Clinical manifestations of subtle cavus foot can affect the entire lower limb.
Table 1 lists the clinical findings associated with this condition,
whose imaging manifestations can be found on ankle MR imaging studies.
5
Table 1
Image findings associated with subtle cavus foot
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Image findings in and around ankle:
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Peroneus longus/ brevis tendinopathy and/ or tears
Peroneus tendon subluxation/ dislocation
Enlarged peroneal tubercle
Os peroneum syndrome
Recurrent ankle sprain or instability
Anteromedial impingement
Degenerative changes and osteochondral lesion in the medial half of the ankle joint.
Plantar fasciitis or plantar fascia tears
Achilles tendinopathy
Haglund syndrome
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Image findings away from the ankle:
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Metatarsal stress fractures
Fracture and/ or non-union of the lesser metatarsals
Stress tibial fractures
Vertical sheer frature of the medial malleolus
Medial knee compartment disarrangement
Iliotibial band syndrome
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1-Assessment of hindfoot malalignment (sagittal and coronal planes)
Posterior cavus or calcaneocavus is characterized by a high calcaneal pitch of greater than 30º,
which is difficult to assess in a study with no weight bearing,
such as ankle MRI.
However,
posterior deviation of the lateral talar process from the apex of the angle of Gissane,
with rotatory subluxation of the subtalar joint,
on sagittal images of the ankle,
as a consequence of high calcaneal pitch,
might be a useful finding.
(Fig.
1)
On coronal non-weight-bearing MR images,
calcaneus varus can be depicted by measuring the angle between the distal tibial shaft (most central coronal image,
where the shaft diameter is maximal and the cortex is clearly defined) and the calcaneal axis (measured by four points at the calcaneal surface: a line between the tip of the sustentaculum tali and the superolateral edge of the calcaneus and another line from the lateral contours of the posterior process of the calcaneus,
on the most posterior image that includes the plantar fascia; then,
joining the mid point of these lines the calcaneal axis is obtained),
the so called adapted Cobey.
6 (Fig.
2)
Another measurement,
possibly most accurate,
for accessing hindfoot varus is using the angle between the distal tibial shaft and the medial and lateral surfaces of the calcaneus and then,
a tangent between the tip of the sustentaculum tali and the plantar medial surface of the calcaneus (sustentaculum tangent).
6 Any degree of hindfoot varus,
from 0º,
is considered relevant.
(Fig.
3)
2-Lateral hindfoot overload (peroneal tendinopathy/ tear,
enlarged peroneal tubercle)
Lateral hindfoot overload,
presents with predominantly laterally pain,
can result in peroneal tendinophaty,
tears or subluxation.
(Fig.
4)
An hypertrophied peroneal tubercle of the lateral calcaneus might cause friction of peroneal tendon,
further accentuated by varus orientation of the calcaneus,
resulting in fraying and even laceration of this tendons (Fig.
5)
An os peroneum syndrome can also be associated with mild variation of cavus foot.
3-Ankle instability and recurrent ankle sprains
The varus heel of a cavus foot predispose to chronic ankle instability,
sometimes associated with recurrent ankle sprains.
Although not yet established as a definitive risk,
cavovarus deformity is frequently associated with ankle instability.
7,
8 A varus tibial plafond and posteriorly placed fibula are other factors that predispose to chronic ankle instability.
9,10 These patients may have pain referred to lateral ligament complex,
sometimes with proved anterior talofibular ligament sprain on MR imaging or,
may have failed previous surgical repair of this ligamentous complex.
11 (Fig.
6)
4- Anteromedial impingement
Manoli et al described an increased incidence of anteromedial impingement,
expressed by talar and tibial spurs,
in patients with subtle cavus feet.
12 (Fig.
7) Together,
supination and adduction movements of “calcaneopedal unit” (bone and articular foot segments,
except talus),
results in talus external rotation and dorsiflexion,
the latest causing medial conflict between talus and tibial surfaces.
Over time,
varus overload can lead to secondary arthrosis or osteochondral lesions in the medial half of the ankle joint.
5- Achilles tendinopathy,
retrocalcaneal bursitis and Haglund syndrome
In the hindfoot,
symptoms from reduced shock absorption and gastrocnemius contraction,
may include Achilles tendinopaty and plantar fasciitis.
Prominence of the posterior superior calcaneal tuberosity,
due to varus heel position,
contributes to retrocalcaneal bursitis or Haglund syndrome.
(Fig.
8)
6- Plantar fasciitis and plantar fascia tears
Clinically,
most patients with mild cavus foot have a tight gastrocnemius and plantar fascia,
with time resulting in painful plantar fasciitis.
(Fig.
9)
7- Degenerative changes
Over time,
varus overload and/ or recurrent sprains can lead to secondary arthrosis or osteochondral lesion in the medial half of the ankle joint.
(Fig.
10)
8- Image findings at the ankle limits (metatarsals,
tibial shaft)
Occasionally,
findings of lateral midfoot overload may be depicted in the limits of an ankle MRI image.
Edema or stress fractures of the lesser metatarsal are not uncommon.
(Fig.
11)
In long standing conditions,
stress fractures of tibia,
vertical sheer stress fractures of the medial malleolus or medial tibial stress syndrome and shin splints may be found.