Pathologies of the tendinous apparatus
The Achilles tendon most frequently suffers from degenerative changes leading to tendinopathy. On MRI, this appears as a fusiform thickening with increased signal intensity on T1- and T2-weighted images, while Doppler ultrasound can reveal neovascularization. A specific condition is Haglund syndrome, which includes the MRI triad: insertional tendinopathy, retrocalcaneal bursitis, and calcaneal deformity (exostosis).
Ankle tendons are divided into groups, each having its own typical injuries:
- Posteromedial: The tibialis posterior tendon (musculus tibialis posterior) is the primary supporter of the medial arch. Its rupture leads to flatfoot. In tenosynovitis on MRI, the cross-sectional area of fluid exceeds that of the tendon itself.
- Peroneal: The peroneus brevis tendon is prone to longitudinal splits (the «boomerang» sign). Upon rupture of the superior retinaculum, these tendons subluxate, which is clearly visible on dynamic ultrasound.
- Anterior: Injured rarely; ruptures of the tibialis anterior muscle are typical in elderly patients in the region of the medial cuneiform bone.
Impingement syndromes and osteochondral defects
Osteochondral lesions are most frequently localized on the talar dome. Standard radiography often fails to detect them, making MRI the gold standard. If fluid signal is identified around the lesion on scans, it is a reliable sign of fragment instability.
Soft tissue and bone impingement causes chronic pain:
- Anterior impingement: Occurs in soccer players due to bone spurs on the anterior tibial margin and talar neck. Well visualized on weight-bearing radiographs.
- Posterior impingement: Typical for ballet dancers. Associated with repetitive plantarflexion in the presence of a large os trigonum (os trigonum). MRI in this area reveals marked bone marrow edema and synovitis.
Soft tissue lesions of the foot
Chronic microtrauma of the plantar fascia leads to plantar fasciitis. Ultrasound diagnoses thickening of the central cord of the fascia and loss of fibrillar echostructure. MRI (in STIR mode) shows inflammatory edema of the fascia and adjacent bone. It is worth noting that a calcaneal spur on radiography is not a diagnostic criterion for fasciitis.
When evaluating foot pain, it is also important to rule out entrapment neuropathies:
- Tarsal tunnel syndrome: Compression of the tibial nerve. MRI and ultrasound aim to identify a space-occupying lesion (ganglion cyst, accessory muscle) compressing the nerve, as well as fatty atrophy of denervated muscles.
- Morton neuroma: Perineural fibrosis of the common plantar digital nerve, typically between the 2nd and 3rd metatarsal bones. On ultrasound, this appears as a hypoechoic mass, and on MRI, as an ovoid lesion with intermediate to low signal. Ultrasound is particularly useful here as it allows for immediate targeted therapeutic injection.
Another frequent injury is a rupture of the first MTP joint plantar plate («turf toe»), in which MRI reveals a fiber defect and secondary synovitis.
Briefly: answers to topical questions
Which tendons form the posteromedial group of the ankle joint?
The posteromedial group of the ankle joint is formed by three tendons.
- Tibialis posterior tendon (TP) — the strongest, supports the medial longitudinal arch of the foot, most frequently subject to trauma.
- Flexor digitorum longus tendon (FDL).
- Flexor hallucis longus tendon (FHL).
The tendon sheaths of the long flexors communicate with the ankle joint cavity, therefore fluid within them may be a result of joint effusion.
What space-occupying lesions can cause tibial nerve compression in tarsal tunnel syndrome?
Compression of the tibial nerve in tarsal tunnel syndrome can be caused by various space-occupying lesions. Magnetic resonance imaging or ultrasound is used to detect them. These lesions include:
- Ganglion cyst;
- Bone fracture;
- Nerve sheath tumor;
- Accessory muscle (FDL).
An additional sign of compression on MRI is edema or fatty atrophy in denervated muscles supplied by the affected nerve.
Which ligaments comprise the lateral collateral ligament complex of the ankle joint?
The lateral collateral ligament complex of the ankle joint comprises three ligaments, although available data do not describe all of them completely.
- Anterior talofibular ligament (anterior talofibular ligament) — most vulnerable to trauma.
- Calcaneofibular ligament (partially mentioned in the text).
The third ligament is not specified. Injuries to this complex typically result from inversion (supination), therefore lateral ligaments are injured more frequently than medial ones.
Which radiographic projections are standard for evaluating ankle trauma?
Standard evaluation of ankle trauma requires at least two mutually perpendicular projections.
- Anteroposterior projection (Anteroposterior — AP).
- Lateral projection (lateral).
Performing a multi-positional examination is absolutely essential to rule out occult injuries, as certain fractures (e.g., oblique fractures) may be clearly visualized on a lateral radiograph while remaining completely undetectable on an AP view.
Class and exam questions
How to confirm sinus tarsi syndrome on MRI?
Normally, the adipose tissue within the sinus tarsi produces a bright, high-intensity signal on T1-weighted images. In this syndrome, this signal drops and is replaced by an intermediate-intensity signal due to inflammation.
Why does fluid around the flexor tendons not always indicate tenosynovitis?
The tendon sheaths of the flexor digitorum longus and flexor hallucis longus anatomically communicate with the ankle joint cavity. Fluid may appear in them simply as a consequence of joint effusion.
What is the main advantage of ultrasound over MRI in the evaluation of the Achilles tendon?
Ultrasound has higher spatial resolution, allows the use of Doppler imaging to assess atypical vascularization (inflammation), and enables dynamic functional tests to evaluate diastasis upon rupture.
What else to study on this topic
- Radiographic and MRI features of various types of tarsal coalitions
- Differential diagnosis of lower extremity bone marrow edema
- Imaging findings in systemic inflammatory arthropathies of the ankle
- Anatomy and pathology of the plantar plate
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