Summary

Acute low back pain is a common musculoskeletal disorder and the most prevalent work-related illness. This article discusses the common causes of low back pain, as well as potential red flags; the role of a focused history and physical examination in differentiating between non-specific and more sinister causes of low back pain; the indications for the judicious use of special investigations; and the prescription of evidence-based treatments to improve pain control and functional limitations. 

摘要

急性下背痛是一種常見的肌肉骨骼問題，也是最普遍的與工作有關的疾病。本文討論了下背痛的成因和潛在的危險信號；通用針對性的問診和身體檢查鑒別非特異性和嚴重的病因；明智而審慎地使用特別檢查，以及處方有實証基礎的藥物以減少痛楚和改善功能。

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Introduction

Acute low back pain (LBP) is a common musculoskeletal disorder and is seen daily by most primary care doctors. Indeed, LBP is the most prevalent work-related illness with sick leave taken in Hong Kong.¹ Consequently, LBP is an important cause of disability that results in the utilisation of health care resources and presents a socioeconomic burden to society.²  

Definition

Acute LBP is defined as LBP that lasts for less than four weeks. Chronic LBP lasts for more than three months and sub-acute LBP lasts somewhere in between. Nearly 80% of acute LBP cases are self-limiting, with patients not needing to seek medical treatment; these cases usually improve rapidly in the first month.⁴ However, 20% of people with an initial episode of acute LBP will have persistent LBP one year later, and 20% will have LBP which limits their usual activities.⁵ 

Clinical evaluation 

A practical approach to acute LBP involves taking a focused history and physical examination to determine the likelihood of specific underlying conditions and to measure the presence and level of neurological involvement. This will determine whether further investigations (such as imaging) and/or referral to other specialties are indicated. After assessment, patients may be classified into one of four broad groups (Table 1): non-specific LBP (most common), LBP associated with radiculopathy, LBP associated with a specific spinal cause, and back pain originating from sources outside the spine.⁷

Table 1:  Types of low back pain (LBP)

History

History-taking should start with characteristics of the low back pain (including onset, duration, severity, aggravating and relieving factors). In addition, if there is a history of trauma, details must be taken regarding the mechanism of injury, status of the patient immediately after injury, and whether the injury occurred whilst on work duty. Assessing for other symptoms or risk factors (Table 2) may help identify a specific aetiology of the back pain. It is also important to determine the effect of the LBP on daily (including work) functioning.

Table 2:  Focused history for the evaluation of low back pain

Yellow flags are psychosocial factors which, when present, predict poor recovery and a higher risk of progression from acute to chronic LBP. These factors include: history of depression and anxiety, passive coping techniques, current job dissatisfaction, past or ongoing disability claims, disputed compensation claims, and somatisation.⁸ While there is currently no standard practice for assessing and addressing these factors in the primary care consultation, the patient should be asked about any particular concerns, and what they expect the doctor can do for them. 

Physical Examination 

The physical examination should pay particular attention to the L4/5 and L5/S1 levels because 90% of symptomatic lumbar disc herniations occur in these regions.⁷ It is therefore necessary to test the quadriceps strength and knee jerk (L4), big toe and ankle dorsiflexion (L5), and foot plantarflexion and ankle jerk (S1). A positive straight leg raising test (Figure 1) reproduces sciatica between 30-70 degrees of leg elevation on the affected side. This manoeuvre has high sensitivity (91%) but only moderate specificity (26%) for diagnosing herniated lumbar disc. In contrast, the crossed straight leg raise test (reproduction of sciatica with leg elevation on the normal side) is more specific (88%) but much less sensitive (29%).⁷

Investigations

Imaging is rarely indicated in non-specific LBP. A recent guideline jointly issued by the American College of Physicians and the American Pain Society as well as guideline from NICE states that routine X-ray of the lumbosacral spine for LBP does not improve patient outcome compared with selective imaging.⁷ Furthermore, radiation from one X-ray of the lumbosacral spine (AP, lateral) is equivalent to the radiation from chest X-rays daily for more than a year. While X-rays are not routinely indicated, cases where they may be considered include lack of improvement after one month and high suspicion of a specific spinal cause.

Routine advanced imaging (eg. CT, MRI) of the spine should be avoided, as they are not associated with improved patient outcomes but exposing the patient to radiation (in the case of CT) and are costly. In addition, they may identify radiological abnormalities that do not correlate with symptoms and likely to lead to additional, and possibly unnecessary, and expensive further investigations or interventions. Cases in which advanced imaging would be indicated include severe or progressive neurological deficits, or a suspected underlying spinal condition, such as infection, cauda equina syndrome, or cancer with cord compression. In these cases, MRI is preferred to CT. Advanced imaging is only useful for lumbar disc herniation if there are neurological deficits or when considering surgery or epidural steroid injection. Otherwise, MRI is not routinely indicated even for suspected herniated lumbar disc. 

Treatment

The treatment discussed here will apply to cases of non-specific acute low back pain. 

(A)Recommended non-drug treatment

Non-drug treatment can be advised in all patients with acute LBP. The following have been shown to be useful:

1. Education and counselling: educating the patient on the likely cause of his LBP and expected progress, tips on how to avoid future episodes of LBP, and counselling with regards to any concerns the patient may have;⁷
2. Superficial heat: there is good evidence to show that moderate benefit can be obtained from superficial heat, whether it be hot packs, hot water bottles, or towels, etc. It does not seem to matter whether the heat is wet or dry;⁸
3. Advice to stay active: there is recent good evidence that advice to stay active (ie. To avoid bed rest and to continue with usual activities as tolerated) results in less pain and a better functional recovery compared with bed rest;⁹
4. Physiotherapy: a small Hong Kong study has found that early physiotherapy (within 24 hours of the acute episode) is effective in reducing pain and increasing satisfaction in patients with acute LBP. (In this instance, physiotherapy included education, reassurance, mobility and walking training). It should be noted that these are all factors we can implement even without the help of our allied health colleagues by noting points 1 and 3 above;¹⁰ and
5. Spinal manipulation: when performed by physiotherapists with special education in spinal manipulation, there is fair evidence that it can reduce pain and increase function in acute low back pain.⁸

(B)Recommended drug treatment 

Drug treatment may be considered when the LBP is not relieved by non-drug measures, if the pain is more than mild in intensity, or when there is limitation of function due to the pain. Drug treatment may include: 

1. Paracetamol/Acetaminophen: many individual trials have found that paracetamol is better than placebo in treating pain in acute LBP. However a recent systematic review failed to find evidence that paracetamol is effective in the treatment of non-specific low back pain.¹¹ It should be noted however that the studies in this review were of generally poor quality, with the authors commenting on poor reporting of methods and results, and poor measurement of outcomes. A recent guideline on the treatment of low back pain from the American College of Physicians and the American Pain Society recommends the use of paracetamol as first-line medication for most patients because of its possible efficacy, favourable side-effect profile, and low cost;⁷
2. Non-steroidal anti-inflammatory drugs (NSAID):  when NSAIDs were compared to placebo in the treatment of acute LBP, they resulted in increased global improvement in the treated subjects; however there were also more side-effects, predominantly gastrointestinal (relative risk 1.76.)¹³ 

(C)Treatment not recommended

There is no good evidence to support the use of the following in acute non-specific LBP:

1. Lumbar supports;
2. Bed rest;
3. Opioid analgesia (eg.Acetaminophen/Phenyltoloxamine - Dologesic): no evidence to support the use of opioid analgesia in acute LBP, however is useful for chronic LBP. One must be wary of side-effects, including: constipation, dizziness, and the dangers of long-term use in patients with a potential for abuse or addiction;
4. Anti-depressants (eg. Tricyclic antidepressants): more effective than placebo for pain relief in chronic LBP, however have side-effects (eg. drowsiness, dry mouth, dizziness, and constipation); 
5. Anti-epileptic drugs: may be used in chronic LBP, but not useful in acute LBP; side-effects include drowsiness, dizziness, and liver damage; 
6. Systemic corticosteroids: no difference (compared to placebo in the treatment of acute LBP whether it be in the form of injection or a short oral course with tapering), and have significant side-effects.

It should be noted that there is some evidence to support the use of skeletal muscle relaxants in acute back pain; they are moderately superior to placebo for pain relief if given in the first 2-4 days of acute low back pain,⁷ however these are less widely available in Hong Kong and are not recommended as first-line therapy as they have significant side-effects (for examples: drowsiness, dizziness, central nervous system depression, and in severe cases cardiac and respiratory failure).

Follow-up

Most acute LBP is self-limiting and will improve within one month. It is reasonable to re-assess the patient at one month if symptoms have not resolved. An earlier follow-up should be arranged if certain factors are present, including patients with advanced age, co-morbidities, disease factors that might suggest a sinister cause of LBP, or patients with psychosocial risk factors for poor prognosis. 

Referral to specialists

In general, most cases of acute non-specific LBP may be managed effectively in the primary care setting. However there may be some instances where referral to orthopaedics specialists may be indicated: 

1. Back pain not responding to maximal conservative therapy;
2. Uncertainty about the diagnosis;
3. Specific spinal causes are suspected: eg. Spinal stenosis, radiculopathy, cancer, fracture; and
4. To perform imaging that may not be readily available in the primary care setting.

Conclusion

Acute LBP is a common and self-limiting condition, with most cases improving within one month. History should cover details of the pain and injury, as well as screening for points suggestive of more sinister causes.  Physical examination should be focused, aiming to confirm or refute certain diagnoses. Once a diagnosis is reached, further investigations or referral can be considered if indicated. For most cases of acute LBP, they can be managed effectively in the primary care setting without need for further investigations, with the use of both non-drug and drug measures. Patients should be advised of the good prognosis of acute LBP in order to limit any anxiety.

Key messages

1. Acute low back pain is a common condition, and usually self-limiting;
2. History taking should ask for symptoms and risk factors suggesting of a specific aetiology, as well as psychosocial factors that may affect recovery from acute LBP. Physical examination may show signs of intervertebral disc herniation;
3. After clinical assessment, back pain may be classified as non-specific, or due to other (possibly sinister) causes;
4. Imaging is rarely indicated in acute LBP;
5. Recommended treatment for acute LBP includes:  non-drug (education, superficial heat, avoidance of bed rest, physiotherapy & spinal manipulation) and drugs (Paracetamol, NSAIDs);
6. Primary care doctors should be aware of instances when referral to orthopaedic specialists may be indicated.

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References