Clinical Presentation

An 11-year-old boy presents with chronic heel pain and mild fever.

Figure 99A

Figure 99B

Radiographic Findings

Chronic osteomyelitis (OM)

Differential Diagnosis

Langerhans’ cell histiocytosis

Discussion

Background

OM is an infection of bone and bone marrow clinically divided into acute, subacute, and chronic entities. Host resistance, virulence of the organism, and the response to treatment with antimicrobials are the major factors contributing to the development of one entity over another. OM is polyostotic in ~6% of cases and has a predilection for rapidly growing sites in the immature skeleton such as the metaphyses (or metaphyseal equivalent) of the distal femur and radius as well as proximal tibia and humerus. Neonatal OM has an incidence of 1 to 3 per 1000 hospital admissions, often involving the hips, and is multifocal in 23 to 47% of cases.

Etiology

Routes for infection include hematogenous seeding infection (most common form in children), contiguous spread from adjacent soft tissue or joint, and direct inoculation due to trauma. Approximately 2% of all orthopedic procedures are complicated by infection.

Clinical Findings

Infection in the neonate and young infant is often clinically silent. Toddlers and children present with pain in limb with passive motion, pseudoparalysis, or a limp. The area may be red, swollen, and warm on examination.

Complications

• Extension of infection into joint with resulting destruction, subluxation/dislocation, or ischemic necrosis (one third of hip OM has septic joint)
  
• Slipped epiphysis
  
• Premature closure of growth plate due to destruction of proliferating cartilage cells
  
• Overgrowth of limb due to chronic hyperemia
  
• Squamous cell carcinoma develops in 0.5% of patients with long-standing draining OM (very rare before 20 years of age)

Pathophysiology

Acute infection via hematogenous seeding results in marrow edema and cellular infiltration usually in the metaphysis of a long bone. The physeal plate in infants and children between ~8 and 18 months of age acts as a relative barrier, localizing the disease process, whereas in both younger infants and older children the infection is more likely to spread to the epiphysis via transphyseal vascular pathways and may extend into the joint space. Progression of infiltrate within the marrow cavity results in an increase in intraosseous pressure leading to extension of the inflammatory process through the cortex and into subperiosteal space via haversian and Volkmann’s canals.

Figure 99D Frontal radiograph of ankle depicts a lytic lesion within distal tibial metaphysis crossing the physis and extending into epiphysis. Margins are ill defined in some segments and well demarcated in others. There is a faint central area of increased bone density.

The process may then continue to spread into periosteum and overlying soft tissues. The increased intraosseous pressure can impair blood flow leading to ischemic necrosis of bone resulting in devas-cularized fragments called sequestra. A subacute OM is a more localized pyogenic process in which the term Brodie’s abscess is used when complicated by surrounding granulation tissue and sclerotic bone. Chronic OM is a low-grade continuing infection classified as active or inactive. The process may be indolent for long periods before re-activation. The clinical diagnosis of chronic osteomyelitis can be made if symptoms have been present for >1 month, if there has been inadequate treatment, or if the infection arose >1 month after surgery for trauma.

Laboratory