Complete tears of the anterior cruciate ligament (ACL) of the knee are common and probably getting commoner. About 20,000 people will sustain a cruciate injury in the United Kingdom this year. Working in a sports injury clinic it seems to be almost an epidemic particularly in young male footballers in their early twenties. In fact, probably the higher risk sport is in young women and especially netball.
The typical story is of a non-contact twisting injury to the knee where a pop is heard and the knee swells almost immediately. Following that, the patient is unable to play on because the knee feels as though it is going to collapse underneath them.
Just because a cruciate ligament, the ACL is torn does not necessarily mean it needs reconstructing. It depends on a number of factors but particularly whether the muscles around the knee can be trained up so that they are better than normal and can take over some of the function of the torn ligament. After a serious injury such as this, with instability, the knee is at increased risk of premature ageing irrespective of treatment and this needs to be borne in mind. It is likely in a young patient who has high demands and wants to continue in a sport involving twisting that anterior cruciate ligament reconstruction will be required.
It is only in the last ten or fifteen years that we have had a reliable operation to reconstruct the ACL, & cure the instability but now the results are extremely good from the point of view of stabilizing the knee. The results are not so good for helping the symptom of aching and pain which is often caused by a secondary problem either with the meniscus, cartilage or the bearing surface of the joint.
The Operation of Cruciate Reconstruction
It is not possible to repair the torn ligament even on day one after injury. ACL repair has been tried and does not work. It must, therefore, be replaced and this is done by passing a suitable graft through drill holes in the shin bone (tibia) and thigh bone (femur). There are various graft choices and various ways of fixing the graft at each end. The commonly used grafts worldwide are are:
- "String". This is a specially designed artificial ligament which has the advantage of being available off the shelf but does not have as good results as the other grafts particularly in the long term.
- Tissue transplanted from a dead body. This also has the advantage as being available off the shelf but does carry the small risk of infection transmission and is also often taken from patients who are a little older and the storage of the tissue may interfere with its strength.
- ACL grafts taken from the patient themselves. These are grouped into grafts taken from the front of the knee and the back of the knee. Some surgeons have very strong views about what is the best graft. My own view is that there is very little difference in the outcome and that the choice needs to be discussed with the patient on an individual basis. Grafts taken from the front of the knee have the advantage of being taken with a block of bone on the end which provides a very secure immediate fixation. The disadvantage is that there is an increased risk of tenderness at the front of the knee particularly with kneeling after the harvest of the graft. The graft taken from the back of the knee is a little stronger but relies on soft tissue rather than bony fixation in the early post-operative period. Technically, it is also a little bit more difficult.
- The operation is more or less the same apart from the choice of graft. It takes between an hour and an hour and a half. My own choice of fixation is to use a screw alongside the bone blocks which dissolve since it is made of a new (CE marked) compound consisting of a mixture of an absorbable polymer and a ceramic which has similar constituents to the bone next to it. This may be expected to disappear over a period of one to two years allowing the bone cells surrounding it to grow in and replace the screw with living bone. When I take the graft from the back of the knee (that is, using the hamstring tendons), I use the same fixation at the bottom end (in the tibia), but the top end (femur) of the graft is fixed with transverse bioabsorbable pins.
“Double bundle” reconstructions are being advocated by some in an attempt to reconstruct the multiple fascicles of the native ACL. At present, the increased risk of these more complicated procedures is not warranted until we have some evidence that there is a definite advantage. We are continuing to work on it!
Problems & Complications
There are risks and complications with the ACL reconstruction. Every operation has small risks associated with the anaesthetic. We are currently using a very light general anaesthetic combined with a nerve block so that the leg is rather numb in the early post-operative period. The local risks associated with the operation are an infection which is rare (and in our operating theatres in Oswestry, we have a rapidly exchanging lamina flow air system which is carefully filtered so that the air is as clean as any operating theatre in the world). We also give antibiotics to prevent infection but inevitably infections will occur. The other small risk is of a clot in the veins of the legs. This is also uncommon, but has been reported to occur in about one in twenty patients. In most of these, the patient is not aware of any problem, but a small proportion can cause trouble and the clot may break off and go to the lungs causing a pulmonary embolus which could certainly potentially be very serious. This complication is so uncommon that no figures are available but is probably a risk of less than one in a thousand. Some patients get some stiffness after the operation and occasionally this excessive scarring may need another operation to free it up.
In view of this, I do not advise routinely thinning the blood to prevent this complication since thinning the blood increases the risk of bleeding both at the operative site and elsewhere - a potentially greater risk.
Following the operation, patients stay in hospital for one night, just while they get over the operation and are taught the exercises by our physiotherapy team. I do not use any postoperative bracing. The post-operative physiotherapy is extremely important and we currently have two PhD students researching the best means of rehabilitation.
Broadly, within the first two weeks my patients are encouraged to get the knee fully straight and passed straight (hyperextended) if possible. It is always easier to get the knee to bend than straighten and it important to straighten the knee within the first few weeks. I do not use any splints or braces since the fixation of the graft is secure enough to stand the stress of walking on the leg without support. There are some modifications if the meniscus (cartilage) needed repair during the surgery.
All the sutures I use are dissolvable underneath the skin so there are no stitches to take out and it takes a couple of weeks for the skin to heal and about six weeks for the graft to "bed-in" and acquire a biological fixation. After the six week period, patients are encouraged to work more on strengthening and may start jogging in a straight line after about three months. I do recommend avoiding so called "open kinetic chain" exercises for a total of three months. These are exercises like the knee extension exercises at the multi gym where the bar rests across the front of the shin. The reason for this is that these sort of knee extension exercises put more stress across the graft than thigh exercises with the foot fixed (as in a squat).
After four months, predictable twisting and “cutting” movements are added with unpredictable twisting about a month later. Patients do progressively increase their activities through straight line running, running and turning and then running with sudden twisting according to an individual programme. It is important as well as strengthening the muscles and getting the knee bending that the muscles are perfectly coordinated so that they contract at the right time and are able to protect the graft. Unrestricted activities should not commence before six months and most footballers are returning soon after this and within eight to nine months. Nature continues to remodel the graft and improvement occurs beyond a year so that patients feel that the knee is more normal at two years than at one.
We are working on more specific criteria for return to sport. These may include measured of coordination and neuro muscular efficiency, as well as the traditional isokinetic dynamometry & hamstring / quadriceps ratios.
I like to follow up the patients for at least this two-year period so that I can get a good idea of how they are progressing and see if it is possible to improve either the surgical technique or rehabilitation for the benefit of future patients. Some patients as well as having post-operative x-rays do have either MRI or CT scans to confirm the perfect placement of the graft and for the purposes of looking at how well it is incorporating and the dissolving internal fixation is disappearing.