spinal infections

Vertebral osteomyelitis

pathophysiology

· spinal infection starts in vertebral end-plate rather than disc

· exception is direct innoculation

Blood supply

Arterial supply

· vertebral bodies receive blood supply from segmental arteries

· vertebral artery

· intercostal artery

· lumbar artery

· posterior spinal branch enters intervertebral foramen

· separates into ascending and descending branches

· descending branch from one artery and ascending branch from subjacent artery supplies each vertebra

· anastomose and enter posterior nutrient foramen

· vessels stop at vertebral end plate

· intervertebral disc is avascular

Venous drainage

· vessels start at vertebral end plate

· drain into horizontal veins

· horizontal system drains into basivertebral veins

· converge to form anterior internal venous plexus

· drains into external venous plexus

Infection

· occurs via 3 means

· in haematogenous and direct spread

· vertebral osteomyelitis occurs primarily

· spread to disc occurs secondarily

· in disc manipulation

· disc infection occurs primarily

· spread to vertebral body occurs secondarily

Haematogenous spread

· skin/soft tissue infection

· urinary tract infection

· respiratory tract infection

· intravenous drug use / catheter

Direct spread

· psoas abscess

· pelvic abscess

· retropharyngeal abscess

· perinephric abscess

Surgical manipulation of disc

· discectomy

· discography

Extension

· infection can extend

· posteriorly to involveepidural space

· anteriorly to involve paraspinal soft tissues

Neurological deficit

· occurs as result of

· epidural abscess

· pathological fracture

aetiology

Microbiology

· usually due to Staph aureus (60%)

· other organisms include

· Staph epidermidis

· coliforms

· Pseudomonas

Risk factors

· diabetes mellitus

· immunosuppression

· alcoholism

· IV drug use

clinical features

Presentation

· pain

· most common (85%)

· often constant

· worse with movement

· fever and night sweats

· in 60%

· neurological symptoms

· radicular pain not uncommon

· weakness uncommon

· paralysis rare

· constitutional symptoms

· malaise

· weight loss

Findings

· tenderness

· focal to percussion

· paravertebral spasm

· deformity

· may be kyphos

· neurological signs

· altered sensation most common

· weakness may be present

Diagnosis

· delayed diagnosis very common

investigations

Radiology

Plain x-rays

· characteristic changes with sequential time course

· increased paravertebral soft tissue shadow at 1 wk

· decreased disc space at 2 wks

· vertebral end-plate irregularity and subchondral lysis at 6 wks

· surrounding relative sclerosis at 8 wks

· new bone formation with buttressing at 12 wks

· bony or fibrous ankylosis at 6 mths

· other changes are

· vertebral body collapse

· segmental kyphosis

CT scan

· demonstrates degree of bone destruction

· useful to identify paravertebral soft tissue swelling and abscess

Bone scan

· very sensitive

· nonspecific

MRI

· very useful

· detects

· disc space infection

· epidural abscess

· paravertebral abscess

· T1 image

· decreased signal intensity in disc and vertebral body

· T2 image

· markedly increased signal intensity in disc

· markedly decreased signal intensity in vertebral body

· increased uptake in epidural abscess

Laboratory

ESR

· usually elevated

· > 20 in 80%

· > 50 in 60%

WCC

· often marginally elevated

· unreliable

Blood cultures

· positive in 30%

Biopsy

· controversial

· may be performed as

· open biopsy

· core biopsy

· CT-guided needle biopsy

· advantages

· gives microbiological and histological diagnosis

· disadvantages

· positive in only 60%

· neurological damage

· injury to vascular structures

· pneumothorax in thoracic spine

· false negatives from

· insufficient sample

· prebiopsy antibiotics

· chronic disease

treatment

Nonoperative

· traditional treatment consisted of

· IV antibiotics for 6 weeks

· oral antibiotics to follow until 6 weeks after decline in ESR

· rest in bed for 6 weeks

· TLSO until evidence of new bone formation

· most cases achieve stability with variable deformity

Operative

Indications

· failure of nonsurgical treatment to eradicate symptoms and infectious process after 3 mths

· presence of contiguous epidural abscess

· neurologic deficit

· significant osseous involvement with deformity

· septic course with clinical toxicity from an abscess not affected by antibiotics

· failure of needle biopsy to obtain the necessary culture data (relative)

Goals

· eradication of infection

· prevention of deformity

· relief of pain

Technique

· anterior approach

· debridement

· total removal of the affected disc with all involved adjacent bone down to bleeding granulation tissue

· bone graft

· autogenous using rib struts for thoracic and upper lumbar regions or a tricortical iliac crest wedge for lower lumbar segments

· allograft using calamari ring

· mobilisation with brace when comfortable

Spinal epidural abscess

definition

· collection of pus or inflammatory granulation tissue in the epidural space

epidemiology

· very rare

· prevalence of 37 per million in primary care patients with back pain

· 1 to 2 per 10 000 acute hospital admissions

· may be increasing

· increased IV drug use

· increased invasive spinal procedures, esp. epidural analgesia

· most common in elderly men

· average age 68 yrs

· 75% male

pathoLOGY

Location

· occurs in cervical, thoracic and lumbar spine

· spans an average of 4 vertebrae

· may be anterior or posterior to dural sac

Abscess material

· may be pus or granulation tissue

· duration of illness not predictive of type of tissue present

Entry of bacteria into epidural space

· causes are

· direct spread (1/3)

· haematogenous spread (1/3)

· unknown (1/3)

Direct spread

· vertebral osteomyelitis

· common (30%)

· abscess usually anterior

· following spinal instrumentation

· laminectomy

· myelography

· epidural steroid injection

· spinal/epidural anaesthesia

· lumbar puncture

· adjacent foci

· psoas abscess

· pelvic abscess

· retropharyngeal abscess

· perinephric abscess

· spinal trauma

· penetrating injury

· blunt trauma with haematoma

· pressure sores

Haematogenous spread

· skin/soft tissue infection

· urinary tract infection

· respiratory tract infection

· intravenous drug use / catheter

Spinal cord injury

· from

· direct compression

· vascular occlusion

Direct compression

· from mass effect of pus

· probably causes early symptoms

· pus usually tracks freely in epidural space

Vascular occlusion

· due to

· decreased arterial flow

· thrombosis of epidural veins

· likely responsible for clinical features later in course

· probably more important

Co-morbidity

· usually present (75%)

· may be

· predisposition to infection

· potential source of infection

· local condition that favours settlement of bacteria in epidural space

· are

· diabetes

· degenerative joint disease

· intravenous drug use

· alcohol abuse

· immunosupression

· cancer

Microbiology

· Staph aureus most common (60%)

· other organisms

· other gram positive cocci, esp. Streptococcus (10%)

· enterobacteraciae, esp. E coli (20%)

· M tuberculosis

· in IV drug users, greater incidence of gram-negative aerobes

· organism may not be identified

clinical features

· classical triad is

· back pain and tenderness

· fever

· elevated ESR

Symptoms

· back pain is hallmark

· present in 95%

· usually very severe

· may have root pain

· symptoms of cord compression in less than 50%

· weakness

· urinary retention

· parasthesiae

· often constitutional features

· malaise

Signs

Fever

· present in 2/3

· may be absent with

· chronic disease

· analgesic-antipyretic, NSAID or steroid use

Local signs

· tenderness and pain on movement

· present in majority (60%)

Neurological deficit

· present with

· weakness

· sensory loss

· urinary retention

· at presentation, neurological status is

· normal 20%

· ambulatory weak 30%

· nonambulatory paralysed 50%

investigations

Laboratory

ESR

· almost always elevated

· usually about 100

White cell count

· usually elevated (3/4)

Blood culture

· often identifies organism

Imaging

MRI

· T1 image shows mass with low signal intensity or is isointense with cord

· T2 image shows mass with high signal intensity (bright)

· administration of gadolinium shows peripheral or homogenous enhancement

· MRI has sensitivity of 85%

· gadolinium-enhanced MRI increases sensitivity to 95%

· diagnostic procedure of choice

· non-invasive

· also demonstrates

· vertebral osteomyelitis

· cord pathology

· other possible causes (disc herniation, tumour, cord infarct etc.)

Myelography

· was previously the best form of imaging, esp. when combined with CT

· similar sensitivity (95%)

· myelogram shows block to CSF flow

· CT demonstrates epidural mass

· disadvantages

· invasive

· usual risks of myelography (CSF leak, infection, contrast myelopathy)

· risk of exacerbation of spinal cord compression

· risk of puncture of epidural infection with contamination of other spinal compartments

· should be used when MRI unavailable

Plain radiography

· non-specific findings

· associated vertebral osteomyelitis

· paravertebral soft tissue mass

· directs further investigations to appropriate level

Bone scan

· similar to plain x-ray in that

· non-specific

· directs further investigations to spine

· changes occur sooner than on plain x-rays

diagnosis

Initial diagnosis

· usually wrong

· most commonly musculoskeletal pathology or disc prolapse

· usually delayed

Differential diagnosis

· uncomplicated back or neck pain

· musculoskeletal pain

· degenerative disease

· back or neck pain with fever

· vertebral osteomyelitis

· meningitis

· back or neck pain with neurological deficit

· vertebral metastasis

· herniated disc

· transverse myelitis

TREAtMENT

· surgical debridement plus antibiotic therapy

Surgery

Aims

· decompression of cord

· debridement of infection

· drainage of pus

· biopsy of organism

· stabilisation of spine

Technique

· usually treated by neurosurgeons

· mainstay of treatment has been posterior laminectomy

· good results with posterior abscess with no anterior body osteomyelitis

· if abscess anterior and vertebral osteomyelitis present, collapse with pain and kyphosis may occur

· supplemental posterior fusion may be required

· if anterior involvement severe, anterior vertebrectomy and stabilisation may be indicated

· aggressive approach still appropriate with advanced age and poor general medical state

Antibiotics

· broad spectrum initially

· vancomycin plus gentamicin

· start intraoperatively once specimen obtained

· start preoperatively if

· organism identified from blood culture or other specimen

· prolonged delay to surgery

· choice of antibiotics may be modified by definitive microbiology

· duration of therapy 4-8 weeks

Medical treatment alone

· some advocate medical therapy as treatment of choice in certain circumstances

· may be indicated in

· poor surgical candidates

· very extensive abscess

· minimal neurological deficit

· complete paralysis of more than 3 days

· current literature does not support widespread use of nonsurgical therapy

prognosis

· not significantly improved despite medical advances

Paralysis

· greater risk with

· increased age

· diabetes

· more cephalad level

· Staph aureus

Outcome

· complete recovery 50%

· ambulatory weakness 30%

· nonambulatory paralysis 10%

· death 10%

Indicators

· presurgery delay

· severity of neurological deficit prior to treatment