Approach Considerations
It is important to differentiate uncomplicated versus complicated osteomyelitis: single bone versus two or more bones involved with soft tissue infection, as this will help determine the risk of complications to monitor patient for. [9]
Laboratory Studies
To confirm a clinical diagnosis of osteomyelitis, adequate radiologic and laboratory data are necessary. A blood culture and serum C-reactive protein are recommended as first line.
The white blood cell (WBC) count is elevated in only one half of patients with or without thrombocytosis.
The C-reactive protein and erythrocyte sedimentation rate (ESR) are almost always elevated (except in small bones infections).
There are many methods to attempt to recover the organism causing the bone infection, such as blood, bone, or joint aspirate cultures. It is important to obtain these cultures before any antibiotics are given. However, at times cultures may be negative or difficult to obtain and therapy should be guided by the most common causes in local area of practice.
If one is able to obtain bone and/or joint fluid aspirate for culture, a Gram stain is vital, as the procedure itself can be bactericidal.
Consult with the microbiology laboratory prior to obtaining cultures to ensure proper culture mediums and technique are used.
If a clinician is considering Kingella kingae, notify the microbiology department, as recovery is improved by inoculating synovial fluid directly into blood culture bottles or send off for K kingae PCR testing.
Consider performing a bone biopsy if the patient does not respond to standard therapy.
Imaging Studies
Magnetic resonance imaging
Magnetic resonance imaging (MRI) remains the criterion standard, especially in early infections.
On T2-weighted images, increased marrow intensity with surrounding inflammation is suggestive of osteomyelitis. Gadolinium contrast is important to help elucidate edema from an abscess. [10] These abnormalities need to be correlated with the clinical picture before a diagnosis is made, as they are not specific for osteomyelitis.
A study by Schallert et al found that children with joint effusions identified by MRI, in the setting of metaphyseal osteomyelitis, should be presumed to have septic arthritis until proven otherwise. [11]
Radiography
Initial films may be normal, with or without soft tissue swelling. Bone destruction occurs 10-15 days later and then can be appreciated on radiographs. [12, 13]
Radiography can be useful in revealing bone tumors, fractures, and healing fractures.
Osteopenia, lytic lesions, and periosteal changes are late radiographic signs; their absence does not exclude a diagnosis of acute osteomyelitis.
Three-phase technetium radionuclide bone scanning
Through enhanced uptake of the radioisotope, this procedure reveals increased osteoblastic activity of the infected bone and distinguishes osteomyelitis from deep cellulitis.
Technetium bone scanning has a false-negative rate of as much as 20%, particularly in the first few days of illness.
Chronic recurrent multifocal osteomyelitis, fractures, bone tumors, and surgery also cause enhanced technetium uptake.
It is an inexpensive test without need for sedation and with relatively quick turnaround.
Gallium scanning
This study is usually not recommended because of lower specificity and exposure to higher levels of radiation.
Ultrasonography
Ultrasonography is difficult to use in acute cases of osteomyelitis, with limitations based on availability, technician-dependent results, and an inability to differentiate fluid patterns as infectious versus traumatic.
Clinical suspicion for deep vein thrombosis should be especially high in patients with osteomyelitis caused by CA-MRSA who have an elevated C-reactive protein level. Doppler venous ultrasonography is the first imaging study indicated in such cases. However, routine screening is not yet recommended. [5, 1, 7]
Procedures
Bloood cultures should always be drawn on these children. Bone aspiration may be necessary to identify the pathogen if needed.
The study on 250 children by McNeil et al examined the impact of interventional radiology (IR) and surgically obtained cultures in the diagnosis and management of acute hematogenous osteomyelitis. The study found that IR or operating room culture was the only means of identifying a pathogen in 80 of 216 cases (37%), and the results changed antibiotic therapy in 85% of patients. The authors further added that IR can be used effectively to obtain bone cultures in children with acute hematogenous osteomyelitis not requiring open surgical drainage. IR was able to obtain cultures in difficult to acess areas important to obtaining a positive culture and resulted in a shorter hospital stay. The most common pathogen isolated was Staphyloccus aureus (32.5% MRSA, 9.8% MSSA) and no Kingella cases were reported. [14]
Consider bone biopsy if other diagnoses are possible (eg, tumors).
Joint aspiration is recommended if signs and symptoms suggest pathology near shoulder, knee, or hip joints. This is critical because arthrotomy is indicated if evidence of hip or shoulder arthritis is present.
If signs and symptoms do not begin to resolve within 24-48 hours of initiation of appropriate antimicrobial treatment, consider bone aspiration to drain the pus, in consultation with the pediatric orthopedic surgeon. [9]
Staging
An osteomyelitis staging system is present in the literature for adult treatment and diagnosis of osteomyelitis. The Cierny-Mader classification is the newest system to account for host factors to aid with treatment. It categorizes the first part by anatomical involvement of infection, such as type 1 as medullary osteomyelitis and host type A as a normal host. [15]
