ACL Tear Flashcards
What is the function of the anterior cruciate ligament (ACL)?
The ACL is an important stabiliser of the knee joint, being the primary restraint to limit anterior translation of the tibia (relative to the femur) and also contributing to knee rotational stability (particularly internal).
Briefly describe the anatomy of the ACL
Attaches at the anterior intercondylar region of the tibia where it blends with the medial meniscus. It ascends posteriorly to attach to the femur in the intercondylar fossa. It prevents anterior dislocation of the tibia onto the femur.
How do the majority of ACL tears occur?
An ACL tear typically occurs in an athlete with a history of twisting the knee whilst weight-bearing.
What are the clinical features of an ACL tear?
The majority of ACL injuries occur without contact and result from a sudden change of direction twisting the flexed knee. The patient is usually unable to weight bear.
An ACL tear will typically present with a rapid joint swelling and significant pain. If the presentation is delayed, instability may also be evident, in which the patient describes the leg ‘giving way’.
The specific clinical tests that can identify potential ACL damage are the Lachman Test and Anterior Draw Test.
Briefly describe Lachman’s Test
Lachman’s test involves placing the knee in 30 degrees of flexion and, with one hand stabilising the femur, pulling the tibia forward to assess the amount of anterior movement of the tibia compared to the femur. The other knee is then examined for comparison.
Briefly describe Anterior Draw Test
The anterior draw test involves flexing the knee to 90 degrees, placing the thumbs on the joint line and their index fingers on the hamstring tendons posteriorly. Force is then applied anteriorly to demonstrate any tibial excursion, which is then compared to the opposite site.
Which test is more sensitive Lachman’s or Anterior Drawer?
Lachman’s test is the more sensitive of the two tests for an ACL tear.
What investigations should be ordered for ACL?
A plain film radiograph of the knee (AP and lateral) should be taken to exclude bony injuries, any joint effusion or a lipohaemarthrosis present. A Segond fracture (bony avulsion of the lateral proximal tibia) is pathognomic of ACL injury.
An MRI scan of the knee is gold-standard to confirm the diagnosis (>90% sensitivity), also picking up any associated meniscal tears.
How common is meniscal tears with ACL injury?
50% of ACL tears will also have a meniscal tear, with the medial meniscus the more commonly affected.
Briefly describe the consetvative management of ACL tear
As with any acutely swollen knee, the immediate management of a suspected ACL tear is RICE (Rest, Ice, Compression and Elevation).
Conservative treatment involves rehabilitation, which utilises strength training of the quadriceps to stabilise the knee.
In the emergency setting, inpatient admission is rarely required; the patient can often partially weight bear and a cricket pad knee splint can be applied for comfort.
Briefly describe the surgical management of ACL tear
As with any acutely swollen knee, the immediate management of a suspected ACL tear is RICE (Rest, Ice, Compression and Elevation).
Surgical reconstruction of the ACL involves the use of a tendon or an artificial graft. This is not performed acutely but following a period of ‘prehabilitation’, whereby the patient will engage with a physiotherapist for a period of months prior to the surgery.
Acute surgical repair of the ACL is possible in some cases dependent on the location of the tear within the ligament. If the imaging on MRI is favourable, the patient can be further assessed under GA knee arthroscopy, proceeding to an acute repair where possible, which involves re-suturing the ends of the torn ligament together.
What are the complications of ACL tear
Post-traumatic osteoarthritis is a well-established complication of both ACL injury and ACL reconstructive surgery.
What differentials should be conisdered for an ACL tear?
Differential diagnoses for a patient with an anterior cruciate ligament injury include proximal tibial or distal femur fracture, a meniscal tear, collateral ligament tear, or a quadriceps tendon or patellar ligament tear.
