Definition: This can be primary (haematogenous) or secondary (following an open fracture or bone operation). Haematogenous osteomyelitis is the commonest, and is often seen in children.
Relevant Anatomy
Metaphysis of the long bones: It is a highly vascularised zone where medullary arteries branch into capillaries at the growth plate. The venous system begins here, creating a hair-pin loop arrangement. The resulting blood stasis makes the metaphysis a favorite site for bacteria to settle.
- Extra-articular metaphysis: In most joints, the capsule attaches at the epiphysis-metaphysis junction, preventing spread to the joint.
- Intra-articular metaphysis: In some joints (like the hip or shoulder), part of the metaphysis is inside the joint capsule, allowing infection to spread and cause pyogenic arthritis.
Aetiopathogenesis
Staphylococcus aureus is the commonest causative organism. Others include Streptococcus and Pneumococcus. Bacteria reach the bone via blood circulation, usually lodging in the lower femoral metaphysis (commonest site), or upper tibial, upper femoral, and upper humeral metaphyses.
Pathology & Spread of Pus
The host bone initiates an inflammatory reaction, leading to bone destruction and pus formation in the medullary cavity. Pus spreads in these directions:
- Along the medullary cavity: Causes thrombosis of medullary vessels, cutting off blood supply to a bone segment.
- In other directions: The epiphyseal plate is resistant. Spread to the joint occurs only if the metaphysis is intra-articular.
- Out of the cortex:
Diagnosis
Basically clinical. It is a disease of childhood, more common in boys.
- Complaints: Acute onset of pain and swelling at the end of a bone, with fever. (Parents often falsely attribute it to a coincidental injury).
- Examination: Child is febrile and dehydrated. Classic inflammatory signs (redness, heat) localized to the metaphyseal area. Possible adjacent joint swelling (sympathetic effusion).
Investigations
- Blood: Polymorphonuclear leucocytosis, elevated ESR. Blood culture at peak fever may yield the organism.
- X-rays: Earliest sign is a periosteal reaction at the metaphysis, taking 7-10 days to appear.
- Bone scan: Technetium-99 shows increased uptake before X-ray changes appear. Indium-111 labelled leucocyte scan is most specific.
Differential Diagnosis
Any acute inflammatory disease at the end of a bone in a child should be taken as acute osteomyelitis unless proven otherwise.
| Condition | Differentiating Features |
|---|---|
| Acute Septic Arthritis | Tenderness/swelling localized to the joint (not metaphysis). Joint movement is painful and restricted. Aspirate joint fluid to check for inflammatory cells. |
| Acute Rheumatic Arthritis | Features are similar to septic arthritis, but joint pains are fleeting. Elevated ASLO titre and CRP values help diagnose. |
| Scurvy | Sub-periosteal haematomas mimic osteomyelitis on X-ray, but there is relative absence of pain, tenderness, and fever. Look for malnutrition features. |
| Acute Poliomyelitis | In the acute phase, there is fever and tender muscles, but no bone tenderness. |
Treatment
Early, adequate treatment is the key to success. Treatment varies by duration of illness:
a) Brought within 48 hours (Pre-Pus Phase)
- Systemic Antibiotics: Halt inflammatory process. Blood drawn for culture first.
< 4 months old: Ceftriaxone + Vancomycin.
Older children: Ceftriaxone + Cloxacillin. - Rest & Splinting: Limb put to rest in a splint or by traction. Weight-bearing restricted for 6-8 weeks.
- Monitoring: 4-hourly temp/pulse chart. Outline area of local tenderness with a matchstick to monitor regression.
- Follow-up: After 2 weeks of IV antibiotics, switch to oral route for 6 weeks. If no response in 48 hours, proceed to surgery.
b) Brought after 48 hours (Pus Collection Phase)
- Assumption is pus has already formed. Ultrasound can help detect deep collections.
- Surgical exploration & drainage is the mainstay.
- A drill hole is made in the metaphysis; enlarged until free drainage is obtained.
- Swab taken for culture. Wound closed over sterile suction drain.
- Post-op: Rest, IV hydration, and antibiotics continued for 6 weeks.
Complications
- General: Septicaemia and pyaemia (can be fatal if uncontrolled).
- Local:
- Chronic osteomyelitis: The commonest complication. Due to delayed diagnosis, sequestrum formation, pent-up pus, and poor host resistance.
- Acute pyogenic arthritis: Occurs if the metaphysis is intra-articular (hip, shoulder).
- Pathological fracture: Occurs through bone weakened by disease or surgical window (prevented by splinting).
- Growth plate disturbances: Leads to shortening, lengthening, or deformity of the limb.
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