Osteomyelitis Diagnosis

• Elicit predisposing factors [eg vasculopathy, diabetes mellitus (DM), invasive procedures, etc]

Physical Exam Findings:

• Warmth, erythema & tenderness over the involved part
  • Tenderness disproportionate to soft tissue findings favors osteomyelitis over soft tissue infection

• Tissue ulceration & draining sinus tracts over the affected bone
• Exposed bone on ulcer bed or a probe used to examine an ulcer encounters bone
• Signs of septicemia

Bacterial Culture

• Isolation of the infecting microorganism is extremely important for the diagnosis of long bone osteomyelitis
• Blood, bone & joint fluid should ideally all be cultured to increase the yield of the test
• Sinus tract cultures are reliable for confirming S aureus infection but are not useful for detecting gram-negative pathogens
• Gram-stained smear, aerobic & anaerobic cultures should be performed

Blood Tests

• WBC count may be high or normal in acute hematogenous osteomyelitis & is usually normal in chronic osteomyelitis
• Erythrocyte sedimentation rate (ESR) is usually elevated at the onset & may provide a prognostic guide during therapy
• C-reactive protein (CRP) level is elevated, w/ higher levels predicting a possibly greater risk of sequelae

Bone Biopsy

• Bone biopsy samples isolating bacteria w/ findings histologically of osteonecrosis & inflammatory disease are the reference standard for diagnosis of osteomyelitis
• Recommended if the diagnosis of osteomyelitis is still in doubt after imaging
• Frequently needed to diagnose vertebral osteomyelitis because blood cultures are usually sterile in this situation
• Open biopsy is better than needle biopsy & at least 2 samples should be obtained for histopath & for Gram stain & culture

Polymerase Chain Reaction (PCR)

• Helpful in establishing etiology of osteomyelitis when blood & bone cultures are negative

Plain X-rays

• First imaging procedure in the work up of patients w/ possible osteomyelitis
• Useful for excluding other diseases & can provide clues for other conditions that may be present
• Positive x-rays are fairly specific for osteomyelitis (75-83%), but negative x-rays cannot be used to rule out the disease
• Bone demineralization by 30-75% needs to occur before a change on plain x-ray is seen; therefore, it takes 10 to 21 days for a bone lesion to become apparent
• In children, early changes may be seen w/in 3 days of symptom onset
  • Focal deep soft tissue swelling in the metaphyseal region may be the 1st sign in children & infants, followed by muscle swelling & loss; tissue planes normally seen around affected bone
  • Soft tissue changes are harder to detect in adults

• Later changes include bone lysis, cortical lucency, osteopenia, periosteal elevation, periosteal new bone formation, single or multiple abscesses, involucrum, sequestration
• Findings in vertebral osteomyelitis include narrowing of the intervetebral disk space, bone destruction & new bone formation at the anterior edge of the vertebral disk
• Radiographs should be repeated at 2-wk intervals in diabetes mellitus patients (DM) who have infected foot wounds that do not resolve & whose initial radiographs are normal

Magnetic Resonance Imaging (MRI)

• Highly sensitive for detecting osteomyelitis, test of choice for diabetic foot ulcers
• Useful for differentiating bone infection from soft tissue infection, for confirming the extent of infection in patients w/ established osteomyelitis, & for evaluating intraosseous abscesses
• Able to detect vertebral osteomyelitis early
• Helpful in planning surgical management ie drainage & debridement
• Limitations: Not recommended for whole-body exams; metal implants may produce focal artifacts

Bone Scan

• May already be positive 24-48 hr after symptoms start & therefore can detect osteomyelitis earlier than plain radiographs
• Useful for patients in whom multifocal bone involvement is suspected
• Decreased uptake on bone scan may indicate more aggressive infection that has produced thrombosis or ischemia
• Limitation: May be positive in other conditions eg malignancy, fracture, bone infarction

Other Imaging Techniques

• Radionuclide studies
  • Not routinely required for evaluation of possible osteomyelitis, but may provide more information about the extent of bone & soft tissue inflammation
  • A gallium scan obtained together w/ a technetium scan or white blood cell (WBC) scan may be more useful than doing either test alone

• Computed tomography (CT) scan
  • Useful for defining the extent of bone & soft tissue infection esp in areas of complex anatomy eg the vertebral column & for guiding biopsies & aspiration procedures
  • Less sensitive than MRI except for detecting sequestra & should not be used routinely for evaluating patients w/ possible osteomyelitis

• Ultrasound
  • Noninvasive technique that may be helpful in detection of fluid collection, abscesses or sinus tracts in soft tissues
  • May be used to guide diagnostic or therapeutic drainage, aspiration or tissue biopsy

• Positron emission tomography & single photon emission computed tomography
  • Detects increased intracellular glucose metabolism that occurs in infection & inflammation
  • Highly accurate for confirming or excluding the diagnosis of chronic osteomyelitis

Classification of Osteomyelitis in Children

Acute Hematogenous Osteomyelitis (AHO)

• Bone infection before formation of sequestra (dead bone)
• Primary acute hematogenous osteomyelitis occurs mainly in infants & children
  • Most patients w/ acute hematogenous osteomyelitis  present w/ symptoms lasting <2 wk

• Long bones are most frequently involved, w/ most infections in children localizing in the metaphysis
  • Most frequently affected sites are the distal femur & proximal tibia, followed by the distal humerus, distal radius, proximal femur & proximal humerus

• Multiple bone involvement is common in infants
• Abscess formation & extension of infection into surrounding soft tissue may occur
• Infection in infants tends to be more diffuse because anatomic barriers are not able to efficiently limit infection
• Vertebral osteomyelitis is uncommon in children & often presents as an indolent infection w/ nonspecific symptoms eg septicemia
  • Often involves infection of the endplates of 2 adjacent vertebrae

• In patients w/ pelvic osteomyelitis, the ilium & ischium are most often involved & usually presents as gait abnormality or hip pain

Contiguous Nonhematogenous Osteomyelitis

• Associated w/ open fractures requiring surgical reduction, orthopedic devices, decubitus & neuropathic ulcers, human & animal bites, puncture wounds esp of the foot or knee
• Presents as an indolent condition often w/o fever & w/ continuous drainage or ulceration over the affected bone
• Has a high rate of recurrence

Classification of Osteomyelitis in Adults

Acute Hematogenous Osteomyelitis (AHO)

• Adults usually present in a chronic manner, w/ pain & minimal constitutional symptoms lasting several mth
• Infections usually start in the diaphysis
• Secondary hematogenous osteomyelitis is more common in adults & is usually a reactivation of a childhood infection
• Vertebral osteomyelitis is predominantly a disease of adults, w/ incidence increasing w/ age
  • Condition slowly progresses over wk to mth
  • The lumbar & thoracic spine are most commonly affected
  • Infection may spread from skin & soft tissue, respiratory & genitourinary tract, infected IV sites, endocarditis

Contiguous Nonhematogenous Osteomyelitis

• Associated w/ fractures needing surgical reduction & internal fixation, open fractures, prosthetic devices, soft tissue infections, trauma
• Patients w/ DM are susceptible to osteomyelitis because of impairment of tissue perfusion that is a result of vascular insufficiency
  • Neuropathy & diminished neutrophil function also contribute to the risk
  • Predisposing events include perforating foot ulcers, an ingrown toenail, cellulitis or deep space infection
  • Diabetic patients often develop osteomyelitis even before bone is exposed
    • Positive palpation of bone in probing an infected foot ulcer confirms osteomyelitis

Chronic Osteomyelitis

• Bone infection after sequestra formation
• Diagnosed in patients w/ a history of osteomyelitis w/ recurrence of symptoms ie pain, swelling, erythema, low-grade fever; a sinus tract is pathognomonic
• Pathologic features include presence of necrotic bone, exposed bone, chronic wound over a fracture or surgical hardware, formation of new bone (involucrum) & exudation of polymorphonuclear leukocytes w/ lymphocytes, histiocytes, plasma cells
• An abscess or soft tissue infection may be found, esp if a sinus tract becomes obstructed
• Hematogenous & contiguous-focus osteomyelitis may become chronic