J Korean Soc Radiol.  2019 Sep;80(5):969-974. 10.3348/jksr.2019.80.5.969.

Snapping Pes Anserinus Caused By Gracilis Tendon: A New Mechanism Proposed by Dynamic Knee Ultrasonography

• Oh HS
• Kim TE

• KMID: 2459023
• DOI: http://doi.org/10.3348/jksr.2019.80.5.969

Abstract

Snapping pes anserinus is the main extra-articular cause of snapping on the medial side of the knee. There are limited articles that describe the mechanism of the condition, especially only when flexion of the knee. We report a case of snapping pes anserinus in a 23-year-old skier, which was reproduced on only active flexion of both knees in the posteromedial aspect of the tibia, with pain for 6 years, diagnosed using dynamic ultrasonography for elucidating a new mechanism of the gracilis tendon. We performed dynamic ultrasonography of the right knee of the patient; the gracilis tendon was twisting and folding and then, snapping occurred when the gracilis tendon passed by the sartorius muscle. The atypical movement of the gracilis tendon was considered the primary factor for snapping in this patient, which was diagnosed with dynamic ultrasonography.

MeSH Terms

Humans
Knee*
Tendons*
Tibia
Ultrasonography*
Young Adult

Figure

• 

  Fig. 1 A 23-year-old male with snapping pes anserinus caused by gracilis tendon. A. Serial axial MRIs (taken 6 years, 2 years, and 1 year ago) of the right knee do not reveal any abnormal finding (arrows : G, S, St). B. Transverse static ultrasonography of the right knee reveals no other remarkable findings. C. Transverse dynamic ultrasonography of the right knee shows twisting of the gracilis tendon (arrows) and sudden bouncing-out by the sartorius muscle (11) during active flexion movement of the right knee. G = gracilis tendon, M = medial femoral condyle, PDWI = proton density weighted, S = sartorius muscle, St = semitendinosus tendon, T2WI = T2-weighted image, T2FSAT = T2 fat-suppressed

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