Anterior Cruciate Ligament Tear

Question 1

Purpose of ACL

Answer 1

Stabiliser of knee joint

Limit anterior translation of the tibia relative to the femur.

Contributes to knee rotational stability and especially internal rotation.

Question 2

Mechanism of injury

Answer 2

In an athlete with a hx of suddenly twisting a flexed knee whilst weight-bearing.

Usually occur without contact.

Question 3

Clinical features

Answer 3

Unable to bear weight

Rapid joint swelling (haemarthrosis)

Leg “giving way”

Question 4

Specific clinical examinations

Answer 4

Lachman test

Anterior drawer test

Question 5

Explain Lachman’s test

Answer 5

Place the knee in 30 degrees of flexion

One hand should stabilise the femur and pull the tibia forward.

This is to assess the amount of anterior movement of the tibia compared to the femur.

Examine the other knee for comparison.

Question 6

Explain anterior drawer test.

Answer 6

Flex the knee to 90 degrees

Place thumbs on the joint line and index fingers on the hamstring tendons posteriorly.

Apply force anteriorly to demonstrate any tibial excursion

Compare to other knee.

Anterior Drawer test is less sensitive than Lachman’s

Question 7

Dx

Answer 7

Proximal tibial or distal femur fracture

Meniscal tear

Collateral ligament tear

Quadriceps tendon tear

Patellar ligament tear

Question 8

Ix

Answer 8

X-ray (AP + lateral) to exclude bony injuries, joint effusion or a lipohaemarthrosis.

MRI scan of the knee is gold standard to confirm diagnosis with a sensitivity of 90% and will pick up meniscal tears (50% have a meniscal tear)

Question 9

What is a Segond fracture?

Answer 9

Bony avulsion of the lateral proximal tibia

It is pathognomic of ACL injury

Question 10

Immediate management

Answer 10

Of any acutely swollen knee

RICE

Rest
Ice
Compression
Elevation

Question 11

What dictates whether you’re going to use conservative management or surgical?

Answer 11

Suitability

Current levels of activity (not age)

Question 12

Explain conservative treatment of ACL tear

Answer 12

Rehab to utilise the strength of the quadriceps to stabilise the knee

Patient can usually partially weight bear so a cricket pad knee splint can be applied for comfort.

Question 13

Explain surgical reconstruction

Answer 13

Involves using a tendon (patellar, hamstring, quadriceps), an allograft or an artifical graft.

It is not performed acutely but instead after a period of prehabilitation with physio for a few months.

Acute surgical repair is possible depending on the location of the tear where you re-suture the ends of the torn ligament together again, but they usually fail over time.

Question 14

Complications

Answer 14

Post-traumatic OA

Can happen both in injury and post-surgery

Question 15

Mechanism of injury PCL

Answer 15

High-energy trauma like a direct blow to the proximal tibia during a RTC.

Or low-energy trauma when there is hyperflexion of the knee with a plantar-flexed foot (less common).

Question 16

Purpose of PCL

Answer 16

Primary restraint to posterior tibial translation on femur.

Works to prevent hyperflexion of the knee

Question 17

Clinical features

Answer 17

Immediate posterior knee pain

Instability of joint and a +ve posterior drawer test with a posterior sag on examination.

Question 18

Gold-standard ix for diagnosis

Answer 18

MRI scan (like in ACL)

Question 19

Management

Answer 19

Often treated conservatively with a knee brace and physio.

If they are still symptomatic they may require surgery with insertion of a graft.

If associated with other injuries like a meniscal tear or multi-ligament injury specialist knee surgery for reconstruction is often required.