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Patient Info

Cruciate Ligaments

The anterior cruciate ligament (ACL) is a major ligament within the knee that connects the femur and the tibia and is very important for the stability and function of the knee. It is a fascinating mechanical stabiliser. Composed of collagen, it has 2 main functional bundles. An intact ACL opposes excessive translation between the femur and tibia in the anterior to posterior (front to back) direction and it also has a critical role in stabilising rotational movement. Activities which involve changing direction or pivoting are most reliant on having an intact ACL. Really when you think about it, this is most sports and leisure activities.

ACL rupture is a common injury both in the sporting population, and also in the general community. It usually involves a deceleration – type injury with a rotational (or pivoting) force. The foot on the injured side is usually taking most of the weight at the time of injury, with the knee loaded. Then it`s just simple mechanics – if the forces or energy of the injury outweigh the tensile strength of the ACL, it will rupture. Sometimes other structures in the knee are injured also. A very common pattern of injury involves a sideways (valgus) force and pivot – causing an injury to the medial collateral injury also. (See the section on collateral ligaments). Sometimes the cartilage ‘shock absorbers’ (the menisci) are torn also. (See the section on meniscal injuries).

This injury is commonly seen during sport but not exclusively. Patients will recall a sharp burst of pain in the knee, sometimes associated with an audible ‘pop’ or ‘snap’ at the time of injury, and are usually unable to play on. The knee becomes swollen quickly. Active patients with an ACL-deficient knee experience instability and ‘giving way’. Often, there will be the feeling of not being confident with the knee, leading to avoidance of certain activities or a lack of participation. The diagnosis is made with a careful history and a clinical examination. X-rays are taken to exclude a fracture and an MRI is arranged to confirm the injury and any other injuries that may be suspected.

Treatment of ACL Injuries

Not everyone with an ACL rupture needs it fixed. Older, less active patients can function very well without pain with a chronic ACL tear. However, for most people coming to the clinic, an ACL reconstruction is performed.

The surgery is performed arthroscopically (key hole). It simply involves replacing the torn ACL with a substitute ligament graft taken either from the hamstrings tendons or patella tendon. Each has their own merits. The new ACL is passed through drilled tunnels in the distal femur and proximal tibia and fixed at each end. ACL reconstruction is a very common operation and as you would guess, there are many different variations on the same basic technique. Presently, our most common procedure is using a hamstring graft looped over a small metal pin at the top end and fixed with a screw at the bottom end. This technique has produced excellent results.

  • Ruptured anterior cruciate ligament
  • Reconstructed ACL with a hamstrings graft

The surgery takes about an hour, and patients go home the next day. Follow-up appointments are made for progress checks at 2, 6, and 12 weeks. Post – op rehabilitation follows a simple program which is supervised by a physiotherapist. Typically patients are back to running at the 3 month mark.

Graft choices

Hamstrings graft

This technique involves making a small incision on the front of the knee where the hamstrings tendon inserts. 2 of these tendons (semitendinosis and gracilis) are lifted up from their insertion and a length of graft is taken from each. The two tendons are then fashioned into a four bundle new ACL ‘ligament’. A quadruple hamstrings graft is actually stronger than your native ACL.

Patella tendon graft

Using this graft involves making a small incision over the front of the knee to expose the tendon joining the knee cap to the tibial tuberosity. A midline central third of the patella tendon is taken along with small bone blocks at each end. The bone blocks are fixed at each end with a screw in the femoral and tibial tunnels with the new ligament in between. There is bone to bone healing in the tunnels which may be an advantage. The bone-patella tendon-bone graft is actually the strongest construct – however, some patients may experience patellar tendonitis and anterior knee pain which may take some time to settle after the surgery.

Synthetic ligament reconstruction?

A word of caution – recently there has been intense interest in newer synthetic ligament reconstructions. This has been driven by some ‘high profile’ surgeries, the media, the orthopaedic industry, and some surgeons. Interestingly, the use of synthetic ligaments has been tried before and are part of the history of ACL reconstruction, dating back to the 1980s. Unfortunately for many patients, they were atrocious operations with unacceptable failures and synovitis. It is claimed that the newer materials circumvent some of these problems, which if true is great – and some authors are reporting some encouraging very early results. As yet however, no long term studies have proven that their use is any better than what we are doing already. My own philosophy is that currently a synthetic ligament has some appeal in the ‘elite athlete’ or as a ‘last resort’ but is still largely experimental. But watch this space!!! As the evidence unfolds things may change.

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