Introduction:
Knee ligament injuries are common in sports and trauma. MRI is the modality of choice for evaluating ligamentous injuries due to its excellent soft tissue contrast and multiplanar capability. The anterior cruciate ligament (ACL) and medial collateral ligament (MCL) are among the most commonly injured structures.
Normal Ligament Anatomy on MRI:
📌 ACL (Anterior Cruciate Ligament):
- Origin: Posteromedial aspect of lateral femoral condyle
- Insertion: Anterior intercondylar area of tibia
- Best seen on sagittal and coronal planes
- Appears as a low-signal band (on all sequences)
📌 MCL (Medial Collateral Ligament):
- Origin: Medial femoral epicondyle
- Insertion: Medial tibial metaphysis
- Has superficial and deep layers
- Appears as a hypointense band on all sequences
MRI Protocol:
- Sequences:
- PD-weighted and T2-weighted with fat saturation (axial, sagittal, coronal)
- Optional: 3D isotropic sequences for multiplanar reconstruction
- Field strength: Preferably 1.5T or 3T
- Coil: Dedicated knee coil
MRI Findings in ACL Injury:
✅ Acute ACL Tear:
- Discontinuity of fibers
- Abnormal course or wavy appearance of ligament
- Increased signal intensity on T2-weighted or PD fat-sat images
- Bone contusions (lateral femoral condyle + posterolateral tibial plateau) – “kissing contusion”
- Anterior tibial translation >7 mm
- Uncovering of the posterior horn of lateral meniscus
✅ Chronic ACL Tear:
- Ligament thinning, scarring, or nonvisualization
- Secondary signs: Notch osteophytes, joint degeneration
MRI Findings in MCL Injury:
🩺 Grading System:
| Grade | MRI Findings |
|---|---|
| I | Periligamentous edema, intact fibers |
| II | Partial tear, thickened ligament, high signal |
| III | Complete discontinuity or retraction |
🧠 Associated Findings:
- Meniscocapsular separation
- Medial meniscus tear
- Pellegrini-Stieda lesion (chronic MCL injury calcification at origin)
Associated Injuries:
- Meniscal tears (especially medial with MCL, lateral with ACL)
- Bone marrow edema
- Segond fracture (avulsion at lateral tibial plateau) – highly suggestive of ACL tear
- Posterolateral corner injuries
Role of MRI:
- Confirms diagnosis of ligament tears
- Grades partial vs complete tear
- Detects associated meniscal and chondral injuries
- Useful in preoperative planning
- Helps differentiate acute vs chronic injuries
Conclusion:
MRI provides detailed assessment of knee ligament injuries, especially of ACL and MCL. It allows precise grading, detects associated injuries, and aids in treatment planning. Its non-invasive nature and high soft tissue contrast make it indispensable in modern musculoskeletal imaging.
