Infections Of Bone And Joint

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Chapter 13 Infections of Bone and Joint

Although bone and joint infection remains a serious problem, acute, fulminating bone involvement is seen much less frequently than in the past. The cause of these disorders is usually bacterial. Although more effective antibiotics continue to be developed, treatment of the established chronic infection remains a challenging problem.

Acute Osteomyelitis

Osteomyelitis is an infection of the bone or bone marrow. It is often classified as either acute, subacute, or chronic. Acute and subacute osteomyelitis are usually disorders of childhood and are less common in adults. The subacute form represents an altered host–organism response and is often the result of antibiotics given for other infections or nonspecific febrile illnesses. Chronic osteomyelitis, in contrast, is primarily a disease of adult life and usually develops as a result of an open wound, either traumatic or surgical.

The most common site of acute osteomyelitis in childhood is the metaphyseal end of a single long bone, frequently near the knee joint. The route of infection is usually hematogenous, although local direct extension from a neighboring soft tissue infection occasionally occurs. A history of trauma may be elicited. A primary site of infection is only rarely found. The metaphyseal area of growing bone is most frequently involved because as enchondral ossification proceeds, the blood vessels that normally invade the growth zone are looped, and, as a result, the circulation is sluggish. This can allow a nidus of infection to become established. The metaphyses also have fewer phagocytes, which may make it more susceptible.

In patients older than 50 years of age, the spine is the most common site of infection. These patients often have a history of genitourinary disease and/or manipulation, and the onset of the infection can be insidious.

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).

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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.

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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.

Subacute Osteomyelitis

This form of osteomyelitis may now be more common than the acute form and often results when the patient has been treated with antibiotics. The result is a semi-contained bone lesion. These children typically present at least 2 weeks after the onset of the infectious process. Staphylococcus organisms are the most common causes. Clinical signs are generally less severe than in patients with the acute form, and although pain is usually present, systemic signs are often absent. The erythrocyte sedimentation rate (ESR) may be elevated, and bone tenderness is present. The condition is often confused with neoplasm. The bone scan is positive and biopsy is usually required with curettage of the lesion helpful in resolving the condition.

Brodie’s abscess is a form of subacute osteomyelitis in which a small, localized, painful cavity develops in the metaphysis. The lesion is surrounded by dense, sclerotic bone (Fig. 13-3). The disorder is insidious in onset and lacks the systemic symptoms of acute osteomyelitis.

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Fig. 13-3 Brodie’s abscess. Note the surrounding sclerosis.

Chronic Osteomyelitis

This disorder can occasionally be the end result of an acute hematogenous osteomyelitis, but it is more commonly caused by an open fracture or wound and rarely by a surgical procedure. It is often seen in the lower extremities of patients with diabetes. All forms of chronic osteomyelitis are difficult to eradicate. The cause is often polymicrobial.

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.

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

COMPLICATIONS

The most common complications of acute osteomyelitis are soft tissue abscess formation, septic arthritis from extension to the adjacent joints, and metastatic infections from the initial focus. Occasionally, chronic osteomyelitis can be a complication of acute osteomyelitis. However, this is relatively uncommon in children, because the bone of growing children is a more active substance and has the ability to “turn over” and clear itself of infection. Overgrowth of bone because of stimulation and shortening caused by growth plate destruction can also occur in the young.

The problem most often seen as a result of chronic osteomyelitis is recurrent episodes of inflammation and drainage, or even simply chronic drainage. If this occurs after the insertion of an orthopedic implant, it is often necessary to remove the orthopedic implant before the infection will subside. In weight-bearing joints, this often results in less than optimal function, but removal of the foreign body does increase the chances of curing the infection.

Development of a chronically draining sinus can also be debilitating because of the extensive protein loss through the sinus tract. On rare occasions, squamous cell carcinoma can even develop at the drainage site. Amputation is even occasionally necessary in patients with diabetes or other individuals with poor local tissue health. Extensive spinal involvement may lead to paraplegia, and pathologic fractures may even occur in weight-bearing bones.

DIAGNOSIS

Cultures of the blood or of the lesion are essential to determine the exact causative agent and to institute the proper antimicrobial therapy. Blood cultures are positive in approximately 50% of children with acute osteomyelitis, but are frequently negative in adults. Every attempt should be made to isolate the organism. Needle aspiration of the site may be attempted, but this is sometimes inadequate. Biopsy may be needed. If a primary focus can be identified, blood samples for a smear, Gram stain, and culture and sensitivity should be taken from this site. Cultures of chronic sinus tract drainage frequently are not representative of the cause of the chronic osteomyelitis, and deep cultures of the involved bone should be obtained. The laboratory workup should include a sedimentation rate determination and a complete blood cell count (CBC) in addition to the above cultures. There is usually a leukocytosis and an elevation of the ESR. The ESR and C-reactive protein level are sometimes useful to follow the patient’s progress during treatment.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis includes: (1) acute suppurative arthritis, (2) rheumatic fever, (3) cellulitis, and (4) tumor. The most common cause of acute septic arthritis in young adults is Neisseria gonorrhoeae, whereas S. aureus is the major nongonoccal pathogen in older adults. Also, in the older population septic arthritis is often superimposed on some other bone disease, most commonly rheumatoid arthritis. In general, the clinical manifestations of septic arthritis are variable and related to the type of organism causing the underlying infection. Most patients with gonococcal septic arthritis have prominent prodromal symptoms such as fever, chills, headaches, anorexia, and malaise, followed by the development of monoarticular septic arthritis. In gonococcal arthritis, an important portion of the diagnosis lies in the history of a migratory polyarthralgia. A tenosynovitis may be present, but cultures from this involved synovium are usually sterile; however, the skin lesions and small joint effusions are generally positive for the offending organism. The arthritis seen in gonococcal disease is that of involvement of the large joints, primarily the knee, followed by the wrists, ankles, and elbows.

The clinical picture of patients with acute rheumatic fever, gout, and rheumatoid arthritis may mimic that seen in acute septic arthritis. Synovial fluid examination is helpful. The diagnosis of acute rheumatic fever is based on Jones’ criteria of major and minor manifestations (Table 13-1).

Table 13-1 Modified Jones Criteria (Revised)

Major Manifestations
Carditis
Polyarthritis
Chorea
Erythema marginatum
Subcutaneous nodules
Minor Manifestations
Arthralgia
Fever
Prolonged PR interval
Elevated ESR, C-reactive protein
Supporting evidence of previous group A streptococcal infection
• Positive throat culture or rapid streptococcal antigen test
• Elevated or rising streptococcal antibody titer
NOTE: The presence of two major or one major and two minor manifestations indicates a high probability of acute rheumatic fever if supported by evidence of preceding group A streptococcal infection.
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