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Osteomyelitis

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Vol. 24 •Issue 2 • Page 54
Osteomyelitis

Bacterial infections of bone can carry serious and costly consequences

Osteomyelitis is a bacterial infection of bone that can produce serious long-term sequelae and require significant health care expenditures. The term osteomyelitis is a fusion of "osteo" (bone), "myelo" (marrow) and "-itis" (inflammation).1 Osteomyelitis may affect all or only a portion of a bone. The most common sites of osteomyelitis infection are the legs, feet, pelvis and spine.

Factors that increase osteomyelitis risk are listed in Table 1. A patient who has a chronic wound that is resistant to standard healing methods or exceeds a reasonable amount of healing time for the particular wound site may have this condition.

Acute vs. Chronic

Depending on the length of time the infection has been present, osteomyelitis can be classified as acute or chronic (Table 2). Acute osteomyelitis is a new bone infection of less than six weeks' duration. Chronic osteomyelitis is a bone infection that has been present longer than six weeks or a bone infection that has recurred. Recurrent infections are most common in adults with chronic wounds.

Staphylococcus aureus is the most common pathogen in acute osteomyelitis. Staphylococcus epidermidis, Pseudomonas aeruginosa, Serratia marcescens and Escherichia coli are commonly isolated in patients with chronic osteomyelitis.3

Patients with diabetes are at increased risk for chronic osteomyelitis due to the microvascular and neuropathic changes that occur with diabetes. Patients with diabetes can be predisposed to osteomyelitis as a result of ischemia, poor glycemic control, -diminished sensation, structural deformities, gait abnormalities and altered immune response. Often, minor foot wounds can serve as portals for bacterial entry to the bone. In patients with diabetes, osteomyelitis tends to occur in the calcaneous bone, the talus bone and the small bones of the feet.

Other high-risk groups include patients with sickle cell anemia, patients who receive hemodialysis, patients with cancer, older adults and IV drug abusers.

The term "cure" is not generally applicable to chronic osteomyelitis because the condition may recur years after an apparent successful treatment due to new trauma to the area or suppression of the patient's immune response.4 In such cases, the goal of treatment is to stop the progression of the osteomyelitis rather than cure it.

Classification

Two classification systems for osteomyelitis have been described in the literature.

The Waldvogel classification system is based on the pathogenesis of the bone infection. It divides osteomyelitis into hematogenous osteomyelitis, contiguous osteomyelitis and osteomyelitis due to vascular insufficiency.

  • Hematogenous (transported by blood) osteomyelitis is more common in children and usually involves the femur and tibia bones. It is often due to trauma with accompanying hematoma or cellulitis.

  • Osteomyelitis from contiguous (adjacent) infections usually involves the long bones and may result from open fractures, infected prostheses and chronic soft tissue infections. Osteomyelitis from contiguous sources is more common in adults.

  • Osteomyelitis due to vascular insufficiency or inadequate blood supply is more common in older adults and patients with diabetes. Because of the peripheral neuropathy that is often present in patients with diabetes, clinical signs and symptoms of bone infection may not be present. Chronic osteomyelitis tends to be a polymicrobial bacterial infection rather than an infection by a single organism, another distinction from the hematogenous and contiguous classifications.2

    The Cierny-Mader classification or staging system reflects the amount of bone involvement and the host's clinical status.

  • Type 1 or stage 1 is intramedullary osteomyelitis from hematogenous seeding and may be referred to as medullary osteomyelitis.

  • Type 2 or stage 2 involves the superficial bone surface. It usually results from contiguous infection spread and may be referred to as superficial osteomyelitis.

  • Type 3 or stage 3 is a localized osteo-myelitis.

  • Type 4 or stage 4 is diffuse osteomyelitis. It is most common with chronic wounds such as pressure ulcers and involvesthe entire bone segment.5

    The Cierny-Mader classification system also describes the host's clinical status, since this status affects the patient's ability to withstand infection. It also affects treatment choice and potential morbidity. Healthy patients are listed as Class A hosts because they have the greatest chance of arresting the osteomyelitis infection.

    Class B hosts are divided into local (Bl) and systemic (Bs). Patients who are both locally and systemically immunocompromised are classified as Bls. Examples of local host or Bl deficiencies are chronic lymphedema, venous ulcers, smoking more than two packs per day, major blood vessel compromise, neuropathy and radiation fibrosis. Examples of systemic host or Bs deficiencies are diabetes, older age, cancer, malnutrition, renal disease and chronic hypoxia.5

    Diagnosis

    Acute osteomyelitis is most common in children. It usually involves the long bones and is contracted through blood stream infections. Diagnosis is based on a positive bacterial culture of the bone or the growth of the infecting pathogen in cultures of purulent material obtained by needle aspiration from the painful infected area. Clinical findings may include fever, irritability, lethargy, tenderness over the bone, and decreased range of motion in adjacent joints.6 The treatment of suspected acute osteomyelitis should begin immediately.

    In contrast to acute osteomyelitis, the diagnosis of chronic osteomyelitis can usually precede therapy. The diagnosis of chronic osteomyelitis also differs in that it is most common in adults and is usually associated with an open draining wound or sinus tract from the infected bone to the overlying skin. It is particularly difficult to diagnose in patients with diabetes because diabetes-related vascular changes and peripheral neuropathy may mask clinical signs and symptoms of infection. In addition, chronic osteomyelitis in patients with diabetes is usually polymicrobial.

    Laboratory studies such as white blood cell count, erythrocyte sedimentation rates and C-reactive protein may be elevated in the patient with osteomyelitis, but these tests can be nonspecific in the presence of any type of inflammatory process. In addition, the characteristic radiologic changes that are suggestive of osteomyelitis may be obscured by osteoarthropathy in patients with diabetes.

    Given these issues, bone biopsy is considered the gold standard for diagnosing chronic osteomyelitis. Despite its high accuracy level, the test warrants careful consideration because bone biopsy is an invasive procedure that is performed through uninvolved skin. In some cases, it requires taking the patient to the operating room to obtain the sample of bone.

    A simple, commonly used bedside assessment, the probe-to-bone test, is often used to predict osteomyelitis before ordering expensive imaging studies. However, the reliability of this test recently came into question. Several radiologic imaging techniques are also used to diagnose osteomyelitis, including plain film x-ray, computed tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine imaging.

    Treatment

    The traditional treatment approach to osteomyelitis is surgery followed by four to six weeks of parenteral antibiotics. No evidence shows that parenteral antibiotics penetrate necrotic bone. Therefore, surgical debridement is necessary to ensure that vascularized bone is treated. It takes four to six weeks for debrided bone to be protected by the revascularized tissue.12

    Antibiotic selection should be based on targeting the causative organisms. In most cases, a broad-spectrum antibiotic is necessary because many of these chronic infections are polymicrobial.

    Due to a lack of controlled trials and the heterogeneous nature of osteomyelitis, some treatment issues remain undecided. The optimal duration of antibiotic therapy and the most effective combination of medications are unknown. Medical treatment can involve the use of parenteral antibiotics, a combination of parenteral and oral antibiotics, or long-term, high-dose oral therapy.9

    Debridement of all nonviable bone is critical to prevent reccurrence. The remaining healthy bone should show punctuate bleeding known as the "paprika sign," which distinguishes it from the dead bone.13 Surgery is also important to eliminate dead space left after the bone is removed, to restore skin integrity through the use of skin grafts and flaps, and to enhance vascular supply to the area.

    Systemic disorders, which are common in patients with infections classified as Cierny-Mader Bs, affect prognosis. Even with optimal care, 20-30 percent of patients will develop recurrence within two years.2 Recurrent osteomyelitis is often resistant to treatment with surgery and antibiotics, leading to the conclusion that the infection may not have been totally eliminated.

    Recently, hyperbaric oxygen therapy (HBO) has been used as an adjunct to surgery and antibiotics to treat chronic osteomyelitis. This approach is based on the premise that HBO improves available oxygen at the bone site, enhancing the ability of white blood cells to phagocytize the bacteria and promote osteogenesis.14 Research about this therapy is limited, however, and more studies are needed to define the adjunctive role of HBO in chronic osteomyelitis.

    Prevention

    Because osteomyelitis is such a complex and costly condition, its prevention should be a top health priority. Measures to decrease risk include the following:

  • Smoking cessation: Health care providers should encourage cessation in every patient who smokes, but for patients at risk for osteomyelitis, this act has additional importance.

  • Improved nutrition: Patients who are malnourished may have difficulty fighting off an infection such as osteomyelitis. The importance of a well-balanced diet to deliver adequate fluid and nutrients to the infection site cannot be overemphasized.

  • Glycemic control: Nationally recognized guidelines recommend that patients with diabetes achieve an A1c level of 7 percent or less.

  • Offloading of pressure to bony areas: Patients with diabetes often develop neuropathy, which can result in structural deformities of the feet and inability to sense pain. Shoes may cause blisters or sores but go unnoticed because of the lack of feeling in the feet. When a standard shoe does not fit a patient's foot, referral to a certified pedorthist is warranted. A pedorthist can recommend appropriate types and styles of shoes, modify existing shoes or even order special shoes or orthoses to offload pressure areas. Advise all patients with diabetes to check shoes for rocks and other objects before putting shoes on. Also advise them never to wear shoes without stockings or socks.

  • Appropriate wound care: Osteomyelitis often presents as a draining wound or sinus tract. Absorbent wound care products or dressings, such as calcium alginates, can be helpful in managing the drainage. Negative pressure therapies can also be beneficial if the osteomyelitis is already being treated.

  • Patient education: Provide detailed education about the clinical signs and symptoms of osteomyelitis to all patients at risk. Early diagnosis and treatment can improve outcomes.

    References available at www.advanceweb.com/OT or upon request.

    Catherine Ratliff, NP, is a nurse practitioner and associate professor at the University of Virginia Health System in Charlottesville, VA. She is also certified in wound, ostomy and continence care.

    Table 1: Risk Factors for Osteomyelitis

    Decreased peripheral circulation

    Presence of a wound

    Prior history of osteomyelitis

    Poor glycemic control

    Malnutrition

    Decreased sensation

    Structural deformities

    Gait abnormalities

    Male gender

    Table 2: Characteristics of Acutevs. Chronic Osteomyelitis

    Acute Osteomyelitis

    Infection has been present for less thansix weeks.

    Symptoms may include fever or chills, malaise and, at the infection site, pain, limited range of motion and redness, warmth or swelling.

    This condition requires antibiotic treatment targeted to the specific infectious organism.

    Chronic Osteomyelitis

    Infection has been present for more thansix weeks.

    This infection is common in adults whohave a recurring or chronic wound.

    Symptoms may include chronic low-grade fever, chronic localized pain, and a draining sinus tract that has been present for months or even years.

    Patients with diabetes are at higher risk for chronic osteomyelitis compared with non-diabetics.

    This condition requires surgical debridement of the infected bone plus antibiotics targeted to the specific infectious organism.




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