Ulnar collateral ligament (UCL) injuries
Normally, on coronal fat-suppressed MR images (FS T2-weighted), the collateral ligament has distinct contours and a homogeneous signal. The imaging appearance varies depending on the age of the injury:
- Acute injuries: MRI reveals marked soft tissue edema and an area of hemorrhage around the injured ligament. Acute valgus stress most frequently results in a tear at the site of proximal attachment to the humeral epicondyle. Important clarification: although the medial area suffers biomechanically, some classic sources may mention the lateral epicondyle.
- Chronic tears: Conventional MRI may be insufficient, so preference is given to MR arthrography. The tissue defect in a chronic course is typically localized distally — at the attachment site to the sublime tubercle of the ulna (sublime tubercle of the ulna).
Osteochondritis dissecans and early osteoarthritis
Two common pathologies requiring careful analysis of subchondral structures and the joint cavity.
Osteochondritis dissecans of the humeral capitellum (Osteochondritis Dissecans) The primary task of the radiologist is to determine whether the osteochondral fragment is stable. On T1-weighted MR arthrograms (including the FS T1 sequence), the pathology manifests as a low-signal area in the subchondral bone. If contrast medium does not track around the base of the lesion, this is a reliable sign of articular cartilage intactness and focus stability. These findings can be confirmed using coronal CT arthrography.
Early osteoarthritis (OA) of the elbow joint Computed tomography is optimal for detecting initial bone deformations:
- Axial CT scans clearly visualize marginal osteophytes growing from the olecranon (olecranon).
- Sagittal CT arthrograms frequently reveal radiolucent (invisible on conventional radiographs) intra-articular cartilage bodies that accumulate in the posterior recess of the joint capsule.
Combined biomechanics: forearm and wrist joint
The elbow joint functions in a single biomechanical chain with the distal radioulnar joint (DRUJ), which provides pronation and supination of the forearm. The stability of this complex largely depends on the condition of the hand and wrist.
The proximal row of carpal bones (scaphoid, lunate, triquetrum) acts as an intercalated segment between the forearm bones and the rigid distal row. A key role here is played by the lunate bone (lunate), which acts as a biomechanical "keystone".
Assessment of correct carpal alignment is performed on posteroanterior radiographs using Gilula's arcs — smooth lines formed by the articular surfaces. Disruption of intrinsic ligaments (e.g., scapholunate) leads to dissociative carpal instability. On radiographs, this manifests as a diastase between the bones of more than 3 mm and an increase in the scapholunate angle exceeding 60 degrees.
Carpal bone complications
Since elbow injuries and falls on an outstretched hand are frequently combined, it is important to exclude scaphoid fractures. The fracture line in the area of its waist is associated with a high risk of avascular necrosis (AVN) of the proximal pole (the more proximal the fracture, the higher the risk of nonunion).
Radiological signs of AVN:
- MRI: Sclerosis produces a low signal on T1-weighted and STIR images. If bone marrow edema persists on STIR, perfusion is still present. The absence of gadolinium enhancement in the sclerotic area on fat-suppressed T1-weighted images is a 100% sign of loss of vascularization.
- CT: The best method for assessing fracture healing, as the fracture line may be masked by sclerosis on radiographs.
A similar pattern of necrosis, but involving the lunate bone, is called Kienböck's disease (Kienböck's disease), which is frequently accompanied by ulnar shortening (negative ulnar variance).
Briefly: answers to topical questions
Which bones make up the proximal carpal row?
The proximal row of carpal bones consists of four bones.
- Scaphoid (os scaphoideum) — transmits force from the deviated hand to the radius.
- Lunate (os lunatum) — transmits force from the adducted hand to the radius, acts as a "keystone".
- Triquetrum (os triquetrum) — transmits load to the articular disc during hand adduction.
- Pisiform (os pisiforme) — is a sesamoid bone within the tendon of the flexor carpi ulnaris.
Which nerves pass through the elbow region and are at risk during its injuries?
In the region of the elbow joint and cubital fossa, sources describe the ulnar, median, and radial nerves.
- Ulnar nerve (n. ulnaris) — runs in the ulnar nerve groove on the posterior surface of the medial epicondyle of the humerus. Compression of the ulnar nerve at the elbow level is possible in the retroepicondylar groove or cubital canal; causes include trauma, traction during prolonged elbow flexion, arthritis, synovitis, ganglia, and subluxation of the ulnar nerve.
- Median nerve (n. medianus) — runs in the anterior elbow region, in the cubital fossa, as part of the neurovascular bundle.
- Radial nerve (n. radialis) — mentioned in connection with the cubital fossa region and pathways of spread along the course of the radial nerve; also, pus can spread distally into the anterior fascial compartment of the forearm along the neurovascular bundle with the radial artery.
To remember the sign of stable osteochondritis dissecans, use the "Dry Base" rule: if contrast does not track under the base of the defect, it means the "roof" (cartilage) is intact, and the fragment will not displace anywhere.
Class and exam questions
Which radiological imaging method best shows radiolucent intra-articular bodies?
The optimal method is CT arthrography (especially in the sagittal projection), as it allows visualization of cartilage bodies hidden in the posterior recess of the joint.
How to determine from an MRI that blood supply is impaired in a scaphoid fracture?
A reliable sign of complete lack of vascularization (AVN) is the absence of contrast medium (gadolinium) enhancement in sclerotic areas on fat-suppressed T1-weighted images.
What else to study on this topic
- Anatomy and tears of the triangular fibrocartilage complex (TFC)
- Radiological evaluation of carpal instability using Gilula's arcs
- Specifics of performing MR and CT arthrography of the elbow joint
- Kienböck's disease: stages of progression and relationship with ulnar length
- Topography of the carpal tunnel and tendon retinacula
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