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.

Cellulitis may sometimes be difficult to differentiate from septic tissue swelling on roentgenographic examination. The soft tissue swelling is primarily superficial, usually involving skin and subcutaneous tissue. The offending oranism is usually hemolytic streptococcus. Occasionally, the cellulitis can evoke a sympathetic effusion in an adjacent joint, but passive and active movements of that joint are generally not as painful as they are in acute septic arthritis. In addition, the clinical response to treatment is usually dramatic. If there is a sympathetic effusion in an adjacent joint and there is a problem in differentiation among cellulitis, septic arthritis, and acute osteomyelitis, the joint may be aspirated through an area of healthy skin, but great care must be taken to avoid contaminating a normal joint. MRI is useful is distinguishing cellulitis from osteomyelitis. The condition is commonly confused with vascular disorders in the lower leg. The tumor goes away with elevation if it is caused by peripheral vascular disease, but not if cellulitis is present.

To establish the diagnosis of tumor, special roentgenographic studies and biopsy are necessary. The rule of culturing all biopsies and taking biopsies of all cultures is always followed.

TREATMENT AND PROGNOSIS

After proper cultures are obtained, the treatment of acute osteomyelitis should begin immediately and not be delayed while waiting for the identification of the offending organism. Because the majority of cases in the young are caused by S. aureus, it is appropriate to use an IV antibiotic to cover this pathogen as well as group B streptococcus, enteric rods, and probably H. influenza as well. In addition to the proper antibiotic coverage, the patient should have general supportive measures. Dehydration and anemia should be corrected, and the diet should be high in vitamins and protein. Early surgical drainage and debridement are indicated in acute osteomyelitis unless there has been a rapid clinical response within 24 to 36 hours. The extremity should be properly immobilized for a period of 3 to 4 weeks.

If necessary, changes are made in the antibiotic coverage when the offending organism is identified. The sedimentation rate and C-reactive protein levels are followed during treatment. IV antibiotic coverage is usually continued for 4 weeks, but each case should be treated individually, and there is no consensus regarding the route and length of antibiotic coverage. Treatment for the subacute form is essentially the same.

Sometimes fever may recur after an initially good response to the appropriate antibiotic treatment. At this time, a careful clinical reevaluation is necessary, and several conditions should be considered: (1) laboratory error in identification of the organism, (2) drug fever (usually due to a cephalosporin or a penicillin), (3) superinfection, (4) abscess formation, or (5) inadequate drainage.

In general, the prognosis for acute osteomyelitis is good, although complications have been reported in as many as 25% of cases. If antibiotic treatment is begun before bone and tissue necrosis has occurred, surgery is less often required. A delay in diagnosis and treatment may lead to chronic osteomyelitis or multiple recurrences. These recurrences can develop as long 30 years later and are usually caused by the same organism. They are often reactivated by minor local trauma.

The treatment of chronic osteomyelitis is similar to that of the acute form, but prevention remains the most important aspect of this disease. All open fractures are meticulously cleaned and debrided, and great care is taken to eliminate contamination. Once chronic osteomyelitis develops, it may be treated by incision and drainage, radical debridement, and appropriate antibiotic coverage for 4 to 6 weeks. However, once it is established, chronic osteomyelitis is difficult to cure. Recurrent drainage and residual deformity both add to the morbidity. Local infection that develops in the presence of a prosthetic device may necessitate removal of the device before the infection can be controlled.

Infections of the bones of the feet are common in diabetic patients, who often have coincidental peripheral vascular disease. Painless ulcers may develop secondary to diabetic polyneuropathy and diabetic vascular disease. Hyperemia and swelling are frequently noted clinically. If a fracture occurs in the foot of a diabetic patient, it may be accompanied by a similar redness and swelling and be a source of some confusion. A roentgenogram usually clarifies the diagnosis.

Septic Arthritis

Septic arthritis may occur in any age group but is more common in the young. It is usually monoarticular, and large peripheral joints are most frequently involved, usually the knee or hip. Polyarticular disease is rare but may occur in patients with preexisting inflammatory disease or chronic illness. Unusual sites (sacroiliac, sternoclavicular joints, and symphysis pubis) may be involved in IV drug abusers. The etiology of most cases is bacterial, although viral and even fungal causes have been demonstrated.

Gonococcal infection often leads to a distinct clinical syndrome and is discussed separately.

PATHOGENESIS

The offending organism is usually S. aureus, but a variety of other bacteria may be causative including N. gonorrhoeae. H. influenzae may still be seen in children, but the prevalence is decreasing because of vaccinations. Gram-negative rods are frequently involved in IV drug users. Entrance to the joint is usually gained by hematogenous seeding, rarely by direct extension from an adjacent infection, such as a contiguous osteomyelitis. In the hip, it may be introduced by an improperly performed venipuncture from the groin. The disorder is more common in patients with underlying chronic disease states or those undergoing immunosuppressive therapy.

Upon invasion of the joint by the pathogenic bacteria, the organisms seed the synovial membrane, which becomes swollen and hyperemic. It begins to produce large amounts of fluid that distend the joint capsule. Frank pus eventually accumulates, and destruction of articular cartilage may even occur.

CLINICAL FEATURES

The onset is usually acute, with pain being the most common early symptom. A history of infection elsewhere is occasionally obtainable. If a weight-bearing joint is involved, ambulation is usually difficult and may become impossible because of the pain. Fever and other signs of systemic infection are usually present.

Examination generally reveals a warm, swollen, diffusely tender joint. The joint is usually held in slight flexion because, in this position, the intracapsular pressure is decreased, and discomfort is thereby minimized. Attempts at passive motion tend to be extremely painful.

SPECIAL STUDIES

Roentgenographic findings early in the disease process are usually minimal and consist primarily of distention of the joint capsule. The peripheral white blood cell (WBC) count is markedly elevated as a rule, and blood cultures may be positive. The sedimentation rate is generally high, but neonates and geriatric patients may show only minimal laboratory abnormalities. Bone scanning and other studies are of limited value but may be very helpful in the evaluation of the patient whose symptoms are of uncertain cause.

Confirmation of the diagnosis is best made by joint aspiration under sterile conditions. Most joints are best aspirated on the extensor side, except the hip, which may be aspirated from the anterior or lateral aspect. Because the joint is usually distended, aspiration is ordinarily not difficult. The fluid is initially cloudy and thin but may be purulent. The joint glucose level is decreased, and the WBC count is markedly increased. A Gram stain is performed, and cultures are taken. The specimen should always be inspected for crystals.

TREATMENT

Treatment should begin immediately after cultures to prevent joint destruction and, in the case of the hip joint, dislocation (see Chapter 10). Rest and immobilization diminish the pain. The definitive antibiotic therapy depends on Gram stain and culture results. The IV route should always be used. Intraarticular injection is unnecessary because most antibiotics readily pass through the synovial membrane. Direct instillation may even provoke an inflammatory synovitis.

Some superficial joints may respond to repeated aspiration, but surgical drainage is indicated if symptoms do not resolve rapidly. This is especially true of the hip in children. Surgery diminishes the intraarticular pressure, allows evacuation of the thick fibrous exudate, and prevents the articular destruction that may occur in pyarthrosis. It can often be done arthroscopically. Pyogenic infection of the hip in the child is considered an emergency and often requires immediate drainage to prevent serious hip destruction.

The prognosis is usually good, and complete resolution is expected when diagnosis and treatment have been prompt. The most serious outcome is seen in the hip of the child whose treatment has been delayed. When irreversible joint destruction has occurred, a salvage procedure such as arthrodesis may be necessary. Joint replacement might be attempted, but there is some risk of reactivating the dormant infection.

GONOCOCCAL INFECTION

The disease states caused by the bacteria N. gonorrhoeae may range from asymptomatic carrier to the condition known as disseminated gonococcal infection. Gonococcal infection is the most common form of pyogenic arthritis in many areas. It often presents in the young, sexually active individual with a distinct clinical syndrome of polyarthritis, tenosynovitis, and dermatitis. In these patients, the gonococcal organism is often difficult to demonstrate. Blood cultures are usually negative, and the organism can be recovered from joint fluid less than 50% of the time. Although most patients with gonococcal arthritis do not have genitourinary symptoms, gonococcus can be recovered from these sites about 80% of the time, and these sites should always be cultured if gonococcal infection is suspected clinically. A rapid response to the appropriate antibiotic is almost diagnostic. Nonsteroidal antiinflammatory drugs also help speed the resolution of symptoms. Joint destruction caused by N. gonorrhoeae is uncommon, and complete recovery is the rule.

VIRAL “ARTHRITIS”

Inflammatory changes with pain in the joints is sometimes seen after vaccination for rubella. Signs of bacterial infection are absent. The condition is diagnosed by exclusion, and the treatment is symptomatic. The prognosis is good.

Arthralgias also accompany a number of viral illnesses, but the pathogenesis of these arthritis-like symptoms is not known. Rarely, viral illnesses may present as a monoarticular synovitis.

Special Problems

CELLULITIS

Cellulitis is a common diffuse spreading superficial infection of the skin and subcutaneous tissue. It may arise from a break in the skin (often from a skin fissure between the toes) or a surgical wound, although in most patients no obvious cause is found. It is more common in diabetic patients and patients with lymphatic or venous compromise. The deeper structures are usually not involved, and abscess formation is rare.

The offending organism is usually hemolytic streptococcus, although S. aureus, and, rarely, Gram-negative rods may be causative. The clinical presentation varies depending on the organism, but streptococcus usually causes a superficial warm, tender erythematous lesion characterized by an elevated, indurated margin. Vesicle formation may occur. Samples for Gram stain and culture may be obtained from this fluid or any local drainage. MRI may rarely be needed to determine the extent of soft tissue involvement and to rule out bony involvement.

Treatment consists of elevation, rest (with immobilization, if needed), and the appropriate antibiotic. The oral route is often sufficient, but intravenous antibiotics may be needed in more severe cases. Surgery is generally not required unless an abscess develops. The prognosis is usually good.

Cellulitis may be mistaken for vascular disease in the lower leg. As a rule, the rubor associated with vascular insufficiency goes away with elevation but not if due to infection. Chronic venous stasis can also be a source of confusion, and the two conditions may occasionally coexist.

NOTE: If cellulitis develops near a joint, a reactive, sterile effusion may develop in that joint. Care must be taken to differentiate cellulitis from a joint infection. If a needle is passed through the soft tissue infection and into the joint in the process of analyzing the effusion, sepsis can be introduced, creating a pyogenic joint infection.

DISC SPACE INFECTION

Disc space infection is not an uncommon cause of back pain, especially in the child. The condition is thought to develop from a hematogenous source. Because the disc is avascular in the adult, a primary disc space infection (discitis) would be unusual in this age group. S. aureus is the most common infecting bacteria. The disorder may be seen more often in the adolescent IV drug abuser. The chief complaint is usually pain that is localized to the area of the underlying infection, and there may be tenderness on palpation of the spine over the infected disc space. The child limps or does not walk at all. Flexion of the spine may increase the discomfort, and hip extension is often painful. Systemic signs of illness are commonly absent. Early roentgenograms are usually not beneficial, although there may be occasional disc space narrowing. The vertebral body is not involved. The bone scan is usually positive, but false-negative results have been described. MRI may be the best imaging modality. There is usually mild leukocytosis and an elevated sedimentation rate. Management consists of IV antistaphylococcal antibiotics and rest. Light immobilization with a brace may relieve pain. If there is not a rapid resolution of symptoms, aspiration and culture of disc space material may be necessary to identify the causative organism.

ANAEROBIC INFECTIONS

Anaerobes are becoming increasingly recognized as causes of significant clinical infection. The more common organisms involved are Bacteroides fragilis, Peptococcus, Propionibacterium, Clostridium, and Fusobacterium. They are often mixed with aerobes, and it is often difficult to tell which is the pathogen. These mixed infections are also more difficult to cure.

Anaerobic bone infections are often associated with the presence of a metallic foreign body such as a prosthesis. They may be found in infected decubitus ulcers. When they are present in infections in the foot, they are almost always associated with diabetes or vascular insufficiency.

Treatment includes debridement of necrotic tissue and appropriate antibiotic coverage.

GAS GANGRENE

Clostridia organisms are widely distributed in nature, but only a few are severe pathogens. Several species can cause gas gangrene in humans. The most common is Clostridium perfringens (C. welchii). Other causes are C. novyi, C. histolyticum, C. septicum, C. bifermentans, and C. fallax.

Gas gangrene is an uncommon clinical infection in which a severe soft tissue wound or surgical trauma allows the tissue to become contaminated with the Clostridium spore. Local anaerobic conditions (a closed wound) favor conversion from the spore form to the vegetative form, which produces the potent toxins typical of this disorder. These toxins destroy soft tissue and muscle and can cause severe septic shock and death. Other organisms, including group A β-hemolytic streptococcus, may cause necrotizing soft tissue infections.

CLINICAL FEATURES

This disease can result from a small innocuous wound but usually results from a severe wound that has received improperly care. It may also follow abdominal surgery because clostridia normally inhabit the gastrointestinal tract. The presentation may vary from a mild local cellulitis to the most lethal myonecrosis. Signs of infection are usually present within 24 hours after the trauma. Pain often precedes local or systemic signs and is frequently out of proportion to the severity of the injury. The wound is usually swollen and red and produces a dark, odorous exudate.

The more severe forms are accompanied by chills, fever, tachycardia, delirium, and all of the other signs of a rapidly progressing infection. Renal shutdown and death may occur. The involved skin and muscle undergo further necrosis, and vesicles appear in the infected area.

Gas may be present in the soft tissue but is not diagnostic of clostridia. It also may be because of mechanical reasons (such as open trauma or pulmonary injuries), or it may be a result of infection by other bacteria such as the coliforms or anaerobic streptococci. The roentgenogram may reveal edema and gas within muscle groups. (In bacterial infections not caused by clostridia, the gas is often in the deeper tissue.)

TREATMENT

Prevention is accomplished by a thorough debridement of all potentially contaminated cases and by leaving the wound open if necessary. Mild local infection may need only modest debridement and drainage. The more severe forms require early and radical excision of all involved tissue. Amputation may even be necessary. The appropriate antibiotics are administered intravenously in large doses and general supportive care is given.

Because moderate levels of oxygen have been shown to suppress bacterial activity, hyperbaric oxygen has been used as an adjunct to surgical debridement. The oxygen is supplied by placing the patient in a special chamber several times a day until the symptoms improve. At this time, these chambers are only available at a modest number of medical facilities.

SEPTIC BURSITIS

Infection of superficial bursae is a common occurrence. The bunion, olecranon, and prepatellar bursae are the most commonly affected. In contrast to septic arthritis, this disorder usually occurs in healthy individuals and commonly results from local spread. Occupations that predispose to chronic trauma and fluid collection in the bursa (e.g., carpet layers, plumbers) are more prone to sepsis in this area. There may be evidence of a recent local abrasion or break in the skin. S. aureus is the most common offending organism.

CLINICAL FEATURES

A painful localized bursal swelling is usually present. It is frequently accompanied by an intense cellulitis. A partially healed skin abrasion may be seen nearby. Systemic signs of sepsis are commonly present, including regional lymphadenopathy. A sympathetic joint effusion is fairly common, especially in the knee. The joint itself is not usually tender, and motion is only mildly restricted. The effusion may suggest joint involvement.

TREATMENT

The bursa is aspirated and the fluid evaluated in the standard manner by Gram stain, culture, and sensitivity (Fig. 13-5). Blood cultures, blood counts, and sedimentation rates are also performed as indicated. (NOTE: It is important not to aspirate the joint itself. Passing the needle through the area of cellulitis and then into the joint could spread the infection into the joint.)

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Fig. 13-5 Aspiration of septic prepatellar bursa.

Community-acquired septic bursitis is usually caused by S. aureus or β-hemolytic streptococcus sensitive to a penicillinase-resistant semisynthetic penicillin, such as oxacillin or nafcillin. Surgical drainage of the bursa may be necessary, but many patients respond well to repeated aspirations.

PROSTHETIC JOINT INFECTION

Fewer than 1% of joint replacements become infected, but the complication can be disastrous to the joint and difficult to cure. It may occur at any time after surgery. Early involvement is usually the result of skin contamination, often by coagulase-negative staphylococci. Later, the source is hematogenous, with a variety of pathogens being causative. Joints that have had previous surgery are also more predisposed to infection.

The diagnosis may be difficult. Pain is a common occurrence, but fever and systemic signs may be lacking. Various bone scans may be helpful, but local aspiration with culture is usually necessary. Frequently, all of the hardware must be removed permanently to cure the infection. Because of the risk of reactivating the dormant infection, only occasionally is the joint replaced again and, then, only after a long period of antibiotic therapy and local wound care.

PENETRATING WOUNDS

GUNSHOT WOUNDS

The amount of damage done to tissues by gunshot wounds depends on the velocity of the weapon. Low-velocity weapons usually cause minimal wound tract injury. Important structures are usually pushed away by the missile. These injuries are best treated on an outpatient basis by minimal local debridement of the entrance (and exit) wound, irrigation, a sterile dressing, and a broad-spectrum antibiotic. Tetanus prophylaxis is administered, and if necessary, delayed closure is performed later. Associated fractures are usually undisplaced and are treated by external immobilization.

Bullet removal or operative exploration is undertaken only if the bullet is superficial or symptomatic or if minor fragment migration could cause damage to major adjacent structures. Missile wounds of the knee joint probably should be explored surgically and debrided if fragments are present or if the joint was traversed. The missile and osteochondral fragments are removed. It is possible for lead to be dissolved by synovial tissue and lead to arthritis (lead arthropathy) and, rarely, chronic lead intoxication. Factors involved in systemic lead intoxication include the surface area and amount of fragmentation of the bullet, as well as duration of exposure. Elsewhere in the body, the fragments are usually encapsulated by scar tissue, thereby eliminating their exposure to bodily fluids. Fragments near the spine are usually left alone unless a significant or progressive neural loss occurs.

Wounds caused by high-velocity weapons are managed the same way as those caused by low-velocity weapons, except that more extensive debridement is usually necessary. Their complication rate is much higher, and delayed closure is the rule.

Shotgun wounds also require more extensive debridement. They are often the most serious of missile wounds. The projectile consists of multiple pellets and a wadding (usually fiber or burlap) that transmits the force. Wounds inflicted from a weapon closer than 20 yards are assumed to contain some of this wadding, and exploration and removal are necessary. If the “scatter pattern” of the shotgun is wide, more damage is assumed, especially if the shotgun was fired at close range. A small wound can disguise extensive deeper destruction.

POWER GUN NAIL WOUNDS

These injuries result from the use, mainly by carpenters, of air power gun systems to drive nails. Occasionally, they are accidentally driven into extremities, often directly into bone. They usually can be simply pulled out of the bone with the patient under local anesthesia. The benefit of more extensive debridement does not appear to outweigh the risk involved. The wound is then treated similarly to any other low-velocity weapon injury. Small metallic pieces that remain embedded in bone are probably best left alone. Antibiotics and tetanus prophylaxis are administered.

BITE WOUNDS

More than 1% of all emergency room visits are the result of bites, and the majority of these wounds are superficial. Dog bites account for most of these wounds. They usually present as small puncture wounds. The infection rate is low, and very loose closure of any extensive wound is usually acceptable after thorough cleansing, irrigation, and debridement. Extremity wounds may be left open; however, small puncture wounds should not be opened. Prophylactic antibiotic therapy is indicated, using an agent with activity against S. aureus, β-hemolytic streptococci, anaerobic streptococci, and Pasturella multocida, which is a frequent cause of infection after dog and cat bites. Antirabies therapy and tetanus prophylaxis are provided when indicated.

Human bites require especially careful evaluation and examination. The most common site of injury is a closed fist that has struck the mouth (see Chapter 7). The injury that often occurs is a laceration over the metacarpophalangeal joint that may disrupt the extensor tendon and even penetrate into bone (Fig. 13-6). The wound may be small, and if the hand is examined with the fingers extended, the true extent of the injury may be overlooked because the injury was sustained with the fingers flexed. If joint involvement is noted, extra care is taken to ensure good cleansing and debridement. The wound should be treated open. Antibiotics are administered, and the wound is followed closely. The most common infecting organisms are S. aureus, streptococci, and anaerobes found in the normal flora of the human mouth. In addition, prophylactic therapy is indicated for those who are bitten by individuals with HIV or hepatitis B.

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Fig. 13-6 Osteomyelitis of the proximal phalanx secondary to a human bite (arrow).

PUNCTURE WOUNDS

The most common site of puncture wounds is the foot. The typical clinical picture is that of early improvement followed in 1 to 2 weeks by worsening local signs. A foreign body is sometimes found in the wound, and the most common organism is Pseudomonas. Staphylococci and streptococci are also frequently involved. Osteomyelitis and even joint damage can result. Treatment involves drainage, removal of the foreign body (if present), and the appropriate antibiotic.

Local debridement in the emergency department at the time of the original injury may help prevent late infection. Roentgenograms are indicated to rule out foreign bodies. The decision to use antibiotics at the time of initial wound care remains controversial.

Antibiotics in Orthopedics

The initial therapy in severe infections should always be broad enough to cover the most common organisms. More specific therapy depends on the proper identification of the offending agent and its sensitivity to the various antimicrobial drugs. With the ever-increasing number of antibiotics becoming available, the physician should become sufficiently familiar with a number of well-established ones. It is better to become familiar with several good ones than to try every new antibiotic that comes on the market. Cost and safety are also important factors to consider. The duration of antibiotic therapy, especially for bone, joint, and bursa infections, varies depending on response and the bacteria involved, but in general, antibiotic therapy is usually continued for 3 to 6 weeks. With the availability of home IV therapy, prolonged hospitalization is usually not required.

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