Bone bruises are focal abnormalities in subchondral bone marrow due to trabecular microfractures as a result from a traumatic force.
[1] They can be due to a direct blow to the bone,
application of compressive forces on contiguous bones with a consequent impact mechanism and the action of torsion force,
or traction forces that occur during an avulsion injury.
[2,3] MRI is better than conventional radiographs,
ultrasound,
computed tomography and also arthroscopy to describe bone bruises and associated soft tissues injuries.
In fact,
MRI has the ability to identify bone bruise and to characterize,
using different sequences,
the entire spectrum of alterations associated with it,
including bleeding,
hemorrhage and edema.
[1] In the setting of trauma,
radiographically occult osseous injuries are frequently identified at MRI as areas of poorly marginated signal intensity abnormalities in the bone marrow (decreased signal intensity on T1-weighted sequences and increased signal intensity on T2-weighted or proton density (PD) weighted fat-suppressed (FS) or Short Tau Inversion Recovery (STIR) sequences).
[1,3] The recovery period is quiet variable,
ranging from 3 weeks to 2 years.
These lesions may have deleterious effect on the overlying articular cartilage evolving to articular cartilage degeneration.
[1] Additionally,
it is of utmost importance to diagnose fracture lines when present,
a finding more accurately seen on T1-weighted sequences.
Special care should also be taken to search for subchondral or osteochondral injuries.
Pattern of bone contusion in knee injuries can give clues for the mechanism and associated injuries.
Five classic bone contusion patterns have been described: pivot-shift injury,
dashboard injury,
hyperextension injury,
clip injury and lateral patellar dislocation.
PIVOT-SHIFT INJURY
Pivot-shift injury occurs when a valgus load is applied to the knee in various states of flexion combined with external rotation of tibia or internal rotation of femur.
This lesion results from maneuvers such as rapid deceleration and simultaneous direction change.
It is a noncontact injury commonly seen in skiers and american football players.
[3] This event can often induce an anterior cruciate ligament (ACL) tear (most commonly in its midsubstance),
which may lead to anterior subluxation of the tibia relative to the femur and consequent impaction of the lateral femoral condyle against the posterolateral margin of the lateral tibial plateau.
[4-6] Fig. 1 The characteristic bone contusion involves the posterior aspect of the lateral tibial plateau and the midportion of the lateral femoral condyle near the condylopatellar sulcus.
[3] Fig. 2 Additionally,
other soft tissue abnormalities that can be associated include tears of the posterior capsule,
the posterior horn of the lateral or medial meniscus,
the medial collateral ligament,
and also the arcuate ligament,
which is variably present,
being found in about 65% of knees.
A countercoup injury can also be associated,
resulting from reduction after the pivot shift injury causing a bone contusion of the posterior lip of the medial tibial plateau.
Fig. 3 It is highly associated with ACL tears and peripheral tear or meniscocapsular separation of the medial meniscus posterior horn.
[7]
DASHBOARD INJURY
Dashboard injury results from a force that is applied to the anterior aspect of the tibia while the knee is a flexed position.
Fig. 4 This injury can occur for example when the knee strikes against the dashboard during a vehicle accident or against the ground during a fall.
[1,8] The characteristic bone contusion pattern involves the anterior aspect of the tibia and,
occasionally,
the posterior surface of the patella.
Fig. 5 This injury is very commonly associated with posterior cruciate ligament (PCL) tear (most commonly in its midsubstance) and rupture of the posterior joint capsule [1,9] Fig. 6.
The PCL is more commonly involved than the ACL tear because,
with the knee flexed,
the PCL is stretched and the ACL is lax.
In addition,
the PCL usually limits posterior tibial translation,
whereas the ACL limits anterior translation.
[3]
HYPEREXTENSION INJURY
Hyperextension injury can result from a direct blow applied to the anterior tibia while the foot is fixed (such as a car bumper impacting the anterior tibia of a pedestrian),
which is more severe,
or from an indirect blow such as forceful kicking motion.
The final result is that the anterior aspect of the tibial plateau strikes the anterior aspect of femoral condyle,
leading to a “kissing contusion” pattern.
Fig.
7 These injuries are particularly serious because they involve the critical posteromedial and/or posterolateral corners of the knee.
[1,3]
The hyperextension injury is subdivided in pure hyperextension,
hyperextension with valgus and hyperextension with varus,
which is the most common.
[1,3] In pure hyperextension BME can be depicted in anterior central tibia and external femoral condyle.
[1] In the hyperextension with valgus BME is usually more pronounced in anterolateral tibia,
femoral condyle (impaction force) and posteromedial tibia (avulsion force).
Fig. 8 Finally,
in the hyperextension with varus stress produces bone abnormalities in anteromedial tibial,
femoral condyle (impaction force),
posterolateral corner and proximal fibula (avulsion force) [1,3] Fig. 9.
Depending on the amount of force applied,
associated soft-tissue abnormalities may include injury to ACL,
PCL or meniscus.
In more severe cases,
dislocation of the knee can occur.
[10]
CLIP INJURY
Clip injury occurs when a pure valgus stress is applied while the knee is in a state of mild flexion (10-30°).
This event often results in BME involving the lateral femoral condyle secondary to direct blow,
and a smaller area of BME in the medial femoral condyle resulting from an avulsive stress to the medial collateral ligament (MCL).
Fig. 10 Fig. 11 The MCL can be affect in various degrees: grade 1 consists in a sprain of the ligament,
with contour irregularity and superficial edema; grade 2 consists in a partial tear; and grade 3 represents a complete disruption.
[1,3] With increased degrees of knee flexion,
this injury mechanism can lead to the so called O´Donoghue triad,
a combination of a simultaneous ACL tear,
MCL tear/sprain and medial/lateral meniscus tear.
[3] Fig. 12 This lesion can also arise during the pivot shift movement.
LATERAL PATELLAR DISLOCATION
Lateral patellar dislocation results from twisting motion of the knee while it is in a state of flexion.
[11] The femur rotates internally on a flexed tibia and contraction of the quadriceps occurs resulting in lateral dislocation of the patella out of the trochlear groove.
[3] This injury is more common in individuals with shallow trochlear groove.
The classic bone contusion pattern includes involvement of the anterolateral aspect of the lateral condyle and inferomedial aspect of the patella. Fig. 13 Fig. 14 This bone contusion pattern is located more anteriorly and peripherally than bone bruise associated with pivot-shift injury,
which is more centrally or posteriorly located on the lateral femoral condyle.
[1,3] Fig. 15
Associated soft-tissue abnormalities include sprain or disruption of the medial retinaculum,
the medial patellofemoral ligament (MPFL) and the medial patellotibial ligament.
[3] Fig. 16 On axial images,
MPFL is located just deep to the vastus medialis oblique muscle (corresponding to the section of the vastus medialis muscle that is just above the kneecap).
The medial retinaculum arises from the midpole of the patella and is located just distal to the MFPL.
[12] The MFPL is most commonly injured near its femoral attachment,
and it may be sprained,
torn or avulsed.
After avulsion fluid can be seen between the MPFL and the femoral attachment on the adductor tubercle.
Radiologists should perform a meticulous evaluation and search for any osteochondral defect or disruption of the MPFL,
since these injuries may be an indication for surgery.
[3]