Collateral Ligament Injury MRI

Magnetic resonance imaging (MRI) has a primary role in the diagnosis of musculoskeletal soft tissue injuries of the knee. MRI is an accurate and cost-effective means of evaluating a wide spectrum of knee injuries, ranging from cruciate-collateral ligament injuries to cartilage deficiencies. MRI enables the most comprehensive imaging assessment of the knee and, when performed early after injury, can aid in predicting which patients require further treatment. Detection of associated internal derangements of the knee makes MRI superior to ultrasonographic imaging.[1, 2, 3, 4, 5]  

Radiographs may demonstrate an acute fracture but commonly are either negative or may demonstrate indirect signs of an acute soft-tissue injury. Computed tomography (CT) is usually reserved for diagnosis of suspected fractures or assessment of complex fractures, although associated ligamentous injuries may be evident on CT scans obtained for evaluation of osseous injuries.[6]  

Medial collateral ligament (MCL) injury is the most common knee injury in high school, collegiate, and professional football athletes and typically occurs when a valgus force is applied to the knee. The annual incidence of MCL injuries in high school football players is 24.2 per 100,000 athletes.[7] ​

MCL tears are rarely isolated. More commonly, they are associated with other soft tissue injuries of the knee, such as anterior cruciate ligament (ACL) tears and medial meniscal tears (O'Donoghue's unhappy triad). In one study, nearly 78% of patients who sustained a grade III MCL injury had an injury to another associated structure. Of those additional injuries, 95% involved the ACL.[8]

The differential diagnosis includes damage to other medial structures of the knee: the pes anserinus or semitendinosus, vastus medialis, femoral quadriceps, or medial gastrocnemius tendons. Tears to the lateral collateral ligament (LCL) are less common and never occur in isolation. Typically, these injuries are associated with damage to the popliteal tendon arcuate ligament (the posterolateral reinforcement of the joint capsule), the ACL, and the posterior cruciate ligament (PCL).[9]   

(A coronal, proton-density (PD) MRI scan of the MCL is shown below.)

Grading system

The grading system for MCL and LCL tears, which is the same as that used for other ligaments evaluated by MRI, is as follows:

• Grade 1 - Microscopic tears

• Grade 2 - Partial tears

• Grade 3 - Complete tears

Examples of these injuries are seen in the images below.

There have been studies on the superficial MCL (sMCL) tibial side avulsion classification. The sMCL tibial side avulsion revealed the characteristic waving of the sMCL midsubstance portion on MRI images, which Taketomi et al called the "wave sign." The sMCL tibial avulsions were classified into 3 types, depending on the location of the ruptured end with respect to the pes anserinus tendons[10] :

• Type 1: The sMCL was detached from the original tibial insertion, and the ruptured end was identified beneath the pes anserinus tendons.
• Type 2: The sMCL was located over or above the pes anserinus tendons (the Stener-like lesion).
• Type 3: The sMCL was entrapped in the medial knee joint space.

For excellent patient education resources, visit eMedicineHealth's First Aid and Injuries Center. Also, see eMedicineHealth's patient education articles Knee Injury and Magnetic Resonance Imaging (MRI).

Calcification, particularly in the proximal portion of the MCL (seen in the radiograph below), may be seen in persons with chronic MCL tears and is known as Pellegrini-Stieda disease.

Avulsions of the fibular head (seen below) or of the lateral tibial metaphysis may be seen with injuries of the LCL/biceps femoris tendon or lateral capsule, respectively.

Capsular avulsion of the lateral tibial metaphysis (presented in the image below) is called a Segond fracture and is highly associated with ACL tears.

Routine MRI sequences for the evaluation of the knee vary among institutions and scanners. The knee should be imaged in all 3 planes—sagittal, coronal, and axial. At a minimum, scans should include sequences to define anatomy, edema, and cartilage.[11, 12, 13, 14, 15, 16, 17, 18]  Sequences for anatomic definition include spin-echo (SE) and fast spin-echo (FSE), proton-density (PD) sequences. Fluid-sensitive sequences, such as SE/FSE PD fat-suppressed or short tau inversion recovery (STIR), detect edema. Cartilage may be characterized by fat-suppressed FSE PD sequences; fat-suppressed, gradient-echo (GRE) sequences; or spoiled gradient, fat-suppressed sequences.[9]

The anterior vertical component and the posterior oblique component of the MCL are depicted consistently on coronal T1-weighted or SE/FSE T2-weighted sequences. As seen in the image below, the MCL is visualized as a thin, taut, well-defined, low T1/T2-signal structure extending from the medial femoral epicondyle to the medial tibial metaphysis.

Surrounded by high T1-weighted signal fibrofatty tissue throughout its full extent, the MCL is parallel to and closely applied to the medial femoral epicondyle and medial tibial metaphysis. The anterior vertical or superficial component is best visualized at the level of the intercondylar notch in the vicinity of the distal insertion of the ACL.

The MRI appearance of acute MCL tears depends on the degree of tearing. With grade I, or microscopic, ligamentous tears (seen below), an intact ligament of normal thickness surrounded, to a variable degree, by intermediate T1-weighted and high T2-weighted signals (indicative of surrounding edema) is seen. The ligament remains closely applied to the underlying cortical bone.

With grade II tears (seen below), thickening and/or partial disruption of the fibers of the MCL is demonstrated, along with an increase in the amount of surrounding intermediate T1-weighted and high T2-weighted signals, indicative of increased edema and concomitant hemorrhage.

With grade III tears (seen below), complete disruption of the ligament with corresponding surrounding hemorrhage and edema is seen.

Distinguishing between MRI grade II and grade III tears is difficult. Clinical evaluation of the presence (grade II) or absence (grade III) of an end point to valgus laxity is helpful. The presence of a concomitant ACL tear is suggestive of a complete disruption of the MCL.

A chronic MCL tear is seen as an ill-defined, thickened ligament with low T1-weighted and T2-weighted signals. Occasionally, the MCL ossifies, and normal bone marrow signal may be seen within its proximal portion (see the first image below). With healing of subacute tears, a thickened, low T1/T2-signal ligament is demonstrated; the ligament reaches approximately 50% of its original strength at 12 months (see the second image below).

To include the LCL, the lateral supporting structures are depicted consistently on posterior coronal and far lateral sagittal T1-weighted or SE/FSE T2-weighted sequences. The arcuate popliteofibular and fabellofibular ligaments are visualized inconsistently.

Because of its posterior course, the entire LCL rarely is visualized on a single coronal image. Specialized coronal oblique (parallel to typical course of normal LCL) and sagittal, 1-mm, 3-dimensional, volume-rendered sequences depict the LCL and posterior lateral corner (PLC) structures particularly well. The LCL is seen as a thin, taut, well-defined, low T1/T2-signal structure extending laterally and posteriorly from the lateral femoral epicondyle to the fibular head (see the images below).

Unlike MCL tears, the appearance of an LCL tear on MRI depends less on the degree of tearing. The LCL is extracapsular; therefore, it excludes accumulated extravasated joint fluid and, as a result, does not demonstrate the high surrounding T2-weighted signal seen with MCL tears.

In contrast to MCL tears, an acute LCL tear is seen as a serpiginous or lax ligament with discontinuous fibers (or avulsed fibular head), often without significant thickening of the ligament. LCL tears are rarely isolated, and an LCL tear becomes more likely as associated PLC and cruciate ligament injuries increase in severity. Characteristics of acute LCL tears are demonstrated in the images below.

A chronic LCL tear (seen below) appears as a thickened, low T1/T2-weighted signal ligament.

Degree of confidence

MRI has a high degree of confidence for tears of the collateral ligaments, and confidence increases with the increasing grade of the tear. A prospective study of normal knees and knees with surgically verified grade III LCL injuries demonstrated a sensitivity, specificity, and accuracy of 94.4%, 100%, and 95%, respectively, for MRI.

The sensitivity, specificity, and accuracy of MRI for MCL injuries are less well established because of the nonsurgical nature of the injury, but they may be assumed to be similar to those of the LCL.

Loose, high T1-weighted areolar tissue interposed between the 2 layers of the MCL is a normal finding that may mimic disease.

On ultrasound images, the normal MCL appears as 2 parallel, hyperechoic bands with loose, hypoechoic areolar tissue imposed between them. The dimensions of the MCL in various ultrasound planes are approximately 2.1 mm (±0.6 mm) in thickness, 32.1 mm (±3.1 mm) in width, and 112.1 mm (±5.9 mm) in length.[19]  An MCL tear appears as a thickened ligament with decreased echogenicity. A complete disruption appears as a discontinuity in the ligament.

The normal LCL appears as a single hyperechoic band just deep to the biceps femoris tendon, with estimated dimensions of 2.6 mm (±0.3 mm) in thickness, 4.7 mm (±1.1 mm) in width, and 69.9 mm (±6.4 mm) in length.[19] Similar to an MCL tear, an LCL tear appears as a discontinuity in the ligament or as thickening and loss of echogenicity.