Back pain

Notes

Overview

Back pain refers to pain experienced in a patients’ back that is often in the lower regions.

Back pain is an extremely common presentation that is estimated to affect a significant proportion of adults at some point during their life. The majority of back pain is felt in the lower lumbar region (known as low back pain) and is usually self-limiting.

There are a variety of causes and it is important to be able to differentiate non-specific back (i.e. in the absence of an underlying disorder) from a sinister cause (e.g. discitis, cancer).

Location

The location of back pain is usually related to the region of the vertebral column.

  • Low back pain (lumbar region)
  • Mid-back pain (thoracic region)
  • Upper back pain or neck pain (cervical region)

The vast majority of back pain is located in the lower lumbar region known as low back pain. This note will focus on low back pain, which is one of the ten most common reasons for presentation to the emergency department.

Timing

The onset of back pain can be broadly divided based on acuity.

  • Acute: back pain < 4 weeks
  • Subacute: back pain for 4 - 12 weeks
  • Chronic: back pain for ≥ 12 weeks

Most patients with acute lower back pain will have a self-limiting episode that improves and extensive investigations are not required. The clinical assessment is important to exclude a more serious underlying pathology.

Differential diagnosis

The causes of back pain can be broadly divided into musculoskeletal, non-musculoskeletal, and referred pain.

The spine is associated with numerous supporting structures including muscles, joints, ligaments, fascia, intervertebral discs, and even nerve roots. Damage or dysfunction of any of these structures can give rise to pain felt in the back.

Back pain can be broadly divided into three categories:

  • Musculoskeletal (i.e. mechanical)
  • Non-musculoskeletal (i.e. non-mechanical)
  • Referred pain (i.e. from visceral organ)

Despite numerous possible causes, a significant proportion of adults (> 85%) will not have an identified cause of their back pain. This is often described as ‘non-specific back pain’ and usually resolves within a few weeks. Many of these cases may be musculoskeletal in origin. Importantly, < 1% of cases of back pain presenting to primary care (i.e. general practice) will have a serious underlying aetiology.

Musculoskeletal (mechanical)

Musculoskeletal-type pain can relate to any of the structures that help make up and support back movement. It is often termed mechanical because the pain is elicited with spinal movement.

  • Muscular: strain or sprain within the paraspinal lumbar muscles accounts for a significant proportion of low back pain. Often leads to intense pain for 24-48 hours. A strain is an injury to a muscle(s) or muscle-tendon(s) and a sprain is an injury to a ligament(s).
  • Degenerative discs: herniation or bulging of the intervertebral discs can lead to back pain and discomfort. If the disc impingements on nerve roots it can lead to radicular pain (i.e. shooting pain along a nerve root) that passes into the leg.
  • Spondylosis (i.e. osteoarthritis of the spine): this refers to degenerative arthritis affecting the spine that can cause aching, pain, or stiffness in the back
  • Spondylolisthesis: this refers to one of the vertebral bones slipped out of alignment. It may be related to degenerative changes, trauma, or a stress fracture in the bone known as spondylolysis
  • Spinal fracture: numerous types of fracture can occur along the length of the spine. The type of fracture depends on the location and mechanism of injury. For example, patients with osteoporosis are at risk of compression fractures, often with no preceding trauma. It is important to determine the stability of a spinal fracture that essentially determines whether there is a risk of spinal cord injury without realignment.
  • Spinal stenosis: this describes narrowing of the spinal canal. Typically multifactorial due to spondylosis, spondylolisthesis, and/or ligament changes (e.g. ligamentum flavum hypertrophy). Classically causes back pain and lower limb claudication (i.e. leg pain/cramping on movement). The pain is differentiated from vascular lower limb claudication by the presence of paraesthesia-type pain that is worse with the back extended (e.g. going downhill) and relived on sitting/lying within minutes not immediately.
  • Scoliosis: this refers to lateral curvature of the spine.
  • Sacroiliitis: this refers to inflammation of the sacroiliac joints that are commonly seen in ankylosing spondylitis. It is characteristically worse in the morning and better with exercise.
  • Radiculopathy: refers to symptoms or impairments related to the involvement of a spinal nerve root. Classically causes back pain and radicular pain felt in the distribution of the spinal dermatome.

Non-musculoskeletal (non-mechanical)

A variety of systemic disorders can lead to back pain. The development of pain is often due to disruption of the musculoskeletal components of the back and spine. These disorders are much less common but usually require urgent intervention.

  • Malignancy: back pain in association with malignancy is commonly due to metastasis to the spine. As cancer deposited within the spine continues to grow it may damage surrounding structures lead to spinal instability and can lead to cord compression or caudal equina syndrome. Pain may also be from a primary boney tumour or sarcoma.
  • Epidural abscess: this may cause localised pain and fever. Depending on the size it may compress nerve roots leading to radiculopathy or the spinal cord causing compression. Usually, there is a history of an epidural, spinal injection, or adjacent soft tissue infection.
  • Discitis: this refers to an infection of the intervertebral disc and is commonly due to a Staphylococcal infection. Commonly associated with iatrogenic line infections or endocarditis. Causes localised back pain.
  • Osteomyelitis: this refers to infection of the bone. Typically causes gradually worsening pain over weeks in association with fever and other constitutional symptoms. Many cases are healthcare-related due to bacteraemia following a procedure.
  • Inflammatory arthropathy: many connective tissue disorders can affect the musculoskeletal structures of the spine leading to back pain.

Referred pain

Pain felt in the back may be referred pain from a visceral organ. Some of these causes can be life-threatening so it is important to have a high index of suspicion. Classic examples include:

  • Pancreatitis
  • Aortic dissection
  • Renal calculi
  • Ruptured aortic aneurysm
  • Pyelonephritis
  • Biliary colic

Spinal cord & cauda equina

It is essential to exclude spinal cord or cauda equina compression in patients with back pain.

In patients with back pain, it is important to exclude injury to the spinal cord or cauda equina through a thorough history and examination. In early involvement, pain is often a prominent feature with subsequent motor, sensory, and/or bladder/bowel dysfunction.

In simple terms, back pain with new neurological features may suggest spinal cord or cauda equina involvement and a full neurological examination with an inquiry about bladder/bowel function is essential.

Spinal cord compression

This refers to compression of the spinal cord anywhere along its course from the foramen magnum to the L1/2 vertebrae. Spinal cord compression is commonly due to metastatic cancer or mechanical causes (e.g. unstable spinal fracture).

Back pain is often the presenting feature. Cord compression is characterised by:

  • Back pain (usually symmetrical and bilateral)
  • Bilateral leg weakness
  • Increased reflexes (upgoing planters, increased knee reflex)
  • Sensory level (the lowest spinal cord level that still has normal pinprick and touch sensation. Below this there is abnormal sensation. The level corresponds to the dermatomes)
  • Bladder/bowel dysfunction (late sign)

Cauda equina syndrome

This refers to compression of the cauda equina, which describes the collection of spinal nerves composed of lumbar, sacral, and coccygeal nerves beyond the terminal part of the spinal cord. Cauda equina syndrome is commonly due to malignancy or mechanical causes (e.g. disc disease, trauma).

Low back pain is commonly a feature. Caudal equina syndrome is characterised by:

  • Back pain (more asymmetrical and radicular)
  • Asymmetrical leg weakness
  • Reduced reflexes (downing planters, absent knee reflex)
  • Radicular sensory loss (dermatomal pattern)
  • Urinary retention
  • Reduced anal tone
  • Saddle anaesthesia

History

When evaluating back pain it is important to consider the mechanism of injury.

It is often not possible to determine the exact cause of back pain. The history is important to determine any features that may indicate serious underlying pathology. In particular, it is important to exclude specific causes such as cancer, infection, trauma, and inflammatory diseases.

When inquiring about the pain be sure to use the ‘SOCRATES’ mnemonic for your pain history. This mnemonic refers to:

  • Site: is the pain located in the lower back or upper back? Is it in the paraspinal muscles or centrally over the spine?
  • Onset: How did the pain come on? Was there associated trauma?
  • Character: musculoskeletal back pain may be described in many ways including dull, stabbing, gnawing, tearing, or associated with muscular spasm.
  • Radiation: does the pain radiate down the leg with a radicular quality or stay localised in the back?
  • Associated features: determine any neurological features (e.g. weakness, sensory changes, bladder/bowel dysfunction)
  • Timing: establish whether the pain is one-off or has been persistent for many weeks. In particular, has the pain changed in anyway?
  • Exaggerating and relieving factors: is the pain relieved with movement (e.g. ankylosing spondylitis) or made worse? Down it get better on lying down or standing up? Postural changes may trigger neurogenic claudication in patients with spinal stenosis
  • Severity: establish a severity score out of 10 and compare this to any previous episodes

Onset

The mechanism of injury is very important to establish. Determine whether there was a preceding history of trauma or was the patient carrying out their usual activities.

  • Traumatic: establish the mechanism of trauma (e.g. high impact versus low impact). Even a low impact injury in a frail or elderly patient may cause a significant injury such as a spinal fracture.
  • Non-traumatic: often there is only history of minor injury such as bending over, hoovering or walking downstairs. In patients with osteoporosis, a minor injury may lead to compression fractures.

Constitutional symptoms

This refers to generalised symptoms that can affect the overall well-being of a patient. They are associated with systemic diseases such as an underlying infection, inflammatory disorders, or cancer.

  • Fatigue
  • Fever
  • Weight loss
  • Night sweats
  • Myalgia/Arthralgia
  • Anorexia

Neurological features

A range of neurological features can develop in patients with back pain if there is involvement of the spinal cord, cauda equina or spinal nerve roots. Irritation of a spinal nerve root may lead to radicular pain that describes shooting pain or paraesthesia in the distribution of the spinal nerve root dermatome (i.e. area of skin supplied by the nerve root).

In patients with compression of the spinal cord or cauda equina, there is usually marked neurological changes with weakness, sensory loss, and/or bladder/bowel involvement. These are serious signs and would warrant immediate imaging.

Red flags

This refers to clinical features that warrant additional imaging of the spine to exclude a serious underlying cause. Some of these features are highly concerning for spinal cord or cauda equina involvement so would warrant same-day imaging.

  • Saddle anaesthesia
  • Bladder or bowel dysfunction (e.g. retention, incontinence, loss of anal sphincter tone)
  • New-onset weakness
  • History of malignancy with new back pain
  • Constitutional features (e.g. fevers, night sweats, rigours, unexplained weight loss)
  • Intravenous drug use
  • Immunosuppression
  • Trauma (including minor trauma in older adults)
  • Presence of contusion or abrasions over the spine
  • History of osteoporosis
  • Pain that is refractory to conservative management
  • Thoracic pain
  • Non-mechanical pain
  • Older age (> 50 years)

Yellow flags

Chronic lower back pain can be a very disabling condition and lead to increased morbidity, loss of work, chronic analgesic use and mental health disorders.

Various tools are available to help establish additional psychosocial aspects of back pain. Some of these features are referred to as ‘yellow flags’ and include:

  • Attitudes: towards the current problem
  • Beliefs: do they believe something serious is causing the pain
  • Compensation: awaiting any payment or compensation through injury?
  • Diagnosis: poor communication around diagnosis (e.g. your spine has popped out)
  • Emotions: depression, anxiety
  • Family: overbearing or unsupportive families
  • Work: relationship with work

The STarTBack screening tool was also developed by Keele University as a way of establishing the risk of developing chronic back pain and helps to tailor specific treatment.

Examination

A full neurological examination is essential in patients with back pain.

Assessment of patients with back pain should focus on both a musculoskeletal and neurological examination.

Musculoskeletal

The musculoskeletal examination centres on the three principles of inspect, palpate, move:

  • Inspect: look for any deformity or obvious abnormality (e.g. abscess, fracture). Is the spine curved consistent with scoliosis? Is there hyperkyphosis that may suggest compression fracture and osteoporosis?
  • Palpate: ensure you palpate both the central spinal processes and the paraspinal muscles. Localised tenderness over a spinal process may suggest an infection or acute fracture
  • Move: assess both the active and passive ranges of movement in all directions. This includes flexion, extension, and lateral flexion. In acute back pain, it may be difficult to assess all these modalities properly due to pain. Gait should also be observed during the assessment.

Provocation tests can be used in patients with suspected nerve root impingement. The two commonly used tests in suspected lumbosacral radiculopathies are straight leg raise and reverse straight leg raise:

  • Straight leg raise for L5/S1 radiculopathy: worsening radicular pain on raising the leg with the knee extended. Pain should be relieved if the knee is flexed
  • Reverse straight leg raise for L2-4 radiculopathy: worsening radicular pain on extending the leg with the patient prone

Neurological

A full neurological examination is important to exclude spinal cord, spinal root, or cauda equina involvement. This should follow the principles of assessing tone, power, reflexes, coordination, and sensation. If cauda equina or spinal cord compression is suspected, remember to assess for saddle anaesthesia and poor anal tone.

Increased tone, hyperreflexia, and weakness indicate a central nervous system problem such as spinal cord compression or spinal stenosis. These are collectively upper motor neuron features. Be careful with acute cord compression because weakness is often flaccid initially then progresses to become spastic. Spinal cord compression will also cause a sensory level, although the exact level of the sensory findings does not always correspond well with the level of injury.

Asymmetrical sensory and/or motor changes may indicate a nerve root problem or compression of the cauda equina. In radiculopathy, look for a dermatomal distribution of sensory changes and a myotomal distribution of weakness (e.g. Weak dorsiflexion in L5 radiculopathy).

Investigations

The majority of patients with acute lower back pain do not require imaging.

Most patients who present with back pain in a non-specialist setting will not require imaging of the spine. This is because in most cases there is no specific underlying cause and the symptoms will improve with time. This is particularly true among patients with no red flag features.

Blood tests

When a serious underlying cause is suspected such as malignancy, infection or an inflammatory disorder then blood tests are essential.

  • Full blood count: assess for anaemia and raised inflammatory markers
  • Renal profile: look for electrolyte abnormalities or contraindications to possible treatments
  • Bone profile: assess calcium
  • Liver function tests: especially if biliary disease is thought to be the cause (i.e. referred pain)
  • CRP: sign of underlying infection/inflammation
  • Coagulation: if intervention may be needed (e.g. cord compression)
  • Blood cultures: if infection suspected

More specific blood tests depend on the suspected case (e.g. tumour markers in cancer or HLA-B27 in ankylosing spondylitis).

Imaging

Imaging should not routinely be offered in a non-specialist setting for people with low back pain with or without sciatica (radicular pain due to nerve root irritation). This is particularly important for patients with acute back pain and no associated features (e.g. red flag signs).

Imaging options when utilised include:

  • X-rays
  • CT
  • MRI

X-rays

X-rays still have a role in the assessment of boney injuries of the spine (e.g. vertebral compression fracture in osteoporosis) or assessment of sacroiliitis (e.g ankylosing spondylitis). Anteroposterior and lateral views should be obtained. Additional views may be needed depending on the site of suspected pathology (e.g. cervical versus lumbar spine). Despite this, x-rays have largely been superseded by CT in the emergency setting and MRI in the outpatient setting.

CT spine

CT is often the first-line investigation in patients presenting with suspected spinal trauma. In this situation, a full ‘trauma scan’ is often requested to look for major structural abnormalities including within the spine. Indications for spinal imaging in trauma include:

  • Midline thoracolumbar tenderness
  • High energy mechanism of injury
  • >60 years
  • Unable to be examined due to intoxication
  • Glasgow Coma Score <15
  • Distracting injury

CT is more sensitive for detecting fractures than conventional x-rays and has the added benefit of being quick, easily accessible and able to assess surrounding soft tissue structures.

MRI spine

An MRI spine is the imaging modality of choice in suspected cauda equina syndrome or cord compression. If these are suspected, patients should undergo urgent imaging within 24 hours. MRI is also useful for assessing suspected spinal infections (e.g. osteomyelitis) and malignancy (e.g. spinal metastasis).

In patients with ongoing back pain who require spinal imaging, MRI is often the first choice. MRI can give a very detailed picture of the spine, surrounding soft tissue and nerve roots. However, one of the major problems is that the degenerative changes seen on MRI do not always correspond with the clinical presentations that could lead to unnecessary surgery.

Key tip

Although uncommon, it is essential to rule out cord or cauda equina involvement in patients presenting with acute back pain.

Remember that the vast majority of patients with low back pain will have a self-limiting episode that has no identifiable cause and does not require extensive investigations. The role of the clinician is to accurately assess the patient taking a full history and performing a musculoskeletal and neurological examination to exclude major red flag features that would warrant imaging. If there is any concern about cord compression or cauda equina syndrome then patients need urgent MRI imaging within 24 hours.

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