Pyogenic Infection of Spine

Pyogenic infection or bacterial infection of the he spine is rare but it has potential for long-term morbidity.

About 2-8% of overall pyogenic infection in the musculoskeletal system involves spine.

It is more common in males and has a bimodal distribution.

Males are more often affected than females. Age distribution is bimodal. The peak of affection is found in ages 10-20 years in children and in people older than 50 years.

A third subgroup [20-40 years] is emerging second­ary to intravenous drug abuse and HIV in­fection. Atypical presentation and location of infection is more common in this group.

Pathology of Pyogenic Infections of Spine

Infection of the spinal column may typi­cally manifest as discitis, vertebral osteomyelitis or epidural abscess.

Gram-positive aerobic cocci are the most common organisms. Staphylococcus aureusls the predominant organism (55%). In infants and children S. aureus is still the commonest but Streptococcus pyogenis is seen more frequently than in adults.

When the lesion is secondary to urinary tract in­fection or instrumentation, Gram-negative bacteria may be the common organism which includes E. coli and rarely Proteus, Klebsiella, Enterobacterand Serratia. Intra­venous drug users frequently yield Pseudomonas.

Postoperative wound infection is most commonly due to S. aureus but multiple organisms are frequently seen in this group. Rare organisms include anaerobic bacteria, fungi and parasites.

Discitis

Discitis is more common in children, be­cause of extensive anastomosis between the metaphyseal arteries and richly vascularized vertebral endplates. It responds quite well to antibiotics leading to rapid healing.

Vertebral Osteomyelitis

Vertebral osteomyelitis is more com­mon in the adults and elderly. By that time anastomoses have reduced and blood supply to the disc decreases, and is limited to periphery.  The focus of infection is the endplate of the vertebral body as the septic emboli are caught in the end arterioles of the verte­bral metaphyses.

Epidural Abscess

It is most commonly af­fect patients in the older age group, but an increasing frequency is being reported among the intravenous drug users and HIV patients.

Post-operative Spine Infections

Post-operative spine infections are a distinct from the three described three spontaneous forms of pyogenic infection in the spine.

There are three determinants

• Presence of focus of organisms or contamination of wound
• Surgical factors
  • Posterior surgeries at higher risk than anterior
  • Instrumentation have higher rate of infection
• Patient factors
  • Diabe­tes
  • Malignancy
  • Radiation therapy
  • Smoking
  • Steroid use
  • Rheumatoid arthritis
  • Intravenous drug abuse
  • Poor nutritional status

Lumbar spine is the most common loca­tion, followed by thoracic and cervical spine.

Clinical Presentation

Adults

Gradual onset back pain is the commonest presentation. Pain is worse at night and activity may aggravate pain mim­icking mechanical back pain. Paravertebral muscle spasm and stiffness may be out of proportion to pain. Intra-venous drug abusers and diabetics may present more acutely with 89% being diagnosed within 3 months.

Atypical presentation like acute abdomen or chest pain is less common. Radicular pain is uncommon unless there is epidural ab­scess. History of trauma is present rarely and is most often unrelated to the infection. However osteomyelitis may present as nontraumatic compression fracture.

A patient presenting with fracture may be suspected to have osteomyelitis if the patient has fever and ESR is raised.

This may be suspected when such fracture is associated with fever and raised ESR.  [Co­existence of infection and tumor has been reported and tumors should be ruled out]

Epidural abscess may present more acutely with a Classic triad of back pain, fever and spinal tenderness. However, 50-80% patients may have normal or only mild temperature elevation.

Neurological deficit is less common. Risk factors for neuro­logical deficit includes

• Diabetes
• Infection at more cephalad levels
• Rheumatoid arthritis
• Old age

Neurological deficit are more common with epidural abscess and in intra­venous drug users.

Children

The presentation of discitis in children depends on age.

Younger than 3 years

• Irritability
• Refusal to walk or even sit
• Prefer lying

Between 3-10 years

• Abdominal pain
• Tight hamstrings
• Back tenderness
• Rigidity

>10 years

These children usually present with predominant back pain. Marked fever is less likely. His­tory of trauma may be present but usually unrelated to the cause of infection.

In infants, vertebral osteomyelitis pre­sents as an with pain, fever, gibbus, raised leucocyte count, and com­plete dissolution of the vertebral body. These patients require a very aggressive treatment.

Post-operative infection

Postoperative wound infection is most of­ten diagnosed between 10 days and 2 weeks. Fever beyond first few days, and continued wound discharge beyond 10 days and discharges which initially wanes and then increases often indicate infection.

Fever may not be present in nearly half the patients. Treatment must be initiated aggres­sively and early on the basis of clinical diag­nosis.

Lab Studies

WBC count is elevated in less than one third of pa­tients and is not of much diagnostic value. Epidural abscess is an exception where WBC is very high in range of 22000 in almost all the cases.

ESR is raised 90-100% of children with discitis, 85% to 100% of adults with osteomyelitis [Levels are in range of  40-100 mm/h]. ESR responds to therapy and a decrease in ESR signifies the reduction of disease activity.

In patients after surgery, normally ESR rises and peaks between days 3 and 6, then falls to normal levels around 4-6 postoperative weeks. Elevated values after a week strongly suggest postoperative infections

C-reactive protein is a plasma acute-phase protein synthesised in liver, and nor­mally present at a low level. It has a half-life of only 24 hours. Therefore it is a more acute marker than ESR.

Blood culture is  positive in only 24% to 77%.

Other biochemistry tests should be done to know the patient profile in detail.

Imaging

X-rays

The non specific changes of infection may take as long as 2 to 12 weeks to appear in plain radiographs. The earliest changes usually observed are erosion of the endplate and loss of disc height, and these usually occur within 3 to 6 weeks.

More destructive changes occur during the next 6 to 12 weeks, which includes osteolytic compression of the ver­tebral body, paravertebral soft tissue shad­ows.

Reactive sclerosis may be observed after 2 months, followed later by bone bridges across the disc, and then, typically, autofusion. Fusion may take as long as 5 years.

Others develop a fibrous union.

Children with discitis present early radiological findings. Narrowing of disc space may be observed within 2 weeks of first symptoms. Endplate erosion occurs later, progressing to reactive sclerosis without vertebral body destruction. Restoration of disc height may occur within 3-12 months with successful early treatment.

CT

CT offers a superior definition of extra-spinal soft-tis­sue abscess and epidural abscess. It is also useful in distinguishing between pyogenic and tubercular infections and tu­mors.

Pyogenic infection causes diffuse bony destruction and soft tissue involve­ment whereas tuberculosis exhibits patchy lytic le­sions with sclerosed margins at times, and a large well defined paravertebral mass or abscess.

CT scan with metrizamide myelography may be useful to define epidural abscess. The commonest use of the CT lies in CT guided biopsy and aspiration of paravertebral abscess.

MRI

This is the most helpful diag­nostic imaging test for pyogenic infection in the spine. MRI scan identify the  decreased intensity in the disc and adja­cent vertebral body. There would be loss of endplate definition on T1-weighted image and in­creased signal intensity on T2-weighted im­ages.

MRI are specially helpful in detecting the epidural abscesses that often have signal characteristics similar to CSF and may be missed in unenhanced MRI, but show rim enhancement with gadolinium. The addition of fat-suppressed images further increased the specificity of MRI in the detection of in­fection.

Bone scan

May become positive in half the cases within the first few days. A nega­tive bone scan virtually eliminates the pos­sibility of pyogenic infection.

Treatment

Nonoperative treatment:

This includes spinal immobilization, early ambulation, and anti­biotics. Depending on the organ­ism, they usually require 4-6 weeks of IV antibiotic, followed by oral antibiotics. ESR and CRP are useful monitoring tools.

Choice of antibiotics depends on the or­ganism and its sensitivity.

Surgery

Over one-third of patients fail to respond to conservative therapy.

Indications for sur­gery are

• Neurologi­cal impairment
• Presence of abscess
• Septicemia
• Severe pain
• Progressive kyphosis
• Gross instability
• Need for open biopsy

Posterior decompression without fusion

An isolated posterior decompression fur­ther destabilizes the spine producing pro­gressive deformity and worsening neurologi­cal deficit. In rare instances, when infection principally involves posterior ele­ments, or the epidural abscess is posterior or lateral to the dural sac, a laminectomy may be indicated.

Posterior decompression with fusion and instrumentation

Extensive surgery than just a abscess drainage is required when the disease includes anterior elements too. To approach the disease posteriorly various approaches like posterolateral approaches, transpedicular decompression or costotransversectomy approaches are often required to achieve decompression.

Following debridement, it is usually necessary to restore stability with interbody bone grafts, using autograft rib or fibular allograft. Posterior instrumentation is often required for adequate stabilization.

When instrumentation is required, it could be done in the second stage after the posterior wound is healed following the initial debridement.

Alternately one stage procedure can be done.

Anterior decompression with or without autologous bone graft and instrumentation:

Here the disease is approached by an anterior approach and is the best approach for anterior diseases.he most satisfactory method to achieve a thorough debridement of the destructive lesion is by anterior approach. It is often nec­essary to use autograft or allografts to restore stability.

Instrumentation may be done to decrease the need for prolonged immobilization. In presence of frank pus, and no prior antibiotic treatment, anterior in­strumentation may preferably be avoided. In the cervical spine it is common to use ante­rior plate fixation together with debridement as a single-stage procedure.

Treatment of Postoperative Spine Infections

If the wound drainage continues beyond 10 days, or there is a strong suspicion of wound infection, aggressive treatment with debridement and irrigation using pulse lavage and primary closure over a drain may be done.

Drain should be left until the draining fluid has dropped to minimal.

In case of deep wound infection, debridement should be extended deep to the fascia.

The bone graft and internal fixation should be left in place, contemplating their removal only in recalcitrant cases.