Anterior Cruciate Ligament Injury

Anterior Cruciate Ligament Injury

Ligaments are tough fibrous bands that hold the bones together in a joint. The anterior cruciate ligament (ACL) is one of a pair of intracapsular ligaments that hold the upper and lower leg bones together in the knee joint. It is called cruciate because along with its counterpart it forms a cross (X) in the middle of the knee joint. It runs from the outer back of the knee end of the femur (the thighbone) to the inner front of the joint surface of the tibia (the stronger lower leg bone).

Jerky movements, sudden starts and stops, as well as sideways running or hopping, can all lead to an ACL injury. Soccer, tennis, basketball players and skiers are most at risk of acquiring ACL injuries, especially females. The reason behind the higher incidence of ACL injuries in females is yet unclear; however, anatomical differences and hormonal influence are suspected to be factors.

How the injury occurs:

A direct impact such as an accident or a bad collision during contact sports may cause tearing of the ACL; however, the cause is most often suddenly slowing down and rotating the knee at the same time (to change direction), landing on a twisted or outward extended knee, knee hyper extension, etc.


  • A popping sound may signal the ligament injury at the time of the incident.
  • There is a sudden onset of moderate to severe pain on the back and outside of the knee
  • The joint feels wavering and unstable
  • Placing weight on the affected leg aggravates the pain
  • Swelling develops soon thereafter and limits joint movement

An acute injury may convert to a chronic problem, referred to as Chronic ACL Deficiency. The knee joint is unsteady, as the ACL is unable to play its role in holding the leg bones together and controlling the movement at the joint. The knee gives way under load; this abnormal pattern of movement may damage adjacent joint structures such as the cartilage covering the joint ends of the bones, and may predispose to bone inflammation (osteoarthritis).


Several orthopaedic tests are used for definitive diagnosis such as the Lachman test, Anterior drawer test and Pivot shift test.

The Lachman test is considered the most reliable diagnostic test. With the patient lying supine on the table, the examiner pulls the lower leg anteriorly, keeping one hand on the thigh. This gives the relative anterior shift of the lower leg bone, which in the case of a damaged ACL is 2 mm or more.

Lachman test (an exaggerated view on the right to explain the test)

In addition, MRI and ultrasound are helpful diagnostic aids in determining the extent of damage to the ligament and other structures involved (this has a strong bearing on the treatment planning and prognosis).

X-rays help to locate any broken bone fragments as well as bleeding in the joint space.

It is imperative to evaluate the integrity of other joint ligaments and associated structures.


The first line of treatment includes:

  • Immediate cessation of physical activity, no weight bearing on the affected side
  • Support and elevate the affected leg.
  • Apply ice packs to reduce pain and swelling.
  • Take painkillers if required.
  • Seek medical help.

Treatment depends on the extent of injury as well as the extent to which a person is involved in sports, a person’s age, activity level and general physical health.

The main aim of the treatment is getting rid of the pain, restoring joint function back to normal and preventing progressive damage to the joint structures

About six to nine months of rehabilitation is required for complete recovery.

Conservative Treatment involves

  • Supporting the joint with the help of crutches or a knee brace
  • Physiotherapy, to improve range of movement at the joint, as well as to strengthen the muscles responsible for mobilising the joint (the hamstrings and quadriceps). Strong adjacent muscles help improve stability of the joint and may compensate for the loss of ACL efficiency.

Conservative treatment works well for elderly and people with a sedentary lifestyle. However, for young patients, particularly those involved in sports and other rigorous activities, working without an intact ACL may be quite problematic, thus in such cases surgery is often recommended.

Surgical treatment involves:

    • Repairing the ligament by

– Suturing the torn ends together or
– If the ligament’s bone attachment has been severed, fixing the ligament along with the detached bone fragment to its original location.

  • Reconstructing the ligament by using part of the adjacent tendons such as the hamstring tendon or patellar tendon, this replaces the damaged ACL.

ACL injury increases the risk of developing osteoarthritis of the knee in the future, characterised by pain and stiffness of the joint. Proper training to reduce the load on the ACL is the key to preventing ACL injuries in sportspersons.