Osteomyelitis

Infection of the bone and/or bone marrow

Aetiology

  • More common in children but can occur in adults
  • Infection is usually caused by bacteria, occasionally fungal

Risk factors

  • Immunocompromised patients
  • Patients with chronic disease
  • Elderly
  • Young

Causative organisms

  • Newborns (<4 months) - S. aureus, Enterobacter sp., and group A and B Strep
  • Children (4 months to 4 years) - S. aureus, group A Strep, H. influenzae, Enterobacter sp.
  • Children/adolescents (4 years to adult) - S. aureus (80%), group A Strep, H. influenzae, and Enterobacter sp.
  • Adult - S. aureus, occasionally Enterobacter or Streptococcus sp
  • Sickle cell anaemia patients - S. aureus the most common, Salmonella species common and fairly unique to sickle cell patients

Pathophysiology

Routes of infection

  • Haematogenous - infection travelled in the blood from another infected site e.g. cellulitis, PWIDs, central lines/dialysis
    • Most commonly due to a single pathogen
    • Common localisation:
      • Children - long bone metaphysis
      • Adults - vertebral involvement is the most common
  • Exogenous - post-traumatic or contigous spread
    • Post-traumatic - following deep injury e.g. open fractures
    • Contigous spread - spread of infection from adjacent tissue e.g. injuries, secondary to infected foot ulcer in diabetic patients, secondary to pressure sore in elderly patients
    • Usually due to multiple pathogens

Immune system impairment

  • Once infected, enzymes from leucocytes cause local osteolysis and pus forms which impairs local blood flow making the infection very difficult to eradicate
  • A dead fragment of bone known as a sequestrum can form which usually breaks off and once a sequestrum is present, antibiotics alone will not cure the infection
  • New bone will form around the area of necrosis known as an involucrum

Acute osteomyelitis

  • Acute osteomyelitis in the absence of recent surgery usually occurs in children
  • The metaphyses of children's long bones contain abundant tortuous vessels with sluggish flow which can result in accumulation of bacteria and infection spreads towards the epiphysis
  • In neonates and infants, certain metaphyses are intra‐articular e.g. proximal femur, proximal humerus, radial head and ankle, and infection can spread into the joint causing co‐ existent septic arthritis
  • Infants have loosely applied periosteum and an abscess can extend widely along the subperiosteal space
  • Children can also develop a subacute osteomyelitis with a more insidious onset and where the bone reacts by walling off the abscess with a thin rim of sclerotic bone - Brodie’s abscess

Chronic osteomyelitis

  • Develops from an untreated acute osteomyelitis and may be associated with a sequestrum and/or involucrum
  • In adults the infection tends to be in the axial skeleton (spine or pelvis) with haematogenous spread from pulmonary or urinary infections, or from infection of the intervertebral disc (discitis)
  • Tuberculosis can also cause chronic OM, particularly in the spine through haematogenous spread from the primary lung infection

Unusual patient groups

  • Sickle cell osteomyelitis - during sickle cell crisis
  • Gaucher's disease - lysosomal storage disorder which can mimic OM
  • SAPHO and CRMO
    • Commonly chest wall affected

Clinical presentation

Acute oseomyelitis

  • Gradual onset pain at site of infection
  • Point tenderness
  • Swelling, redness, warmth
  • Systemic findings: malaise, fever, chills

Chronic osteomylitis

  • Recurrent pain usually following a prior episode of osteomyelitis
  • Swelling, redness
  • In spinal OM, patients present with insidious onset of back pain which is constant and unremitting (see notes)

Investigations

  • Probe - bone/visible bone, non-healing ulcer, sinus
  • Bloods - CRP useful to monitor response, blood culture
  • Imaging - X ray, MRI, CT, PET scan, bone scan
  • Biopsy - bone biopsy to confirm (gold standard)
    • Wound swap/blood cultures not always diagnostic
    • If first biopsy negative consider another
      • notion image

Management

  • Await microbiological diagnosis unless septic patient or soft tissue infection

Acute osteomyelitis

  • 'Best guess' antibiotics IV unless there is an abscess which requires drainage
  • If infection fails to resolve - second line antibiotics, surgery to take a sample for culture and remove infected bone/tissue

Chronic osteomyelitis

  • Cannot be cured or eradicated by antibiotics alone
  • Active infection can be suppressed with antibiotics but this may prove unsuccessful
  • Surgery is usually recommended to gain deep bone tissue cultures, to remove any sequestrum and to excise any infected or non‐viable bone (debridement)
  • If debridement of bone results in instability, the bone must be stabilized by internal or external fixation
  • Other strategies may include local antibiotic delivery systems and bone grafting
  • Plastic surgery may be required if skin and soft tissue coverage of bone is not possible
  • IV antibiotics are continued for several weeks after surgery