2. MSK (Soft Tissue/Acquired - Lower Limb)

Question 1

Knee ligaments (anatomy) (5)

Answer 1

ACL has 2 bundles
- Long one (anteromedial) tightens the knee in flexion.
- Short one (posterolateral) tightens the knee in extension
PLC is strongest ligament in the knee
- Posterior dislocation of the knee can result in popliteal artery dissection.

Question 2

Knee meniscus anatomy (5)

Answer 2

C shaped
Thicker along periphery and thin centrally
Medial meniscus is thicker posteriorly, lateral meniscus is equally thick anterior and posterior.
Peripheral zone is vascular and can heal, central zone is avascular and won’t heal.
Blood supply comes from geniculate arteries which enter peripherally.

Question 3

Meniscofemoral ligaments (3)

Answer 3

2 of them, Wrisberg and Humphry.
Can me mimics of meniscal tears.
Wrisberg is posterior, Humphry is anterior (H before W in alphabet)

Question 4

Knee tendons anatomy (4)

Answer 4

Conjoint tendon formed by biceps femoris tendon and the LCL.
PCL and patellar tendon may have foci of intermediate signal intensity on sagittal images (with short echo time sequences), where the tendon forms an angle of 55 degrees with the main magnetic field (magic angle phenomenon).
Not seen on t2 sequences.
Phenomenon is reduced at higher field strengths due to greater shortening of t2 relaxation times.

Question 5

Meniscal tears (3)

Answer 5

Peripheral (red) zone has better vascularity than central 2/3 (white zone), and can heal on it’s own.
Vertical or horizontal tears.
Vertical can be radial and longitudinal

Question 6

Meniscal cysts (2)

Answer 6

Most often near lateral meniscus, most often associated with horizontal cleavage tears.

Question 7

Bakers cyst

Answer 7

Occurs between semimembranosus and the medial head of gastrocnemius.

Question 8

Meniscocapsular separation (2)

Answer 8

Deepest layer of MCL complex (capsular liagment) is relatively weak and first to tear, therefore associated with meniscocapsular separation.

Question 9

Discoid meniscus (3)

Answer 9

Normal variant of lateral meniscus that is prone to tear.
Not C-shaped, but disc shaped. It’s essentially too big.
3 types. Rarest and most prone to injury is Wrisberg variant.

Question 10

Bucket handle tear (3)

Answer 10

Torn meniscus, usually medial (80%), which flips medially to lie anterior to the PCL.
Double PCL sign is aunt minnie.
Double PCL can only happen in context of intact ACL.

Question 11

Meniscal ossicle (3)

Answer 11

Focal ossification of posterior horn of medial meniscus.
Can be secondary to trauma, or developmental.
Often associated with radial root tears.

Question 12

ACL tears trivia (5)

Answer 12

Usually occurs in people who are stopping and pivoting.
Associated with segond fracture.
ACL angle lesser than Blumensaat’s line
O’Donoghue’s unhappy triad: ACL tear, MCL tear, Medial meniscal tear.
Classic kissing contusion pattern: Lateral femoral condyle collides with posterior lateral tibial plateau, 95% specific in adults.

Question 13

ACL mucoid degeneration (5)

Answer 13

Can mimic acute or chronic partial ACL tear.
No secondary signs of injury (contusions etc).
Predisposes to ACL ganglion cysts.
T2/STIR - celery stalk appearance due to striations.
T1 drumstick appearance.

Question 14

ACL repair (5)

Answer 14

Method 1:
- Middle third of patellar tendon, patella bone plug attached to one end and tibial bone plug attached to other
Method 2:
- 4 strand hamstring graft, often made of semitendinosus or gracilis tendon, or both.
- Fold and braid the segment to form quadruple thickness structure.
- Graft then attached with interference screws, endobuttons or staples.
- Lower reported morbidity to harvest site using this method.

Question 15

Posterior lateral corner (PCL)

Answer 15

Injury to LCL, IT band, Biceps femoris or popliteus tendon, or fibular head oedema, consider PLC injury (instability).
Missed PLC injury is common cause of ACL reconstruction failure.

Question 16

ACL repair complications (10)

Answer 16

Roof impingement
- tibial tunnel placed too far anteriorly, graft may bump against anterior inferior margin of the intercondylar roof.
- Tibial tunnel positioning is primary factor in preventing impingement
Maintaining isometry
- Positioning of the femoral tunnel is the primary factor in maintaining isometry (constant length and tension during full ROM)
Arthofibrosis
- Focal (cyclops lesion) or diffuse.
- Called cyclops because of arthroscopic appearance.
- Low signal spiculated mass-like scar in hoffa’s fat pad.
- Limits extension
Graft tear
- Most susceptible during remodelling process, 4-8 months post op.
- Increased T2 signal and fiber discontinuity.
- Uncovering of posterior horn of lateral meniscus and anterior tibia translation are good secondary signs.

Question 17

PCL tear (2)

Answer 17

Strongest ligament in the knee. Tear is uncommon.
Often associated with posterior dislocation.

Question 18

Patella dislocation

Answer 18

Usually lateral, associated with tear of medial patellar femoral ligament)

Question 19

Master Knot of Henry

Answer 19

This is where FDL (Dick) crosses over FHL (Harry) at the medial ankle

Question 20

Commonest ankle ligament injury

Answer 20

Anterior talofibular ligament, because it’s weakest

Question 21

Posterior tibial tendon injury/dysfunction

Answer 21

Causes progressive flat foot, as it’s the primary stabilizer of longitudinal arch.
Chronic: tear commonly behind the medial malleolus (most friction).
Acute: tear commonly at insertion into the navicular bone.
Acute flat foot = PTT tear.
Hindfoot valgus deformity (unopposed peroneus brevis action).
Spring ligament is secondary supporter of arch, and will thicken and degenerate without PTT, but almost never ruptures.

Question 22

Classic progression of PTT injury

Answer 22

PTT ruptures, then spring ligament out.
Then Sinus tarsi gets hypertrophy.
Then heel strike on painful flat foot –> Plantar fasciitis

Question 23

Split peroneus brevis

Answer 23

Longitudinal splits seen in inversion injuries, usually present with chronic ankle pain.
Tendon will be C shaped or boomerang shaped, with central thinning and partial envelopment of peroneus longus.
Alternatively, may be 3 tendons instead of 2.
Tear occurs at lateral malleolus.
80% association with lateral ligament injury.

Question 24

Anterolateral impingement syndrome

Answer 24

Injury to anterior talofibular ligaments and tibiofibular ligaments (usually inversion injury) causes lateral instability and chronic synovial inflammation.
Eventually form a mass of hypertrophic synovial tissue in the lateral gutter.
MRI: Meniscoid mass in the lateral ankle gutter, which is a balled up scar (T1 and T2 dark)

Question 25

Sinus Tarsi Syndrome

Answer 25

Sinus tarsi - space between lateral talus and calcaneus.
Syndrome caused by haemorrhage or inflammation of the synovial recess with/out tears of the assocated ligaments (talocalcaneal ligaments, inferior extensor retinaculum).
Associated with rheumatologic disorders and abnormal loading (flat foot in setting of PTT tear).
MRI: obliteration of fat in sinus tarsi, replacement with scar.

Question 26

Tarsal tunnel syndrome

Answer 26

Pain in distribution of tibial nerve, first 3 toes, from compression as it passes through tarsal tunnel (behind medial malleolus).
Usually unilateral (unlike carpal tunnel)

Question 27

Achilles tendon injury

Answer 27

Acute rupture usually obvious.
Loss of ability to plantarflex (unless plantaris muscle is intact)

Question 28

Xanthoma

Answer 28

Achilles tendon significantly enlarged/fusiform thickened.
Can be seen with familial hypercholesterolaemia, often bilateral.

Question 29

Plantar fasciitis

Answer 29

Inflammation of plantar fascia due to repetitive trauma.
Pain localized to origin of plantar fascia, worsened on dorsiflexion of toes.
Most severe in morning.
XR: may show heel spurs
MR: Thickened fascia (>4mm), high T2 signal esp near insertion at heel.
Increased calcaneal uptake on bone scan, due to periosteal inflammation)

Question 30

Morton’s neuroma

Answer 30

Big, dumbbell scar between 3rd and 4th metatarsals, usually unilateral.
Results from compression/entrapment of plantar digital nerve in this location by the intermetatarsal ligament.
Over time, results in thickening and development of perineural fibrosis.