Medial collateral ligament (MCL) injury is the most common ligament injury of the knee joint, resulting from valgus stress. The MCL extends from the medial femoral epicondyle to the medial tibial surface and consists of two layers: superficial (sMCL) and deep (dMCL). Injury grades: Grade 1 — periligamentous edema, fibers intact (strain); Grade 2 — partial tear, some fibers discontinuous; Grade 3 — complete tear, completely discontinuous fibers. MCL injury is generally treated conservatively when isolated because its extra-articular location and good vascularity provide high healing capacity. However, O'Donoghue triad (ACL + MCL + medial meniscus) combination or Grade 3 injuries may require surgery. On MRI, periligamentous edema (Grade 1), ligament thickening with partial signal increase (Grade 2), or complete discontinuity (Grade 3) is seen around MCL.
Age Range
15-50
Peak Age
25
Gender
Male predominant
Prevalence
Common
The MCL is the medial stabilizer of the knee joint providing primary resistance to valgus stress. The superficial MCL (sMCL) extends as a broad ~10 cm band from the femoral epicondyle to the medial tibial surface. The deep MCL (dMCL) consists of meniscotibial and meniscofemoral ligaments and is directly attached to the medial meniscus — therefore dMCL injury frequently accompanies medial meniscus injury. The injury mechanism is typically valgus stress from lateral impact to the knee — this stretches medial structures and tears the MCL. Strain (Grade 1) represents microscopic fiber damage — macroscopic fiber integrity is maintained but periligamentous edema has formed. Partial tear (Grade 2) means some fibers are torn, complete tear (Grade 3) means all fibers are torn. MCL's good healing capacity is based on its extra-articular location allowing blood supply nourishment — unlike ACL, it is not washed by synovial fluid and the fibrin clot remains as healing scaffold.
Hyperintense fluid/edema accumulation around MCL on coronal T2 fat-sat/STIR MRI. In Grade 1 injury, ligament fibers are intact with only surrounding edema; in Grade 2, signal increase begins within the ligament; in Grade 3, complete discontinuity is seen. Periligamentous edema is the earliest and most sensitive MRI finding of MCL injury.
On coronal T2 fat-suppressed/STIR sequences, high-signal periligamentous edema/fluid is seen around the MCL. Ligament fibers are intact and of normal thickness. This finding is the MRI correlate of Grade 1 (strain) injury. Edema usually begins at the femoral attachment and may extend distally. MCL's internal structure is preserved as homogeneous low signal.
Report Sentence
Periligamentous edema is seen around the MCL with intact ligament fibers; consistent with Grade 1 MCL injury.
On coronal PD or T2 fat-sat images, focal hyperintense signal increase and thickening in MCL fibers is seen. Some fibers are discontinuous while others remain intact. The ligament is thicker than normal (>5 mm) with irregular margins. Grade 2 injury clinically correlates with mild-to-moderate laxity on valgus stress test. Isolated deep MCL layer injury may be associated with meniscocapsular separation.
Report Sentence
Focal signal increase and thickening in MCL fibers with discontinuity in some fibers is seen; consistent with Grade 2 partial MCL tear.
On coronal T2 fat-sat images, all MCL fibers are discontinuous with hyperintense fluid/edema-filled gap between torn ends. Ligament ends may show retraction. Periligamentous fluid collection is prominent. Grade 3 injury correlates with significant valgus instability. Both superficial and deep MCL layer tears should be evaluated. Stener-like lesion (sMCL distal end folding over pes anserinus) may create surgical indication.
Report Sentence
MCL fibers are completely discontinuous with fluid collection between torn ends, consistent with Grade 3 complete MCL tear.
On coronal T2 images, separation of deep MCL layer from the medial meniscus — seen as fluid at the meniscocapsular junction. This finding represents meniscocapsular separation and is a special form of peripheral medial meniscus tear. Without deep MCL injury, the meniscus may appear superficially intact but is detached from its capsular attachment. This separation contributes to instability.
Report Sentence
Fluid at the medial meniscocapsular junction is seen, consistent with deep MCL injury and meniscocapsular separation.
In valgus stress mechanism, impaction occurs in the lateral compartment and distraction in the medial compartment. Compressive bone marrow edema ('kissing contusion') may be seen in lateral femoral condyle and lateral tibial plateau. Simultaneously, bone edema may be seen in medial femoral condyle or medial tibial plateau with MCL injury on the medial side. This contusion pattern reflects the injury mechanism.
Report Sentence
Bone marrow edema consistent with kissing contusion pattern in the lateral compartment is seen, supporting valgus stress mechanism.
Criteria
Periligamentous edema, fibers intact, normal thickness
Distinct Features
Most common, conservative treatment, healing in 1-3 weeks, no laxity on valgus stress test
Criteria
Ligament thickened, focal signal increase, some fibers discontinuous
Distinct Features
Conservative treatment usually successful, healing in 4-6 weeks, mild-to-moderate laxity on valgus test
Criteria
All fibers discontinuous, retraction, periligamentous fluid collection
Distinct Features
Significant valgus instability, combined injury common (O'Donoghue), surgery may be needed, 6-12 weeks healing
Distinguishing Feature
ACL is intra-articular, MCL is extra-articular — different anatomy and mechanism; may coexist in O'Donoghue triad
Distinguishing Feature
Medial meniscus tear is intra-articular meniscal pathology; MCL injury is extra-articular ligament pathology — may coexist as deep MCL is attached to meniscus
Distinguishing Feature
Bone contusion is bone marrow pathology, MCL injury is ligament pathology — both may coexist in valgus mechanism
Urgency
urgentManagement
conservativeBiopsy
Not NeededFollow-up
specialist-referralIsolated MCL injury generally yields excellent results with conservative treatment — immobilization (brace), ice, elevation, NSAIDs, and rehabilitation. Grade 1 injury heals in 1-3 weeks, Grade 2 in 4-6 weeks, Grade 3 in 6-12 weeks. MCL's extra-articular location and good vascularity support healing. Surgical indications: Grade 3 tear + combined ligament injury (especially O'Donoghue triad), chronic MCL instability, Stener-like lesion. In patients planned for ACL reconstruction, conservative rather than surgical MCL treatment is preferred — MCL usually heals spontaneously during ACL recovery.
Most MCL injuries (Grade 1-2) heal with conservative treatment. Grade 3 injuries may require surgical intervention, especially when combined with multiligamentous damage. The 'unhappy triad' (ACL + MCL + medial meniscus) indicates severe knee instability and requires surgical planning.