Anterior Cruciate Ligament Injuries

The anterior cruciate ligament (ACL) is one of 4 major static stabilisers of the knee. It is primary function is preventing anterior (forward) translation of the tibia (shin bone) on the femur ( thigh bone). It also plays a secondary role with varus and valgus (sideways) and an important role in rotational stability.

Mode of injury


  • Valgus internal rotation deceleration injury.
  • Varus external rotation deceleration injury


  • Major valgus or varus forces( after medial or lateral collateral ligament has failed.
  • Knee dislocation or subluxation.

Who is at risk?

  • Athletes that participate in cutting sports like rugby, netball, football, tennis, alpine skiing, action cricket, etc.
  • Females are more at risk than male participants
  • There is a genetic link so the family history is important
  • Extreme sports like motocross, enduro motorbiking, kite boarding, etc.

Functional anatomy

The anterior cruciate ligament consists in the human knee of 2 definite bundles; anteromedial and postero- lateral bundles. The anterior cruciate ligament functions as secondary stabiliser to support the lateral (outside) and medial (inside) collateral ligaments. The posterior cruciate ligament prevents posteriorly (backwards) movement of the tibia (shin bone) on the femur (thigh bone) and forms a cross in the notch (middle of the knee between the 2 femoral condyles)

Grades Failure of ligament

Grade 1    mild sprain and ligament can recover full function
Grade 2     partial (one of the bundles) tear this form of tear is rare in ACL injuries
Grade 3    complete tear

Avulsion injury when bony attachment of the ACL on tibia fractures (breaks) off and is pulled away from its position. There is a small ligament in between the 2 menisci ( transverse ligament)which stops it from being displaced, but in some cases also stops reduction when it into position between the fragment and a host bone. This injury happens in 2nd and 3rd decades

Indications for ACL reconstruction

Hard indications

  • Multi ligament injuries
  • Associated meniscus injuries


  • High performance athletes
  • Participants in cutting sports

Soft indications

  • Recurrent feeling of instability
  • Prevention of meniscus injuries
  • To decelerate chondral cartilage deterioration.
  • To enable ability to do unicompartment knee replacement

Anatomic ACL reconstruction techniques

The results of ACL reconstructions by modern methods are improving all the time. There are many examples of high performance athletes that that returned to high demand sports at the highest level after ACL reconstructions. There is also a constant search for improvement in the results of this very common injury. The recurrence rate of ACL reconstruction failures, although less than 20%, is still a field of constant research. Substituting the ACL ligament with the patient’s own substitute tendon (hamstrings , quadriceps or patellar tendons) still gives the best results.

The key of this surgery is to use a graft of comparable strength to the negative ACL, anatomic placement of the drill holes in the bones, secure fixation and tensioning of the graft.

Doubling or tripling 2 hamstring tendons (semitendinosus and gracilis) provides a strong and long enough graft that is used and the majority of ACL reconstructions in the world these days. The middle 3rd patellar tendon with 2 cm bone blocks on each side was the original graft of choice and still gives excellent results. Quadriceps tendon with 2 cm patellar bone block also provides an excellent graft.

The only downside to using the patient’s own tendons (autograft) is donor site problems. Each of these particular graft materials has their own set of complications/side effects. Allograft (cadaver tendons treated to make it safe for reimplantation) and synthetic ligaments (LARS ligaments) do not give the same outcomes as autografts at this stage and is only used for salvage procedures.

Arthroscopic (keyhole) fibreoptic instruments and specially designed precise jigs allow surgeons to place the femoral drill holes accurately, whilst following the procedure on monitors.

The graft is harvested through small incisions, making rehabilitation quicker and minimising scars. An isolated ACL reconstruction can take less than 90 minutes. In most cases one night stay in the hospital and sufficient and the patient can mobilise safely. Partial weight-bearing with crutches and is usually required for 4 weeks.A structured rehabilitation program is followed and return to running at 6 months.

Integration of the graft is a biological process and return to cutting and contact sport is from 9-12 months. It is essential that the athlete/patient recovers full cross sense of position and 90% of the strength of the other leg before he or she can return to the chosen sport.

Frequently asked questions

Does ACL rupture=ACL reconstruction?

Isolated ACL rupture in sedentary patients can certainly be treated conservatively. It will mean an adjustment in sports participation and diligent conditioning of dynamic stabilisers of the knee. When there is associated injuries, (for instance MCL, PCL, posterolateral corner and meniscus injuries) then the ACL would need to be reconstructed. An untreated ACL injury in a growing child is also associated with a bad long-term prognosis.

Can ACL injuries be prevented?

here is certainly a higher incidence of ACL injuries with female athletes and certain sports, for instance netball and female soccer. A specific injury prevention program focusing on core stability, prevention of valgus knee movement on jumps and generalised hamstring conditioning/centralisation can prevent ACL injuries. Hamstring fatigue and loss of footing or too much grip of the shoes on playing surface are all factors that can lead to ACL being at risk. Wearing the correct shoe for each surface is also important. All young female athletes that participate in high risk sports, like netball in female soccer, should follow an ACL injury prevention program.

How is an ACL injury diagnosed?

There is usually a definite injury, forcing the athlete not to finish the match or training session. Often this injury is slipped of the foot or twist of the knee whilst changing direction. The knee swells up acutely in isolated ACL injuries. The swelling can subside quite quickly, but the knee will tend to buckle as soon as athlete returns to running. ACL is injuries also happen during high velocity injuries in extreme sports and motor vehicle accidents. There are 3 clinical tests, anterior drawer, Lachmann and pivot shift tests that helps with the diagnosis. Sometimes these clinical test can be difficult in very muscular patients or when the knee is still too painful. X-rays can have subtle bony injuries that are associated with ACL injuries (avulsion fracture or Second fractures) but the gold standard special investigation to diagnose ACL, and associated injuries, is the MRI scan

When is the right time for ACL reconstruction?

In most cases an isolated ACL ligament reconstruction can be staged, as long as the knees mobility and quadriceps and hamstring strength is maintained. There are special cases where earlier reconstructions will give with the results . When the lateral collateral LCL and posterolateral corner PLC (knee ligament complex at outside of knee) are also torn, the results with an accurate ACL, LCL and PLC reconstruction within 1 month achieve better results. ACL ligament injuries in combination with medial collateral ligament MCL also lead to better results. The ACL needs to be reconstructed when an associated meniscus tear is to be repaired. The only athletes fair better with an early ACL reconstruction, as long as the growth plates are respected. In a very young patient with an ACL ligament injury special care needs to be taken with bony drill holes to prevent early growth plate closure and stunted growth of bone.

Which graft option is the best?

Excellent results can be achieved with all 3 different autograft options (hamstrings, patellar tendon and quadriceps tendon) and there is no much to choose between the 3 options. Donor site morbidity plays a role in the surgeon’s decision which graft to select. Patellar tendon graft harvesting as a reported higher incidence of knee pain in the long run. Hamstring tendon harvesting, although strength returns to 100% within a year as a incidence of sprains and in certain studies a higher recurrence rate. Quadriceps tendon harvesting seem to have surgical scars issues and longer period of quadriceps atrophy. The contact sportsman and high demand patient certainly requires a lower recurrence rate and low donor site complications incidence.

Will I wear a brace after the operation?

A brace is only indicated when there is an associated injury, for instance meniscus repair, collateral ligament injuries or PCL reconstruction

What is the role of physiotherapy and biokinetics in ACL injuries?

Physiotherapists plate of important role in ensuring full range of motion and an exercise program to protect the knee before the index procedure and in the immediate 4 weeks following the surgery. Biokinetics is important from 5 weeks to 1 year when the athlete can return to his were chosen sport