**4. Risk factors**

Some circumstances allow the establishment of CPOP, an important risk factor in the type of surgery, although there are some other factors to be included in these perpetuation of conditions such as acute severe postsurgical pain, biopsychosocial affection, demographics, and lack of control on the intensity of pain in the near postoperative stage. Actual data informs us about the gross number of surgeries made annually throughout the world. This gives us an idea of the estimate for the general frequency of 10% for CPOP, meaning that around 23 million patients per year are suffering with this painful situation [3].

#### **4.1 Abdominal surgery**

In 2014, a report integrated liver donation patients that had a frequency of CPOP of 31% in 6th month and 27% in 12th month and concluded that several risk factors were involved, detecting female gender, young patients, and psychological distress associated with pain states as potential elements for the development of CPOP. In 2015, a retrospective study documented a CPOP frequency of 17% following colorectal surgery and concluded that potential risk for CPOP were redo surgery for anastomotic leakage, inflammatory bowel disease, and acute severe pain. Similarly, in 2016, an analysis found that women who encountered an abdominally based autologous breast reconstruction surgery found a frequency of CPOP of 23–24% in a 6–12 month follow-up; they concluded that the leading cause for the development of CPOP at 6 months is poor control of severe acute pain in the first 24-0 hour postsurgery [3].

#### **4.2 Breast surgery**

Modern analysis has determined a frequency of CPOP of 30–60% with an existence of moderate to severe pain of 14%. It is well documented that preoperative distress may be considered as a key element for CPOP progression, and another nonsignificant risk factors are <65 years of age, breast reconstructive intervention, axillary lymphadenectomy, bad control of acute severe pain in the postsurgical period, inferior presurgical diastolic blood pressure, and signs of somatosensorial damage associated with pain at 1 week [3].

#### **4.3 Cardiac surgery**

Actual reports in patients after sternotomy document a frequency of CPOP at 3 months to be 43%, diminishing substantially over time reporting 11% at 12 months and 3.8% at 5 years. In 2016, several authors concluded that a positive neuropathic sign like hyperalgesia around the sternotomy wound on day 4 of surgery was not linked with CPOP at month 4th and 6th. However, they concluded that the biopsychosocial sphere, age, gender, obesity, complex surgeries, history of previous procedures, osteoarthritis, and poor management of acute severe pain in the postsurgical period may be linked with and increased risk for development of CPOP [3].

#### **4.4 Hysterectomy**

A couple of studies discovered a global frequency of CPOP of 26% at 6 months after laparoscopic or vaginal hysterectomy and a rate of moderate-to-severe CPOP of 10.2 and 9.0%, correspondingly, at 3 and 12 months after these surgical approaches. In a report developed in 2015, they found that procedures performed with this methodology had a strong relationship with CPOP if they had a story of tobacco usage, acute severe pain in the first hours of the postsurgical period, history of infection related to the procedure, and anxiety associated with the surgery [3].

#### **4.5 Inguinal hernia surgery**

A study conducted in 2015 associated with inguinal hernia surgery after 1 year of the surgical procedure reported a frequency of CPOP of 43% in patients aged

18–40 years old, 29% in the 40–60 age interval, and barely 19% for patients with 60 years and above. In patients where the inguinal repair was made with mesh, there is a strong link with CPOP development with a frequency of 9.3% at 3 months and intensity of CPOP was related with robust hemodynamic preoperative changes [3].

#### **4.6 Total knee arthroplasty**

The latest data on osteoarthritis patients document a CPOP frequency of 58%. At 2014, an analysis discovered a strong relationship with severe pain intensity throughout a knee active flexion an extension exercise preceding a total knee arthroplasty (TKA) with moderate to severe pain at 6 months. A meta-analysis conducted by Lewis et al. followed patients during 3 months to 7 years undergoing TKA; they discovered that there was a strong linkage with CPOP and alterations in the biopsychosocial sphere, presurgical knee pain, other chronic pain states associated with current pathology, and catastrophizing [3].

#### **4.7 Thoracic surgery**

Actual reports related to this type of approaches document a frequency of 57% for CPOP at 3 months, 39–56% at 6 months, and 50% at 1 year. Regarding other thoracic approaches that are minimally invasive like the ones that are video-assisted have a lower frequency of CPOP that extend 11–30% [3].

#### **4.8 Thyroidectomy**

Evidence on a report of 2016 sustains a frequency of 37% for CPOP at 3 months preceding minimally invasive video-assisted thyroidectomy. Different studies document a frequency of neuropathic pain preceding thyroidectomy of 12–9% at 3rd and 6th month, respectively. There is a strong linkage with presurgical anxiety and doubt respecting the procedure with the development of CPOP [3].
