66-year-old female with complaints of the right elbow and/or proximal forearm. The clinical question concerns possible tendon, nerve, or intra-articular pathology. Symptoms, duration, occupation, sport activity, and presence or absence of motor weakness are not provided.
Ultrasound examination of the right elbow was performed, including assessment of the flexor and extensor muscle groups, supinator muscle, lateral elbow region including the common extensor tendon and annular ligament, radial nerve, posterior interosseous nerve, distal biceps tendon, and elbow joints.
The distal biceps tendon is thickened and hypoechoic, with several intratendinous hyperechoic reflections, compatible with tendinopathy with a possible limited calcific component. In addition, the distal biceps tendon shows a full-thickness, partial-width tear. The tear involves the full tendon thickness over part of the tendon width, while part of the tendon remains intact. There is therefore no complete distal biceps tendon rupture.
The posterior interosseous nerve, or PIN, shows focal thickening and hypoechogenicity at the entrance of the arcade of Frohse within the supinator muscle. This appearance may be compatible with local nerve irritation or entrapment. In PIN entrapment, ultrasound may demonstrate focal caliber change, compression, and proximal hypoechoic nerve swelling at the entrance of the supinator canal or arcade of Frohse.
The clinical significance of the PIN finding cannot be determined by ultrasound alone and requires correlation with physical examination, particularly motor testing of wrist and finger extension.
1. Final diagnosis
Distal biceps tendinopathy with a full-thickness, partial-width tear of the distal biceps tendon. A possible limited calcific component is present. There is no complete distal biceps tendon rupture. In addition, there is focal thickening and hypoechogenicity of the posterior interosseous nerve at the arcade of Frohse, suspicious for possible PIN entrapment.
2. Differential diagnosis
The differential diagnosis includes distal biceps tendinopathy with full-thickness partial-width tearing, calcific distal biceps tendinopathy, PIN entrapment at the arcade of Frohse or supinator canal, and radial tunnel syndrome. Radial tunnel syndrome is particularly relevant when pain is present without clear motor deficit. If symptoms do not correlate with the tendon or nerve findings, intra-articular elbow pathology, such as radiocapitellar or humeroulnar joint disease, or referred symptoms from the cervical spine or proximal radial nerve pathway should also be considered.
3. Teaching points
A full-thickness, partial-width tear should be distinguished from a complete distal biceps tendon rupture. In a full-thickness partial-width tear, the defect extends through the tendon thickness but does not involve the entire tendon width, leaving part of the tendon intact. Distal biceps tendinopathy may appear as tendon thickening, hypoechogenicity, and intratendinous echogenic foci when degenerative or calcific changes are present. Focal swelling and hypoechogenicity of the PIN at the arcade of Frohse should prompt clinical correlation, as true PIN syndrome usually presents predominantly with motor weakness, whereas radial tunnel syndrome more often presents with pain without clear paresis.
4. Injury/disease information
The distal biceps tendon is important for elbow flexion and forearm supination. Chronic overload, repetitive lifting, traction, or forceful supination may contribute to tendinopathy and partial tendon tearing. The posterior interosseous nerve passes through the supinator region and may be compressed at the arcade of Frohse. Ultrasound can demonstrate focal nerve swelling or caliber change, but clinical examination and, when indicated, EMG or nerve conduction studies are important to determine functional relevance. MRI may be useful when the extent of the distal biceps tear, structural nerve compression, intra-articular elbow pathology, or treatment planning requires further assessment.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
More Cases from Marc Schmitz
