Osteomyelitis of the spine is a bone infection that develops in one or more vertebrae, most often caused by bacteria that travel through the bloodstream from another site in the body. It’s relatively uncommon but has become significantly more frequent in recent decades, with the incidence rising from 0.5 to 4.7 cases per 100,000 people over a 40-year tracking period. The condition primarily affects adults over 60, and men are diagnosed nearly twice as often as women.
How Infection Reaches the Spine
Unlike bone infections in the arms or legs, which often start from a nearby wound or skin ulcer, spinal osteomyelitis almost always begins somewhere else entirely. Bacteria enter the bloodstream from an infection in another part of the body, such as the urinary tract, heart valves, or skin, and settle in the rich blood supply of the vertebrae. This blood-borne route is by far the most common pathway.
The spine is particularly vulnerable because of a network of veins called the Batson plexus, which lacks the one-way valves found in most veins. This allows bacteria to flow backward from the pelvis or abdomen directly into the vertebral blood supply. A second, increasingly recognized pathway is direct contamination during spinal surgery or procedures like epidural or facet joint injections. In rare cases, an infection in the throat can spread directly into the upper spine.
What Causes It
A single bacterial species is responsible in the vast majority of cases. Polymicrobial infections, where more than one organism is involved, occur in fewer than 10% of patients and tend to happen in people with weakened immune systems or chronic wounds.
Staphylococcus aureus is the most frequently identified culprit, and MRSA (methicillin-resistant strains) now accounts for 40% to 57% of those staph cases. Gram-negative bacteria, particularly the family that includes E. coli, show up in 7% to 33% of cases. Streptococci and enterococci are found in 5% to 20% and are often linked to dental infections or heart valve infections. Anaerobic bacteria cause about 3% of cases and appear more frequently in people with diabetes. Fungal infections are possible but uncommon, typically affecting people with severely suppressed immune systems.
Diabetes is a major driver behind rising rates of spinal osteomyelitis. Diabetes-related osteomyelitis tripled over four decades, jumping from 2.3 to 7.6 cases per 100,000 people. Other risk factors include intravenous drug use, kidney disease requiring dialysis, recent surgery, and any condition that weakens the immune system.
Symptoms and Warning Signs
Back pain is the hallmark symptom, and it tends to be persistent, worsening, and not relieved by rest. Unlike typical muscle strain, this pain is deep and localized to the area of the infected vertebra. It often intensifies at night. Fever is present in some cases but not reliably so, which is one reason the diagnosis is frequently delayed. Many people go weeks or even months with back pain before the infection is identified.
The more concerning symptoms involve the nervous system. Because infected vertebrae sit close to the spinal cord and nerve roots, swelling or abscess formation can compress these structures. Weakness in the legs, numbness, tingling, or difficulty with bladder or bowel control are red flags that suggest the infection is threatening the spinal cord. These symptoms require urgent evaluation.
How It’s Diagnosed
MRI is the gold standard for detecting spinal osteomyelitis. It has a sensitivity and specificity above 90%, meaning it catches nearly all true cases while rarely producing false alarms. One study found 100% sensitivity even when patients had symptoms for fewer than 14 days, making MRI effective for early detection. It reveals not only changes in the bone itself but also any abscesses pressing on the spinal cord or spreading into surrounding tissue.
Blood tests play a supporting role. Two inflammatory markers, ESR (erythrocyte sedimentation rate) and CRP (C-reactive protein), are typically elevated during active infection. These numbers aren’t specific enough to confirm the diagnosis on their own, but they’re useful for tracking whether treatment is working. An ESR above 60 combined with a CRP above 7.9 makes osteomyelitis highly likely, with about 91% specificity.
Identifying the exact organism is critical for choosing the right treatment. Blood cultures catch the bacteria in some patients, but when they come back negative, a CT-guided needle biopsy of the infected vertebra is the next step. The diagnostic yield of these biopsies ranges widely, from 31% to 91%, depending on technique and whether the patient has already received antibiotics. Open surgical biopsy has a higher success rate of 76% to 91% but is more invasive. Samples are tested for aerobic bacteria, anaerobic bacteria, and fungi to ensure nothing is missed.
Antibiotic Treatment
The standard course of treatment is six weeks of antibiotics. This can be delivered intravenously, orally, or as a combination of both. In practice, many patients start with IV antibiotics in the hospital and then switch to oral medication partway through. One study found that 72% of patients transitioned to oral antibiotics after a median of about 2.7 weeks of IV therapy, with no recurrences observed. The switch is generally considered safe once inflammation markers are trending downward and any significant abscesses have been drained.
For infections caused by Brucella, a less common bacterium associated with animal contact or unpasteurized dairy, treatment extends to three months. The specific antibiotic chosen depends entirely on which organism is identified, which is why getting an accurate culture result matters so much.
Throughout treatment, doctors track CRP levels to gauge whether the infection is responding. A steadily declining CRP is a reassuring sign. Most patients also undergo follow-up imaging to confirm the infection is resolving and no new complications have developed.
When Surgery Is Needed
Most spinal osteomyelitis is managed with antibiotics alone, but certain situations call for surgery. The clearest indications are neurological deficits (leg weakness, loss of bladder or bowel function) and sepsis, where the infection has overwhelmed the bloodstream. These warrant early surgical intervention.
Other reasons for surgery include spinal instability from extensive bone destruction, significant kyphosis (forward curvature of the spine), an epidural abscess pressing on the spinal cord, and failure of antibiotic treatment to control the infection. Some surgeons also recommend operating on epidural abscesses in the neck or upper back even without neurological symptoms, because compression of the spinal cord in these areas can progress quickly.
The goals of surgery are straightforward: relieve pressure on the spinal cord, remove infected and dead tissue, drain any abscesses, and stabilize the spine if the vertebrae have been weakened. Tissue samples collected during surgery also provide another opportunity to identify the causative organism, which is especially valuable when needle biopsies have been inconclusive.
Recovery and Outlook
Recovery from spinal osteomyelitis is slow. Even with effective antibiotics, the six-week treatment course is a minimum, and many patients deal with lingering back pain and fatigue for months afterward. Physical activity is typically restricted during treatment to protect weakened vertebrae, and gradual rehabilitation follows once the infection is under control.
Recurrence is a real concern. Patients who had incomplete treatment, delayed diagnosis, or infections with resistant organisms like MRSA face a higher risk of the infection returning. Long-term follow-up with repeat imaging and blood work helps catch any relapse early. For patients who required surgery, recovery timelines are longer and depend on the extent of the procedure, but spinal stabilization generally allows a return to normal daily activities over several months.