What Is Vertebral Osteomyelitis? 

Defining vertebral osteomyelitis 

Vertebral osteomyelitis refers to an infection of the bones of the spine (vertebrae) and their associated structures (vertebral segments comprising the vertebral column). Vertebral osteomyelitis is the most common of vertebral infections and can affect all areas of the vertebral segment. These areas include the vertebrae (the bones of the spine), the intervertebral discs (the discs of gel-filled connective tissue between the vertebrae) and the spinal canal (the open area at the centre of all the vertebrae through which the spinal cord passes). Although rare, vertebral osteomyelitis is an incredibly serious condition that requires prompt attention. 

Causes and risk factors for vertebral osteomyelitis 

There are a number of causes and risk factors associated with the development of vertebral osteomyelitis. It is caused by the entry and infiltration of bacteria into the vertebral column, and there are many factors which can heighten this risk of infection. 

The following bacteria are among those most commonly implicated in the development of vertebral osteomyelitis: 

Staphylococcus aureus (Staph. a)

• Staphylococcus aureus is the most common cause of vertebral osteomyelitis¹
• Staphylococcus aureus infection of the vertebrae is a consequence of ‘haematogenous spread’, i.e. the infection travels from a distant site of infection to the vertebral bodies through the bloodstream.¹ Due to the large amount of blood supplied to the vertebral column, the bacteria are able to enter this area with ease.¹
• These distant infections can be from wounds arising from previous spinal surgeries, surgical devices used to fix the spinal structure, or epidural injections used for the management of pain.

Escherichia coli (E. coli)

• E. coli is the second most common cause of vertebral osteomyelitis 
• In a similar manner to Staph. a, E. coli reaches the vertebral column by spreading through the blood from an initial source of infection 
• Urinary tract infections (UTIs) are most commonly caused by E. coli infection.² Left untreated, UTIs can lead to bacteremia (infection of the blood), which, in turn, has been reported to lead to vertebral osteomyelitis³

Risk factors for the development of vertebral osteomyelitis 

Alongside these common bacterial causes of vertebral osteomyelitis, there are also a number of risk factors which can predispose a patient to infection and subsequent development of the condition: 

Immunocompromisation 

• In conditions such as HIV and AIDS, patients' immune systems are severely weakened. This means that they are unable to fight off infections as well as a patient with a fully functioning immune system. 
• Due to this, patients who are immunocompromised are susceptible to a greater number of severe infections. Fungal infective causes of vertebral osteomyelitis are also more common in this type of patient.⁴

Intravenous drug use

• The use of intravenous drugs (such as injectable cocaine and heroin) brings with it an associated risk of bacterial infection. 
• Due to the high incidence of ‘sharing’ equipment amongst those who use drugs intravenously, needles can become cross-contaminated with bacterial agents such as Staph. a and Pseudomonas aeruginosa⁵ 
• Direct injection of these agents into the bloodstream can lead to bacteraemia and subsequent development of vertebral osteomyelitis. This cohort of patients is more prone to developing cervical osteomyelitis – infection in the neck spine or area of the spine below the base of the skull – rather than other regions of the spine.

Spinal procedures

• Any procedures that involve the spine predispose a patient to the development of vertebral osteomyelitis. Due to either inadequate sterilisation techniques or poor surgical infection control, these procedures provide an easy and accessible route for bacteria to enter the bloodstream 
• Spinal infections are particularly common after a urological procedure (surgery related to the urinary tract) as the veins of the lower spine emerge from the pelvic region. Due to this, the most commonly affected region of the spine in vertebral osteomyelitis is the lumbar region (the lower back)

Other risk factors which can predispose someone to the development of vertebral osteomyelitis due to immune compromisation include: 

• Older age 
• Long-term steroid usage 
• Diabetes mellitus 
• Cancer
• Malnutrition 
• Organ transplantation⁶

How does vertebral osteomyelitis develop? 

As we have already established, the cause of vertebral osteomyelitis can be attributed to the entry and spread of bacteria through the bloodstream. Due to the large blood supply of the spine, these bacteria can then enter the spine and cause vertebral osteomyelitis. 

However, after the infection has reached the spine, how exactly do these bacteria infect and affect the vertebral bodies? Upon reaching an area of the spine, the following has been observed to occur: 

• Following the spread of the bacteria through the bloodstream, the bacteria is able to enter the vertebral bone of the spine 
• Spreading throughout the vertebral body, the bacteria cause inflammation and swelling at the site of infection
• Because the intervertebral discs are avascular (without blood supply), the bacteria can quickly enter and spread through the disc
• If untreated, this then allows the bacteria to spread to the adjacent vertebral body, infecting further bones of the spine. 
• Such widespread damage to both the vertebral bodies and discs can lead to instability and collapse of the vertebral bodies.
• Such damage can directly compress and impact the spinal cord, resulting in the host of symptoms detailed below¹ 

Symptoms of vertebral osteomyelitis 

There are a number of symptoms which are commonly found in those with vertebral osteomyelitis. These include: 

• Severe and persistent back pain
• Fever 
• Weight loss 
• Painful urination or difficulty urinating 
• Chills 
• Weaknesses in the arms and/or legs (depending on the region of the spine affected) 
• Incontinence of the bladder and/or bowels 
• Muscle spasms that may result in abnormal curvature of the spine, otherwise known as scoliosis
• Reduced mobility

Symptoms of intervertebral disc infection

Common to intervertebral disc infection is the presence of back pain. However, in the instance of disc infection, an individual may not develop significant back pain until the later stages of the infection. 

Intervertebral disc infection is also most common following a spinal procedure. Typically occurring one-month post-operation, this pain is usually eased by periods of bed rest and immobilisation. Untreated, this pain can become persistent and resistant to the use of strong pain medication.

In children, a fever and signs of pain may often not be present. However, a common sign in children affected by intervertebral disc infection is the refusal to flex (bend) their spine.¹

Symptoms of spinal cord infection

If the infection reaches the spinal cord (the bundle of nerves that travel through the vertebral bodies), then symptoms tend to be broadly neurological (i.e. relating to the function of nerves). Adult patients will usually progress through the following stages: 

1. Severe, persistent back pain, which is present at rest. There is usually an accompanying fever and tenderness in the region of the spine affected 
2. The development of nerve root pain in the region of the body supplied by nerves from the affected spinal segment level
3. Weakness of the muscles responsible for voluntary movement (i.e. weakness when moving the legs and/or arms). Incontinence of both the bladder and/or bowel may also be present at this point.
4. Paralysis. This is the most severe complication and is the reason vertebral osteomyelitis is considered a medical emergency.

Diagnosing vertebral osteomyelitis 

The symptoms of vertebral osteomyelitis can resemble other medical conditions. As such, a doctor may first ask you a series of questions to further explore and investigate your symptoms. 

In addition to symptom exploration, the doctor may also ask you other questions which will relate to your health and any influencing factors. Through this thorough exploration, a doctor will be able to narrow down their suspicions to just a few conditions. This process is known as taking a ‘medical history.’ 

The doctor may also decide to examine the area of pain, asking you to perform some movements whilst feeling regions of the spine. However, to confirm their suspicions, further tests are essential. These include: 

Blood tests 

• Doctors may perform a series of blood tests to identify any markers of inflammation present in your blood. These markers are known as the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) 
• Elevation of these is an indication that inflammation is present in the body. Monitoring of these allows assessment regarding the efficacy of medical treatment. 

Imaging tools

• To assess which regions of the spine are affected and to assess the extent of infection, doctors may use tools such as an X-ray, magnetic resonance imaging (MRI) or computed tomography (CT) scans.

Biopsy 

• A biopsy involves the removal of either tissue or bone to assist in the diagnosis of vertebral osteomyelitis. The results of the biopsy can also help guide treatment.⁶

Treating vertebral osteomyelitis 

As vertebral osteomyelitis is of bacterial origin, treatment involves the use of antibiotics. Patients are recommended to take antibiotics for at least six weeks, with this period extending in cases of severe infection.⁶ Other additional treatment methods include: 

Surgical intervention 

• Surgery is only recommended in cases of severe infection where there is evidence of extensive neurological involvement.⁶ 
• Surgery is often used to decompress the spinal cord and to stabilise the vertebral bodies if unstable.⁷ It is also used in cases where pus-filled abscesses have formed following infection.

Supportive measures 

• Patients may be referred to physiotherapy for rehabilitation following any surgical procedure. They may also recommend the use of back braces to further stabilise the spine. 

Following treatment of vertebral osteomyelitis, doctors may repeat further blood tests and scans to ensure the treatment has worked. Within these scans, doctors will assess the health of the vertebral bodies and surrounding tissue to ensure the infection has been adequately treated.

Summary 

Vertebral osteomyelitis, although rare, is a severe and complex medical condition requiring urgent attention. Caused by the spread of infection through the blood from other areas of infection, vertebral osteomyelitis can affect all areas of the vertebral column. Intravenous drug use, spinal procedures, and immunocompromisation are all recognised risk factors for the development of osteomyelitis. 

With persistent, severe back pain being the hallmark of vertebral osteomyelitis, patients can also encounter neurological issues such as urinary and/or bladder incontinence. In severe cases, paralysis can occur. As such, treatment requires prompt and urgent use of antibiotics for a minimum of six weeks. In the advent of complex and severe cases, surgical interventions are utilised to ensure stabilisation of the spine and decompression of the spinal cord.