Growth plate (physeal cartilage) injuries
Children's bones have cartilaginous growth plates (physis) that become the «weak link» during trauma. The Salter-Harris (Salter-Harris) classification system is used to categorize these injuries:
- Type I (epiphyseolysis): The fracture line runs strictly along the growth plate, completely detaching the epiphysis from the metaphysis without damaging the bone structures themselves. Since cartilage is radiolucent, radiographs only show pathological widening of the epiphyseal plate. In questionable cases, MRI is ordered: on T2-weighted images, an acute fracture manifests as a hyperintense signal (edema and hemorrhage).
- Type II: The most common variant, in which the fracture line passes through the physis and extends into the metaphysis.
- Type III: An intra-articular injury where the fracture crosses the growth plate and extends into the epiphysis.
Physeal cartilage injuries are dangerous due to their long-term consequences. Improper healing can lead to premature local closure of the growth plate. Sometimes, as MRI shows, a bridge — bony bar (bony bar) — forms between the epiphysis and metaphysis. This structure blocks normal bone elongation, resulting in asymmetric growth and severe angular deformities requiring surgical intervention.
Radiodiagnosis of elbow joint injuries
Evaluation of the elbow joint after trauma is impossible without high-quality radiographs strictly in two projections: anteroposterior (AP) and lateral (lateral). The physician must analyze anatomical landmarks and the correct alignment of articular surfaces.
The most important radiological marker of occult trauma is the fat pad sign (fat pad sign). Blood or effusion in the joint cavity stretches the capsule, displacing adjacent fat accumulations:
- Posterior fat pad: Normally hidden. If visible on a lateral view, it is 100% pathological. It indicates an occult fracture (most commonly of the radial head/neck or nondisplaced supracondylar fracture).
- Anterior fat pad: May also be visualized in healthy children.
Important nuance: the medial and lateral epicondyles are located outside the joint capsule. Their isolated avulsion fractures do not lead to fluid accumulation in the joint, so the fat pads are not displaced. The absence of this sign does not guarantee bone integrity!
Specific elbow fractures:
- Supracondylar fractures: Lead the way in children under 7 years old. The extension type (from falling on an outstretched hand) is most common, where the distal fragment is displaced posteriorly. The flexion type with anterior displacement is significantly less frequent.
- Medial epicondyle avulsion: Requires utmost attention, as the avulsed epiphysis can migrate and become trapped directly inside the joint cavity.
Pelvic avulsion fractures and pathological fractures
Sudden muscle contraction can lead to avulsion of pelvic bone apophyses to which they attach. Typical localizations and associated muscles:
- Iliac crest: muscles of the anterior abdominal wall.
- Anterior superior iliac spine (ASIS): sartorius muscle.
- Anterior inferior iliac spine (AIIS): rectus femoris muscle.
- Ischial tuberosity: hamstring muscles.
- Pubic symphysis: adductor muscles and gracilis muscle.
- Lesser trochanter of the femur: iliopsoas muscle.
- Greater trochanter: gluteus medius and minimus muscles.
A special category consists of pathological fractures occurring against the background of altered bone structure. A classic example in children is simple bone cysts in the proximal humerus or distal femoral metaphysis. A characteristic radiological sign in such cases is the fallen fragment sign, where a bone fragment is visualized at the bottom of the cystic cavity.
Briefly: answers to topical questions
What are the types of fractures according to the Salter-Harris classification?
According to the Salter-Harris classification, there are five types of fractures involving the growth plate in children.
- Type I — Slipped (Slipped) — isolated injury to the growth plate accompanied by separation of the epiphysis.
- Type II — Above (Above) — the fracture line splits the growth plate and extends into the metaphysis.
- Type III — Below (Below) — the fracture line passes through the epiphysis and then horizontally crosses the growth plate.
- Type IV — Through (Through) — vertically oriented fracture involving the epiphysis and metaphysis.
- Type V — Ruined (Ruined) — occurs as a result of a compressive force crushing the growth plate.
In what sequence do ossification centers appear in the pediatric elbow joint?
Ossification centers in the elbow joint appear in the sequence described by the mnemonic CRITOE (the variant CRITOL is also encountered):
- Capitellum of the humerus (Capitellum) — appears at 0–2 years of age.
- Radial head (Radial head) — appears at 3–6 years.
- Internal / medial epicondyle (Internal / medial epicondyle) — appears at 3–9 years.
- Trochlea of the humerus (Trochlea) — appears at 7–13 years.
- Olecranon (Olecranon) — appears at 8–10 years.
- Lateral / external epicondyle (Lateral / external epicondyle) — appears at 8–12 years.
What specific radiological signs are characteristic of a Salter-Harris type II fracture?
A Salter-Harris type II fracture is characterized by the fracture line passing through the growth plate with extension through the metaphysis. Specific radiological signs include:
- Fragment separation — the fracture line splits the growth plate and detaches a small metaphyseal bone fragment.
- Displacement — the fractured metaphyseal fragment is displaced along with the intact epiphysis, maintaining attachment to it.
- Visualization — the injury is best visualized in the lateral projection.
The order of appearance of elbow ossification centers is easy to remember using the English acronym CRITOE: Capitellum (0–2 years), Radial head (3–6 years), Internal epicondyle (3–9 years), Trochlea (7–13 years), Olecranon (8–10 years), and External epicondyle (8–12 years).
Class and exam questions
How does slipped capital epiphysis (Salter-Harris type I fracture) appear on radiographs?
In such an injury, the fracture line runs strictly through the radiolucent cartilage without involving the bone. The main and often the only sign on the radiograph is pathological widening of the growth plate.
Does the absence of the "fat pad" sign rule out an elbow fracture?
No, it does not rule it out. For example, the medial and lateral epicondyles are located outside the joint capsule, so their isolated fractures do not cause capsule stretching and fat pad elevation.
What is a bone bridge and why is it dangerous?
A bony bridge is an area of pathological osseous fusion between the epiphysis and metaphysis crossing the growth plate after a fracture. It blocks normal longitudinal bone growth and causes severe angular deformities requiring surgery.
What else to study on this topic
- MRI semiotics of acute edema and hemorrhage in the growth plate (features of T2-weighted images).
- Mechanogenesis and biomechanics of pelvic avulsion fractures depending on muscle groups.
- Assessment of articular surface alignment of the elbow joint in anteroposterior and lateral projections.
- Signs of simple bone cysts and differential diagnosis of the fallen fragment sign.
- Surgical tactics and MRI planning in premature closure of growth plates.
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