Wound infections, both superficial and deep, can occur following any surgical procedure on the spine. The reported incidence of these infections ranges from less than 1 to 10 per cent. Prophylactic antibiotics usually reduce the overall infection rate to 1 per cent or better. Furthermore, certain ‘risk’ factors increase the chance for postoperative infection. These risk factors include reconstructive surgery, surgery in a previously operated spine, age over 50, underlying systemic disease such as diabetes mellitus, adult scoliosis, and tobacco smoking. Postoperative infections can present as a range of symptoms, starting with superficial wound dehiscence, disc space infections, and ending with vertebral osteomyelitis and epidural abscess. The final outcome is dependent on the rapidity of diagnosis and treatment, the health of the patient, and the virulence of the infecting organism. The source of the infecting organism is either direct contamination at the time of surgery or a haematogenous spread from a non-contiguous source. Bacteraemia in the perioperative period from the genitourinary or respiratory tract as well as from skin infections has been implicated as a cause of postoperative deep wound infection.

The most common early sign is a persistent postoperative fever. Temperature over 100⁰F persisting beyond 48 h after surgery should be investigated aggressively. Likewise, postoperative pain symptoms that do not lessen progressively, but that plateau or worsen, should be closely investigated. If the infection is in the superficial tissue after 3 to 4 days the wound edges may be erythematous and drainage from the wound may be apparent. However, if the infection is deep, these findings may not be apparent. Patients who develop a disc space infection following discectomy, laminectomy, chemonucleolysis, or discography manifest recurrence of severe back pain and preoperative radicular symptoms. The immunocompromised patient should be followed with a high index of suspicion. If the infection is allowed to persist, extension to the epidural space may occur. Findings that herald the onset of epidural abscess include radicular pain, reflex aberration, sensory changes, motor weakness, loss of bowel and bladder control, and ultimately, paralysis.

Wound aspiration is the initial step in diagnosing a postoperative infection. This procedure can be performed at the bedside. The wound is aspirated, both superficially and deep, with a spinal needle. One should attempt to obtain a sample from the most tender region of the wound, at the same time avoiding insertion of the needle through an area of obvious erythema or drainage. In patients with suspected disc space infection, a sample for culture may be obtained with the help of CT scan guided biopsy. Blood cultures should be obtained in patients who have spiking fevers.

Plain radiographs in the early period of postoperative infection are rarely diagnostic. Similarly bone scans, CT scans, and MRI may be invalidated by postoperative changes and the presence of metallic implants. Patients who present with new or progressive neurological symptoms should be evaluated with myelography, preferably combined with CT scan.

All efforts should be made to avoid initiation of antibiotic therapy until an adequate culture sample is obtained. Once a sample is obtained, antibiotic therapy can be guided by Gram-stain results, the most common organism being Staphylococcus aureus. Patients who are toxic may require coverage with broad spectrum antibiotics until the results of bacteriological culture are available.

Patients diagnosed with isolated disc space infection are treated initially with parenteral antibiotics and bed rest. Intravenous antibiotics are continued for a month, followed by oral antibiotics for an additional 2 to 3 months. Once acute pain subsides, the patient is placed in a brace and is allowed to walk. In general this ‘conservative’ approach is successful and a spontaneous interbody fusion ensues in 50 per cent of cases. If, however, the pain persists, the sedimentation rate rises, and the fevers do not abate, surgical drainage through an anterior approach to the disc space is indicated. The disc space and adjacent end plates are debrided to healthy bleeding bone, and cancellous bone graft is used for interbody fusion. The duration of parenteral antibiotic therapy should be extended to 6 weeks and the course of oral antibiotics for 3 to 5 months if there is evidence for osteomyelitis at the time of surgical debridement.

Patients with postoperative wound infections should be explored in the operating room. Subfascial extension of the infection must be identified. The most important aspect of treatment at this stage is thorough debridement of all necrotic tissue. Sharp excisional debridement may be augmented with pulsatile water lavage. If an epidural abscess has developed, it is evacuated. In early postoperative infections bone graft, if involved, should be removed and cleaned. If bone graft has begun incorporating into the adjacent bone it should be cleaned thoroughly. Internal fixation hardware should not be removed if it is solidly fixed to bone and is providing stability to the spine. Once the wound has been cleaned, the bone graft is replaced and, if necessary, more is added. Wound closure may be undertaken by primary or secondary intention. If the skin edges appear healthy and the wound has been satisfactorily debrided closure over large suction or suction-irrigation drains is likely to be successful. However, if the skin edges are not healthy or if adequate debridement has not been carried out, repeat debridement followed by primary closure over drains can be undertaken. The drainage tubes are generally left in place for at least 5 to 6 days. If the surgeon is reluctant to close the wound, satisfactory secondary healing can be expected to occur, even over exposed hardware. This process imposes a significantly prolonged convalescence and a more unsightly scar.

Postoperative external immobilization is mandatory as are parenteral antibiotics. The duration of parenteral therapy is gauged by the extent of the infection. Superficial wound dehiscence may be treated for 10 to 14 days; deep infection with osteomyelitis requires a full 6-week course. Oral antibiotics are continued for 3 to 6 months.

The population at risk is intravenous drug abusers, alcoholics, diabetics, men, and patients over 50. The pathway by which the infecting organisms reach the vertebral column has been postulated to be both venous and arterial. Batson's valveless plexus may allow bacteria from the genitourinary tract to gain easy access to the vertebral body. Furthermore, the subchondral bone of the vertebral body is richly supplied by end arterioles by which bacteria could be deposited into the vertebral body.

The origin of the infecting organisms is often traced to the genitourinary tract. Respiratory infections, biliary tract infections, superficial skin wounds, dental extractions, and endocarditis have also been implicated. Infection from contaminated needles in intravenous drug abusers is on the increase.

A high index of suspicion is required to diagnose these infections. Not uncommonly there is a delay of between 10 weeks and 1 year before the diagnosis is made. The most common complaint is back pain, a malady that affects 50 to 80 per cent of the population at large. The patient with vertebral osteomyelitis usually complains of pain symptoms out of proportion to clinical findings. The pain persists despite rest; occasionally, fevers may be identified. In chronic or advanced cases a fluctuant area may be palpated in the paravertebral region. Similarly neurological symptoms from cord or root compression or irritation may be found in the later stages. The incidence of true paralysis ranges from 4 to 50 per cent depending on the chronicity of the disease and the region of the spine affected. Naturally the cervical and thoracic regions of the spine, where the cord is more confined, are likely to show neurological involvement sooner than is the lumbar spine.

Plain radiographs show disc space narrowing and localized osteopenia after 2 to 4 weeks. At 3 to 6 weeks a lytic lesion in the vertebral body becomes evident, with associated sclerosis and possibly a soft tissue paravertebral mass. Depending on the amount and pattern of bony destruction, vertebral collapse or a kyphotic deformity may develop. Blood cultures are diagnostic in 24 per cent of cases. Routine sampling of the cerebrospinal fluid is not recommended unless a myelogram is being performed for evaluation of neurological compromise.

Technetium-99m sulphur-colloid bone scan is very helpful showing an area of increased uptake at the focus of the infection. Computed tomography can elucidate bony destruction more clearly than plain radiographs. Radioactive monoclonal antibodies against leucocytes frequently identify occult infection. Perhaps the most critical step in diagnosis is the procurement of a sample for culture. Closed, radiographically-guided biopsy techniques are the preferred method, and are successful in approximately 70 per cent of cases. If closed biopsy is unsuccessful, open surgical biopsy is indicated.

Unless the patient has signs of systemic toxicity, antibiotic therapy should be delayed until a definitive organism is isolated from biopsy specimens. The most common organism isolated is Staphylococcus aureus. Patients with a genitourinary focus may present with Escherichia or Proteus infection. Intravenous drug abusers are predisposed to Pseudomonas infection. The treatment course begins with intravenous antibiotics for a minimum of 6 weeks. Immobilization is a necessary component of the treatment regimen and can be achieved through a variety of methods. For infections of the cervical spine halo vest or cervicothoracic orthosis may provide adequate immobilization. Thoracic and lumbar region infections may require a period of bed rest, up to 6 weeks, followed by casting or removable brace.

Surgery is rarely the first line of treatment in these cases. Specific indications for operative intervention are:

1.The need to decompress the spinal cord in patients with progressing neurological symptoms;

2.Correction of painful or disabling kyphotic deformity;

3.Abscess drainage;

4.Failure of closed biopsy to obtain adequate tissue;

5.Failure of non-operative treatment to bring about a reversal in the disease course.

Anterior debridement is the recommended approach for cervical and thoracolumbar infections. Involvement of vertebral bodies from L2 and caudal may be amenable to posterior debridement and fusion assuming that extensive anterior bony destruction has not occurred. Debridement is routinely followed by bone grafting. With the anterior approach a bicortical strut graft is utilized and there is opportunity for correction of kyphosis. Adequate debridement should remove all necrotic and infected bone and grafting into this site is then quite successful.

Oral antibiotics are started at the completion of 6 weeks of intravenous therapy. The sedimentation rate is followed during this time. General recommendations are for 2 to 8 weeks of oral agents based on virulence of the organism.

This rare and potentially fatal deep infection of the spine can arise from several sources. Haematogenous spread has been implicated most prominently in the intravenous drug abuser. As mentioned above epidural abscess can present as a continuum of postoperative infection or pyogenic vertebral osteomyelitis.

The abscess is commonly found in the posterior portion of the neural canal. In this region there is a potential free space between the dura and the epidural fat, and also a rich venous plexus where bacteria may become lodged. Expansion of the abscess can cause direct pressure on the neural elements as well as ischaemic necrosis thereby leading to neurological compromise.

Pain is the initial complaint and is usually out of proportion to results from the clinical examination. Left untreated the next phase is radicular pain accompanied by reflex changes. Sensory changes, motor weakness, and bowel and bladder incontinence develop in the next stage. The final phase is complete paralysis. Patients with untreated paralysis beyond 48 h have a poor prognosis for recovery.

Routine blood studies and plain radiographs are of varying benefit. As in all cases of progressing neurological deficit the lesion must be clearly identified either on myelogram or MRI. Myelography may be necessary to delineate the superior and inferior borders of the abscess. MRI, however, provides a safe and non-invasive method to delineate an epidural abscess without the risk of transmitting infecting organisms into the thecal sac.

Spinal epidural abscess constitutes a true surgical emergency. These patients should be prepared for operative decompression and drainage without delay. Once the precise location of the abscess has been adequately demonstrated it can be approached for complete drainage and neural decompression. In the typical case with posterior abscess, laminectomy may suffice; however, if the abscess is ventral to the cord an anterior approach is indicated. Antibiotic coverage is tailored according to the results of Gram stain and culture and is continued for at least 2 weeks. If evidence for osteomyelitis is found, antibiotic therapy should be identical to the regimen described above. Immobilization of the spine is guided by the degree of bony destruction and the potential for development of deformity.

Infection or inflammation limited to the disc space is a disease entity occurring in the paediatric population. The peak distribution is between 2 and 6 years of age, when there is a rich vascular supply to the immature disc whereas the adult disc is avascular. Therefore, infecting organisms have a direct route to the disc space in children, whereas in adults this space is probably reached by extension from the vertebral body. Discitis may represent either a bacterial (usually with Staphylococcus aureus) or viral infection occurring most commonly in the lumbar spine.

Pain, limp, or refusal to walk and stand are the most common presenting symptoms. Detailed history may be difficult to elicit from patients in this age category and a high index of suspicion is required. Antecedent upper respiratory tract illness or otitis may be reported by the parents.

Examination reveals a hyperextended spine with paraspinal muscle spasm. Percussion along the spinal column, axial percussion on the heel of the foot, or attempts at spine or hip motion are exquisitely painful.

Complete blood count may show a leucocytosis and the sedimentation rate may be elevated. Plain radiographs are essentially normal in the first 2 weeks of the disease course followed by disc space narrowing and end plate erosion. Bone scanning, specifically with gallium-67, is the study of choice for reliable and early diagnosis.

Given a clear-cut clinical diagnosis supported by a positive bone scan, patients are started on antistaphylococcal antibodies. Bed rest and spine immobilization are important components of the therapy regimen. If symptoms are not diminishing within 48 to 72 h CT scan-guided biopsy is indicated and treatment can proceed based on biopsy results. Antibiotic therapy is continued for 3 to 4 weeks on an oral regimen. Overall prognosis is good given early diagnosis and treatment and there is no evidence for long-term sequelae.

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