Acute back pain

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Contents

Introduction

Back pain is one of the commonest ailments suffered by humans, probably because our erect posture places excess mechanical strain on the spine. In addition, acute stressors of the spine may be cumulative and accelerate a natural tendency to osteoarthritic degeneration. Genetic factors, underlying structural anomalies, occupation, pain tolerance, psychological factors and social circumstances all contribute to the origin and persistence of back pain.

There are many possible pain generators in the back, including discs, ligaments, facet (zygapophysial) joints, nerve roots, paraspinal muscles and extraspinal structures. It is difficult to identify the exact cause of back pain in many cases, particularly as the pain is often emanating from multiple structures at multiple segmental levels in the spine. This makes the treatment of back pain problematic, particularly as much of the treatment available for back pain is not founded on a strong evidence base. Back pain results in a large financial cost to the community and is therefore an important public health issue. Prevention of back injury is an important strategy to reduce the prevalence of back pain.

Applied anatomy

There are seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae and five sacral vertebrae. The spinal cord terminates in the adult at the LI–L2 disc level, where it becomes the filum terminale. The nerve roots of the cauda equina arise from the conus and pass through the lumbar and sacral canal.

The spinal nerve roots exit through the intervertebral foramina, and in the lumbar spine each nerve root passes under the pedicle of its numbered level; for example, the L5 nerve root passes inferiorly across the back of L4–L5 intervertebral disc to exit below the L5 pedicle. Therefore, a posterolateral disc prolapse at L4αL5 will compress the L5 nerve root. A posterolateral disc prolapse at L5–S1 will compress the S1 nerve root. A ‘far’ lateral disc prolapse may compress the lumbar root passing beneath the pedicle above; for example, a far lateral disc prolapse at L4–L5 may compress the L4 nerve root. There are 8 cervical spinal nerve roots, and the pattern is similar to the lumbar spine; for example, C7 passes across the C6–C7 disc and exits the C6–C7 intervertebral foramen. Posterolateral C6–C7 disc prolapse will therefore compress the C7 nerve root.

Pain generators in the back

Pain arising from the bones of the spine, ligaments, muscles, or intervertebral discs is often called mechanical back pain. There is a lot of crossover in segmental nerve supply in the lumbar spine between different structures. The annulus of the intervertebral disc and the facet joints are supplied with nerve fibres. Pain from the disc (discogenic pain) or facet joints is felt in the back centrally (somatic pain) but may radiate to the buttock and upper thigh (somatic referred pain). Somatic back pain may also emanate from musculoskeletal structures, bone and extra- or paraspinal structures.

Nerve root compression or irritation results in radicular pain, which is sharp lancinating pain radiating down the lower limb and may pass into the foot or down the arm into the hand. It may not follow an exact dermatomal pattern. It is often difficult to distinguish somatic referred pain from radicular pain. The overall clinical assessment and correlation with the radiological findings is important. Local anaesthetic facet joint blocks which suppresses facet joint pain, and discograms which evoke discogenic pain, have also been used to identify the principal pain generators in patients with chronic back pain (see below).

The history

A detailed history will provide a likely cause of the patient's back pain and should help to distinguish mechanical, radicular and long tract symptoms. If the patient has limb pain or paraesthesia, a nerve root may be compressed by whatever pathology is causing the back pain. The site of limb pain and paraesthesia will help localize the site of the pathology in the spine. The age of the patient is an important factor in the analysis of cause of back pain. Back pain can be caused by disordres of organs that are not part of the musculo-skeletal system (Differential diagnosis of back pain.).

Examination of the spine

The examination is done in the erect, prone and supine positions. It is important to differentiate between upper and lower motor neuron lesions and to identify the level of spinal pathology.

Spine and joints

Standing

Inspection for midline skin lesions such as a pit, sinus, hairy patch, lipoma, naevus or angioma over the spine. These may indicate underlying occult spinal bifida, spinal dysraphism or tethering of the spinal cord.

Assess general posture and spinal alignment, particularly for scoliosis or kyphosis. Are both feet planted symmetrically on the ground? The cervical spine and the lumbar spine normally have a lordosis (forward curve).

Range of movement includes forward flexion, lateral flexion, rotation and extension. Examine the shoulders and upper limbs if the patient has neck pain.

Supine

Examine the movements of the hips and knees. Examine the sacroiliac joint by adduction and internal rotation of the flexed hip.

Prone

Palpate the back for tenderness, paraspinal mass, paraspinal muscle spasm. Percuss the spine for tenderness. Complete the examination of the hip joint with extension.

Motor function

Neurological examination

Even in the absence of limb pain a careful examination must be made of the limbs, as the neurological signs that may be detected will often lead you to the precise site of pathology in or around the spine.

Gait

Observe for limping, rate of movement, length of stride, and need for walking aid. This will give many clues as to what is wrong and the severity.

Muscles

Muscle wasting and fasciculation imply denervation of muscles - examine all of the muscle groups including the shoulder girdle and gluteal region.

Muscle tone, power and reflexes including the plantars, are measured to determine whether it is an upper or lower motor neurone problem, or a mixed picture (Table 65, “Myotomes and deep tendon reflexes”).

Table 65. Myotomes and deep tendon reflexes
Muscle weakness Tendon reflex
C5 Deltoid, supraspinatus, infraspinatus Biceps
C6 Biceps, brachioradialis (± wrist extension) Brachioradialis
C7 Triceps (± wrist extension) Triceps
C8 Finger flexion -
T1 Interossei -
L2–L3 Iliopsoas -
L4 Quadriceps, tibialis anterior Patella
L5 Extensor hallucis, extensor digitorum -
S1 Gastrocnemius, toe flexors (± hamstrings) Achilles
S2 Glutei, hamstrings

Sensation

If you suspect a spinal cord lesion then full sensory testing should be performed. Test pain with pinprick (spinothalamic tracts), and light touch and proprioception (dorsal columns). Do not forget to test sacral, perianal and scrotal/vulval sensation. Establish a sensory level on the trunk for a suspected case of spinal cord compression. This will help with the localisation of the pathology.

Special tests

Straight leg raising is normally to 90 degrees with the patient in the supine position. Lift the whole lower limb passively whilst it is straight, flexing at the hip joint. This stretches sciatic nerve roots. Record the angle at which sciatica stops the movement.

Lesegue's stretch test is a test of pressure on the sciatic nerve.

The ankle is dorsiflexed with the lower limb outstretched and flexed at the hip, placing extra stress on the sciatic nerve, which, if it is already tethered by some pathology such as a disc prolapse, will cause a sharp jab of pain.

Femoral stretch test is a test of pressure on the upper lumbar nerve roots.

The patient is prone and the lower limb is extended at the hip, placing tension on the upper lumbar roots.

Rectal examination includes prostate and pelvis, anal tone, external sphincter contraction (the patient tightens the anus with the gloved finger in the rectum), perianal and perineal sensation. Assess the abdomen for bladder fullness.

Anal reflex (S4.5) involves contraction of the subcutaneous portion of the external sphincter in response to scratching the perianal skin.

Sacral sparing may occur within a widespread area of sensory loss caused by an intramedullary spinal cord lesion, and is due to the laminar arrangement of the fibres in the spinothalamic tract. The sacral segments are lateral in the tract. It thus means there is an incomplete spinal cord problem and may be the only sign of this.

General examination

The examination includes chest, abdomen and lymph nodes. Rectal and internal pelvic examinations are done when relevant. In a patient with back or radicular pain always consider intra-abdominal and other pathologies as a cause for pain.

Assess the adequacy of the arterial circulation in the lower limbs in the older patient.

Causes of acute back or neck pain (Key points and pitfalls)

Musculo-ligamentous strain

This is the commonest cause of acute back or neck pain. Usually there is an acute event such as a twisting, bending or lifting motion. The pain is localised but may spread to the trapezius, shoulder, occiput, or interscapular region if from the neck, or the buttock and upper thigh if from the lumbar region. There is spinal stiffness, local paraspinal muscle tenderness but no abnormal neurological signs.

Intervertebral disc prolapse

This is a common problem. The fibrous annulus of the disc tears, allowing the softer nucleus of the disc to herniate or prolapse. If the prolapsed nucleus separates from the disc it becomes a sequestrated fragment and may not resolve with expectant treatment. The intervertebral disc usually prolapses posterolaterally and may compress the exiting spinal nerve root which is adjacent to it and cause sciatica or brachialgia. In the acute phase the back pain is usually a minor component. Much less common is the central disc prolapse, which compresses the spinal cord or the cauda equina nerve roots depending on the spinal level.

Disc prolapse is most frequent in the lower cervical spine (C5–C6, C6–C7) and the lower lumbar spine (L4–L5, L5–S1). These are also the levels where degenerative changes are most common. Disc bulging (protrusion) occurs where the there is no prolapse (or extrusion) of nucleus. This is a common finding on CT or MR imaging and is not necessarily the cause of back pain and sciatica.

Thoracic disc prolapse may compress an intercostal nerve laterally and cause radiating pain in the distribution of that nerve or may cause spinal cord compression when central.

Infection

Osteomyelitis may be due to pyogenic infection usually by haematogenous spread, or due to tuberculosis. This will cause acute back pain and may cause neurological deficit due to vertebral deformity, bony instability or secondary epidural abscess.

Primary epidural abscess may occur without osteomyelitis particularly if bacteria are introduced into the spinal epidural space by a needle puncture or placement of an epidural catheter for analgesia. The problem has been reported following childbirth, with the mother developing severe back pain and possibly neurological deficit in the weeks following the placement of an epidural catheter for analgesia during labour. Discitis caused by a bacterial infection may also cause acute (and chronic) back pain.

Trauma

Trauma to the spine may cause vertebral fractures which may be unstable and may cause neurological injury. These injuries cause acute and often severe local pain and tenderness.

Vertebral collapse

Crushing of the anterior portion of the vertebral body in the thoracic or lumbar region is common following a hyperflexion injury to the spine. This causes a wedging of the affected vertebral bodies and acute pain. Wedging and vertebral collapse is also common in elderly patients and may be due to neoplastic infiltration, osteoporosis or, less commonly, infection.

Haematoma

An acute subdural or epidural haematoma in the thoracic spinal canal may cause acute cord compression with severe back pain and paraparesis. The cause of the bleed may be a ruptured vascular malformation or a spontaneous bleed in a patient on anticoagulants such as warfarin.

Spinal stroke

Thrombotic occlusion of the anterior spinal artery usually in a patient with diffuse atherosclerotic vascular disease causes an acute paraplegia, with severe acute back pain in the thoracic region. Myelogram does not show any compressive lesion but MRI may show cord signal hyperintensity, which indicates oedema or developing infarction.

Investigation of back pain

Plain X-rays

Plain X-rays are often done as an initial screen for patients with back pain but have a low sensitivity. Plain cervical X-rays are also used as a routine screen in multiple trauma patients and other regions of the spine if clinically indicated.

Computed tomography

Computed tomography (CT) scan is often ordered as the initial investigation for back pain. It shows the bony anatomy and the facet joints very clearly but is of variable and often inferior quality at showing the soft tissues, including the discs and intraspinal pathology.

Magnetic resonance

Magnetic resonance (MR) is now the main modality for spinal imaging and has virtually replaced CT myelography because it is non-invasive and because of the extensive information provided in different projections including the sagittal.

Myelography

The introduction of intrathecal contrast produces a myelogram which outlines the spinal roots and cord and is a dynamic study which can demonstrate a spinal block of the subarachnoid space by a mass lesion. Myelography is often followed by CT (CT myelography) which shows the contrast on the axial (horizontal) CT images.

Discography

Discography involves the injection of the intervertebral disc with contrast which may show internal derangement of the disc and may be used as a provocative test to identify the origin of back pain. It may not be reliable.

Dynamic (flexion-extension) views

These are plain radiographs, fluoroscopy, orMR scans used to demonstrate mechanical instability of spinal segments.

Biopsy and needle aspirate of vertebral or paraspinal disease

Biopsy and needle aspirate under CT guidance is a useful diagnostic technique which may be used when open surgery is not indicated and provides specimens for histopathology and microbiology analysis.

Blood tests

Blood tests, including blood cultures, full blood examination and inflammatory markers are performed selectively.

Treatment

Nonoperative treatment

Most back pain is benign in nature and cause, and usually resolves in 3 to 4 weeks even with no treatment. Degenerative disease and disc prolapse are initially managed conservatively and surgery should be considered a last resort unless there is spinal cord or cauda equina compression, when urgent surgery may be required (see below). Conservative treatments may include rest, and physiotherapy, which may include cervical collar, massage, traction, interferential heat treatment, and manipulation. Chiropractic treatment and acupuncture offer alternatives. Drugs include non-steroidal inflammatory drugs, analgesics, muscle relaxants, and steroids. Acute sciatica or brachialgia may require opiates to control the pain. Exercises are not useful in treating acute back pain, but have a role once it has largely settled so as to strengthen the paraspinal and abdominal muscles (e.g. Pilates program) which are often weakened in patients with degenerative spinal disease and disc prolapse.

Spinal surgery

A patient with disc prolapse and unremitting sciatica or brachialgia and neurological deficit despite conservative measures and who has radiology correlating with the clinical picture should be considered for surgery. Lumbar disc prolapse can be treated with minimally invasive microdiscectomy via an interlaminar approach. Cervical disc prolapse is usually treated with an anterior cervical discectomy and interbody fusion.

Acute or subacute spinal cord compression and cauda equina syndrome are urgent problems which require urgent referral to a neurosurgeon. Emergency decompressive surgery may be required to preserve neurological function and reverse neurological deficit. Whether the decompression of the spinal canal is done via a posterior approach (laminectomy or costotransversectomy) or via an anterior approach (anterior cervical, thoracotomy or transabdominal) depends upon the nature and site of the pathology and the experience of the surgeon. A diseased vertebral body may require excision and replacement by a prosthesis and the stability of the spine may need to be restored with metallic internal fixation using rods, plates, screws and bone grafts. Following such spinal surgery the patient may require radiotherapy or chemotherapy for a neoplasm or prolonged antibiotic therapy for an infection.

An osteoporotic vertebral collapse can be treated with an injection of acrylic cement into the affected vertebral body under radiological guidance to restore the volume and strength of the bone and relieve pain.
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