Complications of bone and joint infections
Delayed recognition of an infectious process often leads to irreversible changes. Due to subtle or non-specific symptoms, the diagnosis is sometimes established retrospectively when joint structures have already undergone destruction.
- Septic arthritis and meningococcal septicemia can cause a classic complication: premature closure of the central part of the epiphyseal plates. This leads to the formation of characteristic V-shaped (or chevron) deformities of the epiphyses and metaphyses.
- Neonatal septicemia can cause long-term lower limb malalignment due to bilateral but asymmetrical involvement of growth plates.
Ultrasonography is widely used to assess joint status. It helps detect pathological effusion (a difference of 1–2 mm compared to the healthy joint is concerning) and is used for guidance during therapeutic drainage.
Imaging of acute osteomyelitis
Acute osteomyelitis requires careful imaging to assess the extent of involvement of the bone tissue and surrounding structures.
- On radiographs, early signs include focal radiolucency in the metaphyseal region and periosteal reaction extending along the diaphysis.
- Magnetic resonance imaging (MRI) is more informative and allows for the detection of intraosseous pus or fluid collections, as well as associated pronounced edema of adjacent muscle and soft tissue structures.
Spinal infections: discitis and osteomyelitis
Differentiation between discitis and spinal osteomyelitis is crucial for selecting the appropriate patient management strategy.
Discitis is an infection of the intervertebral disc. Inflammatory changes on imaging are limited to the disc itself and the adjacent endplates. The condition most frequently affects the lumbar spine in children under 5 years of age. Such patients typically present with milder systemic toxicity, complain of back pain, refuse to walk, or become irritable. Radiographs and CT scans reveal decreased disc height and irregular contours of the endplates.
Spinal osteomyelitis is characterized by purulent destruction directly involving the vertebral body. The process originates in the bone tissue and may secondarily involve the disc or adjacent vertebrae (including via subligamentous spread). Children with osteomyelitis are generally older and present in more severe condition (marked systemic toxicity).
Diagnostic modalities include:
- Radiography — if the presentation is typical for discitis, this may be sufficient.
- MRI — indicated for equivocal radiographs or severe systemic toxicity. It allows for the exclusion of intraspinal or soft tissue abscesses (e.g., in the psoas muscle). Contrast administration is used in complex cases.
Tuberculous spondylodiscitis
Tuberculous involvement of the spine requires special attention. On MRI, the edema zone in tuberculous discitis is predominantly localized in the epiphyseal growth zone of the vertebra. The infection may form an intraosseous abscess and spread into soft tissues, producing large psoas abscesses (cold abscesses), which are clearly visible on axial CT slices.
On contrast-enhanced MRI, tuberculous spondylitis is characterized by intense, heterogeneous ring-like enhancement. However, imaging data alone are insufficient for definitive confirmation—biopsy (optimally under CT guidance) is required for microbiological tissue analysis.
Briefly: answers to topical questions
What are the radiographic stages of acute hematogenous osteomyelitis?
Based on radiography, the following stages are distinguished:
- Acute hematogenous osteomyelitis — characterized by periostitis and subperiosteal abscess; changes may not be visible in the early stages. Later, osteolysis, focal metaphyseal radiolucency, and periosteal reaction along the diaphysis are detected.
- Chronic hematogenous osteomyelitis — characterized by the formation of an involucrum and the presence of a sequestrum.
What are the anatomical pathways of infection spread in spinal osteomyelitis?
In spinal osteomyelitis, infection can spread via the following pathways:
- Hematogenous route.
- Direct inoculation during spinal surgery.
- From adjacent infected soft tissues.
- To adjacent vertebrae — through the intervertebral disc or via subligamentous spread of pus (e.g., in spinal tuberculosis).
Class and exam questions
What is the main imaging difference between discitis and spinal osteomyelitis?
In discitis, changes are limited to the intervertebral disc and endplates. In osteomyelitis, the vertebral body is primarily destroyed.
Why is ultrasound used in pediatric joint infections?
Ultrasound helps detect pathological joint effusion and serves for precise guidance during joint drainage.
How does acute osteomyelitis appear on a radiograph?
Characteristic features include focal metaphyseal radiolucency and periosteal reaction along the bone diaphysis.
How is the diagnosis of tuberculous spondylitis confirmed?
Despite the characteristic MRI findings, tissue sampling (CT-guided biopsy) for microbiological examination is mandatory.
What else to study on this topic
- Assessment of vertebral fractures in children: comparison of DXA and radiography.
- CT and MRI diagnosis of temporomandibular joint involvement in juvenile idiopathic arthritis.
- Detailed analysis of contrast enhancement patterns in spinal MRI.
- Technique of CT-guided vertebral biopsy.
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