In the first five parts of this tutorial, I went over the function of the ACL, how it may become injured, the management in the first 24 hours, and the first visit to the clinician.

I highlighted the point that not all ACL tears lead to surgery.

So at this point it becomes a little bit more complicated to talk to you. Some of you will already have progressed to surgery, but I still need to explain to those who have not some general principles with regard to rehabilitation following that first visit to the doctor. If you have already had, or are just about to have, ACL reconstruction you will be given specific exercise protocols to follow - so we will not cover that in this tutorial.

Before we get down to the nitty gritty of specific exercises lets look at the principles behind them and the importance of working through various stages.


Reduction of swelling

Following injury this is the first step - a swollen knee restricts movement and has an inhibitory effect on the muscles. You can do lots of exercises but will not progress while the knee is swollen and prolonged swelling can lead to adhesion formation with resultant stiffness.


Range of movement

Any restriction of normal movement will affect return to normal function. The longer a knee remains restricted, the harder it is to regain the movement. The old adage 'if you don't use it, you lose it' certainly does apply to joint movement therefore gradually increasing range, once inflammation has settled down, is important. Swelling in a static knee is the environment in which adhesions form within the joint - if these are allowed to develop and mature they can become very tough and difficult to stretch out at a later date.



Muscles are your joints' first line of protection, so good muscle control is important if joint stability is to be achieved. Strengthening exercises have to be progressed steadily and must be staged so that they do not aggravate the knee or put you at risk of further injury by being too aggressive too soon.

The quadriceps , on the front of your thigh, is a large group of muscles responsible for straightening the knee, and for holding you upright against gravity. They also act as decelerators when doing running and jumping type activities. They are a powerful group of muscles and are important for normal function of the joint. This is putting things rather simply but basic exercises to maintain some level of activity in the muscles is needed from day 1 after injury. This may amount to nothing more than damage limitation as far as muscle wasting is concerned but nevertheless is valuable. The type of exercises performed for the quadriceps is relevant therefore please read the section explaining the 'open and closed kinetic chain' concept.

The hamstrings , on the back of your thigh, are another large group of muscles responsible primarily for bending the knee (they also pass across the back of the hip and help to extend it). The hamstring muscles cross the back of the knee and attach to the bones just below the joint, they have a tendency to hold the tibia back in relation to the femur and thus reinforce the action of the ACL. It therefore follows that strong hamstring muscles will help to stabilise the knee in the absence of the ACL.

The calf, hip and trunk muscles can also become weak very quickly if you have a period of inactivity. It is important to re-establish strength in all muscle groups for the return of normal function.



This is a big word referring to the body's ability to produce balanced, co-ordinated movement, to have spatial awareness and to react to altering conditions.

Ligaments and other soft tissues around the joint have special nerve endings within them, which are responsible for telling the brain where you are in space - if you hold your arm out to the side, you know exactly where it is even though you are not looking at it - it is these proprioceptive nerve endings which are responsible for providing this information.

If you damage a major ligament then information from that source will be lost - specific exercises which encourage balance, co-ordination and reaction will help to sharpen up the responses in the surrounding structures, thus minimising the effect of the lost ligament.


Kinetic Chain Exercises

Physiotherapists talk a lot about kinetic chain exercises. The terminology that we use has been hijacked from engineering but in our context the 'kinetic chain' is referring to a series of joints - in our case the hip, knee and ankle. The kinetic chain is referred to as being either 'open' or 'closed' during various exercises and this does have significant relevance for ACL injured or deficient knees.


Open chain exercises

In an 'open' chain exercise the terminal part of the chain (the ankle or foot) does not meet any resistance and is free to move in space, thus movement is only occurring at one joint and, essentially, only one muscle group is working. Let's look at a few examples...


This is an example of an open chain hamstrings exercise. While the hamstrings musce (back of thigh) is working, the foot is not making contact with any surface.
This is an example of an open chain quadriceps exercise. Resistance has been applied in the form of ankle weights, but when the quadriceps muscle is contracting (front of thigh) the foot is not in contact with any surface.


In both of these examples the foot is free - actual joint movement is only occurring at the knee and consequently only one primary muscle group is active.


Closed chain exercises

Conversely, during a 'closed' chain exercise the foot is in contact with some form of resistance, be it the floor, the pedal of a bike or the plate of a leg-press machine. This means that movement is occurring at all three joints and there is 'co-contraction' of various muscle groups including both the quads and hamstrings.


step ups Here are two different examples of closed chain exercises - step-ups and the static bike
static bike In both of these examples you can see that movement is occurring at the hip, the knee and the ankle. During the step-up the hamstring muscles work to extend the hip and the quads work to extend the knee.


Why is this significant?

We have already discussed the fact that the hamstring muscles pass down the back of the thigh and attach to the top of the lower leg bones, thus tending to hold the tibia back in relation to the femur. Conversely, the quadriceps pass down the front of the thigh and have a tendency to pull the tibia forwards in relation to the femur, particularly in the range of movement from 30 º of flexion to fully straight.

In normal circumstances this 'tibial translation' is controlled by the cruciate ligaments however, if the ACL is damaged, there is nothing to prevent excessive anterior (forward) translation of the tibia when the quadriceps work in isolation (open chain exercise). Working the quadriceps in conjunction with the hamstrings, as in closed chain exercise, allows good strengthening without causing undue translation, as the hamstrings will counteract the tendency for the tibia to be pulled forwards.

Why is excessive translation undesirable?

All joints have a certain amount of play in them, this is termed 'accessory movement' and is usually controlled by ligaments and other soft tissues around the joint. Accessory movement is not voluntary however, damage to the controlling soft tissues can result in gross accessory movement accompanying voluntary movement and this often causes the feeling of instability or giving way.

In the absence of a controlling ligament there is increased accessory movement, this is ultimately limited by other soft tissues around the joint. Over a prolonged period of time these secondary restraints can become stretched.

Continuous increased movement can also lead to secondary damage to other structures which have undue stress placed upon them. The menisci in the knee become more vulnerable to injury and the articular (hyaline or joint surface) cartilage may become damaged by increased wear.

ACL deficient knees are likely to have increased anterior tibial translation and increased rotation (twisting) in the knee and it is commonly during activities which involve twisting that instability is felt.