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Introduction

Surgery is recognised as one of the most frequent causes of chronic pain in patients attending pain clinics. A survey of over 5000 patients found that the largest group, 34.2%, had pain from degenerative disease, but the second largest group, 22.5%, had developed chronic pain following surgery. 1 Usually defined as pain persisting for more than 3 months after surgery, chronic pain is a recognised complication of many common procedures ( table 1 ) and is the most serious long-term complication following inguinal hernia repair. 2 Chronic pain has a significant impact on the quality of life and daily activities of sufferers. There is also a significant cost to society in terms of subsequent healthcare costs and social support systems. 3

Table 1

Type of operation

Incidence of chronic pain (%)

No. of operations in UK 2005-2006

Total operations

-

7 125 000

Mastectomy

20-50

18 000

Caesarean section

6

139 000

Amputation

50-85

15 000

Cardiac surgery

30-55

29 000

Hernia repair

5-35

75 000

Cholecystectomy

5-50

51 000

Hip replacement

12

61 000

Thoracotomy

5-65

-

This paper will explore the pathophysiological mechanisms that contribute to chronic postsurgical pain (CPSP), and the surgical and psychological risk factors that have been identified. Surgical and pharmacological strategies to reduce the development of CPSP will also be discussed. We will also consider how psychosocial factors influence the development and maintenance of chronic pain and the relevance of this to CPSP.

Pathophysiology

The trauma and inflammation that occurs from cutting and handling tissues during surgery activates nociceptors. Nociceptive stimuli are transduced into electrical impulses that are carried to the spinal cord via primary afferent A[delta] and C fibres. Primary afferent neurones synapse with secondary afferent neurones in the dorsal horn of the spinal cord and carry impulses to higher centres via the contralateral spinothalamic and spinoreticular pathways, the two main ascending pain pathways. There are multiple further projections to the cerebral cortex and other higher centres. Central processing of impulses leads to the experience of pain. The complex pathways of nociceptive transmission are well described 5 ( figure 1 ).

Inflammatory pain occurs because sensitising, inflammatory mediators including cytokines, bradykinin and prostaglandins are released from injured and inflammatory cells at the site of tissue damage. Nociceptors...

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