Yo-yo on a string sign - Stener lesion

Last revised by Yahya Baba on 27 Jul 2021

Citation, DOI, disclosures and article data

Citation:

Botz B, Baba Y, Weerakkody Y, et al. Yo-yo on a string sign - Stener lesion. Reference article, Radiopaedia.org (Accessed on 18 Apr 2024) https://doi.org/10.53347/rID-72294

DOI:

https://doi.org/10.53347/rID-72294

Permalink:

https://radiopaedia.org/articles/72294

rID:

72294

Article created:

19 Nov 2019, Bálint Botz ◉

Disclosures:

At the time the article was created Bálint Botz had no recorded disclosures.

View Bálint Botz's current disclosures

Last revised:

27 Jul 2021, Yahya Baba ◉

Disclosures:

At the time the article was last revised Yahya Baba had no recorded disclosures.

View Yahya Baba's current disclosures

Revisions:

9 times, by 7 contributors - see full revision history and disclosures

Systems:

Musculoskeletal, Trauma

Sections:

Signs

Synonyms:

Yoyo on a string sign
Yo yo on a string sign

The yo-yo on a string sign denotes the characteristic appearance of the torn, proximally retracted and superficially displaced ulnar collateral ligament (UCL) due to a Stener lesion.

Mechanism

The sign occurs as a consequence of the tear of the ulnar collateral ligament of the thumb (gamekeeper thumb) whereby the ulnar collateral ligament has displaced superficially to the adductor pollicis muscle ¹.

Radiographic appearance

Diagnosis of the yo-yo on a string can be made with either MRI or ultrasound.

MRI

In MRI it is best observed in the coronal plane, where the "yo-yo" represents the torn ulnar collateral ligament (UCL) which has curled back and the "string" is the aponeurosis of the adductor pollicis muscle. The UCL and aponeurosis are both typically hypointense and can be further outlined by an adjacent joint effusion, which is hyperintense on T2 weighted sequences ².

Ultrasound

On ultrasound, the detection can be made with a high frequency (12-15 MHz) linear array probe having a good contrast resolution in the near field, which can be further improved by using a gel pad. A smaller "hockey stick" probe is particularly well-suited for the evaluation of the ulnar collateral ligament (UCL) ³. The UCL is usually best seen by placing the probe to the medial aspect of the first metacarpophalangeal (MCP) joint, longitudinally to the axis of the thumb. The normal UCL and the more superficial and thinner aponeurosis are both hyperechoic. In the presence of a Stener lesion the retracted, torn UCL typically appears as an inhomogeneous hypoechogenic nodular structure proximally distorting the normally smooth outline of the aponeurosis ⁴.