11.07 Ortho

11.07 Miscellaneous orthopaedics [PDF link]: Charcot joint, Dermatomes, Fat embolism, Osteochondritis dissecans, Osteomalacia, Osteomyelitis (OM)

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More on vertebral osteomyelitis and discitis/diskitis

• Vertebral osteomyelitis = infection of any part of the spinal column

  • ÷ pyogenic vs nonpyogenic

    • Nonpyogenic = granulomatous – usually caused by atypical organisms such as TB, Brucella and fungi.

• Discitis = infection of an intervertebral disc

• Spondylodiscitis = infection of an intervertebral disc plus adjacent vertebral body/bodies. Aka osteodiscitis.

• Epidural abscess = abscess within epidural space of the spinal canal

• Psoas abscess = abscess within psoas muscle

  • Psoas major originates from the lateral surface of bodies of TXII, LI and LV vertebrae, transverse processes of the lumbar vertebrae, and the intervertebral discs between TXII and LI to LV vertebrae

• Risk factors of vertebral OM: ↑age, prosthetic devices, IVDUs, immunosuppression, and diabetes

• Pathophysiology:

  • (1) Haematogenous, eg as a metastatic infection from infectious endocarditis

    • Usually only involves two vertebral bodies ± disc in between

    • Usually caused by single pathogen, of which Staph aureus is the most common microbe – see 08.02 for more

    • Other organisms include Gram negative enteric rods (eg E.coli, Klebsiella, Pseudomonas aeruginosa)

  • (2) Contiguous spread, eg from infected pressure sores

  • (3) Direct inoculation from trauma, eg spinal surgery

• S/smx:

  • ❗️Back pain, usually insidious to begin with and worsening

  • With epidural abscess, there may be radiculopathy, motor and sensory changes (including features of cauda equina)

  • Physical exam points to check for: local spinal tenderness, red flags for cauda equina syndrome (11.01), psoas sign (positive if passive hip flexion causing pain, while hip flexion relieves pain), neurological deficits, peripheral stigmata of infective endocarditis

• Ix:

  • Blood cultures (at least 2 sets), urine cultures

  • Spinal imaging – MRI is preferred (gadolinium contrast offers more information but is not strictly needed)

    • CT where MRI is not available. With CT, contrast is preferred as well (helps to pick up psoas abscesses better). Note high CT false negatives for epidural abscess.

    • Plain XRs may miss OM, and even if they do pick up OM, a secondary form of imaging is necessary for further characterisation

    • Bone scan is an alternative in patients who cannot tolerate MRI (eg if they have MRI-incompatible devices)

  • Bone/disc biopsy – not necessarily needed if blood cultures yield pathogen + imaging is in line with clinical findings

    • Send samples for histopathology, aerobic and anaerobic cultures.

    • If atypical pathogens suspected, send off for TB ± fungal cultures

    • Do not delay abx before biopsy if there are concerns pt may deteriorate neurologically or is becoming septic

  • Others: tests for Brucella or TB if suspicious.

• Mx:

  • Will be based on local guidelines

  • If patient is clinically stable, it is reasonable to wait for blood cultures ± other investigations to guide choice of antimicrobial. Otherwise, empirical therapy may be necessary. This may involve combination therapy (such as vancomycin + cephalosporin, or daptomycin + quinolone – these would cover the most likely organisms causing vertebral OM).

  • Duration of treatment – most guidelines recommend at least 6 weeks of a high bioavailability antimicrobial.

    • If Brucella OM is confirmed, duration should be ≥ 12 weeks

• Guidelines: See IDSA guidelines. I don’t think there are any UK-specific / NICE guidelines for vertebral OM.