Osteomyelitis

Inflammatory Surgical Diseases of Bones, Skin and Soft Tissues

Osteomyelitis is an inflammation of the bone caused by an infecting organism. The infection may be limited to a single portion of the bone or may involve a number of regions such as the marrow, cortex, periosteum, and even the surrounding soft tissue.

The definition of osteomyelitis is broad, and encompasses a wide variety of conditions. Traditionally, the length of time the infection has been present and whether there is suppuration (pus formation) or sclerosis (increased density of bone) is used to arbitrarily classify osteomyelitis.

In reality, there are no distinct subtypes, instead there is a spectrum of pathologic features that reflect balance between the type and severity of the cause of the inflammation, the immune system and local and systemic predisposing factors.

Classification

Classification of osteomyelitis is based on a number of criteria such as the duration and mechanism of infection and the type of host response to the infection. Osteomyelitis can be classified as acute, subacute, or chronic, depending on the duration of symptoms. However, the time limits defining these classes are somewhat arbitrary. The mechanism of infection can be exogenous or hematogenous. Exogenous osteomyelitis is caused by open fractures, surgery (iatrogenic), or contiguous spread from infected local tissue. The hematogenous form results from bacteremia. In English medical school osteomyelitis also can be classified as pyogenic (suppurative) or nonpyogenic (non-suppurative) based on the host response to the disease.

o Suppurative osteomyelitis

· Acute (less than 2 weeks)

· Subacute (2-6weeks)

· Chronic (>6 weeks)

* Primary (no preceding phase)

* Secondary (follows an acute phase)

o Non-suppurative osteomyelitis

· Diffuse sclerosing

· Focal sclerosing (condensing osteitis)

· Proliferative periostitis (periostitis ossificans, Garré's sclerosing osteomyelitis)

· Osteoradionecrosis (is a possible complication following radiotherapy)

Osteomyelitis can also be typed according to the area of the skeleton in which it is present. For example, osteomyelitis of the jaws in different in several respects from osteomyelitis present in a long bone.

Pus spreads into the bone's blood vessels, impairing their flow, and areas of devitalized infected bone, known as sequestra, form the basis of a chronic infection. Often, the body will try to create new bone around the area of necrosis. The resulting new bone is often called an involucrum. On histologic examination, these areas of necrotic bone are the basis for distinguishing between acute osteomyelitis and chronic osteomyelitis.