CAUSE

Most cases of acute hematogenous osteomyelitis are caused by Staphylococcus aureus. In infants and children, other important causes are group B streptococci, gram-negative coliforms, and Haemophilus influenza. Although H. influenza is becoming less common as a result of vaccination, it can still be a problem from infancy to 4 years of age, when the child loses passive immunity from the mother. Gram-negative bacilli are important causes of osteomyelitis involving the vertebral bodies in adults. There is a higher incidence of osteomyelitis in socioeconomically deprived individuals that is caused primarily by Staphylococcus organisms and tuberculosis. Tuberculous and fungal causes of osteomyelitis can usually be traced to the pulmonary system. African Americans with sickle cell disease have a particularly high susceptibility to Salmonella. Osteomyelitis may also follow infections of the genitourinary or biliary tracts or any type of surgical manipulation, particularly colorectal surgery.

With the current incidence of intravenous (IV) drug abuse, there is a much higher rate of osteomyelitis that can affect the spine (usually lumbar vertebrae) and sacroiliac joints. The cause is often Pseudomonas aeruginosa, although the causative organism may vary from one locale to another.

CLINICAL FEATURES

In general, acute hematogenous osteomyelitis occurs primarily in late infancy and at puberty and is often preceded by signs of systemic disease and/or general sepsis for several days. The lower extremity is most commonly affected, and a mild limp may develop. Anorexia, nausea, malaise, irritability, and fever are present, usually during the acute phase. This stage of the disease may last for several days before bone pain and local overlying inflammation appear. Fever, chills, and diaphoresis are the usual systemic complaints. Pain, bone tenderness, heat, and swelling of the soft tissue are the classic physical findings. There is often limitation of motion of an adjacent joint caused by a sympathetic effusion. (Remember: an unexplained fever with bone pain in the child is osteomyelitis until proven otherwise.)

In infants, the disease may be alarming and life-threatening in its onset. The involved area usually shows limitation of motion (pseudoparalysis), and there may be tenderness in the involved bone well before swelling and redness occur.

In the adult, the onset is usually less acute. Constitutional symptoms may be considerably less marked or even absent. In the older child and the adult, it is not uncommon for the first symptoms of osteomyelitis to be those of bone involvement. Usually, there is limitation of joint motion, especially if the osteomyelitis involves the spine or if the primary lesions are particularly close to joints where sympathetic effusions may occur.

Tuberculous, fungal, and rickettsial causes of osteomyelitis generally have an insidious onset. These diseases are more common in patients who are immunologically depressed, who have other underlying diseases, such as alcoholism, or those whose immune systems have been altered by immunosuppressive therapy or human immunodeficiency virus. The primary source of these infections is often pulmonary, and a low-grade fever, weight loss, anorexia, and chronic cough or sputum production may be present. Tuberculous osteomyelitis may involve the vertebral column with pathologic fractures of the involved vertebrae. This usually results in angular kyphosis of the spine or so-called Pott’s disease (Fig. 13-1).

Fig. 13-1 Pott’s disease. Angulation is present on both the anteroposterior (A) and the lateral (B) views.

In the drug-abusing patient who is afebrile and presents with an onset of back pain that is aggravated by moving, coughing, sneezing, or straining at stool, pyogenic spondylitis and gram-negative osteomyelitis should be suspected.

ROENTGENOGRAPHIC FEATURES

The classic roentgenographic finding of acute osteomyelitis in childhood is deep, circumferential soft tissue swelling with obliteration of muscular planes. Spotty rarefactions representing early destruction may appear within 7 to 12 days in the affected bone. Shortly after this, periosteal new bone formation becomes evident and indicates that the infection has spread through the cortex (Fig. 13-2). Plain roentgenograms are of less value in adult osteomyelitis because significant bony changes may not be apparent until at least 50% of bone destruction has occurred, which may be 2 to 4 weeks into the illness. In the spine, infection can involve the vertebral body or the disc space. Disc space infections are uncommon but do occur occasionally in children and in patients who have undergone surgery on the intervertebral disc. In these cases, the roentgenographic changes are vertebral end-plate irregularities and disc space narrowing. Eventually, new bone proliferation occurs, and frequently complete fusion of the disc is the result. In osteomyelitis of the vertebral body, the roentgenographic changes are those of bone destruction with loss of vertebral height. Paravertebral swelling and/or paraspinal masses may also be occasionally demonstrated.

Fig. 13-2 Acute osteomyelitis of the clavicle. Note the periosteal reaction (arrows).

Radioisotope bone scans, usually using technetium, are a mainstay in the early diagnosis of acute osteomyelitis, although any abnormal findings are nonspecific. An advantage of the technetium scan is that it can be performed within a few hours. An isotope-labeled white blood cell (WBC) scan is more specific for infection, although this study is not always available at all facilities.

Magnetic resonance imaging (MRI) and computed tomographic (CT) scanning are also extremely valuable. MRI is more likely to be of assistance in detecting subtle changes, especially those involving the bone marrow and is the best modality for the diagnosis of acute osteomyelitis. Computed tomography can often define early soft tissue changes.

CLINICAL FEATURES

This disorder is characterized by the onset of inflammation and cellulitis after an open fracture or by persistent drainage following an episode of acute osteomyelitis. Occasionally, it develops in the postoperative period after orthopedic procedures. Systemic signs have often subsided from previous infection. Fever, pain, and mild systemic symptoms are typical. External physical findings may be minimal, but soft tissue inflammation and tenderness usually develop.

Frequently, chronic osteomyelitis becomes latent after treatment. The nidus of infection may become surrounded by dense bone and fibrous tissue. This often prevents antibiotic penetration. Later (sometimes years later), minor trauma may reactivate the inflammation, cellulitis, and drainage. Excerbations may occur for years, and some chronic wounds even drain persistently.

ROENTGENOGRAPHIC FINDINGS

Chronic osteomyelitis usually appears as irregular sclerotic bone that may contain several areas of radiolucency. Irregular areas of destruction are commonly present, and there is often periosteal thickening (Fig. 13-4). Small, dense areas of dead bone called sequestra may be present. If the acute hematogenous osteomyelitis has been extensive, the entire shaft may become a sequestrum. This dead bone is then surrounded by a new shell of bone called the involucrum. Fortunately, this extensive involvement is rarely seen in Western society.

Fig. 13-4 Chronic osteomyelitis of the second toe.