MyPACS.net: Radiology Teaching Files > Case 5370673

never visited OS TRIGONUM SYNDROME
Contributed by: Radiology Residency Program Faculty & Staff.
Patient: 30 year old female
History: 30 y/o female with gradually worsening left foot pain over the course of a year.
Images:[small]larger

Fig. 1: A coronal fat-saturated T2WI demonstrates a hypertrophied os trigonum with marrow edema and adjacent fluid within the posterior tibialis and flexor digitorum longus tendon sheaths. A fluid collection overlying the flexor retinaculum is also noted.

Fig. 2: Sagittal GRE T2* demonstrate fluid surrounding the intact flexor digitorum longus tendon consistent with tenosynovitis. The hypertrophied os trigonum is again noted with surrounding fluid.

Fig. 3: Sagittal GRE T2* demonstrate the os trigonum with surrounding fluid.

Fig. 4: fluid surrounding the intact anterior tibialis, posterior tibialis, and flexor digitorum longus tendons consistent with tenosynovitis. The os trigonum is again noted with surrounding fluid. Edema and fluid surrounding the os trigonum is again noted.

Fig. 5: Sagittal fat-saturated T2WI demonstrate fluid surrounding the fluid surrounding the intact anterior tibialis consistent with tenosynovitis.

Fig. 6: Sagittal GRE T2* demonstrate fluid surrounding the intact anterior tibialis, posterior tibialis, and flexor digitorum longus tendons consistent with tenosynovitis. The os trigonum is again noted with surrounding fluid.

Fig. 7: Sagittal fat-saturated T2 image demonstrates marrow edema of the os trigonum and the talus at the synchondrosis along with fluid surrounding the os trigonum

Fig. 8: Sagittal fat-saturated T2 image demonstrates marrow edema of the os trigonum and the talus at the synchondrosis along with fluid surrounding the os trigonum

Fig. 9: Sagittal fat-saturated T2 image demonstrates marrow edema of the os trigonum and the talus at the synchondrosis along with fluid surrounding the os trigonum
Findings:

There is a hypertrophied os trigonum marrow edema of the posterior talus and the os trigonum at the synchondrosis with a small amount of fluid seen surrounding the os trigonum. 

There is fluid seen surrounding the intact anterior tibialis, posterior tibialis, and flexor digitorum longus tendons which are consistent with tenosynovitis. There is a subcutaneous fluid collection overlying the flexor retinaculum.

Diagnosis: Os Trigonum Syndrome with reactive anterior tibialis, posterior tibialis and flexor digitorum longus tenosynovitis.
Discussion:

An os trigonum is an accessory bone that is formed from the lack of fusion with the talus, which normally forms the trigonal process (Steida's process).
       -Fracture of the trigonal process (lateral tubercle) is termed the Shepard's Fracture.

The os trigonum is present in about 10% of the population. 

Normally, having an os trigonum is asymptomatic. However, posterior impingement and talar compression can occur and cause symptoms.

Os Trigonum syndrome is rare representing about 0.2% of ankle pain etiology. Often originally diagnosed as a chronic sprain. Females > Males.

This is a repetitive plantar flexion microtrauma injury which is classically seen in ballet dancers secondary to assuming pointe and demipointe positions. 
 

IMAGING FINDINGS

On Radiographs, a well-corticated ossicle is seen posterior to the talus

T1WI demonstrates marrow signal within the os trigonum with degenerative sclerosis between the os trigonum and the talus with surrounding hypointense fluid.

T2WI demonstrates marrow edema at the synchondrosis and may show degenerative cystic changes. Synovitis and fluid may be seen posterior and superior to the talus. Reactive tenosynovitis of the of the Flexor Hallucis Longus (FHL) tendon sheath, with or without partial teathering of the tendon, is commonly seen due the position of the FHL adjacent to the os trigonum  

Prognosis and Treatment

Symptoms are usually relieved with rest

Conservative treatment includes local steroid injections, cast immobilization to soft tissue swelling, and antiinflammatories.

Surgical intervention includes excision of bony block will often improve motion and eliminate pain with recontouring or the superior calcaneus and posterior talus.

References:

Stoller, S. Tirman, P. Bredella, M. Beltran, S. Branstetter, R. Blease, S. Diagnostic Imaging: Orthopedics. Amirsys: Salt lake City, UT, 2004.

Karasick, D. Schweitzer, M. The Os Trigonum Syndrome: Imaging Features. AJR. 166: pg.125-129, 1996. 

Submitted by Craig Johnson, DO PGY-4 Radiology Resident and Michael Soehnlen, MD Attending Physician Aultman Hospital

 

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Additional Details:

Case Number: 5370673Last Updated: 07-21-2006
Anatomy: Skeletal System   Pathology: Non-Infectious Inflammatory Disease
Modality: MRExam Date: Access Level: Readable by all users
Keywords: os trigonum syndrome

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