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January 2004 Case of the Month |
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History: No specific injury or trauma; patient is a ballet dancer with pain beginning one year ago and getting worse; pain is greatest in lateral aspect Compiled by: Zachary M. Kilpatrick, Jr., M.D.
Technical Factors: Long- and short-axis fat- and water-weighted images were performed.
Findings: The dominant finding is that of a large, posteriorly displaced and somewhat edematous os trigonum with fibrovascular stress reaction noted in the anterosuperior calcaneus at the margin of the posterior subtalar joint. The synchondrosis between the talus and abnormal os trigonum is almost certainly disrupted. Inflammation and capsular fluid is noted about the os trigonum. Also noted between the talus and the posteriorly displaced os trigonum is an approximate 3 mm ovoid focus of low T1 and T2 signal (sagittal sequences) representing either a focal calcified body, a multi-partite os trigonum or possibly a small fracture fragment. A shallow Steida process extends posteriorly from the talus with fibrovascular edema noted to be present within this structure. All of these aforementioned findings are indicative of posterior impingement syndrome.
Capsulosynovitis of the tibiotalar joint is present. Advanced subtalar arthrosis for an 18-year-old is noted and fibrovascular stress-induced osteoedema also affects the anterior aspect and neck of the talus.
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Discussion:
Posterior (posterior tibiotalar) impingement syndrome can be seen in the presence of an (enlarged) os trigonum (os trigonum syndrome), or a prominent or hypertrophic posterlateral talar process, a Stieda process, (talar compression syndrome). The more common causes are osseous in nature, such as the os trigonum (an accessory ossicle of the lateral tubercle of the talus that may persist unfused into adulthood in 7% of individuals), a prominent posterior process of the calcaneus, and loose bodies.³
The syndrome can develop after a significant acute injury, which is relatively rare, but usually arises due to chronic overuse in predisposed athletes. Repetitive forced plantar flexion of the foot results in chronic injury to the posterior osseous and soft tissues. Ballet dancers are especially predisposed to this injury, as the ankle is subjected to extreme plantar flexion. High performance soccer players are also at increased risk because kicking the ball leads to repeated sudden forced plantar flexion. The mechanism of injury has been likened to a nut in a nutcracker. The syndrome may also be seen in the absence of bony hypertrophic changes, due to chronic capsular inflammation and synovial hyperplasia. In any case, there may be associated inflammation in the flexor hallucis longus tendon sheath. Different names have been given to posterior ankle impingement syndrome, including the os trigonum syndrome, talar compression syndrome, posterior block of the ankle and posterior tibiotalar compression syndrome. |
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Figure 1. Depicts osseous anatomic structures and the ‘nutcracker’ phenomenon resulting in posterior impingement.
Illustrations adapted and modified from AJR 2003; 181:557 | | |
PEARLS IN THE DIAGNOSIS OF POSTERIOR TIBIOTALAR IMPINGEMENT SYNDROME (PTTIS)
Etiology
Seen in those with excessive or recurrent plantar flexion (e.g. soccer players, ballet dancers) leading to crush of soft tissue in the tibiocalcaneal pliers
Anatomic Causes
Bone: Fracture or hypertrophy of the posterolateral tibiotalar facet, os trigonum or os trigonum bipartition
Osteocartilaginous
Soft tissue: Capsular inflammation, flexor hallucis longus impingement or inflammatory disease
Anatomy
Tibiocalcaneal pliers which equals the posterolateral tibiotalar and posteromedial tibiotalar facets
Posterolateral talar process which equals posterolateral tibiotalar facet. *
MR Findings
Posterior tibiotalar capsular cyst
Pericapsular edema or phlegmon
Prominent lateral or medial tibiotalar process or spur
Posterior bone fragment, hypertrophy or irregularity of os trigonum or os trigonum bipartition
Deformity of the posterior tibial facet secondary to prior fracture
* The flexor hallucis longus muscle and tendon is surrounded by the posterolateral and posteromedial tibiotalar facets. The posterior talofibular ligament inserts on the posterolateral tibiotalar process. Normally, the myotendinous junction of the flexor hallucis longus sits above the posterior talar process.
Gamuts and Pearls in MRI, 2nd Ed. MRI-EFI Publications 1993; p. 467. | |
Clinical Findings
Clinical symptoms in posterior ankle impingement usually consist of posterior ankle pain exacerbated by plantar flexion or dorsiflexion. Clinical examination shows posterior tenderness anterior to and not involving the Achilles tendon. A palpable soft-tissue pseudo-mass is occasionally present.
Imaging Features
Conventional radiographs may show a prominent lateral talar (Stieda) process or os trigonum, but are usually otherwise limited in the evaluation of posterior ankle impingement. Nuclear medicine bone scans have been used in the past with increased activity noted in the inflamed os trigonum. A negative scan excludes the diagnosis. MR has supplanted other imaging studies in establishing the diagnosis. Aside from the predisposing bony anatomic findings described above, MRI demonstrates pericapsular edema about the posterior ankle joint involving the anterior aspect of Kager’s fat space or triangle. There may be a posterior capsular cyst. In addition, marrow edema is frequently observed in the os trigonum, posterolateral talar process or posterior rim of the distal tibia.
Management
Most cases of posterior impingement of the ankle respond to conservative treatment. Studies have shown that arthroscopic resection of diseased soft-tissue and any associated bony abnormality with joint washout produces satisfactory symptomatic and functional results in resistant cases. MR imaging is particularly valuable in assessment of the soft-tissue and osseous abnormalities implicated in the clinical setting of ankle impingement as well as providing an assessment of the whole joint prior to treatment.
References:
1. Pomeranz, Stephen J & Rolfes Richard J, etal: MRI of the Foot & Ankle, Pearls, Pitfalls & Pathology. MRI-EFI Publications,
2002; pp. 102-104
2. Pomeranz, Stephen J: Gamuts and Pearls in MRI, 2nd Ed. MRI-EFI Publications 1993; p. 467 (G-21)
3. Pomeranz, Stephen J, etal: Gamuts and Pearls in MRI & Orthopedics. MRI-EFI Publications 1997; p. 275
4. AJR 2003;181: 551–559
5. RadioGraphics 2002; 22:1457–1471 |
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