The anterior oblique ligament of the thumb is one of several carpometacarpal ligaments of the thumb and also one of its main stabilizers 1.
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Terminology
The anterior oblique ligament of the thumb is also known as the ‘beak ligament’. It can be divided into a superficial and a deep component and some authors use the name ‘beak ligament’ only for the deep portion.
Gross anatomy
The anterior oblique ligament of the thumb is located at the ulnar volar aspect of the first carpometacarpal joint and the main task of the ligament is to prevent dorsal translocation. It consists of a broad superficial layer and a narrower deep portion positioned 1-5.
Attachments
The anterior oblique ligament of the thumb originates at the palmar tubercle of the trapezium 1,5. Its insertion is located at the volar beak of the first metacarpal base at the palmar and ulnar surface, hence the name beak ligament 1-5.
Radiographic features
Ultrasound
The anterior oblique ligament of the thumb can be identified on ultrasound with thorough anatomical knowledge and state of the art equipment. The transducer, preferably a hockey stick probe, is placed at the volar aspect of the thumb in supination, extension and abduction. The long axis of the ligament is displayed as a hypoechoic, structure with no fibrillary pattern attaching the trapezium to the base of the first metatarsal bone on the volar side 3. Visualization can be enhanced with intraarticular injection of saline.
MRI
The anterior oblique ligament of the thumb is detectable on MRI and can be appreciated on coronal 3D images or sagittal images as a hypointense linear structure, connecting the trapezium to the first metacarpal on the volar side in an oblique fashion 3-5.
Related pathology
The ligament is involved in the following pathologic conditions 2,3:
- traumatic carpometacarpal joint injury
- sprain
- dislocation
- Bennett fracture: the volar fragment remains usually anchored by the anterior oblique ligament
- carpometacarpal joint arthritis