Anterior Cruciate Ligament (ACL) Rupture/ Deficiency

Keywords: Anterior Cruciate Repair, Mechanism of Injury, Physiotherapy, Special tests, Differential Diagnosis, ACL Repair, ACL Exercises and treatment.

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Clinically Relevant Anatomy

A torn ACL is an injury or tear to the anterior cruciate ligament (ACL). The ACL is one of the four main stabilising ligaments of the knee, the others being the Posterior Cruciate Ligament (PCL), Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL). The ACL attaches to the knee end of the Femur (thigh bone), at the  back of the joint (posterior)and passes down through the knee joint to the front (anterior) of the flat upper surface of the Tibia (shin bone)

It passes across the knee joint in a diagonal direction and with the PCL passing in the opposite direction, forms a cross shape, hence the name cruciate ligaments.

The role of the Anterior Cruciate Ligament is to prevent forward movement of the Tibia from underneath the femur. The Posterior Cruciate Ligament prevents movement of the Tibia in a backwards direction. Together these two ligaments are vitally important to the stability of the knee joint, especially in contact sports and those that involve fast changes in direction and twisting and pivoting movements. Therefore a torn ACL has serious implications for the stability and function of the knee joint.


Anterior cruciate ligament injuries are more frequent in females with between 2 and 8 times more females suffering a rupture than males, depending on the sport involved and the literature reviewed. The reason for this is as yet unknown, however areas of current research include anatomical differences; the effect of oestrogen on the ACL and differences in muscle balance in males and females.

Mechanism of Injury: A torn ACL or acl injury is a relatively common knee injury amongst sports people. A torn ACL usually occurs through a twisting force being applied to the knee whilst the foot is firmly planted on the ground or upon landing. A torn ACL can also result from a direct blow to the knee, usually the outside, as may occur during a football or rugby tackle. This injury is sometimes seen in combination with a medial meniscus tear and MCL injury, which is termed O’Donohue’s triad.

Characteristics/Clinical presentation

  • There may be an audible pop or crack at the time of injury
  • A feeling of initial instability, may be masked later by extensive swelling.
  • A torn ACL is extremely painful, in particular immediately after sustaining the injury.
  • Swelling of the knee, usually immediate and extensive, but can be minimal or delayed.
  • Restricted movement, especially an inability to fully straighten the leg
  • Possible widespread mild tenderness
  • Positive signs in the anterior drawer test and Lachman’s test (see assessment).
  • Tenderness at the medial side of the joint which may indicate cartilage injury.

Quick Diagnosis

History/ Symptoms

  • H/o valgus or hyperextension force to knee if contact injury.
  • Sharp change in direction in non contact injury.
  • H/o audible ‘pop’
  • H/o a quick stop, landing with knee fully extended
  • Severe effusion within 4-6 hours.

Objective findings
  • Joint effusion
  • Rarely isolated injury. look for meniscal injury.
  • Positive anterior instability tests.
  • unable to weight bear if knee slightly flexed.


General Advice for a patient

  • Immediately stop play or competition
  • Apply relative rest, compression and elevation.
  • Seek medical attention as soon as possible.


Health professional and Physiotherapy management.

Surgical Management

  • Surgery involves either repairing or reconstructing the torn ACL. With a repair, the exisiting damaged ligament is sutured (stitched) if the tear is in the middle. If the ligament has detached from the bone (avulsed) then the bony fragment is reattached.
  • Surgical reconstruction of the torn ACL is performed using either an extraarticular technique (taking a structure that lies outside the joint capsule such as a portion of the hamstring tendon) or an intraarticular technique (using a structure from within the knee such as part of the patellar tendon) which will replace the anterior cruciate ligament.


When is Surgery Required?

  • Surgery is performed more often than not following Anterior Cruciate ligament tears
  • The decision on whether to operate is based on a number of factors, including the athletes age; lifestyle; sporting involvement; occupation; degree of knee instability and any other associated injuries
  • Older people who are less active and perhaps injured their ACL following a fall as opposed to during sport would be unlikely to undergo surgery
  • A younger, fit person who regularly plays sport and would be more likely to adhere to a complex rehabilitation program is very likely to be offered surgery


How long will the athlete with a torn ACL be out of action?

  • This largely depends on your surgeon or physiotherapists approach to rehabilitation. Some therapists advocate an accelerated rehabilitation programme returning the athlete to full competition within 6 months, others prefer a 9 month rehabilitation period.
ACL repair patella graft

ACL repair Hamstring Graft (More commonly used)

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