Answer for BIR CoW 08 Dec 2024
Posterior Ankle Impingement Syndrome and Os Naviculare Syndrome
Findings
Findings
- X-ray:
- AP view of the ankle shows evidence of an accessory navicular bone.
- CT:
- Axial image: Os naviculare noted involving the medial aspect of the foot.
- Sagittal image: Os peroneum with adjacent subchondral arthritic changes involving the talus.
- Volume-rendered image: Os naviculare and os trigonum visualized.
- MRI:
- T1 sagittal image: Os trigonum noted.
- PD-fat saturated (PDFS) sagittal image: Os trigonum with adjacent signal changes in the talus, indicating degenerative changes.
- PDFS axial image: Signal changes in the flexor hallucis longus tendon, reflecting tendinopathy.
- PDFS axial image: Hyperintensities involving the navicular bone.
- PDFS sagittal image: Fluid signal intensity around the tibialis posterior tendon, reflecting tendinopathy. Hyperintensities noted in the navicular bone.
- Typically unilateral but rarely bilateral.
- Commonly observed in ballet dancers.
- Located posterior to the talus on lateral foot radiographs.
- Results from failure of fusion of the lateral tubercle of the posterior talar process.
- Prevalence:
- ~7% in adults.
- Bilateral ossa trigona in ~2% of individuals.
- Ossicle usually forms between ages 7-13 and fuses by ~17 years in most cases; persistent cases form an os trigonum.
- Pathology:
- Repetitive plantar flexion leads to compression, synovitis, capsulitis, and eventual scarring.
- Predisposing anatomical factors:
- Stieda process
- Os trigonum
- Fractures of the lateral tubercle of the posterior talar process
- Prominent superior surface of the calcaneal tuberosity
- Abnormal calcification/ossification posterior to the ankle
- MRI Features:
- Posterolateral capsular thickening and synovitis involving an intact posterior talofibular ligament.
- Tenosynovitis involving the flexor hallucis longus.
- Bone contusion of the lateral tubercle of the posterior talar process.
- Fluid and/or edema in posterior joint recesses.
- Signal characteristics:
- T1: Low signal in areas of bone bruising.
- T2/STIR: High signal in bruised areas.
- PD-fat saturated: High signal posterior to the ankle.
- An accessory navicular is a large ossicle adjacent to the medial side of the navicular bone.
- The tibialis posterior tendon often inserts into the ossicle.
- Types:
- Type 1:
- Small (2-3 mm) sesamoid bone within the posterior tibial tendon.
- No cartilaginous connection to the navicular tuberosity.
- Accounts for ~30% of cases, typically asymptomatic.
- Type 2:
- Triangular or heart-shaped, ~12 mm in size.
- Connected to the navicular tuberosity by fibrocartilage or hyaline cartilage (~1-2 mm thick).
- Accounts for ~55% of cases.
- Can fuse with the navicular tuberosity or cause painful movement at the pseudo-joint.
- Type 3:
- Enlarged navicular tuberosity (cornuate navicular).
- Often results from fusion of a Type 2 ossicle.
- Occasionally symptomatic due to bunion formation.
- Type 1:
- Imaging Features:
- Radiographs:
- Medial navicular eminence best seen on lateral-oblique views.
- MRI:
- Bone marrow edema signal intensities.
- Signal characteristics:
- T1: Hypointense.
- T2/STIR: Hyperintense.
- Changes may involve both the accessory ossicle and navicular bone.
- Radiographs:
Note:
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!
We do not discourage differential diagnosis. But all the differentials must satisfy the findings noted in the case.
If you feel you have answered rightly but cannot find your name in the above list, please call 09551942599.
Did you Know?
The order in which the names appear in this winner's list is based on the time of submission. The first person to send the correct answer gets his/her name on top of the list!