Forearm and elbow joint injuries
The forearm bones are firmly connected by ligaments, so a fracture of only one bone without injury to the other is rare. If a fracture with displacement or overlapping fragments is visible on the radiograph, an occult dislocation must be ruled out.
Combined injuries include:
- Monteggia fracture-dislocation (Monteggia fracture dislocation): a fracture of the ulnar diaphysis accompanied by dislocation of the radial head at the elbow joint.
- Galeazzi fracture-dislocation (Galeazzi fracture dislocation): a fracture of the radial diaphysis combined with dislocation of the ulna at the radiocarpal joint.
In adults, distal humeral fractures involving the condyles and articular surfaces are common. Rare fractures of the capitellum (capitellum) are best visualized on the lateral view: the displaced fragment takes on a crescent shape and is located anteriorly and superiorly to the forearm. Ulnar fractures are most frequently localized in the olecranon region (olecranon), where the proximal fragment is displaced due to the pull of the triceps brachii muscle. Fractures of the coronoid process are rare but lead to persistent joint instability.
Radiological landmarks of the elbow joint
Specific signs and lines are used to identify occult elbow injuries:
- Fat pad sign (Fat pad sign): visualization of displaced anterior and posterior humeral fat pads indicates fluid accumulation (effusion) within the joint. In adults, this often points to an occult radial head fracture.
- Anterior humeral line (Anterior humeral line): drawn along the anterior cortical margin of the humerus. Normally, it intersects the capitellum, leaving at least 1/3 of its volume anteriorly. If the line passes anterior to the capitellum or intersects only the anterior third, it indicates displacement in a supracondylar fracture.
- Radiocapitellar line (Radiocapitellar line): an axis drawn through the middle of the radial diaphysis normally passes strictly through the capitellum in any projection. The absence of this intersection is a reliable sign of radial head dislocation.
Pathologies of the femur and hip joint
Slipped capital femoral epiphysis (SCFE) Manifests as mild widening of the growth plate on an AP radiograph, but the slippage is better visualized on the Lauenstein (frog-leg) projection or on MRI. To assess severity, the slip angle is measured: mild (< 30°), moderate (31–50°), and severe (> 51°). Klein's line is also used: normally, it intersects the lateral 1/6 of the epiphysis, whereas in pathology, it misses it entirely or cuts off a smaller portion.
Developmental dysplasia of the hip (DDH) On ultrasound, the head is normally centered, coverage is adequate, and Graf angles are within normal limits (e.g., alpha angle = 63°). On radiographs, Putti's triad is used for diagnosis:
- Increased acetabular angle.
- Small epiphysis or delayed ossification of the femoral head ossification center.
- Superolateral displacement of the proximal femur.
To assess displacement, reference lines are drawn: Hilgenreiner's horizontal line (through the triradiate cartilages) and Perkin's vertical line (from the lateral edge of the acetabular roof). Shenton's arcuate line becomes interrupted in dislocation, and the medial space between the acetabular floor and the femoral head widens.
Developmental abnormalities of the femur (Dysplasia)
The spectrum of dysplasia ranges from mild forms to severe bone hypoplasia.
- Idiopathic coxa vara: characterized by a decreased neck-shaft angle (less than 100 degrees requires surgery) and the presence of a separate bone fragment near the lower part of the femoral neck — the Fairbank triangle (Fairbank triangle).
- Proximal focal femoral deficiency (PFFD): classified according to Aitken (groups A–D) depending on the presence of the femoral head, connection to the diaphysis, acetabular morphology, and shortening. Frequently associated with fibular hemimelia and absence of cruciate ligaments (assessed via knee MRI).
CRITOL — the ossification sequence of the elbow joint: Capitellum, Radius, Internal (medial) epicondyle, Trochlea, Olecranon, Lateral epicondyle. The lateral epicondyle appears last. If a lateral fragment is visible without the other ossification centers, it is a fracture.
Class and exam questions
How to differentiate a lateral epicondyle fracture from a normal growth plate in children?
The CRITOL rule must be applied. If only the capitellum is visible among all ossification centers, any radiolucency in the region of the lateral epicondyle represents a fracture, as it ossifies last.
Where can a detached medial epicondyle displace?
During trauma, a detached ossification center may displace into the joint: on the AP view, it superimposes over the humeral trochlea, and on the lateral view, it is identified between the olecranon and the humerus.
What does an interrupted Shenton's line mean?
Interruption of Shenton's arcuate line, which runs along the medial margin of the femoral neck and the pubic bone, indicates dislocation or subluxation in the hip joint.
What else to study on this topic
- MRI semiotics of SCFE in early (pre-radiographic) stages.
- Principles of postoperative CT control (3D reconstruction) following hip reduction.
- Radiological signs of medial epicondyle avulsion fractures in children.
- Diagnostic imaging of tibia vara (Blount disease).
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