Osteomyelitis: A Comprehensive Overview of Bone Infection, Slides of Medicine

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Osteomyelitis

Tan Zhen yang^ Ilya Maisara Dr Faiq, Mr GaneshaSupervisor:

Anatomy

Anatomy of long bone

● Periosteum ○ Fibrous layer: fibroblasts ○ Cellular layer: osteoprogenitor cells → osteoblasts, osteoclasts ○ Contains blood vessels, nerves, and lymphatic vessels that nourish compact bone

● Endosteum ○ Inner membranous lining of compact bone that lines the medullary cavity

Blood supply

Nutrient / medullary artery system: (High pressure system)

● Enter the cortex then medullary canal through nutrient foramen (mid-shaft) ● Branches into: ascending & descending → goes laterally to end of the bone → anastomosis with metaphyseal and epiphyseal vessels

Pathogenesis and Types of

Osteomyelitis

Common pathogens

Age group Most common organisms Newborns (<4 months)

S. aureus , Enterobacter species, and group A and B Streptococcus species Children (4 months - 4 years)

S. aureus , group A Streptococcus species, Kingella kingae , and Enterobacter species Children, adolescents (4 years - adult)

S. aureus (80%), group A Streptococcus species, H. influenzae , and Enterobacter species

Adult

S. aureus , occasionally Enterobacter or Streptococcus species

Acute hematogenous osteomyelitis

Organisms reach the bone through the bloodstream.

● Adult (5%) ○ Most common affected site = Vertebrae ○ infection reaches the vertebral column through spinal venous plexus ● ● Infant and children (95%) ○ Most common affected site = Long bone metaphysis

Contiguous-focus and posttraumatic

osteomyelitis

● Direct inoculation of bacteria ○ Trauma, open fracture, surgical reduction and internal fixation of fractures, prosthetic devices ○ ● Septic arthritis ○ Infection extend into the underlying bone → Erosions and osteomyelitis ○ ● Vascular compromise ○ Diabetes mellitus are predisposed to osteomyelitis due to inadequate local tissue response ○ Minor trauma to the feet → Multi-organism infection → Foot ulcers allow bacteria to reach the bone ○ Patients may not experience any resulting pain, because of peripheral neuropathy → Delayed treatment

● Organisms reach the bone through the bloodstream from a septic focus elsewhere in the body ● ● Infection begins in the metaphysis of a long bone (productive medium for bacterial growth) ● ● It may spread to involve a large part of the bone. ● ● The organisms induce an acute inflammatory reaction but rigid structure of the bone not allow swelling. ● ● Pus is formed and soon finds its way to the surface of the bone where it forms a subperiosteal abscess

Sequel to acute osteomyelitis

● Abscess may burst into the soft tissues and form a sinus

● Usually the blood supply to a part of the bone will be cut off by septic thrombosis ● ● The ischaemic bone dies and eventually separates from the surrounding living bone as a sequestrum ● ● New bone laid down beneath the stripped-up periosteum, forming an investing layer known as the involucrum

Vertebral Osteomyelitis / Epidural Abscess

● Neurologic deficits present in 10-20% ○ direct infectious involvement of neural elements ○ compression from instability of the spine ○ compression from an epidural abscess ■ collection of pus or inflammatory granulation tissue between dura mater and surrounding adipose tissue

Implant-associated osteomyelitis

● Early onset (within 30 days of implant insertion) ○ Staphylococcus aureus, Beta-hemolytic streptococci, Gram-negative bacilli ○ Common cause: intraoperative contamination ● ● Late onset (>30 days of implant insertion) ○ Staphylococcus aureus, Corynebacterium spp., P. acnes ○ Frequently due to haematogenous infection

Symptoms ● Dull pain at the involved site with or without movement ● Refuse to bear weight (pediatrics) ● Fever

Signs ● Fever, tachycardia, hypotension ⇒ sepsis ● Erythematous, edematous limb ● Tenderness over the affected bone ● Increased local temperature ● Restricted ROM ● Draining sinus tract

Investigation