Osteomyelitis is an infection in a bone. Infections can reach a bone by traveling through the bloodstream or spreading from nearby tissue. Osteomyelitis can also begin in the bone itself if an injury exposes the bone to germs.
In children, osteomyelitis most commonly affects the long bones of the legs and upper arm, while adults are more likely to develop osteomyelitis in the bones that make up the spine (vertebrae). People who have diabetes may develop osteomyelitis in their feet if they have foot ulcers.
Once considered an incurable condition, osteomyelitis can be successfully treated today. Most people require surgery to remove parts of the bone that have died — followed by strong antibiotics, often delivered intravenously, typically for at least six weeks.
TYPES OF OSTEOMYELITIS:
Acute osteomyelitis:
An acute attack of osteomyelitis can lead to chronic osteomyelitis, characterised by dead areas of bone. This condition can fail to respond to treatment and recur for a long time. In many cases, chronic osteomyelitis is polymicrobial, which means more than one infectious agent is involved.
Waldvogel classification system:
Osteomyelitis is classified according to the mechanism of infection (hematogenous or contiguous) and the presence of vascular insufficiency:
• Hematogenous osteomyelitis
o Occurs when bone tissue is seeded by pathogenic organisms during the course of bacteremia
o Accounts for 20% of cases of osteomyelitis in adults
o The vertebrae are the most common site of hematogenous infection in adults, but the long bones, pelvis, and clavicle may also be affected
Vertebral osteomyelitis is divided into the following two categories:
Pyogenic infections, which are most commonly caused by S. aureus(40%-45% of all cases)
Nonpyogenic (granulomatous) infections, which are most commonly caused by Mycobacterium tuberculosis
Vertebral osteomyelitis occurs most commonly in men between 60 and 70 years of age and involves the lumbar spine
• Osteomyelitis secondary to a contiguous focus of infection
o Occurs after a traumatic bone injury or as a result of the spread of infection from a nearby source (eg, soft tissue infection)
o Common associated factors include a history of surgical reduction and internal fixation of fractures, prosthetic devices, open fractures, and chronic soft tissue infections; decubitus ulcer; burn; or regional soft tissue infection
o More common in older patients, who generally develop infections following cellulitis or arthroplasties; infection in younger patients usually occurs as a result of trauma or surgery
o Most often affects the tibia and femur
• Osteomyelitis associated with vascular insufficiency
o Caused by impaired blood supply to susceptible tissues
o Usually occurs in older patients and in patients with diabetes mellitus or severe atherosclerosis
In patients with diabetes, the small bones of the feet are most often involved; neuropathy may also be present
The risk of developing osteomyelitis is greater in patients with large (>2 cm in diameter) and deep (>3 mm) diabetic ulcers and if the bone is exposed
Osteomyelitis may be classified as acute, subacute, or chronic, depending on the time to clinical presentation relative to the introduction of infection.
• Acute osteomyelitis is characterized as a suppurative infection presenting with edema, small vessel thrombosis, and vascular congestion within 2 weeks of onset
• Subacute osteomyelitis may be more indolent, presenting 1 to several months after infection
• Chronic osteomyelitis is the result of longstanding infection, which may take months or years to develop or which has been suppressed by the host (‘remission’) or partially treated so that it remains relatively dormant for long periods before becoming clinically apparent. Chronic osteomyelitis is characterized by the presence of necrotic bone (sequestrum); new bone formation; drainage or sinus tracts; and the presence of leukocytes, lymphocytes, and histiocytes. It can be recognized in patients with a history of osteomyelitis who experience a recurrence of pain, erythema, and swelling, along with a draining sinus
Cierny-Mader staging and classification system:
Osteomyelitis is categorized according to the portion of bone affected; the physiologic status of the patient; and risk factors that affect immunity, metabolism, and vascularity. The first part of the system categorizes osteomyelitis according to anatomic type, as follows:
• Stage 1: medullary osteomyelitis
o Limited to the medullary cavity
o Often caused by a solitary organism
o Causes include hematogenous spread and infections from orthopedic devices (intramedullary rods)
Stage 2: superficial osteomyelitis
o Involves the cortex
o Often caused by an adjacent soft tissue infection
o Exposed, infected outer necrotic surface of bone is observed at the base of a soft tissue wound
o Local ischemia is seen
• Stage 3: localized osteomyelitis
o May involve both the medulla and cortex, but the bone generally remains stable, as the infection does not involve its entire diameter
• Stage 4: diffuse osteomyelitis
o Extensive disease
o May occur on both sides of a nonunion or a joint
o Involves the entire thickness of the bone, with loss of stability
The second part of the system describes the patient’s physiologic status, as deficiencies of leukocyte recruitment, phagocytosis, or vascular supplies may promote osteomyelitis and contribute to its chronicity. The physiologic class of the infected patient is often more important than the anatomic type because the state of the host is the strongest predictor of treatment failure.
• Class A: normal host
o Normal physiologic, metabolic, and immune functions
o Associated with a much better prognosis
• Class B: host factors limit normal immune response and healing
o Immunocompromised, either locally (Bl), systemically (Bs), or both (Bls)
o Local factors include problems of perfusion (peripheral vascular disease, vasculitis, venous stasis, lymphedema)
o Systemic factors include hypoxemia, illnesses associated with impaired immune function (chronic renal or hepatic insufficiency, malignancy, diabetes), or use of immunosuppressive medication (steroids)
o The goal of treatment is to remove the factors that lead to the development of osteomyelitis
• Class C: health of host does not allow full treatment
o Treatment poses a greater risk than the infection itself
o Surgery may not be possible because of the patient’s debilitated or immunocompromised status
How do you get osteomyelitis?
If some germs (bacteria) settle on a small section of bone, they can multiply and cause infection. Bacteria can get to a bone:
• Via the bloodstream
. This is the common cause in children. Bacteria sometimes get into the blood from an infection in another part of the body and then travel to a bone. Even if you are healthy, bacteria can sometimes get into the blood from the nose or gut (bowel).
• Following an injury
. Bacteria can spread to bone if you have a deep cut on the skin. In particular, if you have a broken bone which you can see through the cut skin.
Who is at risk of developing osteomyelitis?
Anyone at any age can develop osteomyelitis. However, you have an increased risk if you:
• Have recently broken (fractured) a bone.
• Have a bone prosthesis (an artificial hip, a screw in a bone following surgery, etc).
• Have recently had surgery to a bone.
• Have a poor immune system. For example, if you haveAIDS, if you are taking chemotherapy, if you are seriously ill with another disease, etc.
• Inject street drugs which can be contaminated with germs (bacteria).
• Are dependent on alcohol.
• Have had a previous episode of osteomyelitis.
• Have certain types of blood disorders. For example, sickle cell disease.
• Have reduced skin sensation. This can lead to damage and infection of the skin, which can spread to the blood or to local bone. For example, some people with diabetes have reduced sensation in their feet.
• Have regular kidney dialysis.
• Take steroids regularly.
Osteomyelitis does not occur more commonly in a particular race or gender. However, some people are more at risk for developing the disease, including:
• People with diabetes
• Patients receiving hemodialysis
• People with weakened immune systems
• People with sickle cell disease
• Intravenous drug abusers
• The elderly
Which bones can be affected?
The long bones of the leg (femur, tibia and fibula) are the most commonly affected. However, osteomyelitis can affect any bone (although it is very rare in some bones).
Causes
Most cases of osteomyelitis are caused by staphylococcus bacteria, a type of germ commonly found on the skin or in the nose of even healthy individuals.
Germs can enter a bone in a variety of ways, including:
• Via the bloodstream.
Germs in other parts of your body — for example, from pneumonia or a urinary tract infection — can travel through your bloodstream to a weakened spot in a bone. In children, osteomyelitis most commonly occurs in the softer areas, called growth plates, at either end of the long bones of the arms and legs.
• From a nearby infection.
Severe puncture wounds can carry germs deep inside your body. If such an injury becomes infected, the germs can spread into a nearby bone.
• Direct contamination.
This may occur if you have broken a bone so severely that part of it is sticking out through your skin. Direct contamination can also occur during surgeries to replace joints or repair fractures.
• An open injury to the bone, such as an open fracture with the bone ends piercing the skin.
• An infection from elsewhere in the body, such as pneumonia or a urinary tract infection that has spread to the bone through the blood (bacteremia, sepsis).
• A minor trauma, which can lead to a blood clot around the bone and then a secondary infection from seeding of bacteria.
• Bacteria in the bloodstream bacteremia (poor dentition), which is deposited in a focal (localized) area of the bone. This bacterial site in the bone then grows, resulting in destruction of the bone. However, new bone often forms around the site.
A chronic open wound or soft tissue infection can eventually extend down to the bone surface, leading to a secondary bone infection.
Osteomyelitis affects about two out of every 10,000 people. If left untreated, the infection can become chronic and cause a loss of blood supply to the affected bone. When this happens, it can lead to the eventual death of the bone tissue
.
Osteomyelitis can affect both adults and children. The bacteria or fungus that can cause osteomyelitis, however, differs among age groups. In adults, osteomyelitis often affects the vertebrae and the pelvis. In children, osteomyelitis usually affects the adjacent ends of long bones. Long bones (bones of the limbs) are large, dense bones that provide strength, structure, and mobility. They include the femur and tibia in the legs and the humerus and radius in the arms.
Symptoms of osteomyelitis:
The symptoms of osteomyelitis can include
:
• Pain and/or tenderness in the infected area
• Swelling and warmth in the infected area
• Fever
• Nausea, secondarily from being ill with infection
• General discomfort, uneasiness, or ill feeling
• Drainage of pus through the skin
Additional symptoms that may be associated with this disease include:
• Excessive sweating
• Chills
• Lower back pain (if the spine is involved)
• Swelling of the ankles, feet, and legs
• Changes in gait (walking pattern that is a painful, yielding a limp)
Diagnosing osteomyelitis
To diagnose osteomyelitis, the doctor will first perform a history, review of systems, and a complete physical examination. In doing so, the physician will look for signs or symptoms of soft tissue and bone tenderness and possibly swelling and redness. The doctor will also ask you to describe your symptoms and will evaluate your personal and family medical history. The doctor can then order any of the following tests to assist in confirming the diagnosis:
• Physical examination
• Medical history
• Blood tests:
When testing the blood, measurements are taken to confirm an infection: a CBC (complete blood count), which will show if there is an increased white blood cell count; an ESR (erythrocyte sedimentation rate); and/or CRP (C-reactive protein) in the bloodstream, which detects and measures inflammation in the body.
• Blood culture:
A blood culture is a test used to detect bacteria. A sample of blood is taken and then placed into an environment that will support the growth of bacteria. By allowing the bacteria to grow, the infectious agent can then be identified and tested against different antibiotics in hopes of finding the most effective treatment.
• Needle aspiration:
During this test, a needle is used to remove a sample of fluid and cells from the vertebral space, or bony area. It is then sent to the lab to be evaluated by allowing the infectious agent to grow on media.
• Biopsy:
A biopsy (tissue sample) of the infected bone may be taken and tested for signs of an invading organism.
• Bone scan:
During this test, a small amount of Technetium-99 pyrophosphate, a radioactive material, is injected intravenously into the body. If the bone tissue is healthy, the material will spread in a uniform fashion. However, a tumor or infection in the bone will absorb the material and show an increased concentration of the radioactive material, which can be seen with a special camera that produces the images on a computer screen. The scan can help your doctor detect these abnormalities in their early stages, when X-ray findings may only show normal findings.
Imaging tests:
• X-rays.
X-rays can reveal damage to your bone. However, damage may not be visible until osteomyelitis has been present for several weeks. More detailed imaging tests may be necessary if your osteomyelitis has developed more recently.
• Computerized tomography (CT) scan.
A CT scan combines X-ray images taken from many different angles, creating detailed cross-sectional views of a person’s internal structures.
• Magnetic resonance imaging (MRI).
Using radio waves and a strong magnetic field, MRIs can produce exceptionally detailed images of bones and the soft tissues that surround it.
Treating and managing osteomyelitis:
The objective of treating osteomyelitis is to eliminate the infection and prevent the development of chronic infection. Chronic osteomyelitis can lead to permanent deformity, possible fracture, and chronic problems, so it is important to treat the disease as soon as possible.
Drainage:
If there is an open wound or abscess, it may be drained through a procedure called needle aspiration. In this procedure, a needle is inserted into the infected area and the fluid is withdrawn. For culturing to identify the bacteria, deep aspiration is preferred over often-unreliable surface swabs. Most pockets of infected fluid collections (pus pocket or abscess) are drained by open surgical procedures.
Medications:
Prescribing antibiotics is the first step in treating osteomyelitis. Antibiotics help the body get rid of bacteria in the bloodstream that may otherwise re-infect the bone. The dosage and type of antibiotic prescribed depends on the type of bacteria present and the extent of infection. While antibiotics are often given intravenously, some are also very effective when given in an oral dosage. It is important to first identify the offending organism through blood cultures, aspiration, and biopsy so that the organism is not masked by an initial inappropriate dose of antibiotics. The preference is to first make attempts to do procedures (aspiration or bone biopsy) to identify the organisms prior to starting antibiotics.
Splinting or cast immobilization:
This may be necessary to immobilize the affected bone and nearby joints in order to avoid further trauma and to help the area heal
adequately and as quickly as possible. Splinting and cast immobilization are frequently done in children, although motion of joints after initial control is important to prevent stiffness and atrophy.
Surgery:
Depending on the severity of the infection, osteomyelitis surgery may include one or more of the following procedures:
• Drain the infected area.
Opening up the area around your infected bone allows your surgeon to drain any pus or fluid that has accumulated in response to the infection.
• Remove diseased bone and tissue.
In a procedure called debridement, the surgeon removes as much of the diseased bone as possible, taking a small margin of healthy bone to ensure that all the infected areas have been removed. Surrounding tissue that shows signs of infection also may be removed.
• Restore blood flow to the bone.
Your surgeon may fill any empty space left by the debridement procedure with a piece of bone or other tissue, such as skin or muscle, from another part of your body. Sometimes temporary fillers are placed in the pocket until you’re healthy enough to undergo a bone graft or tissue graft. The graft helps your body repair damaged blood vessels and form new bone.
• Remove any foreign objects.
In some cases, foreign objects, such as surgical plates or screws placed during a previous surgery, may have to be removed.
• Amputate the limb.
As a last resort, surgeons may amputate the affected limb to stop the infection from spreading further.
What is the outlook (prognosis)?
If the infection is treated promptly, there is a good chance of a complete cure. The best outcome occurs if you have treatment within 3-5 days of the start of infection. (In the days before antibiotic medicines, osteomyelitis was a very serious illness which sometimes caused death, and often caused severe disability.)
Possible complications are listed below. As a rule, there is more risk of developing complications if the infection develops after a serious bone injury, or after surgery to a bone:
• If the infection is left untreated, a ball of pus (abscess) may develop in the bone and surrounding tissue. In time, this may burst on to the skin and leave a track (sinus) between the infected bone and surface of the skin.
• Blood infection (septicaemia) which can cause serious illness.
• If the infection follows a bone break (fracture) then there is a chance that the fracture will not heal (non-union of fracture).
• Compression of other structures next to the infection.
• Some bone infections are caused by a germ (bacterium) called meticillin-resistant S. aureus (MRSA) which is difficult to clear with antibiotics.
• Persistent infection of the bone (chronic osteomyelitis) sometimes develops and can be difficult to clear.
Once you have had one bout of osteomyelitis, your risk of a further bout is higher than average. Therefore, if you have had a previous bout of osteomyelitis, see a doctor quickly if you develop the symptoms described above.
Primary prevention:
• Patients with diabetes should have a complete examination of the lower extremities annually and inspection of the feet for wounds at interim routine follow-up visits. Measures to prevent diabetic foot ulcers should be emphasized. A high index of suspicion should be maintained for the contiguous spread of local diabetic foot infections to the bone, with continuous evaluation for signs and symptoms of the development of osteomyelitis
• Patients with open fractures who are able to receive antibiotics within 6 hours of injury and prompt surgical treatment have a reduced risk of developing osteomyelitis
• The use of prophylactic antibiotics prior to bone surgery has been shown to prevent wound infections
• Scrupulous care should be taken to avoid health care–associated osteomyelitis, with careful attention to intravascular and urinary catheters, surgical incisions, and other wounds
Preventive measures:
• Measures to prevent diabetic foot include excellent foot hygiene, glycemic control, and use of protective footwear
• Patients should be instructed to examine their feet daily and to seek prompt medical care for new wounds or other injuries to the feet
• A complete evaluation of the lower extremities should be done annually, and the feet should be inspected for wounds at periodic follow-up visits in the interim
• Patients with Charcot joints or other abnormalities that result in friction with shoes may require specially adapted shoes
• In patients undergoing foot surgery or amputation, the use of protective footwear postoperatively is helpful in preventing subsequent ulceration and infection
In patients with open fractures:
• Administration of antibiotics within 6 hours of injury and prompt surgical treatment are associated with a reduced risk of developing osteomyelitis
• A continued 24-hour regimen of penicillin or first-generation or second-generation cephalosporins is also beneficial
In patients undergoing bone surgery
:
• Administration of prophylactic antibiotics has proven to be successful in the prevention of infection following surgery, particularly in patients with noncompound hip fractures and those receiving total hip and knee prostheses
o In patients undergoing clean bone surgery, intravenous antibiotics are administered 30 minutes before skin incision and up to 24 hours following the procedure. A first-generation or second-generation cephalosporin is appropriate in many cases; vancomycin may be used in patients who are allergic to cephalosporin and in settings with a high prevalence of methicillin-resistant staphylococci
o In patients undergoing surgery for closed fractures, the use of penicillin, first-generation cephalosporins (eg, cefazolin), or second-generation cephalosporins (eg, cefamandole, cefuroxime) has led to a reduction in postsurgical infection
• Standard preoperative procedures, such as the use of antimicrobial shower, shaving, and topical disinfectants, should be followed. Observation of such procedures, together with the use of surgical rooms with laminar airflow and prophylactic antibiotic therapy, has led to a reduction in the postsurgical rate of infection to 0.5% to 2%, depending on the type of joint replacement
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