eMedicine Specialties > Radiology > Musculoskeletal
Knee, Collateral Ligament Injuries (MRI)
Updated: Dec 15, 2008
Introduction
Grade I medial collateral ligament tear with surrounding intermediate signal consistent with edema (straight arrows) on a coronal proton density sequence. Note the normal thickness and signal of the medial collateral ligament and continued close apposition to the femoral and tibial cortices.
Corresponding fast spin-echo inversion recovery image demonstrates surrounding edema (white arrows).
Background
MRI has revolutionized the evaluation of musculoskeletal soft tissue injuries. Nowhere is this more evident than in the evaluation of internal derangements 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. For interpreting radiologists and clinicians, evaluation of an injured knee using MRI requires knowledge of the proper imaging techniques, normal and aberrant anatomy, and the clinical significance of detected abnormalities.1
For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles Knee Injury and Magnetic Resonance Imaging (MRI).
Collateral Ligament Pathology, Knee (Orthopedic Surgery)
Medial Collateral and Lateral Collateral Ligament Injury (Physical Medicine and Rehabilitation)
Pathophysiology
Both the medial and lateral supporting structures of the knee are complex arrangements of ligaments, fascial layers, and tendon insertions. For this reason, injuries may range from isolated single-element injuries to combined multiple-element injuries. In addition, injuries may range from strains or partial tears to complete disruptions.
Isolated medial collateral ligament (MCL) injuries result from a valgus stress without a rotary component. Biomechanical studies indicate that the primary function of the MCL as a limit to valgus is crucial only during flexion; therefore, most injuries occur when the knee is flexed.
MCL tears rarely are 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). Of complete MCL tears, 73% are associated with additional significant knee injuries, usually an ACL tear. Other associations include meniscocapsular separations and bone bruises.
Isolated injuries of the lateral collateral ligament (LCL) result from the placement of an abnormal varus stress on an internally rotated knee. Posterior lateral corner (PLC) injuries may occur as a result of both direct and nondirect forces that cause hyperextension or hyperextension and external rotation. Similar to MCL tears, isolated injuries of the LCL are uncommon and typically occur in association with ACL or posterior cruciate ligament (PCL) tears. Injuries of the lateral compartment are complex, usually with injuries to multiple components; they are often more disabling than injuries of the medial structures because of the greater forces to which lateral structures are subjected during normal gait.2
The grading system for classifying both MCL and LCL tears is the same as that used for other ligaments evaluated by MRI as follows:
- Grade 1 — Microscopic tears
- Grade 2 — Partial tears
- Grade 3 — Complete tears
Frequency
United States
The medial collateral ligament (MCL) is the weakest of the 3 primary stabilizers of the knee (ACL, LCL, MCL); therefore, it is injured most commonly. Disruption of the MCL has been reported in as many as 61% of skiing injuries; it is reported to occur commonly as a result of clipping during football games (in clipping, one football players blocks an opponent from behind).
Injury of the LCL occurs significantly less commonly than injury of the MCL.
Mortality/Morbidity
Medial collateral ligament (MCL) tears are not associated with significant morbidity. Most MCL tears heal uneventfully with functional rehabilitation.
Chronic LCL and PLC tears can result in chronic instability, leading to buckling into hyperextension and subsequent injuries to additional ligaments. LCL and PLC instability eventually results in degenerative changes of the joint.
Anatomy
The medical collateral ligament (MCL) is a ligament measuring approximately 8-11 cm long by 10-15 mm wide. The MCL arises 5 cm above the joint from the medial femoral epicondyle and inserts 6-7 cm below the joint on the medial tibial metaphysis. Its insertion onto the tibia is covered by the muscle group of the pes anserinus. The MCL is considered to be a composition of the 2 deepest layers of the 3 layers forming the medial supporting structures of the knee.
The 3 layers include (1) layer I, or the superficial layer, consisting of crural fascia, (2) layer II, or the intermediate layer, consisting of what classically is considered the superficial MCL, and (3) layer III, or the deep layer, consisting of the medial capsular ligament and meniscofemoral/meniscotibial ligaments. Fibrofatty tissue and a small bursa are interposed between layers II and III. Layers I and II fuse anteriorly to form the medial patellar retinaculum. Layers II and III fuse posteriorly to form the posterior oblique ligament (POL) component of the MCL (see top Image below and Image 1 in Multimedia). The MCL has 2 components including an anterior vertical component (layer II) and a POL component (fused layers II and III; see bottom Image below and Image 2 in Multimedia).
Coronal drawing shows the 3 layers of the medial supporting structures of the knee, including the medial collateral ligament.
Sagittal drawing of the medial supporting structures of the knee shows the anterior vertical and posterior oblique ligament components of the medial collateral ligament and their relationship to the pes anserinus and semimembranosus tendon.
The LCL is 5-7 cm long; it is extracapsular and is free from meniscal attachments. It arises from the lateral epicondyle and inserts conjointly with the biceps femoris tendon onto the fibular head. The LCL is considered to be a layer II structure. The lateral supporting structures of the knee may be divided into anterior, middle, and posterior thirds and may be classified into superficial, intermediate, and deep layers I-III, respectively. Layer I is composed of the iliotibial band anteriorly and the biceps femoris muscle posteriorly. Layer II is composed of the patellofemoral ligaments anteriorly and the LCL posteriorly (LCL is considered a layer II structure despite its envelopment by a portion of layer III). Layer III is composed of the lateral joint capsule, including lateral meniscal attachments, and meniscofemoral and meniscotibial components.
The lateral supporting structures of the knee may be subdivided further into more functionally anatomic divisions that include a group of structures commonly and collectively referred to as the PLC or posterior lateral arcuate complex. The PLC includes the LCL, the popliteus tendon, the lateral head of the gastrocnemius, the arcuate ligament and, occasionally, the popliteofibular and fabellofibular ligaments.
The popliteus muscle/tendon arises from the posterior aspect of the tibia, extends laterally and superiorly deep to the LCL, traverses the popliteal hiatus, and inserts onto the popliteal groove of the lateral femoral condyle (see top Image below and Image 3 in Multimedia). The arcuate ligament is a Y-shaped thickening of the capsule in which the medial limb curves over the popliteus muscle and tendon to join the oblique popliteal ligament, and the lateral limb ascends to blend with the capsule near the lateral gastrocnemius muscle insertion (see bottom Image below and Image 4 in Multimedia).
Sagittal drawing of the lateral supporting structures of the knee, including the lateral collateral ligament.
Coronal drawing of the lateral supporting structures of the knee demonstrating the arcuate ligament's relationship to the popliteus muscle and the lateral collateral ligament.
Presentation
Individuals with medial collateral ligament (MCL) tears often report feeling a pop after a direct lateral blow to the knee. Clinicians should suspect concomitant cruciate ligament tears if the mechanism of injury was indirect. MCL tears may be classified according to physical examination.
- Grade I tears are not characterized by laxity, only by tenderness upon palpation of the MCL.
- In grade II tears, some laxity may be demonstrated upon valgus stress, but the endpoint is firm.
- In grade III tears, an increase in laxity is demonstrated and there is no identifiable endpoint.
Grade I, grade II, and isolated grade III tears are treated nonsurgically; treatment is limited to functional rehabilitation. Grade III tears with associated ACL tears are treated surgically by repairing the ACL only.
Individuals with LCL tears rarely report feeling a pop, because their symptoms usually are dominated by associated and more severe injuries. A hyperextension varus stress is the most common mechanism of isolated LCL tears, whereas hyperextension and external rotation is a common mechanism of PLC injuries. Patients present with instability, buckling into hyperextension, and posterior lateral pain. The LCL is a completely extracapsular structure; therefore, isolated injuries are associated with little swelling and no effusions. Treatment of injuries to the lateral supporting structures remains controversial, but surgical reconstruction is favored in athletes with significant instability or if an avulsion fracture of the fibular head is present.
Preferred Examination
MRI is the preferred modality for examining both MCL and LCL injuries. Detection of associated internal derangements of the knee makes MRI superior to ultrasonographic imaging; however, with isolated injuries, the accuracy of ultrasound is comparable to that of MRI.
Limitations of Techniques
The usual limitations of MRI pertain to MRI evaluation of the MCL and LCL. The usefulness of MRI is limited in patients with claustrophobia; in patients who are obese; in patients who have a pacemaker; and by the presence of artifacts created by nearby orthopedic hardware. The use of open MRI units, as well as dedicated extremity units, has decreased the number of patients for whom MRI cannot be used because of claustrophobia or obesity.
Differential Diagnoses
Other Problems to Be Considered
MCL tear
Medial meniscal tears
Medial tibial plateau or medial femoral condyle bone bruises/fractures
Pes anserinus bursitis/avulsions
Medial plica syndrome
MRI differential diagnosis (limited to interlayer [between layers II and III] bursitis)
Lateral meniscal tears
Lateral tibial plateau or medial femoral condyle bone bruises/fractures
Iliotibial band syndrome
MRI differential diagnosis (limited to iliotibial band syndrome)
More on Knee, Collateral Ligament Injuries (MRI) |
 Overview: Knee, Collateral Ligament Injuries (MRI) |
| Imaging: Knee, Collateral Ligament Injuries (MRI) |
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References
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Further Reading
Keywords
knee collateral ligament injury, collateral ligament injury of knee, medial collateral ligament injury of knee, knee medial collateral ligament injury, medial collateral ligament, MCL, lateral collateral ligament, LCL, anterior cruciate ligament, ACL, medial supporting structures of the knee, lateral supporting structures of the knee, posterior lateral corner
