What is Osteomyelitis?
An infection of the bone, a rare but serious condition. Bones can become infected in a number of ways: Infection in one part of the body may spread through the bloodstream into the bone, or an open fracture or surgery may expose the bone to infection.
What Causes Osteomyelitis?
In most cases, a bacteria called Staphylococcus aureus, a type of staph bacteria, causes osteomyelitis. Certain chronic conditions like diabetes may increase your risk for osteomyelitis.
Who Gets Osteomyelitis?
Only 2 out of every 10,000 people get osteomyelitis. The condition affects children and adults, although in different ways. Certain conditions and behaviors that weaken the immune system increase a person's risk for osteomyelitis, including:
- Diabetes (most cases of osteomyelitis stem from diabetes)
- Sickle cell disease
- HIV or AIDS
- Rheumatoid arthritis
- Intravenous drug use
- Long-term use of steroids
- Poor blood supply
- Recent injury
Bone surgery, including hip and knee replacements, also increase the chance of bone infection.
Osteomyelitis in Children and Adults
In children, osteomyelitis is usually acute. Acute osteomyelitis comes on quickly, is easier to treat, and overall turns out better than chronic osteomyelitis. In children, osteomyelitis usually shows up in arm or leg bones.
In adults, osteomyelitis can be either acute or chronic. People with diabetes, HIV, or peripheral vascular disease are more prone to chronic osteomyelitis, which persists or recurs, despite treatment. Whether chronic or acute, osteomyelitis often affects an adult's pelvis or vertebrae of the spine. It can also occur in the feet, especially in a person with diabetes.
Symptoms of Osteomyelitis
Acute osteomyelitis develops rapidly over a period of seven to 10 days. The symptoms for acute and chronic osteomyelitis are very similar and include:
- Fever, irritability, fatigue
- Tenderness, redness, and warmth in the area of the infection
- Swelling around the affected bone
- Lost range of motion
Osteomyelitis in the vertebrae makes itself known through severe back pain, especially at night.
Figuring out if a person has osteomyelitis is the first step in treatment. It's also surprisingly difficult. Doctors rely on X-rays, blood tests, MRI, and bone scans to get a picture of what's going on. A bone biopsy is necessary to confirm a diagnosis of osteomyelitis. This also helps determine the type of organism, typically bacteria, causing the infection so the right medication can be prescribed.
Questions When a Loved One Has Osteomyelitis
The Cierny-Madder osteomyelitis classification system takes into consideration the anatomic extent of bone involvement, the quality of the host and treatment factors. This has been used as a staging system to describe extent and severity of osteomyelitis and compare effectiveness of treatment protocols.
Foot osteomyelitis typically develops by spread of infection in the patient with underlying polyneuropathies. The insensate foot receives increased repetitive microtrauma at high axial load areas, such as bony prominences. This leads to localized tissue necrosis and ulcer formation. Diabetic patients usually have some degree of proximal arterial vascular disease. At times this proximal vascular disease can be segmental with high grade stenosis or occlusions which severely impair the bodies’ ability to manage this type of neuropathic ulceration. Uncontrolled hyperglycemia, especially in the brittle diabetic, decreased the immune capacity to fight to infection. Trauma, ulceration, and bacterial invasion therefore precede the development of osteomyelitis. It is this sequela that leads to chronic ulcer formation with a bacterial load that then colonizes and infects the neighboring bone (contiguous-focused). Underlying osteomyelitis is present in as many as 2/3 of patients hospitalized for diabetic foot ulcer.
In contiguous-focused osteomyelitis any deep soft tissue wound infection adjacent to bone can be the source of osteomyelitis. Bacteria from necrotic tissue as seen with a stage IV pressure ulcer or non-stagable mal perforans ulcer can invade the outer surface of bone. Wound on the pretibial surface of the leg can quickly deep to the bone surface, exposing the bone to the environment, and initiating the osteomyelitis process. The pretibial surface of the leg is rather dysvascular and has a thinner tissue depth than the other leg compartments.
Suspicious wounds include those that probe to the bone, joint or deep fascial compartments.
Generally, any wound in near proximity to bone and over six month’s duration should be suspected for osteomyelitis. When a history of a wound that heals and then opens again preceded by an episode for extreme warmth and abscess formation, osteomyelitis should be suspected.
Bacterial, fungal, and mycobacterium are common agents associated with ostemyeilits. The most common bacterial pathogen of osteomyelitis is S. aureus. Other infective bacterial pathogens seen are S. epidermidis, and streptococci. These bacterial pathogens account for up to 73% of the osteomyelitis following musculoskeletal surgery. S. epidermidis has been more frequently the causative pathogen of osteomyelitis after implant arthroplasty. Diabetic patients, especially those with vascular disease, have a mixed polymicrobial infection of gram positive and negative bacteria. Salmonella is seen in a higher incidence with sickle cell disease or other hemoglobinopathies. Pseudomonas and other gram negative bacteria are seen in a higher incidence with drug addicts.
Fungi involved in osteomyelitis are Blastomyces, Cryptococcus, and Coccidiodes. These fungi pathogens usually occur in non-compromised hosts. Fungi pathogens in osteomyelitis that are seen in compromised hosts are Aspergillus and Candida. Fungal osteomyelitis may be rather recalcitrant to therapy and may require amputation of the effected body part.
Tuberculosis osteomyelitis is seen usually in the bacteremic phase of the mycobacterium infection generated by hematogenous spread. This type of osteomyelitis occurs in approximately 1% of tuberculosis patients. Mycobacterium is seen in a higher incidence with renal transplant patients. Even though it may occur at any age, it is seen most frequently in adults. Negative purified protein derivative (PPD) skin tests do not exclude the diagnosis. These patients generally respond well to oral therapy.
P. aeruginosa and then P. multocida and other gram negative rods. P. aeruginosa osteomyelitis secondary to puncture wounds is not uncommon. P. aeruginosa is inoculated 2% in all puncture wounds and is 90% the etiologic agent. The phalanges, metatarsals, and calcaneus are the most commonly involved bones of the feet. Therapy for P. aeruginosa osteomyelitis includes surgical debridement and a minimum of 14 days of appropriate antibiotics.
Mycetoma is a chronic infection of soft tissue structures and bone that is characterized by multiple sinus tracts draining pus containing mycotic granules with indurated swelling of the effected area. Treatment of mycetoma is difficult and medical cure is rarely obtained. Males aged 20-40 are more frequently involved than females. The lower extremities are involved in 56-70% of the patients. The most common site is the dorsum of the forefoot. Treatment with Iatroconazole has been promising. Diagnosis of this condition is made by the clinical triad: mycotic granules, sinus tracts, and appropriate bacterial and fungal cultures. Surgical debridement alone is rarely curative. Treatment of mycetoma is difficult and eventually amputation for mycetoma may be required.
Hematogenous osteomyelitis is the spread of bacterial from an internal source such as an upper respiratory infection, through the circulation, to an osseous location where bacterial reproduction occurs leading to an infective process. Hematogenous osteomyelitis is most commonly a disease of children. Other sources of infection are colonized intravenous devices, dental infection, and urinary tract infections. In the presence of urinary tract infections the, hematogenous osteomyelitis may result in streptococci or gram negative organisms. Hematogenous osteomyelitis of the foot is rather uncommon, compared with other sites. In children 5-11% and in adults 8% have involvement of the foot bones. The most common foot bone affected is the calcaneus, followed by the metatarsal, tarsal bones, talus, and then phalanges. S. aureus is the most common pathogen in children and adults, occurring in 60% of patients. Gram negative rods are seen more commonly in adults. Poly microbial infection is uncommon. Fungi and mycobacterium are also spread by dissemination with hematogenous osteomyelitis.
Classically acute hematogenous osteomyelitis in a child presents as an abrupt onset of high fever, sudden pain, systemic toxicity, and local signs of infection and suppuration along the effected bone. The presentation in adults is less definitive. Leukocytosis and elevated sedimentation rate is common.
Contiguous focus osteomyelitis is the result of the spread of infection from an adjacent soft tissue focus. Such an adjacent soft tissue focus that would spread infection would be a wound, laceration, abscess, open reduction of a compound fracture, post-operative infection, or a septic joint. Contiguous focus osteomyelitis is usually seen in adults, usually over the age of 50. The phalanges and metatarsals are most commonly involved. The most common pathogen is S. aureus, but frequently a polymicrobial infection is encountered. Pathogens encountered as well are S. epidermidis, gram negative rods, and anaerobes.
Contiguous focus osteomyelitis in this age group demonstrates significant co-morbidities to consider when assessing possible outcomes. Some of the more significant co-morbidities are diabetes, vascular disease, hypertension, coronary vascular disease, hyper lipidemia, renal disease, venous insufficiency, and auto immune disease. Osteomyelitis occurring with vascular insufficiency often occurs with diabetic patients. Patients with tobacco usage alone have higher significant morbidity for wound/bone complications and limb loss.
Soft tissue swelling, subperiosteal elevation and lytic/sclerotic changes of bone are the classic radiographic findings of osteomyelitis. Bone changes are usually not evident for 10 to 14 days or until 35-50% on the bone has been destroyed. Sequestrum is the segmentation of dead bone from living bone, highly suggestive of chronic osteomyelitis. Sequestrum appears on x-ray as more dense in appearance than surrounding bone that may be osteoporotic or hyperemic. Sequetra are usually not present for at least three weeks. Sequestrum findings on x-ray mimic the findings osteoarthropathy (charcot deformity) in the diabetic. Invoucrum or new bone formation at the periosteum is suggestive of osteomyelitis. Cloaca formation is found at the bone-periosteum interface for extrusion of sequestrum and dead bone products.
Initial findings of hematogenous osteomyelitis initially are limited to swelling of the soft tissue over the metatphysis. The first radiographic findings are one or more lytic areas surrounded by a wide area of radiolucency. This is followed by periosteal elevation with cortex taking on a moth eaten appearance. Radiographic evidence of subacute or chronic hematogenous osteomyelitis (i.e., brodie’s abscess) is a radiolucent area in the metaphysic surrounded by sclerotic or hypertrophic bone.
The radiographic features of contiguous focus osteomyelitis are bone destruction and reabsorbtion at the area of adjacent soft tissue focus. Bone involvement begins in the outer bone cortex and periosteum. Cortical and cancellous involvement follows the reverse of hematogenous osteomyelitis. Radiographic findings of an infected arthroplasty are a progressively enlarging radiolucent zone at the bone-prothesis interface, endosteal scalloping, and focal lytic areas. Sequential radiographic studies are always usefull in the evaluation of either type of osteomyelitis.
Radiographic evaluation for findings consistent with osteomyelitis may not be evident for at least ten days and may lag weeks behind the clinical presentation. This is because 50% of the bone matrix must be destroyed until lytic lesions are seen. Radiographic lytic lesions are seen 3-4 weeks after onset of symptoms in 90% of patients. Initial radiographic findings of osteomyelitis, when present, are often vague and inconclusive. A periosteal elevation of a metatarsal may be the start in the infective process or an old stress fracture with bone exocallous present. Wounds or non-stagable eschar at the posterior and plantar aspect of the heel with suspicious calcaneal cortical bone findings may be misleading. This type of calcaneal finding may represent an early infective process or the normal irregular cortical surface seen with the posterior calcaneus. A periosteal elevation of the tibia or fibula may represent an early infective process or normal findings associated with chronic venous insufficiency. The radiographic findings of osteoarthropathy (charcot deformity) and atrophic or hypertrophic non-unions of the foot, ankle, and knee are usually the same as seen with osteomyelitis. To confuse matters further, magnetic resonance imaging has similar pitfalls between the two pathologies and nuclear imaging is usually required. Reabsorptive or destructive changes to bone may be noted in such disorders as rheumatoid arthritis or gout.
A technetium bone scan is more sensitive than plain film imaging in detecting early infections and may be positive as early as three days. Nuclear imaging (bone scans) can clarify and distinguish osteomyelitis from a healed, old fracture with bone callous, irregular, chronic bone changes, periosteal reactions from venous insufficiency and charcot deformity. Indium-111 white blood cell scanning is useful in the early detection of osteomyelitis. In charcot deformity, a dual nuclear imaging scans are utilized, technetium sulfur colloid and indium-111 labeled white blood cell study.
However, bone scans in general are sensitive for bone turnover, but are generally not specific for osteomyelitis. There is a high incidence of false positive osteomyelitis nuclear medicine studies. These studies are less sensitive when done with contiguous foci or soft tissue infection is present. Galium scans are less sensitive and also lack specificity in the presence of soft tissue infections.
Type one osteomyelitis is confined to the meduallary canal without cortical involvement. Type two osteomyelitis (ostitis) is confined to the cortical and not meduallary bone. Type three osteomyelitis involves the cortical bone at one cortice and meduallary bone as well. This type is the most commonly encountered osteomyelitis. Type four osteomyelitis involves the cortical bone at multiple cortices and the meduallary bone as well.