Knee MRI Recognition Pattern

Systematic approach to interpreting knee MRI with anatomical landmarks, common pathologies, and protocol optimization

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1. MRI Protocol

A. Standard Sequences

• • T1-weighted:
  - Anatomical detail
  - Bone marrow evaluation
  - Slice thickness: 3-4mm
• • PD-weighted fat-sat:
  - Meniscal pathology
  - Cartilage assessment
  - Ligament evaluation
• • T2-weighted:
  - Joint effusion
  - Bone marrow edema
  - STIR alternative

B. Specialized Sequences

• • 3D SPGR/DESS:
  - Cartilage mapping
  - Isotropic voxels for reformats
• • DWI:
  - Osteomyelitis evaluation
  - Tumor characterization

2. Anatomical Evaluation

A. Compartment Approach

Compartment

Key Structures

Common Pathology

Medial

MCL, medial meniscus

Bucket handle tears, MCL sprains

Lateral

LCL, lateral meniscus

Segond fractures, popliteus injury

Central

ACL, PCL

ACL tears, PCL avulsions

B. Imaging Planes

• • Sagittal:
  - Cruciate ligaments
  - Meniscal horns
• • Coronal:
  - Collateral ligaments
  - Meniscal bodies
• • Axial:
  - Patellofemoral joint
  - Synovial evaluation

3. Meniscal Evaluation

A. Tear Classification

Type

MRI Signs

Location

Horizontal

Linear signal parallel to tibial plateau

Degenerative, posterior horn

Vertical

Perpendicular to tibial plateau

Traumatic, peripheral

Bucket handle

Displaced fragment, double PCL sign

Medial > lateral

B. Meniscocapsular Separation

• • Features:
  - >3mm meniscal extrusion
  - Fluid between capsule and meniscus
  - Peripheral meniscal signal

4. Ligament Pathology

A. ACL Tears

Feature

Partial Tear

Complete Tear

Fiber continuity

Some fibers intact

Complete disruption

Signal

Increased but organized

Disorganized, wavy

Bone bruises

May be absent

Lateral femoral condyle + tibia

B. Collateral Ligaments

• • MCL:
  - Grade 1: Periligamentous edema
  - Grade 2: Partial thickness tear
  - Grade 3: Complete disruption

5. Cartilage Assessment

A. Outerbridge Classification

Grade

Description

I

Signal change, intact surface

II

<50% thickness defect

III

>50% thickness defect

IV

Full thickness + subchondral bone

B. Common Locations

• • Patella:
  - Lateral facet (malalignment)
  - Median ridge
• • Femoral condyles:
  - Weight-bearing surfaces
  - Trochlear groove

6. Reporting Template

• 1. Technique: Sequences, planes
• 2. Meniscus:
  - Medial/lateral tears
  - Extrusion/migration
• 3. Ligaments:
  - ACL/PCL integrity
  - Collateral grading
• 4. Cartilage:
  - Outerbridge grading
  - Location/extent
• 5. Other:
  - Bone marrow edema
  - Synovial pathology

Always correlate with clinical history and mechanism of injury. For ACL tears, evaluate secondary signs (bone bruises, PCL buckling). In older patients, differentiate degenerative meniscal signal from true tears. Document cartilage lesions using standardized grading systems. For postoperative knees, note graft position and hardware artifacts. Include relevant measurements (meniscal extrusion, patellar height) when clinically significant.

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