Osteomyelitis

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Medical Student Clinical Pearl by Jared Mullen

 

MD Candidate, Class of 2024

Dalhousie University

Reviewed by Dr. R Goss

Copy Edited by Dr. J Vonkeman

Pdf Download: EMSJ Osteomyelitis JMullin

 

 

Case Overview 

A 40-year-old man presents to the ER with falls and new confusion. His vitals signs are BP of 110/72, HR 135, RR 28, Temp 39.4, and GCS 14.

History of Presenting Illness

He is 2 months post-operative for ORIF of a significant R tibial plateau fracture that led to an extended hospital stay. Post-operative course was complicated by compartment syndrome requiring fasciotomy and persistent soft tissue infections that required treatment with IV antibiotics followed by PO step down after discharge. Collateral history from his wife indicates that he had been doing well at home on his PO antibiotics with daily wound dressing changes, but his status began deteriorating 2 days ago following completion of his antibiotics. He had several falls at home in the 24 hours leading to his ER presentation and his wife noted new confusion and difficulty in conversation. His leg had been looking “good” until stopping the antibiotics.

Physical Exam

On exam he appears unwell, lethargic, and he has difficulty cooperating in the assessment due to confusion. He has clear lungs, normal heart sounds, and equal and reactive pupils. Notably, his right leg is swollen, erythematic, tender, and hot to the touch from the level just above the patella to the midfoot. There are four wounds draining purulent discharge and one of the wounds has a significant sinus tract 4cm in depth with a bony endpoint.

Investigations & Initial Management

Wound swabs are obtained, and arthrocentesis of the right knee joint shows serosanguinous fluid pending analysis. Initial orders include chest x-ray, urinalysis + culture, blood cultures, routine labs + ALkPhos and CRP. Empiric antibiotics (IV cefazolin + IV vancomycin) and IV fluids are initiated.

Background

Osteomyelitis is an infection of the bone (most often bacterial) that can be broadly categorized as acute or chronic.

  • Acute osteomyelitis generally occurs following hematogenous spread and less often following direct inoculation (e.g., trauma/surgery)1. More than 50% of cases occur in children < 5 years of age2. IV drug use (IVDU) is a common cause acute osteomyelitis through hematogenous spread most often affecting the vertebral bodies3. Acute osteomyelitis presents with local clinical findings such as erythema, tenderness, edema, and warm skin.
    • Systemic findings such as fever, tachycardia, and hypotension may also be present.
    • The non-specific signs and symptoms of osteomyelitis make it difficult to differentiate from conditions such as cellulitis, septic arthritis, and even crystalline arthropathies.
      • Cellulitis is more likely to present in association with a preceding wound and findings of erythema and edema radiating from the focus of the infection/wound. In contrast, these findings in osteomyelitis are more diffuse and circumferential to the affected bone.
      • When osteomyelitis presents close to a joint it is difficult to rule-out a septic or crystalline arthropathy clinically, however, arthrocentesis and synovial fluid analysis/culture can clarify this.
  • Chronic osteomyelitis is far more common in adults and the most common mechanism is contiguous spread of infection from adjacent tissues (e.g., from a diabetic ulcer)4. It is associated with conditions and lifestyle factors that contribute to poor limb perfusion and wound healing including peripheral vascular disease, diabetes, renal/hepatic failure, EtOH abuse, and IV drug use3,5. In these populations, hematogenous spread accounts for only 20% of cases.
  • Chronic osteomyelitis should be suspected in patients who have non-healing ulcers, persistent soft tissue infections/failed antibiotic course, and draining sinus tracts5. Chronic osteomyelitis has been reported to be polymicrobial in 30 – 60% of cases with polymicrobial infections accounting for 5% of acute infections6.

In both acute and chronic, the most common offending organisms include Staphylococcus aureus (incl. methicillin-resistant Staphylococcus aureus [MRSA]), Staphylococcus epidermidis, Streptococcus species, Enterococcus species, and Pseudomonas species7. An increasing number of cases of osteomyelitis are caused by MRSA with MRSA accounting for more than one-third of infections in numerous studies7,8. IVDU is associated with an increased incidence of osteomyelitis caused by MRSA9,10.

Diagnosis

Diagnosing osteomyelitis clinically is difficult for several reasons including its overlap in presentation with other common conditions and because the presenting complaints might be non-specific with no external exam findings.

Laboratory findings such as leukocytosis, thrombocytosis, and increased CRP and ESR support the diagnosis of osteomyelitis but are non-specific5. It can take up to 2 weeks for radiographic evidence of osteomyelitis to appear (features include periosteal reaction, focal bone lysis/cortical loss, and regional osteopenia). X-rays have a reported sensitivity of 14-54% and a specificity of 68-70%1,4. With MRI, sensitivity is improved to 78-90% and specificity to 60-90%1.

In systemically unwell patients it is reasonable to do a broad infectious work-up. Blood cultures are positive in 50% of acute osteomyelitis cases but do not rule-out the diagnosis when negative1,4. A probe-to-bone test is supportive of the diagnosis of osteomyelitis and the test is positive when a blunt metal probe can be passed through a sinus tract directly to bone without intervening soft tissue. Care should be taken with the probe-to-bone test so that existing tracts are not extended deeper through soft tissues. Advanced imaging including a white blood cell (WBC) scan can be performed to visualize WBC infiltration to bone; this may also be used to determine treatment success with a reported sensitivity of 91% and specificity of 92%11. The gold standard for definitive diagnosis of osteomyelitis is bone biopsy (generally image guided) with culture and histologic examination. In osteomyelitis, CT-guide percutaneous needle bone biopsy (CTNBB) is reported as having a sensitivity of 43.0-64.6% and a specificity of 71.9-93.1%12.

Management

Initial management of osteomyelitis is with empiric antibiotics followed by targeted antibiotic selection based on culture and susceptibility testing.

  • Empiric therapy with vancomycin and Gram-negative coverage (ceftriaxone, cefepime, ciprofloxacin, etc.) is appropriate1,3.
  • Alternatives to vancomycin include daptomycin, TMP-SMX, and clindamycin.
  • Initial parenteral administration is appropriate with step-down to PO antibiotics after clinical stability, but PO can be considered alone in otherwise well patients.
  • A 4-week course and a 6-week course of antibiotics is typical for acute osteomyelitis in pediatric and adult populations, respectively5. Chronic osteomyelitis may require up to 8 weeks with several weeks of parenteral antibiotics to begin.

A surgical approach may be required in patients who fail antibiotic therapy alone, have implanted hardware, and those with tissue necrosis1.

  • Surgery primarily involves drainage and debridement of necrotic tissue, but extensive disease may cause instability that must be corrected with surgical fixation.
  • The Cierny-Mader classification of osteomyelitis can help provide insight into which patients require surgery (Figure 1)4. In this classification patients are first designated a type based on radiographic/anatomic findings followed by classification according to clinical status based on pre-existing systemic/local risk factors. Type III and IV often require surgical intervention to address “deadspace” from debrided necrotic bone (type III and IV) and to restore stability (type IV).

 

Case Conclusion 

Investigations come back with a normal chest x-ray, normal urinalysis with negative cultures, and normal arthrocentesis. Blood cultures are positive for Gram-positive cocci in clusters suggestive of Staphylococcus species (likely S. aureus). Labs show CRP elevated at 227, LKC 16.6, HGB 103, and otherwise unremarkable. X-ray series of the right leg shows several lytic lesions in the proximal third of the tibia with apparent bone resorption surrounding the implanted hardware. He is admitted to the orthopedics service pending urgent I&D and hardware removal. He is maintained on IV cefazolin and vancomycin pending culture and susceptibility testing of bone and tissue samples collected intraoperatively.

References

  1. Hatzenbuehler, J., & Pulling, T. J. (2011). Diagnosis and Management of Osteomyelitis.American Family Physician, 84(9), 1027–1033.
  2. Chiappini, E., Mastrangelo, G., & Lazzeri, S. (2016). A Case of Acute Osteomyelitis: An Update on Diagnosis and Treatment.International Journal of Environmental Research and Public Health, 13(6), 539.
  3. Yuschak, E., Chase, S., Haq, F., & Vandever, C. (2019). Demographics and Length of Stay for Osteomyelitis in Opioid Drug Users: A Unique Population with High Healthcare Costs.Cureus, 11(3), e4339.
  4. Calhoun, J. H., & Manring, M. M. (2005). Adult Osteomyelitis.Infectious Disease Clinics of North America, 19(4), 765–786.
  5. Hogan, A., Heppert, V. G., & Suda, A. J. (2013). Osteomyelitis.Archives of Orthopaedic and Trauma Surgery, 133(9), 1183–1196.
  6. Pichichero, M. E., & Friesen, H. A. (1982). Polymicrobial Osteomyelitis: Report of Three Cases and Review of the Literature.Clinical Infectious Diseases, 4(1), 86–96.
  7. Momodu, I.I., & Savaliya, V. Osteomyelitis. ]. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan. Updated 2023 May 31.
  8. Arnold, S. R., Elias, D., Buckingham, S. C., Thomas, E. D., Novais, E., Arkader, A., & Howard, C. (2006). Changing Patterns of Acute Hematogenous Osteomyelitis and Septic Arthritis: Emergence of Community-associated Methicillin-resistant Staphylococcus aureus.Journal of Pediatric Orthopaedics, 26(6), 703–708.
  9. Parikh, M. P., Octaria, R., & Kainer, M. A. (2020). Methicillin-Resistant Staphylococcus aureus Bloodstream Infections and Injection Drug Use, Tennessee, USA, 2015-2017.Emerging Infectious Diseases, 26(3), 446–453.
  10. Best, K., Hussien, S., Malik, A., Patel, S., & Michael, M. B. (2022). Suprapubic Osteomyelitis in an Intravenous Drug User: A Case Report. InCureus (Vol. 14, Issue 1, pp. e21312–e21312).
  11. Lauri, C., Tamminga, M., Glaudemans, A. W. J. M., Juárez Orozco, L. E., Erba, P. A., Jutte, P. C., Lipsky, B. A., IJzerman, M. J., Signore, A., & Slart, R. H. J. A. (2017). Detection of Osteomyelitis in the Diabetic Foot by Imaging Techniques: A Systematic Review and Meta-analysis Comparing MRI, White Blood Cell Scintigraphy, and FDG-PET.Diabetes Care, 40(8), 1111–1120.
  12. Schirò, S., Foreman, S. C., Bucknor, M., Chin, C. T., Joseph, G. B., & Link, T. M. (2020). Diagnostic Performance of CT-Guided Bone Biopsies in Patients with Suspected Osteomyelitis of the Appendicular and Axial Skeleton with a Focus on Clinical and Technical Factors Associated with Positive Microbiology Culture Results.Journal of Vascular and Interventional Radiology, 31(3), 464–472.
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