Osteomyelitis

Osteomyelitis is an inflammation of the bone and the bone marrow, usually as a result of an infection. Basically, osteomyelitis can be defined as bone infection.

Osteomyelitis can be a complication of any systemic disease, but usually, it is only confined in a single bone.

Several germs (viruses, bacteria, fungi or parasites) may be the cause, but the most common ones involved are pyogenic bacteria (where pus is produced) and mycobacteria.

The bone affected may depend on different conditions. For example, the spine or the ribs can be affected in patients undergoing dialysis or the clavicle in case of intravenous drug users.

Osteomyelitis can be classified into:

• Acute: Develops within two weeks after a sudden onset
• Subacute: Develops within one to several months
• Chronic: Long standing infection (many months)

The causes are different depending on the type of osteomyelitis:

• Acute osteomyelitis
  
  It may be due to a trauma that exposes the bone to the infection. The infection can also reach a bone through the bloodstream (hematogenous osteomyelitis).
  
  In children, it is usually located in the long bones. In adults, the bones more usually affected are the spine and the pelvis.
  
  Bacteria (Staphylococcus aureus) and fungi are the most common germs involved.
  
  The affected bones usually contain pus. The pus can lead to a bone abscess (pocket of pus) altering the normal blood supply to the bone.
  
  
• Chronic osteomyelitis
  
  The main cause of chronic osteomyelitis is a lack of blood supply (oxygen and nutrients) to the bone leading to bone death.
  
  A sequestrum formation (a piece of necrotic bone detached from the healthy tissue) is characteristic for chronic osteomyelitis.
  
  Risk factor for chronic osteomyelitis are recent trauma, diabetes, and intravenous drug use.

The main risk factors to develop any type of osteomyelitis are:

• Recent trauma or bone surgery
• Immunocompromised patient
• Intravenous drug use
• Alteration in vascularity (for example arterial insufficiency)
• Systemic diseases such as diabetes or sickle cell disease

According to the way the infection reaches the bone osteomyelitis can be classified into:

• Hematogenous: caused by a systemic infection. In children, the most common cause is due to an infection by Staphylococcus aureus
• Direct inoculation: can occur from penetrating injuries or open fractures
• Contagious spread: secondary to a contiguous focus of infection

The main symptoms of osteomyelitis are:

• Pain and tenderness of the affected limb.
• Swelling of the foot, ankle or leg.
• Fever, chills, sweating.
• General discomfort.
• Fluid or pus near the infection in the case of chronic osteomyelitis.

To get a proper diagnosis the following tests and procedures may be helpful:

• Physical exam: The tenderness and the swelling of the bone may be evident
• Blood test: WBC (White Blood Cells) can be higher than normal as well as ESR (Erythrocyte Sedimentation Rate)
• Blood culture: It may detect the germ of the infection
• Biopsy: It can be helpful also to detect the germ
• X-rays: They can be altered in the bone affected

The Cierny-Mader classification, based on the anatomical and physiological findings, provides assistance for the treatment and prognosis of the patient:

Treatment of osteomyelitis depends on the type:

1. Acute infection: The ultimate goal of the treatment is to stop the infection and prevents the development of a chronic infection. The recommended treatment is to take high doses of intravenous antibiotics until the blood culture results are negative several times.
2. Chronic infection: In case of chronic infections, surgical removal of dead bone tissue is the best practice. The dead bone will be replaced with a bone graft or packing material. After surgery, it is necessary to keep on with drug therapy for at least 3 more weeks.

The mortality rate is very low (almost zero) in normal situations. The mortality rate is significantly higher in the case of chronic infection, even after surgery. Chronic osteomyelitis sometimes can end with an amputation.