About This Page
This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Bone infection, most commonly due to Staphylococcus aureus
- Routes: hematogenous, contiguous, open fracture, surgery/hardware, diabetic foot ulcer
- MRI is best imaging test in most settings
- Bone biopsy culture is diagnostic gold standard when feasible
- Treatment requires targeted antibiotics and source control
Overview
Osteomyelitis is infection of bone and marrow. It can be hematogenous, vertebral, contiguous from ulcers, postoperative, or hardware-associated. Necrotic bone and abscess require source control.
Epidemiology
Risk factors include diabetes, PAD, neuropathy, chronic ulcers, dialysis, injection drug use, bacteremia, immunosuppression, sickle cell disease, hardware, and open fracture.
Clinical Features
Symptoms
Localized bone pain, tenderness, swelling, warmth
Fever may be absent in chronic or diabetic foot disease
Deep diabetic foot ulcer or exposed bone
Persistent focal back pain in vertebral osteomyelitis
Neurologic deficits suggest epidural abscess
Signs
Focal bony tenderness
Chronic draining sinus tract or exposed bone
Positive probe-to-bone test in diabetic foot ulcer
Reduced pulses or ischemic changes
Spinal tenderness with neurologic deficits is emergency
Investigations
First-line
Focused clinical assessmentPattern recognition, red flags, functional impact, and targeted examination
Basic labs when indicatedCBC, CMP, ESR/CRP, CK, urinalysis, or disease-specific testing depending on suspected condition
Initial imaging when indicatedPlain radiographs or MRI/ultrasound based on suspected structural, inflammatory, infectious, or neurologic disease
Second-line
Disease-specific confirmatory testingAutoantibodies, HLA-B27, synovial fluid, nerve conduction studies, DEXA, or cultures as appropriate
MRI/ultrasound/CTUsed for early inflammatory disease, occult fracture, tendon tear, infection, or surgical planning
Screening before immunosuppressionTB, hepatitis, vaccination review, and baseline labs when biologic or high-risk therapy is planned
Specialist
Specialist referralRheumatology, orthopedics, infectious disease, ophthalmology, neurology, or spine surgery depending on red flags and disease severity
Management
IDSA Native Vertebral Osteomyelitis Guideline and IWGDF/IDSA Diabetic Foot Infection Guideline1
Initial management
- Address red flags and emergencies first
- Use guideline-directed first-line therapy matched to disease severity
- Educate the patient and set functional goals
- Use analgesia and rehabilitation when appropriate
2
Escalation
- Escalate to specialist-directed therapy if severe, refractory, progressive, or organ-threatening disease
- Use imaging, procedures, immunosuppression, antibiotics, or surgery according to diagnosis
- Monitor response objectively and revise diagnosis if response is atypical
3
Prevention and follow-up
- Manage comorbidities and medication toxicity
- Vaccinate and screen when immunosuppression is used
- Prevent disability, falls, fracture, infection, and functional decline
Complications
- Functional impairment: Pain, weakness, stiffness, deformity, or disability depending on disease
- Diagnostic delay: Missed infection, fracture, inflammatory disease, neurologic compromise, or organ-threatening complication
- Medication toxicity: NSAID, steroid, antibiotic, anticoagulation, opioid, or immunosuppressive adverse effects
- Chronic disease burden: Reduced quality of life, work impairment, deconditioning, and mental health impact
USMLE Step 2 CK Exam Tips
- 1Best imaging test = MRI
- 2Gold standard = bone biopsy culture
- 3Most common organism = Staphylococcus aureus
- 4Sickle cell disease: Salmonella is classic but S aureus remains common
- 5Sneaker puncture wound = Pseudomonas
- 6Probe-to-bone suggests diabetic foot osteomyelitis
practicetest your knowledge on osteomyelitisApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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