Anterior cruciate ligament (ACL) tear

Question 1

What is the mechanism of injury in ACL tears?

Answer 1

acute non-contact deceleration injury,

forceful hyperextension,

or excessive rotational forces about the knee

Question 2

What are the clinical features of ACL tear?

Answer 2

• Audible pop
• Rapid knee swelling
• Inability to return to sports
• Sensation of knee instability or buckling
• Pain
• Tenderness at lateral femoral condyle, lateral tibial plateau
• Positive Lachman’s test
• Positive pivot shift maneouvre

Question 3

What are the risk factors for ACL injury?

Answer 3

• Acute trauma - hyperextension, valgus stress
• Female sex
• Hx of previous ACL injury
• Use of cleats or spikes - on grassy surfaces, increases risk of planting foot and twisting body without release
• Rough/uneven playing surface
• Poor weather conditions
• Fatigue
• Adolescent-middle aged atheletes

Question 4

What investigations are used to assess for ACL injury?

Answer 4

Usually diagnosed based on clinical findings alone.

XR - based on Ottawa guidelines for the knee incl any of: 1) inability to weight bear, 2) tenderness at patelalr or fibular head, 3) active flexion of knee <90, 4) age >55. Usuallly negative unless avulsion tear within capsule is present.

MRI - ACL fibres appear disrupted, blurry on T1-weighted images, with abnormal high signal on T2-weighted images

Arthroscopy - usually performed as part of reconstruction procedure

Question 5

What is the most accurate maneouvre for detecting acute ACL tear?

Answer 5

Lachman’s test is the most SENSITIVE test

Question 6

What is Segond’s fracture?

Answer 6

Sign on XR showing lateral capsular sign/Segond’s fracture = a small capsular avulsion off the lateral aspect of the proximal tibia.This is uncommon but virtually pathognomonic for ACL tear.

Question 7

What is the management of ACL tears?

Answer 7

Conservative

• PRICEM +
• Physiotherapy - to relieve pain and swelling, then to strengthen muscles and regain dynamic stability. May be done at home in those who are usually sedentary.

Medical

• NSAIDs

Surgical

• ACL reconstruction - only in some patients or those who are athletes; usually done 1-2 weeks after injury. Usually allows return to high-demand activities
• PRICEM acronym for initial management of ACL tear:*
• P = Protected weight-bearing exercise with crutches or crutch assisted with a knee immobiliser or similar brace. Avoid prolonged immobiliser use, as severe stiffness and discomfort can develop
• R = Relative rest
• I = Ice: useful for initial few days as helps minimise pain and swelling
• C = Compression
• E = Elevation
• M = Medicines (analgesics, NSAIDs as needed).

Question 8

What are the complications of ACL injury?

Answer 8

Short term:

• Bone bruising
• MCL injury
• Meniscal tear - occurs in up to 80% of ACL injuries
• Articular cartilage injury

Long term:

• Post traumatic arthrosis

Question 9

What is the prognosis with ACL tears?

Answer 9

No longer considered a career-ending injury for athletes and up to 90% can return to sports

Question 10

What is the ‘unhappy triad’?

Answer 10

• MCL injury
• Meniscal tear
• ACL injury

= often present together