Biomechanics and specificity of pediatric fractures
Under the influence of force (compression, tension, or shear), stress arises in the bone tissue. In children, there is a vast difference between the yield strength (the point where plastic deformation begins) and the ultimate tensile strength (the moment of physical destruction). Pediatric bone can bend significantly before breaking.
The cortical layer of the developing skeleton withstands compression well, but is vulnerable to tension and shearing forces. Microfractures frequently form on the tension side; initially invisible on radiographs, they manifest later as a periosteal reaction (a sign of healing).
High elasticity leads to specific incomplete fractures:
- Greenstick fractures (greenstick fracture): the cortical layer breaks on only one side, while the opposite side remains intact.
- Buckle fractures (buckle or torus fracture): the bone buckles under axial load, forming a cortical bulge.
- Plastic bowing (plastic bowing): persistent deformation without a visible fracture line.
Growth plate injuries (physeal injuries)
The cartilaginous growth plate (physis) is located between the epiphysis and metaphysis, ensuring bone elongation. Since physeal cartilage is weaker than bone tissue and ligaments, traumatic force (most commonly shear or avulsion) damages the growth plate itself. Such injuries account for up to 15% of all long bone fractures in pediatrics.
The Salter-Harris classification (Salter-Harris) is used to assess the severity of physeal injuries. The higher the grade on this scale, the more serious the prognosis. Complications of severe injuries include malunion, avascular necrosis (the risk is particularly high in fractures of the femoral neck, radius, and scaphoid), as well as premature formation of a bony bridge, which leads to growth arrest and limb shortening.
Apophyseal injuries
Apophyses are areas of bone where muscle-tendon complexes attach. The apophyseal growth plate acts as the weakest link in the bone-tendon-muscle chain.
Two types of injuries are distinguished:
- Acute (avulsion) fractures: occur during sudden muscle contraction (strong traction), leading to the detachment of a bone or cartilage fragment. Common in sports practice; typical zones are the pelvis and elbow joint.
- Chronic apophysitis: develops due to repetitive low-energy stress. A classic example is "little leaguer's elbow" (little leaguer's elbow), which represents a chronic apophysitis of the medial epicondyle of the humerus.
Features of upper extremity injuries
Clavicle fractures are the most common (especially in the middle third). Due to the dense periosteum, they tend to occur as greenstick fractures. The clavicle is also the most frequent location for birth injuries, which are associated with shoulder dystocia and obstetric palsies.
Shoulder dislocations in patients under 10 years of age are extremely rare—the robust growth plate of the proximal humerus absorbs the impact energy. Fractures in this area are critical, as the proximal physis provides up to 80% of the length of the humerus.
Pathological fractures frequently occur in the proximal humerus in the setting of simple bone cysts. They are characterized by the radiological "fallen fragment sign" (fallen fragment sign), where a detached piece of the cortical layer lies within the fluid-filled cyst.
Briefly: answers to topical questions
What types of growth plate injuries are distinguished according to the Salter-Harris classification?
According to the Salter-Harris classification, there are 5 main and 4 additional types of growth plate injuries.
- Type I (Salter-Harris I) — epiphyseolysis (the fracture line runs straight through the growth plate).
- Type II (Salter-Harris II) — metaepiphyseolysis (the fracture line passes above or away from the growth plate).
- Type III (Salter-Harris III) — epiphyseal fracture (the fracture line passes below the growth plate).
- Type IV (Salter-Harris IV) — metaepiphyseal fracture (the fracture line passes through the metaphysis, growth plate, and epiphysis).
- Type V (Salter-Harris V) — impacted fracture with growth plate injury.
- Type VI (Salter-Harris VI) — injury to perichondral structures at the periphery of the growth plate.
- Type VII (Salter-Harris VII) — isolated local growth plate injury.
- Type VIII (Salter-Harris VIII) — isolated metaphyseal injury above the growth plate.
- Type IX (Salter-Harris IX) — periosteal injury.
What radiological signs are characteristic of chronic apophysitis of the medial epicondyle of the humerus?
Magnetic resonance imaging and ultrasound are informative for visualizing chronic apophysitis of the medial epicondyle of the humerus.
- Soft tissue edema — detected in chronic conditions.
- Joint effusion — determined by MRI and ultrasound methods.
- Bone marrow edema — visualized in chronic conditions.
Radiography is sufficient to diagnose acute avulsion fractures, provided that the avulsed fragment is ossified.
Which bones are most frequently injured during birth trauma?
The clavicle is the most frequently injured bone during birth trauma, although fractures of other bones are also possible.
- Clavicle — the most common site of birth-related fractures (associated with shoulder dystocia).
- Skull bones — fractures, cracks, and depressions are possible (parietal, frontal, and occipital bones are most frequently injured).
- Vertebrae — fractures and avulsions of vertebral bodies are most frequently localized in the area of the CVI–CVII vertebrae.
To memorize the sequence of appearance of the six ossification centers of the elbow joint, the acronym CRITOL is used. The most important rule: the internal apophysis must always appear on radiographs before the trochlea. Any violation of this chronology during trauma indicates an avulsion fracture or displacement.
Class and exam questions
Why are ligament ruptures and joint dislocations rarely diagnosed in children?
This is due to the anatomical strength gradient: the physeal cartilage is significantly weaker than the surrounding bone, and the bone is weaker than the ligamentous apparatus. The trauma energy is realized through damage to the growth plate or an avulsion fracture, leaving the ligaments intact.
What is the difference between the epiphysis and the apophysis?
The epiphysis is located at the ends of long bones and participates in joint formation, ensuring longitudinal bone growth. The apophysis is the site of muscle and tendon attachment; it does not participate in the formation of articular surfaces.
What is the «fallen fragment» sign?
This is a sign of a pathological fracture in the presence of a simple bone cyst. A piece of the cortical layer breaks off and lies freely within the fluid-filled cavity of the cyst.
How to distinguish a proximal humeral fracture from a normal growth plate on a radiograph?
The normal growth plate in children has an irregular contour, which an untrained eye may mistake for a fracture. For accurate diagnosis, it is necessary to know age-related anatomical features and, if necessary, compare with a radiograph of the healthy limb.
What else to study on this topic
- Salter-Harris classification of physeal injuries (detailed breakdown of types I-V)
- Radiological signs of non-accidental trauma (child abuse syndrome)
- Features and patterns of lower extremity injuries in children
- Specificity of cervical spine injuries in pediatric practice
- Algorithms for CT and MRI in occult physeal cartilage injuries
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