Anterior Cruciate Ligament (ACL) Tear
Important Considerations – Don Wackwitz, M.D.
The Anterior Cruciate Ligament (ACL) is a strong cord like structure running down the center of the knee. It keeps the knee from sliding forward and over rotating. When it is torn it snaps back like a rubber band and the torn ends lose contact with each other. Because the torn ends do not touch, they cannot heal together. The ends are so shredded that the ligament cannot be repaired and therefore it must be reconstructed, that is, replaced with a graft, if we hope to have a stable knee once more.
If you spend much time researching the treatment of anterior cruciate ligament (ACL) tears you will probably find that there are many different opinions out there and some seem to be contradictory. We are learning more every day and so it’s important that your information is current. I have been doing ACL reconstructions for over twenty five years and have experience with a number of different techniques. Some new techniques make it easier for the surgeon; some make it better for the patient. The second reason should always prevail. Some of the most commonly asked questions regarding the ACL are:
- If and when do I have surgery?
- What type of ACL graft is the best?
- What is the role of physical therapy?
- How long does it take to get back to my sport?
- What is the long term outlook for an ACL injured knee?
I’ll address these questions one at a time, bringing up the important issues. There is no single right answer to any of these questions. The treatment of an ACL tear must be individualized, treating each individual according to their own set of circumstances.
If and when do I have the surgery?
A complete tear of the anterior cruciate ligament will cause the knee to feel unstable. This will cause the knee to give way during some twisting movements related to cutting, stopping or landing from a jump. Individuals who had an otherwise normal healthy knee before the injury and an active lifestyle will in time experience this instability and would benefit in having an arthroscopic reconstruction of the ACL in order to stabilize the knee. Untreated, the instability will change the way the knee moves during normal activity causing increased wear to the joint surface. This also will result in a large increase in the chances of getting a subsequent tear of the menisci (cartilages) which also increases the likelihood of arthritis. Reconstruction of the ACL stabilizes the knee and will protect the meniscus. The long term results of the surgery are influenced by any additional injuries of the knee sustained at the same time and by the accuracy of the graft placement by your surgeon in reproducing the anatomy of the normal ACL. The ACL injury carries an increased risk of arthritis over time especially in younger and heavier individuals.
Older individuals who have arthritis in the injured knee may be best treated with non-surgical measures alone. If your knee has a significant level of arthritis, your likelihood of experiencing instability of the knee is less. This is due in part to your lower level of activity, but we also know that the presence of arthritis in the knee decreases the mobility of the knee and makes the knee less likely to give way. If you are not athletically active, you may have enough intrinsic stability remaining from the secondary restraints (other uninjured knee ligaments) to prevent the knee from giving way during your activities of daily living. It may be a wise choice for people with arthritis or inactive people to initially treat the injury non-operatively and test out the knee as it feels better, the swelling goes down and the knee motion gets back to normal. If no giving way develops, conservative measures can be continued. If the knee gives way after regaining strength and mobility, reconstruction should be considered.
The ACL tear in the growing young teenager is becoming a more common injury. This injury is many times related to a fracture where the ACL attaches to the bone which can be fixed arthroscopically, but we are seeing more and more of these injuries in the middle of the ligament. This type of ACL tear is the same as the adult injury, but in a young person carries more risk. The conventional methods of ACL reconstruction cross the growth plates and may affect the growth of the leg or cause a deformity. In the past this injury was initially treated non-operatively hoping that bracing or activity restriction would prevent further injury until a reconstruction could be done when the growth plates closed. This too often fails with the unfortunate result of meniscal tears or injury to the joint surface. This has definite long term consequences in this young age group. There is a growing enthusiasm to use new growth plate sparing techniques to reconstruct the ACL soon after the injury in these young athletes. This is a very important consideration if the meniscus and ACL are both torn.
In all patients with an ACL injury there is a significant amount of pain, swelling and stiffness within hours after the injury due to bleeding into the knee joint. It is of great benefit for this to be resolved before surgery by using Ice, elevation and compression immediately after the injury and initiating range of motion exercises and quadriceps strengthening exercise as soon as tolerated. Even with the best of circumstances this may take from three to six weeks for the knee to be ready for surgery. Prior to surgery the knee needs to extend out as straight as the other knee, and to bend to near normal. The swelling needs to be down to the point that the knee feels close to normal. Attention to these details will assure less pain and less difficulty regaining strength and flexibility after surgery. If a patient would like to wait longer than this and remains at reduced activity during the interval, delays of even several months are acceptable.
What type of ACL graft is the best?
The most common replacements (grafts) for the ACL are tendons taken from the hamstrings (gracilis and semitendonosis), the patellar tendon (central third), and somebody else (cadaver graft). There is no single graft that universally stands above the others. There are differences among the grafts that can make one type of graft stand out as the right choice for each individual.
The cadaver graft (allograft) is not taken from your body, so there is less surgery needed and in most cases less pain around the time of surgery when compared to the other grafts (autografts). Unfortunately, the disadvantages of the graft being from another person are that the graft does not incorporate as well or as quickly as a graft of your own. This means that even though you may feel better more quickly, you need to wait longer to resume sports activities. Studies have shown a two to three times higher failure rate for the allografts as compared to the autografts. This graft may be the best for an older or less active individual, but should be used with caution in an athlete less than 25 years of age.
The hamstring ACL graft is actually two hamstring tendons, the gracilis and the semitendonosis, both doubled over to form a four stranded tendon substitute. The total size of these tendons is actually larger than the original ACL in most knees. The hamstrings are stronger and stiffer than the normal ACL. The grafts can be very rigidly fixed to bone tunnels in the tibia and the femur with initial strengths that exceed those levels needed for activities of daily living. The grafts are taken through a small incision just below the knee and the loss of the tendons from the leg has very little long term effect. The chief difficulty seen with the hamstring grafts are that in certain individuals the size of tendons is smaller than usual and is not of adequate size to be used. In this situation the patellar tendon can be used.
The central third of the patellar tendon graft is actually a graft consisting of a tendon slightly longer than the original ACL with a bone block about an inch long on both ends. The bone blocks fit snuggly into bone tunnels and are secured with screws. The bone blocks heal to the bone solidly to form rigid fixation. This graft fixation is initially stronger than the hamstring grafts due to the rigid bone fixation. Studies have shown that the tendon removed for the graft regenerates in a year to two years. The graft is stronger and stiffer than the normal ACL and the size of the graft can be adjusted upward for larger individuals, but it usually is smaller than the quadrupled hamstrings. The graft is taken from the front of the knee and it is more common to have pain in the front of the knee after surgery as well as having more difficulty in regaining full extension when compared to the hamstring technique. This extension is not usually a problem with people who exercise regularly, but can be a challenge for some.
You can see that no single graft type excels in all categories. There is a time and place for each of these types and the selection has to be made on an individual basis. The surgeon must be familiar with all of these arthroscopic procedures. I tend to favor the patellar tendon for the teenage athlete as it will tolerate more activity in the first four weeks. I tend to recommend the hamstring graft with an all inside arthroscopic technique to the adult woman as it is less painful, has a smaller incision, but requires a bit more protection early on. Both options deliver equal strength in the long run. By individualizing the surgery the best results can be achieved.
An even more important consideration than the graft type is the graft placement. Precise anatomic placement of the graft is essential to get a good long term result. A poorly placed graft in a position that is too vertical will eliminate the forward sliding of the knee, but will not control the rotational instability of the knee. A very popular technique where the femoral tunnel is placed through a transtibial approach is attractive because of its simplicity and minimal incision, but the graft is placed in a nonanatomic position. New methods using an all inside arthroscopic approach can more accurately reproduce the normal anatomy, while minimizing the pain and rehabilitation difficulty after surgery. Research is underway to develop techniques to place a double bundle ACL graft to even more accurately reproduce the normal stability but there is some disagreement as to exactly where to place these bundles. Until a consensus is reached the most predictable ACL reconstruction is achieved with a single bundle graft extending from a well placed femoral tunnel to a well placed tibial tunnel.
What is the role of physical therapy?
The anterior cruciate ligament injury itself causes swelling, pain and stiffness in the knee. This is even more evident if there is additional injury such as a meniscal tear, a collateral ligament tear, bone bruising, or patella dislocation. The quickest and best way to bring these problems under control is with the guidance and skilled hands of a physical therapist. Once the techniques are learned much of the work can be done independently in your own home or exercise facility. Preparing the knee prior to surgery (Pre-hab) minimizes the pain associated with surgery and makes the subsequent rehabilitation easier. We all realize that visits to physical therapy may be limited by your insurance and may also involve co-pays or other out of pocket expenses related to the post op rehab. This makes it important for us to make the most efficient use of the sessions you have and to plan for other exercise options.
Physical Therapy is very important to help with pain, control swelling, re-establish range of motion and muscle recruitment. Once the ACL has fully healed, the rehab continues to be very important to enable you to return to your sport safely, with minimal chance of recurrence and maximum performance. This is achieved with a good program consisting of neuromuscular reeducation, proprioceptive training, plyometrics and core conditioning.
How long does it take to get back to my sport?
This is a question that cannot be answered with a number. You are ready to return to full sports activity when you are fully conditioned for your sport. This would mean that you would be conditioned enough to be fully competitive, and possess the core strength and neuromuscular skills necessary to prevent a reinjury in either knee. A program such as this usually takes about six weeks to finish, and can be initiated between the fourth and the sixth month after surgery. Return to sports at four months without attention to these parameters has produced an unacceptable level of failures in the past.
What is the long term outlook for an ACL injured knee?
Our main concern with any injury to the knee joint is the possibility of permanent damage. Some recent studies have shown a high rate of osteoarthritis following ACL injury despite a stable ACL reconstruction. One recent study reports a 50% rate of some osteoarthritis at six years after surgery. The arthritis at six years is seen more commonly in knees that have had joint surface damage seen at arthroscopy and those that have had a meniscectomy. In past studies the incidence of arthritis over time in a knee that has had an anterior cruciate ligament tear and a meniscectomy is about 70% despite ACL reconstruction. We have to improve these results. A recently completed study of ACL reconstructed knees showed significantly less arthritis at 14 years after surgery in knees that reached full extension in the weeks following surgery compared to those that did not. Early full extension has always been a top priority in my rehabilitation program.
To achieve the best results, it is very important to fully examine and assess the entire joint at the time of the ACL reconstruction. A preoperative MRI scan is a very important step to determine the status of the meniscus, the condition of the other ligaments and to look for bone bruises which may indicate associated joint surface injury. In addition to reconstructing the ACL any meniscal tears that have any potential for healing should be repaired and the articular surface should be treated as well. In addition it is important to perform an anatomic ACL reconstruction to stabilize both the translation of the joint and the rotation. The present evidence does not support the trans-tibial technique for the femoral attachment.
Summary
As you can see undergoing an anterior cruciate ligament reconstruction involves a lot more than just fixing the ligament. It is important to address the entire injury, do a complete and accurate assessment and repair, and follow it with a well directed rehabilitation program all the way back to the field or court. I want you to return to your previous athletic status with the additional strength and agility needed to prevent a future injury. The emphasis has to be on anatomic reconstruction, safe return to full activity, prevention of recurrence, and prevention of long term degenerative arthritis.
