ACL tears and reconstruction.

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The rate of anterior cruciate ligament injury goes up with the hours playing the sport and with the intensity. Team field sports like rugby, soccer, hurling and Gaelic football are considered high level sports which combine the risk of contact and non-contact injuries. At a lower level are badminton, tennis and squash where no contact takes place. Skiing is the number 1 cause of injury worldwide.

Females have a four times increased risk per hour played over males. This may be related to morphology and hormone influences.

You could speculate that a concentration on explosive power rather than stamina in training could be a factor.

It is felt that some people have poor proprioception anyhow and easily injure their knees. Patients after surgery have double the chance of injuring the opposite knee and 4 times the risk of injuring the same knee than others playing at that level.

Injury Mechanisms

A tear of the anterior cruciate ligament should be the first consideration in any player who suffers a knee injury and has to leave the field. There are 2 mechanisms of injury contact and non-contact. In a contact injury the usual mode is where another player causes a valgus force to the knee in a tackle situation. More common is the non-contact injury where an external rotation, valgus force is applied to the knee when the player turns with the foot planted on the ground or as the player lands from jumping.
The patient may describe a pop or a snap. Without even an examination an ACL tear is foremost in the treating physician’s mind.

Examination

Typically there will be an effusion with a haemarthrosis which in the early stages makes a full examination difficult. Anterior laxity is measured at 20 and 90 degrees of flexion. The Lachman anterior drawer at 20 degrees is the most sensitive test and may be the only test you can do in the first week. This can best be performed with the patient’s thigh resting on the examiner’s flexed knee (see the picture). The patient’s thigh is then stabilised with one hand and the other used to perform the test. It is good practice to perform the test first on the injured knee and then on the good knee and to repeat the process a number of times until you are certain.

The increase in the side to side difference is important but even more important is the end feel. Does the injured knee give a definite stop to anterior drawer or is there a typical soft end feel associated with a tear

Be careful that what is increased laxity is actually anterior drawer and not the return of a posteriorly subluxed knee which indicates a posterior cruciate ligament tear. It is important to note an extension lag as this needs to be corrected before surgery. This may be caused by a meniscus tear but is more commonly caused by the ACL stump impinging in the femoral notch.
A knee with a torn ACL is rotationally unstable. When a normal leg pivots the knee can rotate about its centre. With the ACL torn this is shifted to the medial side and the lateral side subluxes anteriorly. An examination of the pivot shift reproduces the feeling of giving way that the patient with the chronically torn ACL typically experiences. It is a test that is difficult to perform and its presence may only be apparent when the patient is examined under anaesthesia. The absence of the pivot shift in the clinic does not rule out a tear as some patients can control it with their muscles.

About 90 per cent of tears can be diagnosed clinically by an experienced person. The examination should also check the integrity of the medial collateral and lateral collateral ligaments. If it is more than 4 weeks after the injury it may be possible to perform specific meniscal tests and check for postero-lateral and antero-medial laxity.

Investigations

Initially it is important to out rule a fracture in an injured, non-weight bearing patient with a haemarthrosis. An MRI is no substitute for a proper clinical assessment. The doctor ordering the MRI should be aware of its limitations and should be capable of assessing the images.
Scans with the ligament absent on any view can be reported as normal. It is also common to have reports of oedematous, partial intra-substance tears which may leave some doubt as to what to do next. The vast majority of these turn out to be complete tears on examination and on arthroscopy. MRI accuracy is affected by the limitations of the technology, the quality of the images and the accuracy of the reporting. Standard imaging is not capable of showing chondral damage unless it is worn to exposed bone. Important information on the postero-lateral corner and partial tearing of the PCL is seldom seen on standard imaging. Meniscal tears may be both over and under-estimated.
Bone bruising is typically seen but the long term significance of this finding on MRI is not clear. A standard protocol and MRI enhancement techniques may make this finding a predictor of OA change.

MRI is most useful when normal in reassuring the patient that the ACL is intact and they can return to sport. In the case where the ACL is actually torn the MRI can help plan surgery where other pathology such as meniscal tears and chondral lesions are noted. Sometimes patients wish to put off surgery to a more suitable time and the absence of other pathology will guide this.

Patient Counselling

Whether a patient should have surgery or not is actually controversial. In a recent study at the Erasmus University in Rotterdam the subjective and objective outcomes of surgery versus non –surgery are similar. The only difference is in better stability scores and a 1 point higher Tegner activity score in the operated group at 10 year follow up. Symptoms of osteoarthritis were present in 48 of the operated on group and 28 of the non-operated group.

Most surgeons would agree that there is at present no evidence to say that surgery prevents future degenerative wear of the knee. There is some evidence that meniscal tears may be reduced but even this injury is commoner than in the general population. Patients can be counselled that in an isolated ACL injury they need not have surgery if they are willing to accept some degree of laxity and a decreased level of sports participation. Some would argue that to have surgery and return to sport is placing too great a risk on an already damaged knee. When you consider that at least 50 of patients with an ACL tear will have a meniscus tear and / or chondral wear at the time of surgery it is not surprising that osteo-arthritis will develop later.

Having discussed the options most patients that attend surgeons want to return to their previous level of sport and opt for surgery. However even in professional soccer players only 66 per cent return to the level they were at when they injured the knee.

Patients under 18 years of age do relatively less well than older patients with a higher rerupture rate. It may be advisable for the younger patients to take 18 months out before returning to sport.

Surgery

5 years ago international meetings were dominated by arguments about whether a bone patella tendon bone graft was better than a hamstring graft. There were also numerous papers and symposia on methods of fixing the grafts in place. These issues have faded as there is general consensus that either graft with a variety of fixation methods do equally well (as do other graft choices). However probably because of ease of surgery and less anterior knee problems the choice of surgeons has shifted 80/20 in favour of the hamstring graft.
In the last 5 years there has been a change in the positioning of the graft. In the past grafts were placed very vertically in the femoral notch but now surgeons place them on the lateral side of the femoral notch. This has lead to better control of rotational instability.

International meetings are now concerned about double bundle versus single bundle reconstructions. The technique has been pioneered by the Japanese for over 10 years. The idea of replacing the anteromedial and posterolateral bundles with 2 separate grafts grew out of a revisiting of the anatomy and a desire to reconstruct the ligament more anatomically so that rotation would be better controlled. Like a lot of new surgical techniques there have been papers in favour of double bundle and papers showing no difference between double and single bundle reconstruction. As with other advancements in medicine people have been making a decision based on what they feel is right. A growing number of surgeons are changing to the double bundle technique and the evidence showing some advantages to it is growing.

Present surgical techniques do not return normal kinematics to the knee but newer techniques are better than the surgery of 10 years ago and 10 years from now there may be better results in terms of the development of degenerative changes.

It is not however all a question of choosing one method over another but rather performing a good technique well. Improperly positioned grafts are the commonest cause of failure and lack of extension at the end of surgery will not be corrected by physiotherapy.

Failure to appreciate and correct extra-articular instability and malalignment will also lead to graft failure.

Rehabilitation

There is no consensus on when it is safe to return to sport or what type of physiotherapy is best. Aggressive physiotherapy with early mobilisation and a return to sport at 5 months has now started to be questioned. It has been shown that early continuous movement affects the incorporation of the graft in the tunnel and delays the development of the graft’s blood supply. Initial full weight bearing may lead to chondral damage in a knee with an already large effusion and inflammatory reaction. It is probably best to achieve full movement early but not to go for repetitive continuous movement in the first 6 weeks until the graft is more stable in the tunnels.

The use of NSAIDS in animal studies has been shown to adversely affect graft healing and it may be best to try to avoid these drugs. However it may be difficult to convince a patient that inflammation is actually needed for healing as they have been accustomed to using drugs to get rid of what they see as a hindrance to recovery.
Patients follow their physio programme well for the first 3 months but often drift away from it after that. Patient need to be trained in core stability exercises and landing from jumping strategies. Generally most patients take 9 months to return to the field of play. It is best to think in terms of doing a complete rehab programme rather than focus on an early return to sport as a measure of success.

There is no hard evidence to back up what end points are important before passing the patient as fit to return to sport. Even so it is important to use some parameters. Patients should be able to run for 45 minutes 4 times a week, perform at 90 on isokinetic muscle testing (see the picture) and 90 on hop tests when compared to the opposite leg. Even then there is no guarantee that the graft is actually healed. It is most at risk in the first 3 months on returning to sport. It takes at least 2 years for the tendon graft to alter its histology to become more ligament like, a process known as ligamentisation.

Longterm

Unfortunately OA change in the knee is common. It is related to meniscal and chondral damage at the time of the injury and ongoing damage. The rate of radiographic changes of OA is 50 at 12 years. However radiographic evidence of arthritis does not correspond with symptoms.

Future

Future surgical improvements will come from better biological incorporation of the graft. At surgery the graft is taken free from its blood supply and placed in bony tunnels in the tibia and femur. Over about 12 weeks it will bind to the bone and develop a blood supply. The goal is to achieve tight bone to graft integration preferably at the level of the joint to mirror the normal anatomical situation. The use of cytokines gives hope that this can be achieved and the incorporation of these substances into the graft and the fixation device at the time of surgery is possible.

Main Points

  • ACL injuries are related to the intensity of and the hours spent playing sport
  • Non-contact injuries are more common than contact
  • An ACL tear should be suspected when a player leaves the field with a knee injury
  • An MRI is no substitute for a proper clinical assessment
  • Surgery gives the best chance of a return to the same level of sport
  • Patients may choose not to have a reconstruction if they accept a lower level of activity
  • Surgery does not return normal knee kinematics
  • 5 per cent of patients will have redo surgery when the graft fails
  • Up to 20 per cent will have an arthroscopy for further problems
  • Only 66 per cent will return to their previous level of sport with surgery
  • Patients must focus on proper rehab rather than rush back to sport