CHAPTER 56 • MAGNETIC RESONANCE IMAGING: LOWER EXTREMITY 335•Ligaments about the ankle are normally hypointense
bands of tissue in continuity from bone to bone.
- The anterior talofibular ligament, one of the most com-
monly injured ligaments in an ankle sprain is seen to best
advantage on axial images, with the ligament located at
the very inferior tip of the lateral malleolus (Fig. 56-9). - The deltoid ligament is a strong thick ligament located
on the medial side of the ankle, connecting the medial
malleolus to the talus (Fig. 56-10). - The three main tendon compartments about the ankle
should be evaluated on an MR examination of the ankle.
As the tendons angle and curve around the ankle to enter
the foot, care should be taken not to overestimate signal
abnormalities seen on one plane, and confirmation of
findings should be made in at least two planes. - Osteochondral injuries of the tibiotalar joint are well
evaluated with MR. These lesions can occur on the
tibial side of the joint (Bui-Mansfield et al, 2000);
however, they more commonly affect the talar dome
(Hangody et al, 1997; Rosenberg, Beltran, and
Bencardino, 2000) (Fig. 56-11). - Identification and grading of posterior tibial tendon
abnormalities is important in treatment planning.
Posterior tibial tendon pathology is often associated
with other abnormalities in the foot and ankle and so
should be identified. These include abnormalities of
the spring ligament, the sinus tarsi, and plantar fascia,
and often lead to flatfoot deformity (Balen and Helms,
2001; Pomeroy et al, 1999). Considering this, MR
images of the ankle should extend plantarly enough to
cover the plantar fascia, and be high resolution to
identify and evaluate the spring ligament. Chronic
posterior tibial tendon tears usually occur at the level
of the medial malleolus as opposed to an acute more
traumatic tear, which is usually at the insertion
(Rosenberg, Beltran, and Bencardino, 2000).
•Tendon tears are diagnosed by focal high (fluid)
signal within the tendon or identifying discrete tendi-
nous discontinuity.- The Achilles tendon is normally visualized as a thick
hypointense band of tissue inserting onto the calca-
neus. Tendinosis of the Achilles tendon is manifest as
diffuse thickening and inhomogeneity of the tendon,
often with intrasubstance signal (Fig. 56-12). - The Achilles tendon usually tears approximately 2–6
cm proximal to the enthesis. - If an Achilles tendon is seen on MR imaging, the signal
abnormality should be traced cephalad to see if the injury
extends to and involves the muscle tendon junction. - The Achilles tendon can demonstrate dystrophic cal-
cification and ossification in cases of chronic tendi-
nosis (Schweitzer and Karasick, 2000).
FIG. 56-9 Axial fast spin echo image of the ankle demonstrat-
ing an intact, normal anterior talofibular ligament (arrow).
FIG. 56-10 Axial fast spin echo image demonstrating the del-
toid ligament (arrow). Partial, nonacute injury to the deltoid liga-
ment is suspected, with osseous remodeling involving the medial
malleolus.