Nicotine increases platelet aggregation, decreases microvascular prostacyclin levels, and inhibits the function of fibroblasts, erythrocytes, and macrophages. Carbon monoxide binds to hemoglobin many times more easily than oxygen, thus displacing oxygen from the molecule and lowering oxygen tension in tissues.

Smoking is highly addictive. This knowledge mandates that physicians offer help to patients to quit. In the USA alone, there are currently more than 50 million smokers, and smoking is now the leading avoidable cause of morbidity and mortality in the USA.

Osteoporosis

Post-menopausal women smokers have more spine fractures than do age-matched non-smoking women. In a study of 115,000 nurses, a small increase (1.3%) in the risk of hip fractures occurred in smokers, and this increased to 1.6% if the smoker had smoked > 25 cigarettes/day. In a separate study of 500 women, these increases were 1.6% and 2.8%, respectively. A five-fold increase in risk occurred in smokers who also had a low intake of the antioxidant vitamins C and E.

The rate of bone loss among non-smoking women taking estrogen is less than in those not taking estrogen; however the advantage conferred by estrogen is significantly lessened (p<0.01) in women who smoke.

Three risk factors for hip fracture (lean body mass, absence of physical exercise, and smoking) for women also apply as risk factors in elderly men. In one study of 35,000 men and women, the relative risk for hip fracture in women smokers was five-fold, and in men 1.9 times, that in non-smokers.

Bone volume and bone thickness in iliac crest biopsy samples were compared in smokers and non-smokers. The trabecular volume and thickness, and the mean wall thickness, were significantly less in smokers (p<0.05 and p<0.001, respectively).

Low Back Pain

In the Western world, 60-80% of the population will have an episode of incapacitating back pain at some point during their lives. Fifteen epidemiologic studies show an association between smoking and low back pain. Another study showed low back pain sufferers were likely to be smokers (p<0.001), especially if smoking was accompanied by a chronic cough. The association may not be direct - those who smoke may be more likely to exclude an exercise program in their lives.

Among 29,424 twins an association was found between smoking and low back pain, with an odds ratio of 2 for smokers. For those complaining of long-standing (>30 days) back pain, the odds ratio went to 3. And stopping smoking did not reverse these finding. Moreover, similar results were obtained in 264 pairs of monozygotic twins who were discordant for smoking.

Disk Disease

At least three authors believe that smoking adversely affects the intervertebral disks. In one study, smoking in the year prior to a patient's visit to a physician increased the risk of having a prolapsed disk with an odds ratio of 1.7.

Operative failures occurred following disk surgery more frequently in people who had smoked longer than 15 years.

In one study that showed no difference in low back pain among identical twins with discordant smoking histories, but there was a difference in the MRI signs of degeneration of lumbar disks; this amounted to an 18% increased score among smokers (p=0.015), with the involvement throughout the entire lumbar spine.

In another study, the relative risks of lumbar and cervical disk disease among smokers were 2.2 and 2.9, respectively.

Local hypoperfusion of the lumbar spine and alterations in disk metabolism may occur due to the increased risk of nicotine-induced microvascular occlusive disease.

Wound Healing

As far back as 1977, impairment of wound healing in the soft tissues of the hand was shown in smokers. Severe digital vasoconstriction can occur after smoking a single cigarette, and subcutaneous oxygen tension is decreased in the forearm after smoking.

Mature collagen is the main determinant of the tensile strength in a healing wound. Its production is dependent on sufficient perfusion and oxygenation. Both extracellular matrix proliferation and epithelial regeneration are decreased by nicotine and carbon monoxide.

In a group of patients who had a post-operative infection after elective spinal fusion and instrumentation, 90% were heavy smokers.

Fracture Healing

Bone healing is adversely influenced by nicotine, due to a combination of likely mechanisms (vasoconstriction, platelet-activation, and impaired osteoblast function). It has been shown that a non-smoker can build 1 cm of bone in 2 months, but a smoker requires 3 months to build the same amount.

In a small study of outcomes in ankle fusion, there was a 16-times greater failure of fusion among smokers. In another study, smokers after attempted lumbar arthrodesis had a 40% pseudarthrosis rate, compared with an 8% rate in non-smokers.

Practical Implications

While there are no conclusive guidelines about the duration of peri-operative cessation of smoking, both the patient and the physician should thoroughly understand the effects of smoking on the expected surgical outcome and/or on the causation of certain diseases. The evidence weighs heavily in support of stopping smoking before and after surgery, and - even better - permanently. Morbidity and mortality are both diminished by not smoking, as more than 500,000 deaths per year in the USA alone can be attributed to smoking.