Ankle and Foot 47 - Department of Radiology - University of ...

47 Ankle and Foot 2223 47
Figure 47-22. A 57-year-old with
an Achilles tendon that has healed
with chronic scarring. Axial T1-
weighted (A), axial T2-weighted
(B), and sagittal T2-weighted (C)
images reveal that the distal
Achilles tendon is too round and
thick but contains no increased
signal.
A
B
C
The flexor hallucis longus muscle is a posterior structure
originating from the lower two thirds of the back of
the fibula. The musculotendinous junction extends distally
to the level of the ankle joint, and the proximal end of the
tendon passes through a groove along the posterior talus.
Whereas the posterior tibial and flexor digitorum longus
tendons pass under the medial malleolus, the flexor hallucis
longus tendon passes under the sustentaculum tali.
The flexor hallucis longus then crosses deep to the flexor
digitorum longus, extends under the first metatarsal, and
passes between the two great toe sesamoids, to insert on
the plantar base of the distal phalanx (see Fig. 47-9D
and E).
A
Medial
malleolus
B
Injury
Of the three medial ankle tendons, the posterior tibial is
the most prone to tear, characteristically along the portion
that curves around the medial malleolus. The posterior
tibial tendon is relatively hypovascular in this region. 39
This region of the tendon is also susceptible to mechanical
wear as the tendon rubs against the medial malleolus (Fig.
47-23). If the surrounding tendon sheath does not provide
adequate lubrication, such as in stenosing tenosynovitis
or rheumatoid pannus formation, this frictional wear
increases. Perhaps because of these longitudinal frictional
stresses, the posterior tibial tendon tends to tear with a
longitudinal split, rather than the transverse rupture seen
in Achilles tendon tears. When imaged in the axial plane,
a longitudinal split in the posterior tibial tendon resembles
two individual tendons. This longitudinally split posterior
tibial tendon, when grouped with the flexor digitorum and
hallucis longus tendons, has been called the four-tendon
sign (Fig. 47-24).
Tenosynovitis refers to inflammation between the
tendon and the surrounding synovial sheath. This is often
a chronic irritative process, more commonly affecting
C D E
Figure 47-23. Illustration of posterior tibial tendon mechanical
wear becoming a longitudinal tear. A, Medial view of the posterior
tibial tendon (PT; red) as it wraps over the medial malleolus and
under the flexor digitorum longus tendon (FDL; blue). The PT is
susceptible to mechanical wear as it rubs back and forth (as indicated
by the double-headed black arrow) between the underlying medial
malleolus (gray lightning bolts) and the overlying FDL (white lightning
bolts). B, A more anterior view of a partially torn PT as it might appear
if it were laid flat. The tendon is thickened and butterflied open, with
the gray region representing abnormal internal signal. (The dashed
line represents the location of cross sections C to E). C to E, MRI cross
sections of the PT only (now shown as a black ellipse), taken in the
axial or oblique coronal plane through the longitudinal tear as it
develops. In C, there is a gray wedge of abnormally increased
signal along the inner aspect of the flattened PT (black ellipse).
In D, tendinopathy (gray wedges) now involves the outer and inner
surfaces of the PT. In E, the wedges of tendinopathy have progressed
to a longitudinal tear, giving the appearance in cross section that the
PT is two tendons.
Ch047-A05375.indd 2223
9/9/2008 5:33:49 PM