Download The Land of Os: Accessory Ossicles of the Foot

The Land of Os:
Accessory Ossicles of the Foot
Susan Cross, Anshul Rastogi, Rosy Jalan; Dept of Radiology,
Barts Health NHS Trust, London, UK
Contact: [email protected]
Pictorial review
Abstract number EE34
Purpose of exhibit
• Foot pain is often attributed to the presence of accessory ossicles
causing impingement or inflammation
• However, these are normal variants and additional imaging findings
should be sought before attributing these alone as a cause for the
symptoms
• We will provide a review of the clinically important accessory ossicles of
the foot
• We present a series of cases with multimodality imaging, which make
the distinction between normal ossicles, fractures and inflammatory
processes of these ossicles.
Os Trigonum
• Found posterior to the lateral
tubercle of the talus (arrow)
•The cartilaginous synchondrosis
between the ossicle and the
talus usually fuses forming the
trigonal (Steida) process
• A separate os persists in 714% of the population, often
bilaterally
•It is difficult to distinguish this
from an old ununited fracture of
the lateral tubercle (Shepherd’s
fracture)
Os Trigonum Syndrome
Caused by disruption of the
cartilage synchondrosis between
the os trigonum and the lateral
talar tubercle as a result of
repetitive microtrauma or forced
plantar flexion of the foot
Other aetiologies include:
➘Trigonal process fracture
➘Flexor Hallucis Longus
Tenosynovitis
➘Posterior tibial talar
impingement by bone block
➘Intraarticular loose bodies
Ref: Karasick D et al. AJR :166. 1996
Clinical history: 25 yr old football player with 5 month history of posterior ankle pain and
intermittent swelling.
Figure 1 (a-d): Sagittal and Coronal T1W and STIR images demonstrate abnormal degenerative
subchondral cyst formation related to the synchondrosis between the os trigonum and talus (blue
arrows). Note the florid Flexor Hallucis Longus tenosynovitis (red arrows).
(a)
(c)
(b)
(d)
Clinical History: 23 yr old ballet dancer with history of previous excision of os trigonum, with
recurrence of posterior ankle pain
Figure 2: Sagittal T1W and STIR images of hindfoot. Appearances are similar to os trigonum
syndrome, however this is a fracture of the lateral tubercle of the talar process (blue arrow).
Note it is more medially sited than the true os trigonum
Os Naviculare
• Located posterior to the
posteromedial aspect of the
navicular
• Posterior tibial tendon
often has a broad
attachment into the ossicle
• 3 types according to the
Geist classification
•Type 2 is most commonly
associated with medial foot
pain
Geist classification
TYPE 1:
• Small (3mm) ossicle within the distal tibialis posterior tendon (os tibialis externum)
• Usually asymptomatic
TYPE 2:
• Large, up to 12mm, in 10% of the population
• Connected to the adjacent navicular tubercle by a fibrous or cartilaginous
synchondrosis
• Majority of the posterior tibial tendon inserts on this ossicle
TYPE 3:
• The medial tubercle of the navicular is very large and known as the cornuate process
• This can result in altered stresses and premature tendon degeneration
MRI is the most specific imaging modality to assess the synchondrosis , related bone marrow
oedema and posterior tibial morphology
Figure 3: Coronal T2W fat saturated
image of the mid and hindfoot.
Note the abnormal fluid signal within the
synchondrosis of the Type 2 Os with the
navicular implying disruption. (blue
arrow) There is also subchondral bone
marrow oedema in keeping with
microtrabecular bony injury.
The posterior tibial tendon should be
carefully evaluated for tendinopathy or
frank tears.
Treatment can be surgical (Kidner
procedure) to remove the os naviculare
and reattach the posterior tibial tendon
to the navicular
Os peroneum
Located just proximal to the base of the
5th metatarsal, within the substance of
the peroneus longus tendon at the
cuboid tunnel
Painful os peroneum syndrome has a
spectrum of conditions including:
➘ acute os peroneum fracture or
diastasis of a multipartite os with
resultant peroneus longus injury
➘Chronic os peroneum fracture with
resultant stenosing peroneus longus
tenosynovitis
➘Prominent peroneal tubercle on the
calcaneum with ensuing impingement on
the peroneus longus and os.
Ref: Brigidio M et al. Radiology 237; 2005
Clinical details: 40 yr old female with lateral foot pain
Axial T2 fat saturated, sagittal T1W and STIR images of the foot:
Demonstrate os peroneum (white arrow) which has abnormal bone marrow oedema
related to the synchondrosis (red arrows). The peroneus longus is intact but is
tendinopathic (blue arrow)
Hallux sesamoids
The medial and lateral sesamoids are located
within the flexor hallucis brevis tendons at level
of the 1st Metatarsal head and are incorporated
into the 1st MTP articular capsule
They provide mechanical advantage during
flexion of the great toe, reduce friction and
elevate the 1st metatarsal to partially distribute
weight bearing forces to the lateral aspect of the
forefoot
The medial sesamoid is more likely to be involved
with traumatic abnormalities
The lateral sesamoid is more commonly affected
by ischaemic changes with osteonecrosis
Clinical history: 40 yr old male with chronic pain in medial aspect forefoot
Coronal T2W fat saturated image of
the forefoot: Demonstrates abnormal
fluid signal related to the medial
sesamoid in keeping with seasmoiditis
Corresponding Ultrasound image over
theplantar aspect of the forefoot
demonstrates hypoechoic oedema
superficial to the medial sesamoid
Clinical details: forefoot pain, worse on walking
Axial T2 Fat saturated image of forefoot:
Demonstrates lateral hallux sesamoiditis (white arrow). Note also abnormal
fluid signal between 1st MT head and medial sesamoid (green arrow) and
Flexor Hallucis Brevis tenosynovitis
Deltoid ossicles
Located within the deltoid ligament ; Usually a result of previous trauma
Axial T1W and Coronal T2W fat saturated images of the ankle:
Demonstrate abnormal well corticated bony fragments within the
thickened inflamed deltoid ligament (blue arrows)
Conclusion
• Foot pain is often attributed to the presence of
accessory ossicles causing impingment or
inflammation. However, these are normal
variants and additional imaging findings should
be sought before attributing these alone as a
cause for the symptoms.
• Making the distinction is clinically important
in influencing subsequent management.
• No relevant disclosures