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Osteomyelitis

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Edited by Devanshi Mehta — 2021 — App design by Showly Nicholson

Clinical Manifestations

Acute: <2w of sx & absence of necrotic bone or sequestrum. Sx: localized pain & diminished function or evidence of inflammation (fever/chills/night sweats/erythema). Pts can be afebrile

Chronic: previously failed tx, >3w sx, presence of bony sequestrum, persistent drainage or sinus tract; pain (absent if neuropathy), erythema, swelling; poorly healing ulcers; hallmark is necrotic bone

Etiologies: hematogenous seeding (usually monomicrobial) from bacteremia (↑ risk if endocarditis or indwelling device) or contiguous spread (polymicrobial) via direct inoculation after surgery/trauma.

  • Hip, vertebra, pelvis: often have fewer symptoms, can present as septic arthritis

  • Vertebral: point tenderness, unremitting, >50yo (except IVDU), +/- fever (NEJM 2010;362:1022, IDSA: CID 2015;61:e26)

  • Pelvic: a/w bacteremia, sacral pressure ulcers, trauma (esp. athletes), urogyn/pelvic surgery, femoral access site; many present subacutely, may have localized pain or poorly localized, may not have fever

  • Sternoclavicular: ant. chest wall swelling, pain, tenderness; may be mistaken for abscess or atypical cellulitis; can occur via hematog. spread or post-CT surgery +/- mediastinitis (33% mortality: J Thor. Card Surg 2006;132:537)

  • Mandibular: usually contiguous spread of oral flora/odontogenic infxn; often w/ anaerobes

Diagnostic Approach

JAMA 2008;299:806

Risk Factors Likelihood Ratio
Ulcer area > 2 cm 7.2 (1.1-49)
Probe-to-bone 6.4 (3.6-11)
ESR > 70 mm/h 11 (1.6-79)
Abnormal XR 2.3 (1.6-3.3)
MRI c/w OM 3.8 (2.5-5.8)
Normal MRI 0.14 (0.08-0.26)

Exam: probing to bone sufficient for dx in patients w/ DM (83% Sp, 90% PPV) w/o need for further imaging (CID 2016; 63:944)

Blood Cx: often + with hematogenous infxn involving vertebra, clavicle, pelvis (always obtain BCx x2 before starting antibiotics)

Labs: ESR/CRP (if high can use for monitoring response), +/-leukocytosis

Imaging:

  • >2w of sx: obtain plain XR 1st. XR diagnostic and concerning story: obtain advanced imaging (MRI)

  • <2w of sx, suspected vertebral OM, or DM: start w/ advanced imaging (MRI), contrast preferred for vertebral OM

  • MRI: Sn 90%, Sp 82%, high NPV (Arch Intern Med 2007;167:125); best in DM or if c/f vertebral osteo (CID 2015;61:e26)

  • CT: if MRI not available; can demonstrate periosteal reaction and cortical/medullary destruction

  • Radionuclide bone scan: very sens, but non-spec (false + if soft-tissue inflamm.); option if hardware prevents MRI

Bone biopsy: gold standard diagnostic test

  • C/s surgery vs. MSK IR; Surg > IR if concern for overlying cellulitis to mitigate risk of seeding. Open Bx preferred to percutaneous CID 2009;48:888. If perc. Bx ⊝ and suspicion high, repeat vs. obtain open biopsy.

  • Bone Cx may be + even on abx; need 2 specimens: GS/Cx (aerobic, anaerobic, mycobacterial, fungal) + histopath

  • If evidence of OM on imaging or + probe to bone, bone biopsy + up to 86% of cases CID 2006;42:57. Biopsy not required if + blood Cx and clinical/radiographic findings of OM

Treatment

Antibiotics (tx based on culture data, see the table):

om abx

  • Delay empiric tx until Bx_ if pt HD stable, no neurologic compromise or epidural abscess

  • Common organisms: MSSA/MRSA, CoNS, Strep, Enterococci, aerobic GNRs. Other: brucella, mycobacteria, fungi.

  • Can consider adding rifampin if Staph + hardware (for biofilm), (Arch Intern Med 2008;168:805)

  • Duration: ≥6w, PO may be adequate after sufficient response to IV but d/w ID (NEJM 2019;380:425). If PO, FQ+RIF most common

  • No residual infected bone (i.e. amputation): abx 2-5d → up to 10-14 if associated SSTI

  • Consider rechecking ESR/CRP; if elevated at end of abx, consider further w/u (NB: NO routine repeat MRI, findings take weeks to months to resolve)

Surgical Debridement: indicated if failure to respond to medical therapies, chronic OM, complications of pyogenic vertebral OM (e.g. early signs of cord compression, spinal instability, epidural abscess), or infected prosthesis

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