The Knee Anterior Cruciate Ligament

The Knee – Anterior Cruciate Ligament

What is the Anterior Cruciate Ligament?

The Anterior Cruciate Ligament (ACL) is one of four main stabilising ligaments in the knee that is placed deep within the knee joint. It passes proximally to distally from the posterior aspect of the femoral notch and inserting anterior to the intercondylar notch of the tibia with some attachment to the anterior horn of the lateral meniscus (cartilage).

What does the ACL do?

 The ACL has two main functions in the knee:

1.     It provides approximately 85% of the total restraining force of the tibia travelling forwards under the eemur.

2.     It assists with preventing excessive rotation of the tibia under femur, both medially and laterally.

To a much lesser degree, the ACL can help its counterpart, the Posterior Cruciate Ligament (PCL), to check extension and hyperextension of the knee joint. In combination, the ACL & PCL are the deep control of internal centre of rotation of our knees.

The surrounding muscles of the thigh and lower limb help to reduce the loading on the cruciate ligaments so they can happily support the knee in the background. In particular, good functional strength of the deep pelvic rotators, gluteals, hamstrings, quadriceps and calf muscles is essential.

How does the ACL get injured?

Most ACL injuries occur in a sporting environment when the athlete suddenly stops and changes direction or lands heavily from jumping, with the knee in a valgus position (collapsing to the inside). Women are at higher risk of damaging their ACL during sport, believed to be a result of their slightly different anatomy, muscular strength and muscle reaction times.

What happens next?

Clients can be given 2 choices for treating a damaged ACL – conservative or surgical reconstruction.

This decision is largely based on the following:

1.     The extent of the injury

2.     The client’s lifestyle

3.     The expected outcome of surgery

A MRI scan is the investigation of choice for someone who suspects they have damaged their ACL. Following confirmation of the extent of their injury – whether a partial tear or complete rupture of the ACL – their specialist will help determine if surgical intervention is required. Often, if the client has significantly torn their ACL and their lifestyle or professional sport relies heavily on a stable rotating knee then there is no question that surgery is indicated.

However, if the client is happy to modify their lifestyle, avoiding where possible any repetitive, heavy rotational loading on the knee, then conservative management of the injury is acceptable.

In surgical cases, clients have 2 options of reconstruction;

1.     A bone patellar tendon graft (BPTG)

2.     A hamstring graft (HG)

The BPTG reconstruction involves removing the middle third of the patellar tendon (often from the injured side) by detaching a piece of bone from the inferior pole of the patella + the middle third fibres of the tendon itself + a piece of bone from the tibial tuberosity where the tendon inserts. This is then inserted in place of the extracted ACL.

Clients who need to kneel frequently during the day would not be suitable for this type of graft as the bony attachments of the patellar tendon can often remain sensitive to touch for several months. There is also a higher incidence of anterior knee pain in this population post surgery.

In these cases, the hamstring graft is preferred where there is minimal impact to the anterior aspect of the knee joint. The graft in this case is harvested from two of the tendons of the hamstring complex, most commonly the semimembranosus and/or semintendinosus on the medial aspect. They are then folded over and entwined to create the new ACL.

Clients in this case can be susceptible to future hamstring injuries if a concise rehabilitation programme is not followed.

Rehabilitation of an injured or reconstructed ACL

Rehabilitation of the injured or reconstructed ACL is a specialist field and whilst Pilates teachers are in a good position to train clients on ideal exercises for this area, there is an expertise required to monitor the client’s progress closely, knowing when is best to progress and best to ease off. The initial rehabilitation is therefore usually prescribed by a qualified Physiotherapist.

Pilates and ACL injuries

Following a comprehensive pre-, post-surgical or conservative programme of ACL rehabilitation, clients may present wanting either more rehabilitation or having limited their activity as a result of the injury.

Pilates would be great for this population and in particular, addressing any imbalances that they have acquired in the torso, upper limbs and lower limbs during their injured phase. Particular focus should be paid to proprioception of the affected side, so work in standing is of great benefit. Increasing the client’s awareness of their knee without them having to look at it can help to prevent future problems.

Working in the studio environment on the reformer or wunda chair from a good functionally stable trunk using exercises to further strengthen any of the supporting thigh and lower limb muscles can also provide great improvement.

As with any rehabilitation, Pilates taught well will rapidly improve the client’s own body awareness and this itself will help prevent future problems.