Dr Adam KM Woo

The concept of acute pain is intuitive and a requirement for our survival – for example, we all pull away from a flame to protect ourselves. Chronic pain, however, is more complex. In the past few decades there has been considerable interest in the medical community, and in the media of late, regarding such questions as why people with identical injuries end up with significantly different outcomes and have persisting pain despite complete tissue healing.  While most improve and return to their normal lives, some end up with debilitating chronic pain and disabilities. In this article I look at two areas involved in medicolegal practice with reference to current evidence available:  road traffic accidents (RTAs) and chronic post-surgical pain (CPSP).

Chronic Pain after Road Traffic Accidents

Given its high prevalence and perhaps controversy, whiplash associated disorder (WAD) is probably the most studied pain-related road traffic accident outcome in the literature. Its association with medicolegal practice has also garnered interest, with various publications specifically referencing legal implications with regards to outcomes.

Prognostic indicators for WAD have been widely assessed in various journals to elucidate further factors which might predispose to pain chronicity and negative outcomes. Some of these factors are:  severity of post-injury pain and disability, post-injury anxiety, catastrophizing (expecting the worst), ‘compensation and legal factors’ and early healthcare use after the index event.  These factors are consistently associated in the literature with chronic pain and disability after a WAD diagnosis. However, post-injury radiographic (eg MRI) findings, motor dysfunctions (eg weakness), or factors related to the collision are not associated with chronic pain and disabilities.

Some of this may seem counterintuitive: after all, from a biomedical/tissue/organic perspective, radiographic changes (implying significant tissue damage visible on scans) and collision factors would correlate strongly to severity of injuries sustained. Yet, crash-related factors such as collision direction, use and type of head restraints, speed of impact, awareness of collision, position in seat and whether the head was turned at the time of the accident have not been shown to be predictive. The implication is that the ‘unseen’ factors related to a patient’s response to trauma are of vital consideration when applying prognostic indicators to medicolegal assessments.

In many studies involving WAD, the issue of litigation is perhaps one of the main confounders (ie a factor which influences both the subjects and outcomes studied). In a rather unique study pertinent to medicolegal practice, nearly 1000 patients attending the emergency department after an RTA were reviewed 6 weeks later. They were divided into those who pursued litigation and those who did not. Litigants were found to be less educated and had more severe neck and generalised pain at presentation and at 6 weeks. In those not engaged in litigation, persistent pain after the RTA was very common (>40%) including not just in the neck but widespread body pain. Socioeconomic disadvantage predicted worse pain outcomes in litigants but not nonlitigants, and individual pain and psychological symptoms were less predictive of pain outcomes among those engaged in litigation. The conclusion is that involvement in litigation alters presentation and prognosis and requires further studies.

What about the development of chronic widespread pain (CWP) after an RTA? Is the ‘spreading’ of pain to the whole body after WAD backed up by evidence?

Many studies support the association of development of CWP to a precipitating and physically traumatic event such as RTAs or indeed any accidents causing injury. “At risk” individuals (those with inherent genetic, environmental and psychological negative factors) may be predisposed to development of CWP following a trigger event such as RTAs. Patients with new-onset CWP are said to be a third more likely to associate that with a prior, recent, and traumatic event compared to those who do not report such events. Involvement in an RTA, specifically, appears to confer a modest increase in the association of symptom onset compared to other ‘traumatic’ events.

It is important to remember that associations in the medical literature are simply that, and not proof of causation. (As an analogy, coffee or alcohol has had its fair share of ‘good or bad for you’ press in the mainstream over the years due to the nature of association studies).

In what seems to offer further support for development of CWP after WAD, hypersensitivity to pain in the shins (ie an anatomical location remote to the injured neck) is found to be a poor prognostic sign in patients after an RTA. The implication here is that whole-body sensitisation occurs after the RTA in question, which might then account for the development of CWP.

What about other RTAs which are not WAD-related?

In a similar vein, pain catastrophizing, pain-related work disability, self-perceived physical and mental well-being, general psychological distress, and trauma-related distress are all found to play significant roles in predicting long-term pain after non-catastrophic traffic-related injuries. In one study, the injured parties included not just drivers of cars commonly seen in medicolegal practice, but also passengers, motorbike riders, pillion passengers, pedestrians and cyclists. The important point that arose from the study was again the absence of ‘tissue/physical’ matters such as collision factors, but the presence of psychosocial ones. In light of this, the familiar phrase of ‘biopsychosocial’ factors of chronic pain in RTA cases  should perhaps be retitled ‘psychosociobiological’ in order or priority.

How should a medicolegal experts assess such claimants, then, given the evidence in the literature reviewed here?

One author suggests that prognosis after whiplash should focus on factors such as self-reported pain and disabilities post injury, PTSD symptoms and speicifcally pain thresholds in the shins (as discussed above). This would assess a Claimant’s physiological and psychological stress response to the RTA as a key medicolegal marker in predicting prognosis following whiplash injury.  This cluster of symptoms and signs has been termed ‘complex whiplash.’  At the same time, identification of restrictions in range of movement in the neck and presence of tender areas do not predict outcomes, and they do not necessarily signal poor outcomes.

The overarching concept of pain and RTAs is that psychosocial factors are important prognostic indicators and organic factors less so. Within that general conclusion, every case should of course be evaluated on its own merits, since specific injuries may, from an orthopaedic view, alter that individual case significantly.  The careful study of the pre-index history of the claimant and their vulnerabilities, and subsequent trajectory of pain symptoms and disabilities along the range of factors mentioned, can offer guidance on the potential outcomes.

Chronic post surgical pain (CPSP)

What about the ‘traumatic’ event of surgery? At an estimated 10% incidence worldwide, chronic pain after all surgeries is of particular interest to the medical and pain community. 2017 was declared the ‘Global Year Against Pain after Surgery’ by the International Association for the Study of Pain given its long-term costs and suffering worldwide.

It is important to have knowledge of factors which predispose to chronicity, since those which are modifiable could reduce its incidence. In this area much more robust and controlled (non-medicolegal) studies are available compared to the area RTAs, reflecting intense interest in what is seen as a ‘medically induced’ condition.  Some interesting comparisons can be made here, although the nature of the injuries is clearly different.

In contrast to RTAs, ‘tissue’ or organic factors are relevant in CPSP. For example, some types of surgery — ie amputations, breast cancer surgery, thoracotomy (open chest surgery) and inguinal hernia repairs — are notorious for causing chronic pain, implying that these sites are somewhat more invasive in nature with more potential of nerve damage. In addition, longer surgery, open versus laparoscopic (keyhole) surgery, postoperative infection and more extensive tissue dissection all predispose to chronic pain: the more extensive the tissue ‘damage’, the higher chance of CPSP.

In the perioperative period, more severe pain at the site of operation before the procedure, and uncontrolled pain postoperatively are negative factors, the latter being especially important. Patients who do not receive adequate pain control after waking up from operations and suffer uncontrolled pain for lengthy periods after surgery fare especially badly in the long term.

Interestingly, psychological variables such as anxiety, depression, catastrophising, fear of movement postoperatively and low self-efficacy are associated with worse chronic pain outcomes after surgery. This bears striking similarities with the RTA factors discussed above, and reinforce the importance of psychosocial factors in assessment of prognoses in both areas. Of note also are that high dose opioids consumption and generalised pain before surgery are predisposing factors; these are arguably both psychosocial and organic in nature.

It is also observed that being young and female predispose to CPSP, pointing towards genetic factors. There is considerable interest in the ‘epigenetics’ of CPSP, the area of study where genes are noted to be switched/modified in expression without alteration of basic structure. For example, diet, drugs, and psychological stressors might ‘switch on’ some function in genes to induce chronic inflammation or biological changes in the period after surgery, leading to chronic pain. It is also posited that permanent epigenetic changes can occur if overwhelming stresses occur in childhood, which then lead to vulnerability to chronic widespread pain and other chronic pain problems in adulthood. Epigenetics might provide a ‘bridge’ to explain the link between psychological stresses and chronic pain, via altered genetic changes as yet to be fully elucidated. It would be logical to extrapolate some of these findings to other traumatic events leading to chronic pain such as RTAs.

Conclusion

In both groups discussed adverse psychosocial factors, leading perhaps to negative responses by vulnerable patients might be important, if not the most significant factor in predicting chronic pain and disabilities after tissue trauma. A careful appraisal of a claimant’s records before and after the index event may reveal important elements which alter prognosis and change the dynamics between defendant and claimant. In both the medical and medicolegal world, understanding these factors and modifying those which can be, should be pursued in order to provide evidence-based treatments and timely rehabilitation of such claimants.

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