Osteomyelitis

Original Editors -Nathan McCauley as part of the Bellarmine University Pathophysiology of Complex Patient Problems project.

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Definition/Description

Osteomyelitis, or bone infection, is an inflammation of bone caused by an infectious organism such as bacteria. However, fungi, parasites, or viruses can also cause osteomyelitis. Acute osteomyelitis is the clinical term for a new infection in bone that can develop into a chronic reaction when intervention is delayed or inadequate. Osteomyelitis can occur for a variety of reasons and can affect all populations but is most common in infants, children, and older adults. Individuals with compromised immune systems, a history of IV drug abuse, or alcohol abuse are more susceptible to developing this rapidly progressing pyogenic infection. The pathophysiology of osteomyelitis is complex and poorly understood. There are several key factors contributing to the infection including: the virulence of the infectious organism, the individual’s immune status, any underlying disease, and the type, location, and vascularity of the involved bone.

Prevalence

The prevalence of osteomyelitis has decreased throughout the years due to greater control of the spread of infection in hospitals as well as a better understanding of osteomyelitis treatment approaches.  This enables the infection, in many cases, to be caught within 48 hours and prevented from becoming a chronic recurrence.

• The incidence of osteomyelitis in children has decreased to 47/10,000 in 1990 from 87/10,000 in 1970. 
• The incidence of vertebral osteomyelitis has been estimated at 2.4 cases per 100,000, with the risk increasing with age (0.3/100,000 among individuals <20 years of age to 6.5/100,000 among individuals >70 years of age).
• Osteomyelitis of the spine is rare, accounting for only about 2-4% of all cases.

Characteristics/Clinical Presentation

Individuals presenting with osteomyelitis may have the following symptoms:

• Pain and/or tenderness in the infected area
• Inflammation, redness, and warmth in the infected area
• Fever, chills, and excessive sweating
• Nausea and generalized feeling of being ill
• Lower back pain (if the vertebrae are involved)
• Swelling of the legs, ankles, and feet
  

The primary manifestations of osteomyelitis may vary between adults and children. In adults, back pain is typically the chief complaint but once the infection becomes systemic, a low-grade fever may be present. Children are more likely to present with acute, severe complaints, such as high fever and intense pain, but in some cases the predominating symptoms are edema, erythema, and tenderness in the infected area. In both cases, pain may not always be a factor early in the infectious process due to the lack of pain fibers in cancellous bone. When the infection extends into the periosteum of the bone, individuals may experience joint pain, decreased function, and systemic signs, such as fever, swelling, and malaise.

Individuals may also present with increased pain, described as deep and constant, during weight bearing and may exhibit an antalgic gait pattern when the infection involves the lower extremity. Range of motion of the lumbar spine may be decreased and painful at the end range of motion with vertebral involvement.

“Sausage toes”, a clinical sign that has been shown to have good sensitivity and specificity, can help determine the presence of osteomyelitis affecting the phalanges of the feet in diabetic individuals.

Associated Co-morbidities

The following are risk factors and/or associated co-morbidities that could increase an individuals chance of developing osteomyelitis:

• Diabetes
• Peripheral arterial disease (PAD) 
• Sickle cell disease
  

Systemic Lupus Erythematosus (SLE) can also be associated with developing osteomyelitis. In fact, one fourth of all persons with Lupus develop progressive musculoskeletal damage in the form of arthritis, osteoporosis with fracture and vertebral collapse, and osteomyelitis.

Medications

(Table courtesy of American Family Physician. Available at: Diagnosis and Management of Osteomyelitis)

Diagnostic Tests/Lab Tests/Lab Values

Medical diagnosis is often difficult because of the lack of specific signs and symptoms, especially in chronic osteomyelitis. Signs and symptoms that are usually associated with infection may be mistaken for normal postoperative changes.

Radiographs

• May not detect bony abnormality in infections less than 10 days in duration.
• Lytic lesions may be demonstrable on radiographs within 2 weeks of onset of the infection.
• Magnetic resonance imaging (MRI) and isotope bone scans are the procedures of choice to delineate the diseases anatomic extent.
• Flourine-18-flourodeoxyglucose positron emission tomography (FDG-PET) scans provide accurate localization of infection and/or source of fever of undetermined origin, thereby guiding further testing.

(Photo courtesy of The New England Journal of Medicine. Available at: http://blogs.nejm.org/now/index.php/vertebral-osteomyelitis/2010/03/18/)

Etiology/Causes

• Osteomyelitis can occur in a variety of bones in different areas of the body. The area affected often depends on the causative agent, the individuals’ age, and previous medical history as certain types of osteomyelitis can affect different populations. The bones commonly involved in children are long bones (adjacent to growth plates) such as the femur, tibia, humerus, and radius due to the amount of bone marrow present in long bones. Osteomyelitis in adults usually affects the vertebral column, in particular the lumbar spine, the sacrum, and the pelvis.
• Staphylococcus aureus is the usual causative agent of acute osteomyelitis. Once bound to cartilage, the organism produces a protective glycocalyx and stimulates the release of endotoxins. Other organisms such as group B streptococcus, pneumococcus, Pseudomonas aeruginosa, Haemophilus influenza, and Escherichia coli are also capable of producing bone infection. In individuals diagnosed with sickle cell anemia, Salmonella infection can be associated with osteomyelitis.
• Surgical procedures, open fractures, and implanted orthotic devices are also causative agents of acute osteomyelitis. A form of osteomyelitis, exogenous osteomyelitis, occurs when bone extends out from the skin allowing a potentially infectious organism to enter from an abscess or burn, a puncture wound, or other trauma such as an open fracture. These examples of osteomyelitis secondary to infection are common in immunocompromised individuals and in those diagnosed with diabetes mellitus or severe vascular insufficiency.
• Hematogenous osteomyelitis is acquired from the spread of organisms from preexisting infections such that occurs in impetigo; furunculosis (persistent boils); infected lesions of varicella (chickenpox); and sinus, ear, dental, soft tissue, respiratory, and genitourinary infections. Genitourinary infections can lead to osteomyelitis of the sacrum or iliac.

Systemic Involvement

There are several systemic factors that affect immune surveillance, metabolism, and local vascularity that may lead to an increased risk for developing osteomyelitis:

• Malnutrition
• Renal or hepatic failure
• Diabetes mellitus
• Chronic hypoxia
• Immune disease
• Extremes of age
• Immunosuppression
• Immune deficiency
  

Medical Management (current best evidence)

Immediate treatment is indicated for osteomyelitis, especially in the acute phase. Treatment is usually initiated with an antibiotic, determined by the results of the bone biopsy or cultures taken, given intravenously at a high dose. Factors such as the patients age, health status, location of infection, and prior antimicrobial therapy are taken into consideration when determining the antibiotic used for treatment. The antibiotics are usually prescribed for 4-6 weeks followed by >8 weeks of oral therapy.

Osteomyelitis may also need to be treated surgically.  Options include:

• Draining the infected area
• Removal of necrotic bone and soft tissue
• Restoring normal blood flow to the bone
• Removing any foreign objects
• Amputation of the infected limb.

Physical Therapy Management (current best evidence)

• Physical  therapists can play a vital role in the screening process for osteomyelitis.  Individuals who present with signs and symptoms of infection, possibly causing osteomyelitis, should be referred to a physician for further diagnostic testing.  These signs and symptoms are included in the above section.
• Prevention is another area in cases of osteomyelitis where physical therapists can play an important role.  Chronic osteomyelitis is often a result of complication of treatment with open fractures, therefore, prevention of infection is highly important.  Since the role of nutrition is vital in cases of infection, patient need to be properly educated on proper nutrition in early post-surgical intervention due to the fact that most infections occur in the immediate post-operative period.  Individuals who are at risk for developing osteomyelitis should also be taught proper preventative measures and be aware of early warning signs that infection may be present such as, excessive pus present coming from incision line, redness, extreme tenderness, increased skin temperature near area of injury or surgical procedure, and symptoms of nausea or vomiting.
• If treated surgically for osteomyelitis, physical therapy may be indicated post-operatively to address any impairments in strength, ROM, proprioception, etc. as well as treatment for any functional limitations or disabilities secondary to the infection.

Differential Diagnosis

The following are possible conditions that could have similar signs and symptoms or relate in other ways to osteomyelitis:

• Ewing Sarcoma
• Osteosarcoma
• Reactive bone marrow edema
• Traumatic or stress fractures
• Inflammatory arthritis
• Gout
  

Case Reports/ Case Studies

Tomaszewski D, Avella D. Vertebral osteomyelitis in a high school hockey player: a case report. J Athl Train 1999;34(1):29-33.

Kline A. Streptococcal Group-B Osteomyelitis of the foot: a case report. Podiatry Internet Journal 2007;2(1):3.

Resources

The Journal of the American Medical Association. Osteomyelitis

National Institue of Health. Genetic and Rare Diseases Information Center (GARD). [1]

The Nemours Foundation. Teens Health. [2]

Recent Related Research (from Pubmed)

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