Anterior Cruciate Ligament Reconstruction

Anterior Cruciate Ligament reconstruction surgery is very much a “function restoring” operation with the ultimate goal being to provide “functional stability” to the knee joint – that is, the ability of the joint to be trustworthy and withstand twisting / pivoting forces without buckling, collapsing or creating a sense that the knee wants to give way.

A decision about the need for ACL reconstruction surgery and the timing of surgery is made on a case by case basis. The severity of instability symptoms, the presence of additional injuries (meniscus tears), the desire to return to pivoting sports, age and occupation are all relevant factors and will be discussed with your surgeon. 

In general, people who are younger, more symptomatic or who also have significant meniscus tears are much more likely to require surgery. On the other hand, older office-working patients who injured their knee whilst undertaking “one off” sporting activities (e.g. – snow skiing), and who have no real symptoms of instability during their day to day lives may be able to live quite happily with their ACL deficient knee.

Operative Information

The surgical procedure of ACL reconstruction only differs slightly from surgeon to surgeon with the basic principles remaining the same. In essence, the surgery involves replacing the torn ACL ligament (which lies behind the kneecap in the centre of the knee joint) with a new ligament. The new ligament is securely affixed to both the femur bone (thigh bone) and tibia bone (shin bone) within the knee joint – the site of the new ligament mimicking the position and function of the natural ACL ligament.

Although it would seem logical to simply repair the torn ACL by sewing the ends back together, in reality, REPAIR of the ACL is not feasible: The ACL stretches prior to tearing and when it does tear the large release of elastic energy causes significant disruption to the ligament fibres. The ACL itself is mainly composed of longitudinally running fibres that sutures have poor ability to hold (imagine trying to sew a pony-tail back into place). Additionally, the internal environment within the knee joint is not conducive to healing.

Rather than REPAIRING the torn ACL, ACL Reconstruction surgery entails REPLACING the torn ACL with a new ligament – the ACL GRAFT. The most common graft is a “hamstring tendon graft” taken from the inner side of the same leg although a suitable donor graft can be obtained from other locations near to the injured knee. In certain situations, the graft can be obtained from the other leg or even from a tissue bank. Artificial grafts have been developed and trialled over many years, however their usefulness is limited due to issues of poor outcome and rejection.

The Hamstring Tendon graft is obtained via a small incision just below the knee at the inner aspect. Either one tendon (from the Semi-Tendinosus muscle) or two tendons (Tendons from Semi-Tendinosus and Gracilis muscle) are harvested and then prepared to act as the new ACL. The tendons are folded back and forward on themselves and then bound together to form a short, stout and strong replacement ligament. The graft is passed through the middle of the knee joint from a snug tunnel within the upper part of the tibia (shin bone) to a second tunnel within the lower femur (thigh bone). The locations of the tunnel openings inside the knee joint are the attachment sites of the original ACL, and in this manner the new ACL graft is able to anatomically replicate the injured ACL ligament. The graft is then appropriately tensioned and then secured into place within both the femur and tibia.

The majority of the surgery - the part that is performed within the knee joint itself, is performed via keyholes (using the arthroscope). This requires either 2 or 3 small incisions at the front of the knee joint. In addition, another small incision below the knee is required to obtain the hamstring graft and create the tibial tunnel. Some surgeons also utilise a small incision above the knee on the outside for creating the femoral tunnel.

Post Operative Period

The post-operative recovery is very important.  Many Orthopaedic Surgeons ask their patients to wear a limited range of motion brace for the first few weeks to avoid complete straightening of the knee. If a meniscus tear has been performed, bracing is likely to continue for the first 6 weeks.

Thereafter, intensive physiotherapy is required with a gradual reintroduction of usual social, recreational, domestic and work activities. It is important to note that the new graft not only needs to heal into place, but it needs to strengthen also. In the first few months following surgery, the graft actually loses some of its strength, but strength returns as new blood supply feeds into the graft and remodelling occurs.


Typical rehabilitation is comprised of 3 periods of 3-4 months duration each (total of 9-12 months minimum).

In the first 3-4 months, emphasis is on regaining range of motion of the knee, regaining a normal walking gait pattern and limiting loss of thigh/leg musculature through light resistance exercise. During this time, the ACL graft is at its weakest.

The second 3-4 month period allows for an increase in sporting activity to include straight line sports (road running, cycling), but no sports on uneven/unstable surfaces and no court or field sports that require pivoting or stepping.

In the final 3-4 months, athletes can resume cutting and pivoting DRILLS but should avoid competitive play and collision impacts. Emphasis at this stage is on regaining proprioceptive skill so as to avoid re-injury.

Return to normal sporting pursuits is usually delayed until 9-12 months. Return to sport assessment is recommended to be undertaken by the physiotherapist to ensure an appropriate degree of strength and dexterity is evident before this occurs.

Throughout the entire recovery period “Closed Kinetic Chain” exercises of the knee are emphasised and “Open Kinetic Chain” exercises avoided. Closed Chain exercises involve pushing force down through the sole of the foot (e.g. Stairmaster, exercise bike, wall squats) whilst open chain exercises involve a freely moving leg (e.g. swimming). The pattern of muscle recruitment as well as pattern of force placed across the knee (and the ACL graft) are seen to be more beneficial with closed chain exercises following ACL reconstruction surgery.