The frondiform ligament and pseudotenosynovitis of the extensor digitorum longus tendon: MRI evaluation with cadaveric correlation.
OBJECTIVE
Fluid along the frondiform ligament, the sinus tarsi stem of the inferior extensor retinaculum (IER), can approximate the extensor digitorum longus (EDL), at times simulating tenosynovitis. Our purpose, based on MRI and cadaveric studies, was to further evaluate this scantly described phenomenon, to identify associated findings and to alert the radiologists to the potential pitfall of over diagnosing EDL tenosynovitis.


METHODS
Two musculoskeletal radiologists retrospectively reviewed the radiology reports and MRI studies of 258 ankle MRI exams, performed at our institution, for fluid along the frondiform ligament extending toward the EDL. No patient had EDL pathology clinically. MRI was performed in two cadaveric ankles following injection of the sinus tarsi and EDL tendon sheath, under ultrasound guidance.


RESULTS
Altogether, 31 MRIs demonstrated fluid extending from the sinus tarsi along the frondiform ligament toward the EDL. In 30 cases (97 %), the fluid partially surrounded the tendon, without tendon sheath distension. Based on the radiology reports, in 11 of the 31 cases (35 %), the fluid was misinterpreted as abnormal. Most common associated findings included ligamentous injury, posterior tibial tendon (PTT) tear, flat-foot, and osteoarthrosis. In the cadavers, fluid extended along the frondiform ligament toward the EDL after sinus tarsi injection; there was no communication between EDL tendon sheath and the sinus tarsi.


CONCLUSIONS
Fluid within the sinus tarsi can extend along the frondiform ligament and partially surround the EDL, manifesting as pseudotenosynovitis. This phenomenon, often seen with ligamentous tears or PTT dysfunction, should not be misdiagnosed as true pathology of the EDL.
Albert Einstein College of Medicine Jacobi Medical Center, 1400 Pelham Parkway South, Bronx, NY, 10461, USA. jonathan.zember@gmail.com.
Jonathan
J
Zember
NYU Langone Medical Center, New York, NY, USA.
Zehava
Z
Rosenberg
NYU Langone Medical Center, New York, NY, USA.|Centro de Diagnostico Dr. Enrique Rossi, Buenos Aires, Argentina.
Ignacio
I
Rossi
NYU Langone Medical Center, New York, NY, USA.
Chimere
C
Mba-Jones
NYU Langone Medical Center, New York, NY, USA.
Jenny
J
Bencardino
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000842:Ankle / Q000000981:diagnostic imaging* / Q000503:physiopathology; D002102:Cadaver; D005260:Female; D006801:Humans; D008022:Ligaments / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D013710:Tendons / Q000000981:diagnostic imaging* / Q000473:pathology; D013717:Tenosynovitis / Q000000981:diagnostic imaging* / Q000473:pathology
Bursa; Extensor digitorum longus tendon; Extensor retinaculum; Ganglion; MRI; Sinus tarsi; Tenosynovitis