Osteomyelitis is an acute or chronic infection of the bones or surrounding structures which is caused by bacteria or other microorganism (rarely happen). Osteomyelitis is acquired through hematogenous spread, transmission of the infection from the adjacent infected sites or from trauma or surgery (direct inoculation). Musculoskeletal system is affected by osteomyelitis.
In terms of epidemiology, osteomyelitis is predominantly more common in male than female. It has a higher incidence in diabetic and predominantly occurs in the bimodal model in hematogenous inoculation with higher incidence of osteomyelitis in infant and children as well as elderly. In children, osteomyelitis typically affects male age around 5 - 14 years old. Osteomyelitis commonly affects the long bone. In elderly, vertebral osteomyelitis and contiguous focus of infection is common.
The risk factors for developing osteomyelitis include open fractures, local trauma, any prosthetic orthopaedic implant, neuropathy, vascular insufficiency (most common causes of osteomyelitis age 50 - 60 years old), a condition which predisposes to bone infarct, sickle cell disease, IV drug user and diabetes mellitus.
Osteomyelitis is presented with acute hematogenous osteomyelitis, vertebral osteomyelitis, contiguous focus osteomyelitis, vascular insufficiency osteomyelitis and prosthetic device infection that lead to osteomyelitis.
Acute hematogenous osteomyelitis is most commonly caused by staphylococcus aureus , streptococci ( coagulase negative ), gram negative organism and haemophillus influenza ( less common ) .
Vertebral osteomyelitis is caused by gram negative enteric micro organism and staphylococcus aureus (most common) and fungi as well as Mycobacterium tuberculosis.
Contiguous focus osteomyelitis and vascular insufficiency osteomyelitis are caused by mixed aerobic and anaerobic organism.
Prosthetic device infection is related to infection by staphylococcus aureus and coagulase negative staphylococcus ( the most common causes ) and gram negative bacteria and diphtheroids ( the rare case ). Mycobacterium and fungal infection in immunosuppressed patient may also lead to osteomyelitis. However it is rare / less common.
Hematogenous osteomyelitis is also known as hematogenous infection of the long bone that typically affects children around 5 - 14 years old. The children may present with insidious onset of high fever, malaise, irritability and reduce in the range of movement of the involved extremity. The patient may also present with localized signs and symptoms of inflammation.
Vertebral osteomyelitis is also known as hematogenous infection of the vertebrae which mostly affect the adults. The illness may be presented as an acute bacteremic episode which is related to infection of a specific organ. Besides that it may also behave like a chronic infection.
Contiguous focus osteomyelitis and vascular insufficiency osteomyelitis typically presented with signs and symptoms of inflammation.
Chronic osteomyelitis may present with constitutional symptoms which shows the presence of acute suppurative condition in the surrounding tissue and bone. Chronic osteomyelitis may also present with drainage sinus and non healing ulcers.
Associated infection of the prosthetic device is caused either by direct hematogenous spreads or from the contiguous foci which includes postoperative infection, operative contamination and local infection. Fever, tenderness, localized swelling and drainage is associated with acute postoperative infection. Chronic infection is characterized by joint dysfunction, joint swelling, joint discomfort and erythema.
The investigations required for osteomyelitis include lab test and imaging technique. Lab test includes elevation of leukocyte count that is more prominent in acute than chronic osteomyelitis. This is followed by elevation of CRP or sedimentation rate. CRP is useful to determine the treatment response in term of follow up. In 50 % of younger patient with acute hematogenous osteomyelitis, blood culture may be positive. Other diagnosis is made by biopsy of the bone or needle aspiration (definite diagnosis) which able to demonstrate the histological aspect of the bone and the presence of micro organism. The lab result will be affected if the patient has already taken any antimicrobial medication prior to the blood study. Beside that the lab result may also be affected if the culture is taken from the sinus tract due to a high degree of contamination. Superficial cultures are not allowed due to its ability of only identifying MRSA ( methicillin resistant staphylococcus aureus ) .
No imaging technique can confirm the presence of osteomyelitis accurately. It takes around 10 -1 4 days for abnormalities to appear on plain radiography in acute cases of osteomyelitis. Radionuclide scanning (gallium, indium, and technetium) can be used but the usage is limited due to its low specificity. A CT scan provides a good resolution however the presence of artefact will decrease the specificity. MRI is another form of imaging technique. MRI is excellent in detecting osteomyelitis but it is expensive and not useful for follow up due to the persistent appearance of the body oedema.
The gold standard for detection osteomyelitis is open bone biopsy or needle biopsy for the culture of the bacteria. However the outcome of this procedure is limited if anti microbial treatment has been taken.
Other differential diagnosis of osteomyelitis includes neuropathic joint disease, aseptic bone infarction, tumour, gout, systemic infection from another source or infection of the overlying skin and tissue as well as localized inflammation.
The treatment of osteomyelitis may include initial stabilization as well as general measures.
All patients who are suspected with acute hematogenous osteomyelitis should be admitted to confirm the diagnosis and to start the treatment. The initial step is to correct any hyperglycaemia, imbalance of the electrolytes, acidosis and azotaemia. Symptomatic treatment is given for any cases of pain or discomfort. The patient is advised for bed resting and reduces the movement of the affected bone or joint (immobilization).
The drugs needed to treat osteomyelitis consist of a series of antimicrobial agents. The antimicrobial agents are chosen based on the clinical efficacy and susceptibility test. In acute cases of osteomyelitis the duration of treatment is around 4 - 6 weeks. Longer duration is required for chronic osteomyelitis . If the patient is under 15 years old , the treatment of choice includes penicillinase resistant synthetic penicillin or 3rd generation cephalosporin. Alternative drugs include clindamycin or vancomycin with 3 rd generation cephalosporin. In adult the treatment is as above with additional rifampicin and ciprofloxacin.
In diabetic patients, the antimicrobial agents are given based on the severity of the osteomyelitis. In mild infection of osteomyelitis, the treatment includes amoxicillin / clavulanate , cephalexin, clindamycin, dicloxacillin, trimethoprin / sulfamethoxazole and levofloxacin. All these drugs are given orally.
In moderate infection of the osteomyelitis the antibiotics are given either orally or parenteral based on the agents of choice and clinical situation. The agents include amoxicillin/ clavulanate, ceftriaxone, ciprofloxacin, clindamycin, trimethoprin/ sulfamethoxazole, levofloxacin and ticarcillin/ clavulanate.
In severe infection, the treatment includes piperacillin / tazobactam . imipenem- cliastatin , levofloxacin, ciprofloxacin with clindamycin, ceftazidine and vancomycin.
In puncture wound related osteomyelitis, the treatment includes Cefepime, ceftazidime and ciprofloxacin. Traumatic cases of osteomyelitis may be treated with ciprofloxacin, nafcillin and vancomycin as well as 3rd generation cephalosporin with anti pseudomonal antibiotics.
Nafcillin is useful for staphylococcus aureus and coagulase negative staphylococcus. Vancomycin or linezolid are useful for MRSA. Penicillin is required for streptococcus while piperacillin for gram negative enteric bacilli and Pseudomonas aeruginosa. In the presence of the bite wound or diabetic foot with mixed aerobic and anaerobic infection, clindamycin with 3rd generation cephalosporin or quinolone are required. A simplified regimen of antibiotic is given in the form of oral therapy for home treatment. Hyperbaric oxygen usage is also / may be considered.
Surgical treatment may include debridement or removal of necrotic tissue as well as surgical drainage. Amputation may only be the most effective treatment if the patient suffers from vascular insufficiency or gangrenous infection. In some patient, re vascularisation may be an option
Patient required to be monitored in term of blood level of antimicrobial agents, CRP, serum antibacterial titres, repeat CT scan, MRI scan or plain radiography to confirm the healing process.
The complication of osteomyelitis may include postoperative infection, bacteremia, abscess formation, fracture or loosening of the prosthetic implant.
The cure for osteomyelitis based solely on the medical treatment is questionable and unpredictable. The prognosis is good, even without surgery in patients who suffers from acute hematogenous osteomyelitis. 6 weeks are required for the patient to be cured with 3 - 6 months for radiographic improvement. The prognosis is good when all the bones that are infected are removed.
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