Anterior surface anatomy
Knee MRI
Knee MRI
Knee Anatomy: Muscles around the Knee
Anterior thigh muscles
Posterior surface anatomy
Posterior thigh muscles
Muscle and Tendon Attachments around the Knee
Meniscus
Introduction
- The knee is one of the commonest joint imaged
- MRI is useful for soft tissues and bone assessment
- Technique
- Review areas
- Common pathology
Technique
- Dedicated knee coil
- Don’t angle for ACL
- Routine protocol and then assess
- Sagittal PD (TE<30) and fat sat PD (TE36) FOV14, slice 3mm
- ACL, PCL, menisci, cartilage Coronal T1 and fast STIR (or fat sat PD)
- Coronal T1 and Fast STIR (or fat sat PD) FOV14
- LCLC, MCL, menisci, cartilage
- Axial STIR FOV14
- Confirm, support especially ACL, MCL and posterolateral corner pathology
- Patellofemoral joint
- Review areas
- Common pathology
Review areas
- Menisci
- Bone
- Cartilage: each compartment
- Ligaments: ACL, PCL, Collateral ligaments, capsule
- Extensor mechanism
Miscellaneous:
- Loose bodies
- Synovium/plicas
- Masses and cysts
Menisci
- Bow ties: at least two
- Morphology
- Blunted apex – Surgery
- Discoid
- Bucket handle tear
- Flipped meniscus
- Cyst
Meniscus Vascular Anatomy
- Signal change – Meniscus windows
- Grade 1-3
- 2=enclosed tear
- 3=tear
- Sag > Cor to pick up tears
- Pitfalls
-
- Transverse meniscus ligament
- Popliteal tendon
- Ligament of Humphrey
Transverse meniscus ligament
Meniscus Tears
Recurrent Tear
- Type 3 change
- Abnormal morphology
- Fluid signal intensity on all sequences
Osteochondral abnormalities
Bone
- Bone bruise
- Subchondral infraction
- OCD
- SONK
- Subchondral cysts
-
Cartilage
- Femorotibial compartments
- Look for subchondral bone changes
- Look for subchondral bone changes
Osteochondral injuries
- Spectrum of injuries
- Bone bruise
- Osteochondral fracture
- Osteochondritis dissecans
- Stable, unstable in-situ, loose
- Instability
- High SI beneath fragment
- Subchondral cyst
- Cartilage fracture
- Displaced fragment
Ligament injuries
-
-
- Sprain: clinical grading
- Partial vs full-thickness tears
- Tell tale bone contusions to reflect the mechanism of injury
- Healing/repair can be followed
- Ganglion formation
- Some joints: see ligaments better with intra-articular contrast (wrist, elbow, shoulder)
-
ACL mechanism of injury
Football/skiing
- External rotation/abduction/hyperextension
- Direct anterior tibia displacement
- Internal rotation, tibia hyperextension (isolated)
- Valgus or varus stresses
- Valgus in extension rotation (MC)
- Deceleration pivot and internal rotation femur
ACL Tear primary signs
Complete
- Proximal segment
- ⇧ SI
- Angled/wavy fragments
- Cloud, oedema/blood
- Complete absence
Accuracy
- > 90%
ACL secondary signs of tear
- Bone contusions
- Post lat tibia and lat fem condyle
- Post med tibia
- Segond fracture
- Anterior drawer
- Uncovered meniscus
- Buckled PCL
- Absent ACL, coronal
- Fluid in the notch on axial
- Meniscus tear (70%) especially LM
- Ligament (MCL 30 %) or capsule tears (post-lat)
ACL tear bone contusion
Bone Bruise
- Microfracture with haemorrhage in the subchondral bone
- Second “pop” felt at time of injury
Persists for 6-12 weeks - Pain proportional to size of bone bruise
- Geographic better prognosis than focal
- Major prognostic indicator- treat as fracture and don’t weight bear
- Career ending injury- osteoarthritis (die is cast)
ACL graft
- Patellar tendon
- More recently hamstring
- Notch width and osteophytes
- Arthrofibrosis/cyclops lesion
- Graft impingement
- Re-rupture
Cyclops lesion
- Arthrofibrosis post ACL reconstruction
- May limit extension and cause locking
- Easily surgically removed
PCL tear
- PCL discontinuity
- Focal or diffuse SI, size
- Anterolateral fem/tib contusions
- Tibial avulsion fx
- MRI > 90% accurate
- Associated MCL, ACL tears common
PCL mechanism of injury
- Major stresses: athletic, MVA
- Knee: hyperextension, hyperflexion
- Post tibial displacement, knee flexed (dashboard injury)
MCL mechanism of injury
MCL
- Valgus stress to flexed knee
- Clinical grading system: MRI findings
- Partial, complete MCL tears
- Peripheral medial meniscus tear
- Meniscocapsular separation
LCL complex
LCL ligament
Popliteus
- Valgus stress to flexed knee
- Clinical grading system: MRI findings
- Partial, complete MCL tears
- Peripheral medial meniscus tear
- Meniscocapsular separation
Extensor Mechanism
- Patellar tendon
- Sag and ax-uniform thickness and black
- Tendinosis often asymptomatic
- Hoffa’s fat
- Fat pad impingement
- Old surgery fibrosis
- Patellar cartilage
- Chondromalacia
- softening, fissuring and defects
Intact extensor mechanism allow knee range of motion
Tendinopathy
- Tenosynovitis peritendinitis
- Tendinosis
- Partial thickness tear
- Full thickness tear
- Complete tear ± retraction
Patellar dislocation
- Common cause of haemarthrosis
- Present after relocation
- Associated with osteochondral fractures
- Bone contusion present: lateral femoral condyle & medial patellar
- Partial/complete tears of the medial retinaculum
Miscellaneous
- Loose bodies
- Axials & sag
- Suprapatella pouch, ant recess and popliteal cyst
- Tendinosis
- PVNS, erosions
- Masses and cysts
- Popliteal cyst
- Bursitis
- Ganglion
