**2. Incidence**

The occurrence of CPOP varies substantially among the literature and depends on the kind of procedure. It has been documented 20–50% for mastectomy, around 50–80% for amputation, and 5–65% for thoracotomy. There are reports informing that 10 to 50% of the patients undergoing common procedures had CPOP, and 2 to 10% of patients complained of severe pain [3].

In 2015, there was a study implemented in 21 European hospitals, and the significant outcomes were a 6-month postsurgical extension. There were reports of modest severe CPOP in 24% of patients and exceedingly severe CPOP in 16% of patients. At the end of a 12-month follow-up, the incidence of CPOP was reduced 12 to 24% depending on the duration and the intensity of pain in the first 24 hours. With this information they concluded that the pain duration in the first 24 hours is considered as a risk factor for the progress of CPOP [3].

CPOP is a well-defined pathology that affects patients who were exposed to a certain type of surgery (affection of 5 to 75% of surgical patients). This type of pain is very important to consider because it affects importantly the quality of life and results in patient disability and mandate additional health and social expenses. When the evidence points out that the cause of the pain is neuropathic the condition *Chronic Postoperative Pain DOI: http://dx.doi.org/10.5772/intechopen.111878*

exacerbates, with an occurrence of CPOP fluctuating from 6 to 68% of the cases, differing on distinct surgery scenarios. The first publication that identified prior surgery as a cause of chronic pain came from a pain clinic in Northern England in 1998 where Chrombie et al. found that almost one in four patients attributed their pain to an operation. Since that time, it has been shown that depending on the type of surgery, the incidence of CPOP is anywhere between 5 and 85%. The frequency over the last years has not changed over time, the exact mechanisms of CPOP remain uncertain, and the treatment continues to be a challenge [3, 6, 7].
