Anterior Cruciate ligament injuries

What is the Anterior Cruciate Ligament (referred to as ACL)?

The anterior cruciate ligament (ACL) is the most commonly disrupted ligament in the knee. Our understanding of this ligament and our recognition of its importance to knee stability has increased greatly over the past 10 years. Along with this our ability to diagnose and treat this injury has substantially improved. As a result an injury which might have once spelt the end of a sporting career can now be viewed much more optimistically.

What is the function of the ACL?

The anterior cruciate ligament is a major and important ligament in the knee which is commonly injured. Treatment depends on the age of the patient, the exact nature of the injury, the nature of any associated injuries, the lifestyle of the patient and their future sporting aspirations. In those patients who are willing to alter their lifestyle a rehabilitation programme may be adequate, but for the keen athlete who is wanting to return to twisting and turning sports a reconstruction may be the better alternative. With the advent of better operative procedures to reconstruct this ligament the problems that used to be associated with this form of surgery are less common and the function results are better. In general 90% of those undergoing reconstruction will be able to return to their previous sport and more than 70% will be able to compete at their previous level.

Nowadays an inability to return to sport at the pre injury level is rarely due to loss of the anterior cruciate ligament with reconstruction of that ligament being generally successful. Rather it is more usually due to unrepairable damage caused to other parts of the knee at the time of this initial injury or in subsequent injuries.

The normal anatomy of the knee can be defined as the following;

The cruciate ligaments and the collateral ligaments (at the side of the knee) provides stability to the joint by holding the bones together. of these ligaments, the anterior cruciate is important in that it holds the knee together during twisting type activities.

During everyday walking and in straight line running, the ACL is hardly used. As soon as any twisting is performed however, this ligament is essential. It is the feeling of coming apart that gives rise to the instability or loss of confidence in the knee that is seen when the ACL is torn. If major, it may occur in everyday activities however, in some it occurs only during training or sporting activities.

What are Meniscal Cartilages?

The menisci (meniscal cartilages sometimes known as the cartilages) function as fillers to spread the load between the surface of the femur (thighbone) and tibia (shinbone). They primarily function somewhat like shock absorbers but they also have a secondary role to enhance lubrication and nutrition of the articular or lining cartilage and do have a part to play in stability of the knee. Loss of the meniscus (particularly the lateral (outer) 1) leads to a poor spread of weight across the joint surface. This means that loads are taken over small areas of the joint and hence pressures are higher causing increased rates of wear of the lining surface. I.e. osteoarthritis.

What are Articular Cartilages?

This covers the ends of the bones of the knee joint and allows for its smooth movement. It is shiny, white, ultra low friction tissue that acts as a bearing surface for the joints. It is very different from the meniscal cartilages and is the most delicate and essentially irreplaceable structure within the knee. Injury to the lining can be treated by debridement which is a process of removing loose fragments and smoothing the remaining damaged surface. The body attempts to repair these areas with a scar like tissue though this does not have the same properties as the original articular cartilage and in essence it is this damage to the bearing surface of the knee that starts off the progressive process known as osteoarthritis. Newer techniques are becoming available which aim to regenerate the articular cartilage and these at the present stage are experimental and are only suitable for certain defined lesions.

How do injuries to the ACL occur?

Injuries to the ACL occur most often in athletic activities (especially twisting and turning sports such as football and rugby), but maybe ruptured in work injuries and non athletic activities. The injury can occur without contact and is often associated with a sudden change in direction (eg side stepping) or a sudden change in speed (a deceleration or slowing down injury). It may also occur with the body falling over a fixed leg or with a hyperextension (over straightening) injury to the knee.

How will I know if the ACL has been injured?

At the time of the injury, the individual will often hear a pop or a snap or experience a sensation of tearing inside the knee. The knee then swells, almost immediately, because of bleeding from the vessels and the torn ligaments. Generally the injured person finds any attempt to weight bear is difficult because the knee feels unstable. The immediate feeling of instability is due not only to the loss of the ligament but also to a loss of the nerve fibres within that ligament. These nerves provide a sense of where the joint is in space which is called proprioception. Loss of that sense causes a loss of sensation on how bent the joint is, how fast it is bending and so on. Without that knowledge there can be no active feedback to the muscles that move the knee or the muscles that protect the knee and hence control of the joint maybe lost leading to a feeling of instability or loss of confidence.

With time the feeling of proprioception improves and this is because the nerve fibres in other ligaments attempt to compensate. This situation is never quite as good as prior to the injury but if demands on the knee are low it maybe sufficient to cope.

What happens once this injury has occurred?

After the injury there is sudden loss of control of the knee which gradually returns and in most people it takes about 2 months to the level where they can think about playing sport again. If by that time however, full confidence in the knee has not been restored then it is unlikely that the knee will be able to perform a twisting turning sport again without reconstruction. If a return to those sports is made whilst the knee is still unstable then a repeat injury is likely and every time the knee gives way there is the chance that more damage can occur particularly to the meniscal cartilages and articular cartilage which increases the likelihood of developing osteoarthritis in the future. Because of this risk it is now considered preferable to reconstruct the unstable knee to prevent any episodes of giving way.

In general patients with ACL injuries may be divided into three roughly equal size groups. The first group contains people who do well and return to their sport without too much trouble. However, it must be emphasised that reconstruction should be seriously considered even if there is only one further episode of giving way to try and prevent as previously mentioned.

The second group contains people who seem to do well until they attempt to play a demanding sport. They may even do well at training but on taking to the field a re-injury soon occurs. If they are prepared to give up sport an alter their lifestyle then reconstruction may not be necessary though for people wanting to play these sports even at low levels reconstruction is recommended.

The third group contains people whose knees feel frankly unstable in everyday life. This group almost uniformly requires surgery to give their knee a feeling of stability. That stability then protects against further injury and damage to the knee.

Which group would warrant surgery?

Overall it may be seen that a large number of people who injure their ACL might eventually benefit from surgery. The exact number is uncertain but currently it is thought that some 50% or more would be helped. This is somewhat age dependent and the requirement for surgery does decrease with age and this is not only because the demands placed on the knee also decrease but it appears that the ability to cope with proprioceptive loss improves with age. There is no age limit for this type of surgery. Clearly it is related to general health, level of activity and feeling of instability.

Those who sustain injuries to other ligaments of the knee in addition to a tear of the ACL and are more likely to fall into the third group i.e. requiring surgery.

Tears of the meniscal cartilages are commonly associated with ACL tears. A meniscal tear may be excised (removed) or occasionally may be suitable for repair. This can often only be determined at the time of surgery. If the cartilage is to be repaired then ACL reconstruction should be considered as the failure rate of meniscal repairs in an unstable knee is unacceptably high.

Can it be treated without surgery?

Treatment for injuries of the ACL cannot be standadised because of individual difference in injury patterns and because of different expectations of patients in regard to returning to sporting activities. In the patient who sees sport purely as recreation and would consider giving it up if it meant that an operation could be avoided a hamstring re-education and rehabilitation programme may provide a satisfactory knee for everyday use. This type of exercise programme however, is not a substitute for ACL reconstruction because the ligament itself never heals. What it achieves is better control over the knee by improving strength and improving the feedback from the other ligaments (proprioceptive training). Given adequate provocation however, the knee may still give way and further injury may occur. Recurrent giving way needs to be avoided as if these episodes are associated with pain and swelling and are frequent then the knee will develop progressive wear and tear arthritis (osteoarthritis). Patients in this situation need to either consider the option of surgical reconstruction or to change the demands that they are placing on the knee.

What does ACL Reconstruction involve?

Reconstruction of the ACL is a complex surgical procedure and there are many different ways for it to be performed. The preferred method at this time is to use a portion of tendon from elsewhere in your body as a graft. In the majority of cases this means using one of the hamstring tendons on the inner aspect at the back of the knee but other tendons can be used. Artificial ligaments have been used but have a tendency to early failure.

The technique for reconstructing the ACL has improved significantly in recent years and can now be done in an arthroscopically (through a telescope) aided manner. However, this does not mean that there are no incisions as the graft still has to be taken in a standard open type manner. The knee joint itself however, is usually not opened as all the work in the joint can be done via the arthroscope. This generally causes less pain and a shorter hospital stay and allows for earlier and often easier rehabilitation.

Reconstruction of the ACL is now an everyday procedure thanks to the very major advances in instruments and techniques that have occurred over the last 5-10 years. Patients are in hospital for 1 or at the most 2 nights and generally no brace is required except in the immediate post operative period. Crutches are necessary for about 2 weeks though as long as the range of motion is being maintained it does not matter if you prefer to stay on crutches for a few weeks and they should certainly be used on long walks, on uncertain ground or in places where the knee may be at risk. Once motion has been regained the next priority is to get all the swelling out of the knee and this generally takes about 6-8 weeks. By this time most people can walk with only a minimal limp and your rehabilitation will be supervised by a physiotherapist.

When first put into the knee, the graft itself is dead. Over a period of time however, it gains a new blood supply and strengthens. Whilst this process probably takes some 2 years to fully complete it is thought that by 4 months some running can be commenced and by 6 months training for sport can be started. Actually getting back to full sport depends on individual progress at that stage including the regaining of proprioception in the knee. Exercises to promote this stability are essential and are encouraged when running is well progressed. Return to full sport is expected at about 9 months.

What is the recovery period?

Patients can generally return to work at 7-10 days provided that the amount of time spent on their feet is limited. They may also wish to use their crutches for a longer period of time. People in a sit down job can usually return in 2 weeks though if the job involves prolonged standing then 4 weeks may be more realistic. 2-3 months is probably the earliest that a return can be made if there is any heavy work to be done and jobs requiring squatting and bending may take a little longer. Jobs requiring the ability to run, work on uneven ground or climb ladders eg on a building site are the most demanding and these may require 6 or more months for adequate recovery to ensue.

Are there any problems associated with this surgery?

Overall the number of people who have problems following ACL reconstruction is small. Nevertheless problems do occur and these need some consideration.

Bruising in the immediate post operative period is the commonest problem. Obviously everybody has some bruising and in some cases it may be quite marked. It causes discomfort particularly when standing and may last for 2-3 weeks.

Deep Vein Thrombosis (DVTs or clots in the leg) also occur but are uncommon (less than 5%). If a patient is at risk for this complication eg previous DVT then some prophylactic thinning of the blood can be performed. This does increase bruising and bleeding however, and thus is not regarded as routine treatment. Patients on the oral contraceptive pill (except progesterone only pill) are at increased risk of a DVT and this should be stopped 1 month prior to surgery and obviously alternative contraception should be used until the pill is restarted. The concern of having clots in the vein is always that they may spread to the lungs (pulmonary embolis or PE) and this is an extremely rare event but does represent the one major and serious complication of this and other lower limb surgery.

Deep Infection is uncommon and occurs in about 1 in every 200 cases. It requires prompt treatment including arthroscopic washout of the knee and antibiotics into the veins and the risk of deep infection is that the graft may be damaged and fail.

Loss of Full Extension of the knee is the most common medium to a long term problem encountered. Some 5 to 10% of people who undergo ACL reconstruction have a scarring and tightening reaction to that surgery and the reason for this is unknown. Less than 5% have any residual loss and in some cases a further arthroscopy is necessary to remove some of the scar tissue. With newer techniques of reconstruction however, this type of secondary surgery is becoming less and less necessary.

Graft Loosening and Failure may also occur. Just as there is a 5 to 10% group at the tight extreme, so there is a 5 to 10% group who seem to progressively loosen with time. This group regains motion early and easily and with their quick recovery tend not to protect the knee as much as perhaps is ideal. In some instances this can cause early failure of the graft.

A cause of late failure (6-12 months) is where the graft fails to get a new blood supply and fails to come back to life. This is uncommon though if it occurs revision reconstruction may then be necessary and is usually successful.

Graft Re-Rupture can and does occur. No graft is as strong as the normal ligament and hence further injury (like the first one) can cause damage to it. Re-rupture rates within the order of 5% at 2 years following surgery though actually it is more common to rupture the ACL in the other leg rather than in the operated leg.

Patello-Femoral Pain or Ache Under the Kneecap (patella), is common once activity has begun. This is mostly due to the muscles being wasted and weak and therefore responds well to exercise and physiotherapy. Patello-femoral pain can also occur from damage to the articular lining of the patella itself. This happens in about 10% of ACL injuries and unfortunately it can prove relatively difficult to treat. Nevertheless this problem is generally minor and usually does not interfere with sporting activities to any great extent.

ACL reconstruction:
Why have I had this surgery?

Your operation has been to reconstruct or replace the anterior cruciate ligament. This has been done in an arthroscopically aided fashion. This does not mean there are no wounds however, because incisions were still made both to obtain the graft that was used for the reconstruction and also to introduce the graft into the tunnels that have been made in the bone for that graft.

What did this procedure involve?

What arthroscopically aided means, is that the capsule of the knee has not actually been formally opened and that all the main work that has been done in your knee was able to be done with the aid of the arthroscope. This is advantageous because it gives rise to less pain and less scarring within the knee and thus movement is easier to regain, progress is quicker and ultimately function is likely to be better. Because all of the joint was able to be inspected the other structures within your knee were clearly seen and where necessary treated.

The following summarises your surgery:

The graft that was used was 2 of the hamstring tendons on the inner aspect of your knee. Graft fixation is generally quite strong thus allowing for earlier movement and exercises with less chance that the graft will pull away at one end or the other. It also means that splints are no longer required (except for the immediate post operative period) for most cases and early walking is encouraged. Only approximately 10 years ago when this sort of procedure started to become widely used the knee was in plaster for anything up to 6 weeks and then slowly mobilised over several months to regain motion. More recently hinged splints have been used to restrict the range of motion of the knee thus providing a combination of moderate motion with some protection. Now, with the advent of better graft fixation, it has been found safe to not only mobilise the knee from day 1 but also to allow full weight bearing in the first 1-2 weeks following surgery. Whilst this does slightly increase the risk of the graft coming loose the benefits of early motion seem to outweigh those concerns.

The loss of the tendons used for the graft does very slightly weaken the hamstrings muscle but in reality it seems to cause remarkably few problems even in the high performance athlete and there is now some evidence to suggest that these tendons regenerate to some extent.

The graft itself is taken up through a hole that is drilled in the tibia (shinbone) across the knee and then into another hole that is placed in the femur (thighbone). As such it lies in exactly the position in the knee as the original anterior cruciate ligament did and is secured in that position so that it functions, as nearly as possible like the original anterior cruciate ligament.

When the graft is first put in the knee is it is very strong, the strength limitation at that stage being related not to the strength of the graft itself but rather to the strength of the fixation at each end. The graft incorporates into its bone tunnels over about 6-8 weeks and during this period when the fixation is becoming permanent the strength of the graft itself is actually decreasing. This is because a new blood supply grows into it and starts to remove some of the main structural fibres from it. It is thought that at 8 weeks the graft is at its weakest and hence care must be taken even at this stage despite the fact that the knee often feels quite good by then and walking is often possible without a limp. Following this period of relative weakness of the graft there is period during which the graft gradually increases in strength again as new structural fibres are laid down. This is a slow process and takes about 15-18 months to be fully completed. By 6 months however, the graft is usually strong enough to do most activities and most of the strength has been regained by then.

What should I do after the operation?

The single most important thing to regain in the early post-operative period is full extension (straightening) of the knee. Generally this can be achieved within a few days though sometimes it does take a little longer. Nevertheless, once it has been achieved, most other potential problems do not seem to eventuate. Despite the importance of regaining this motion it must be realised that full extension does place the graft under some tension and therefore needs to be done gently and passively as the physiotherapist will demonstrate to you. Because of high stresses in the graft when the knee is in extension it is important not to force it into this position by contracting the quadriceps muscle (at the front of the thigh) with the leg straight.

Similarly it is important not to lift the leg with it straight for the first 6 weeks. Studies have in fact established that the leg should be bent to approximately 40 or more before lifting it in the air and this will also be explained to you by the therapist.

Flexion the knee (bending) is much more easily achieved than full extension. As there is some risk to the graft when the knee is taken through to full flexion it is recommended that flexion be limited to 90 or 100 for the first 6 weeks and then slowly increased thereafter. Regaining full flexion is rarely a problem.

For the first 7-10 days most people prefer to use crutches and over that period of time they gradually increase weight bearing so as to wean off the crutches over a couple of weeks.

As long as the range of motion is being maintained it does not matter if you prefer to stay on crutches for a few weeks. Certainly crutches should be used on long walks, on uncertain ground or in places where the knee may be at risk. This having been said however, there is no doubt about the exercise value of walking and early walking does seem to decrease the amount of wasting of the muscles that is an inevitable part of this type of surgery.

You will be admitted on the day of surgery and overall it is expected that you will be in hospital for 1 night and that you will be on crutches about 2 weeks. Once motion has been regained the next priority is to get all the swelling out of the knee and this generally takes about 6-8 weeks. You will be reviewed in my out patient clinic at approximately 2, 6, 26 and 52 weeks. Your post operative rehabilitation will be supervised by a physiotherapist with experience in looking after this sort of reconstructive procedure.

What if I experience any problems after surgery?

If you are having problems with your knee, please contact your physiotherapist or your consultant during office hours. If a problem occurs out of hours you should contact the orthopaedic ward or your GP for advice.

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