It may also restrict small blood vessel diameter leading to increased scar formation. There is an association between cigarette smoking, back pain and chronic pain syndromes of all types. In a report of 426 spinal surgery patients in Denmark, smoking was shown to have a negative effect on fusion and overall patient satisfaction, but no measurable influence on the functional outcome. There is a validation of the hypothetical assumption that postoperative smoking cessation helps to reverse the impact of cigarette smoking on outcome after spinal fusion. If patients cease cigarette smoking in the immediate post operative period, there is a positive impact on success. Regular smoking in adolescence was associated with low back pain in young adults. Pack-years of smoking showed an exposure-response relationship among girls. A recent study suggested that cigarette smoking adversely affects serum hydrocodone levels. Prescribing physicians should be aware that in some cigarette smokers, serum hydrocodone levels might not be detectable. In a study from Denmark reviewing many reports in the literature, it was concluded that smoking should be considered a weak risk indicator and not a cause of low back pain. In a multitude of epidemiologic studies, an association between smoking and low back pain has been reported, but variations in approach and study results make this literature difficult to reconcile. In a massive study of 3482 patients undergoing lumbar spine surgery from the National Spine Network, comorbidities of (1) smoking, (2) compensation, (3) self reported poor overall health and (4) pre-existing psychological factors were predictive in a high risk of failure. Followup was carried out at 3 months and one year after surgery. Pre-operative depressive disorders tended not to do well. Smoking has been shown to increase the incidence of post operative infection as well as decrease fusion rates. One study showed 90% of post operative infections occurred in smokers, as well as myonecrosis (muscle destruction) around the wound. Pathology Before the advent of CT scanning, the pathology in failed back syndrome was difficult to understand. Computerized tomography in conjunction with metrizamide myelography in the late 1960s and 1970s allowed direct observation of the mechanisms involved in post operative failures. Six distinct pathologic conditions were identified: Recurrent or persistent disc herniation Spinal stenosis Post operative infection Epidural post-operative fibrosis Adhesive arachnoiditis Nerve Injury Recurrent or persistent disc herniation Removal of a disc at one level can lead to disc herniation at a different level