Anterior Cruciate Ligament Injuries

Anterior cruciate ligament:

The anterior cruciate ligament attaches below and in front of the tibia; then, passing backwards, it attaches laterally to the inner surface of the lateral condyle of femur.

• Prevents anterior displacement of tibia on fixed femur
• Prevents femur from moving posterior  during weight bearing
• Stabilizes tibia against excessive internal rotation

MECHANISM OF INJURY

Occurs as a result of twisting force on a semi-flexed knee.

• O’Donoghue triad-  Injury to medial collateral ligament, medial meniscus and anterior cruciate ligament occur together. This is called O donoghue triad

Posterior cruciate ligament:

• It crosses from the back of the tibia and attaches to the to the anterior portion of the lateral surface of the medial condyle of the femur.
• Prevents posterior translation of tibia on fixed femur
• Prevents femur from moving anterior during  weight bearing

MECHANISM OF INJURY

• This ligament is damaged if the anterior aspect of the tibia is struck with the knee semi-flexed so as to force the tibia backwards on to the femur.

CLINICAL FEATURES

•  Swelling
• Loss of range of motion
• Pain or tenderness along the joint line
• Discomfort and unstable walking
• Patient may report having felt a pop, tear, or snapping sound

DIAGNOSIS

Clinical examination:

• Pain at the site of the torn ligament and/or an abnormal opening up of the joint indicate a tear. Cruciate ligaments prevent anterior-posterior gliding of the tibia. The anterior cruciate prevents anterior glide, and the posterior cruciate prevents posterior glide. This property is made use in detecting injury to these ligaments.

• Lachman test:

This is the most reliable diagnostic sign of a rupture of the ACL.

The test is performed with the knee flexed at 30 degrees, and the hamstrings relaxed. The examiner assesses the amount of anterior translation and the presence or absence of an endpoint compared to the opposite knee

• Anterior drawer test:

This is a test to detect injury to the anterior cuciate ligament.

•  Posterior drawer test:

This is a test to detect injury to the posterior cruciate ligament. A posterior sagging
of the upper tibia may be obvious, and indicates a posterior cruciate tear.

Radiological examination:

• A plain X-ray may be normal, or a chip of bone avulsed     from the ligament attachment may be visible.
• A Segond fracture, seen on an AP x-ray (lateral capsular sign) is a capsular avulsion from the lateral tibial metaphysis that is highly associated with ACL disruption.
• MRI is a non invasive method of diagnosing ligament injuries, and may be of use in doubtful cases.

 Other investigation:

• Arthroscopic examination may be needed in cases where doubt persists.

A patient with acute knee hemarthrosis may have sustained: (i) an intra-articular fracture of femur, tibia or patella; (ii) ligament injury; (iii) meniscus tear and (iv) patellar subluxation or dislocation.

TREATMENT

Treatment of ligament injuries is a controversial subject. Conventionally, these injuries have been treated by non-operative methods. With availability of newer techniques, better results have been achieved by operative reconstruction. Therefore, operative treatment has become more popular in high demand athletic individuals, particularly for anterior cruciate ligament tear.

Conservative method:

• The haematoma is aspirated and the knee is immobilised in a cylinder cast or commercially available knee immobiliser. .
• After a few weeks, the swelling subsides, and adequate strength can be regained by physiotherapy.

Operative methods: These are indicated, in young atheletes. The operation is usually performed 2-3 weeks after injury after the acute phase subsides. It consists of the following:

Reconstruction: This is done in cases of ligament injuries presenting late with features of knee instability. A ligament is ‘constructed’ using patient’s tendon or fascia lata. A tendon or fascia taken from another person (allograft) or a synthetic ligament has also been used.

The treatment depends upon activity level of the patient.

• For a patient with sedentary lifestyle, adequate stability is achieved with physiotherapy alone.
• In active patients, ligament reconstruction is necessary. The ACL is the commonest to be ruptured.
• The treatment of choice is arthroscopic ACL reconstruction. In this, the torn ligament is replaced with a tendon graft. This is done endoscopically (arthroscopic surgery), without opening the joint.
• The joint is first examined by a 4 mm telescope (arthroscope). A tendon graft taken from patellar tendon or hamstring tendons is introduced into the knee through bone tunnels.
• The graft is fixed at both ends with screws or other devices. Bio-absorbable screws are now being used.
• Arthroscopic surgery has advantages of being minimally invasive, and results in quick return to function with minimal risks.

COMPLICATIONS

1.  Knee instability: An unhealed ligament leads to instability. The patient ‘loses confidence’ on his knee, and the knee often “gives-way”. Surgery is usually required.

2.  Osteoarthritis: A neglected ligament injury may result in further damage to the knee in the form of meniscus tear, chondral damage etc. This eventually leads to knee osteoarthritis