Spinal infections can be classified by the anatomical location involved: the vertebral column, intervertebral disc space, the spinal canal and adjacent soft tissues. Infection may be caused by bacteria or fungal organisms and can occur after surgery. Most postoperative infections occur between three days and three months after surgery.
Vertebral osteomyelitis is the most common form of vertebral infection. It can develop from direct open spinal trauma, infections in surrounding areas and from bacteria that spreads to a vertebra from the blood.
Intervertebral disc space infections involve the space between adjacent vertebrae. Disc space infections can be divided into three subcategories: adult hematogenous (spontaneous), childhood (discitis) and postoperative.
Spinal canal infections include spinal epidural abscess, which is an infection that develops in the space around the dura (the tissue that surrounds the spinal cord and nerve root). Subdural abscess is far rarer and affects the potential space between the dura and arachnoid (the thin membrane of the spinal cord, between the dura mater and pia mater). Infections within the spinal cord parenchyma (primary tissue) are called intramedullary abscesses.
Adjacent soft-tissue infections include cervical and thoracic paraspinal lesions and lumbar psoas muscle abscesses. Soft-tissue infections generally affect younger patients and are not seen often in older people.
Spinal infections can be caused by either a bacterial or a fungal infection in another part of the body that has been carried into the spine through the bloodstream. The most common source of spinal infections is a bacterium called staphylococcus aureus, followed by Escherichia coli.
Spinal infections may occur after a urological procedure, because the veins in the lower spine come up through the pelvis. The most common area of the spine affected is the lumbar region. Intravenous drug abusers are more prone to infections affecting the cervical region. Recent dental procedures increase the risk of spinal infections, as bacteria that may be introduced into the bloodstream during the procedure can travel to the spine.
Intervertebral disc space infections probably begin in one of the contiguous end plates, and the disc is infected secondarily. In children, there is some controversy as to the origin. Most cultures and biopsies in children are negative, leading experts to believe that childhood discitis may not be an infectious condition, but caused by partial dislocation of the epiphysis (the growth area near the end of a bone), as a result of a flexion injury.
Symptoms vary depending on the type of spinal infection but, generally, pain is localized initially at the site of the infection. In postoperative patients, these additional symptoms may be present:
Redness, swelling or tenderness near the incision
- Severe back pain
- Weight loss
- Muscle spasms
- Painful or difficult urination
- Neurological deficits: weakness and/or numbness of arms or legs, incontinence of bowels and/or bladder
Intervertebral Disc Space Infections
Patients may initially have few symptoms, but eventually develop severe back pain. Generally, younger, preverbal children do not have a fever nor seem to be in pain, but they will refuse to flex their spines. Children age three to nine typically present with back pain as the predominant symptom
Postoperative disc space infection may be present after surgery, occurring, on average, one month after surgery. The pain is usually alleviated by bed rest and immobilization, but increases with movement. If left untreated, the pain gets progressively worse and intractable, unresponsive even to prescription painkillers.
Spinal Canal Infections
Adult patients often progress through the following clinical stages:
- Severe back pain with fever and local tenderness in the spinal column
- Nerve root pain radiating from the infected area
- Weakness of voluntary muscles and bowel/bladder dysfunction
In children, the most overt symptoms are prolonged crying, obvious pain when the area is palpated and hip tenderness.
Adjacent Soft-tissue Infections
In general, symptoms are usually nonspecific. If a paraspinal abscess is present, the patient may experience flank pain, abdominal pain or a limp. If a psoas muscle abscess is present, the patient may feel pain radiating to the hip or thigh area.
Spinal infections often require long-term intravenous antibiotic or antifungal therapy and can equate to extended hospitalization time for the patient. Immobilization may be recommended when there is significant pain or the potential for spine instability. If the patient is neurologically and the spinal column is structurally stable, antibiotic treatment should be administered after the organism causing the infection is properly identified. Patients generally undergo antimicrobial therapy for a minimum of six to eight weeks. The type of medication is determined on a case-by-case basis depending on the patient’s specific circumstances, including his or her age.
Nonsurgical treatment should be considered first when patients have minimal or no neurological deficits and the morbidity and mortality rate of surgical intervention is high. However, surgery may be indicated when any of the following situations are present:
- Significant bone destruction causing spinal instability
- Neurological deficits
- Sepsis with clinical toxicity caused by an abscess unresponsive to antibiotics
- Failure of needle biopsy to obtain needed cultures
- Failure of intravenous antibiotics alone to eradicate the infection
The primary goals of surgery are to:
- Debride (clean and remove) the infected tissue
- Enable the infected tissue to receive adequate blood flow to help promote healing
- Restore spinal stability with the use of instrumentation to fuse the unstable spine
- Restore function or limit the degree of neurological impairment
Once it is determined that the patient requires surgery, imaging tools such as plain x-rays, CT scans or MRI can help further pinpoint the level at which to perform surgery.