pattern seen on MR imaging typically is one of edema
in the posterior aspect of the tibia as well as the ante-
rior margin of the lateral femoral condyle, just supe-
rior to the anterior horn of the lateral meniscus.- There are many injury patterns and mechanisms
encountered in sports injuries to the knee. These (and
their resultant ligamentous injuries) include pure
hyperextension (posterior cruciate ligament (PCL)
and posterior capsule), hyperextension with varus
(posterolateral corner, anterior cruciate ligament
(ACL), popliteus tendon, posterior capsule), hyperex-
tension with valgus (medial collateral ligament
(MCL), posteromedial corner, posterior capsule,
PCL), pure valgus (MCL, ACL ±PCL), pure varus
(iliotibial band, lateral collateral ligament(LCL)),
flexion valgus, external rotation (MCL, ACL), flexion
varus, internal rotation (ACL, posterolateral corner),
flexion with posterior tibial translation (isolated PCL,
possible posterior dislocation), and a patellar disloca-
tion (flexion and internal rotation of femur on fixed
tibia) (medial patellar retinaculum, MCL, possible
ACL) (Hayes et al, 2000). - In view of anterior cruciate ligament injuries, determi-
nation of a full thickness tear is made by observing a
focal discontinuity in the ligament fibers (Fig. 56-5(b)). - Additional secondary signs of ACL injury may sup-
port the diagnosis at MR imaging. One of these is the
Segond fracture, which is an avulsion fracture of the
lateral tibial plateau, indicative of injury to the lateral
capsule and often concomitant ACL injury (Goldman,
Pavlov, and Rubenstein, 1988).
•Partial ACL tears are diagnosed by observing only a
few fibers in discontinuity; these should be graded as
high or low-grade injuries depending on the cross sec-
tional area of ligament fibers that are affected. As
noted above, as the anterior cruciate ligament is an
oblique structure and confirming the diagnosis of a
partial ACL tear in another plane may be necessary;
some authors have found the axial plane to be partic-
ularly helpful (Roychowdhury et al, 1997).- Other MR findings in cases of ACL tears include a
buckled posterior cruciate ligament with anterior
translation of the tibia, an uncovered posterior horn of
the lateral meniscus, visualizing the fibular collateral
ligament in one coronal image due to anterior transla-
tion of the tibia and injury to the medial collateral lig-
ament (Brandser et al, 1996). - Postoperatively, the anterior cruciate ligament can be
evaluated with MR imaging. Care should be taken in
the postoperative setting to utilize fast spin echo
sequences and fast inversion recovery as opposed to
frequency selective fat suppression as a water-sensitive
pulse sequence to evaluate for bone marrow edema as
the latter is more susceptible to regional magnetic field
inhomogeneities and will result in moderate to severe
susceptibility artifact. - As with the native ACL, tears of ACL grafts are diag-
nosed as focal areas of ligamentous discontinuity and
partial tears as areas of partial ligamentous disconti-
nuity (Horton et al, 2000).
•Normally, the postoperative anterior cruciate ligament
graft should be parallel to the roof of the intercondy-
lar notch as seen in the sagittal plane and should not
demonstrate any areas of focal angulation or kinking
(Schatz et al, 1997). - After a complete knee dislocation, all of the support-
ing ligamentous structures of the knee can potentially
be injured. These can all be evaluated with MR imag-
ing. In the setting of a complete knee dislocation,
magnetic resonance angiography can be performed to
332 SECTION 4 • MUSCULOSKELETAL PROBLEMS IN THE ATHLETE
FIG. 56-5(b) Coronal (left)
and sagittal (right) fast spin echo
images of the knee demonstrat-
ing a complete tear of the ante-
rior cruciate ligament (arrows).