What is the Anterior Cruciate Ligament?
The Anterior Cruciate Ligament is a crucial ligament positioned towards the middle/front of the knee that forms a connection between the opposing bones-the femur (thigh bone) and the tibia (shin bone). The ACL is vital to the proper health and function of the knee, but it is unfortunately one of the areas most commonly injured.
The Anterior Cruciate Ligament is responsible for the knee’s stability as it rotates and keeps the opposing femur and tibia in proper alignment. The ACL is aided in supporting the knee by the Posterier Cruciate Ligament and the Medial Ligament on the inside of the knee and the Lateral Collateral Ligament on the exterior. The Anterior Cruciate Ligament and the Posterier Cruciate Ligament form a cross on the inner side of the knee and along with the other ligaments, work to stabilize the knees movements.
Because the knees are critical for mobility, weight bearing and balance, proper maintenance of the knee and its various parts is important. However, despite exercising caution in sports and other high impact activities, ACL injuries still occur frequently. Understanding the physiology behind these injuries, as well as various treatment options can aid in recovery and long term mobility.
Causes of Anterior Cruciate Ligament Tears
As mentioned, the ACL is one of the most frequently damaged ligaments in the knee. Due to its positioning, the ACL will bear the brunt of impact directed at the knee from the front. ACL injuries usually occur when the leg is planted firmly on the ground and an unexpected impact comes from the front. This can be getting hit in the knee in a sporting match or some form of machinery or other object falling on the leg at an angle which forces the knee backwards suddenly. The ACL can also wear out or tear from repeated movements at an awkward angle. Some additional reasons for ACL injuries are:
- Contact Sports (Football, Soccer, Basketball)
- Car Crashes
- Landing incorrectly (on flat feet) when jumping
- Coming to a sudden stop while switching direction quickly
- Senior citizens slipping or falling
- Overextension of the knee
- Abuse and overuse over time
Symptoms of Anterior Cruciate Ligament Tears
A torn ACL is not usually an injury that can be easily ignored. Extremely painful, this injury usually immobilizes the individual and bending the knee is hard to do. Symptoms are varied, but usually include:
- The feeling of your knee or leg giving out suddenly
- A popping or snapping sound upon impact
- Swelling of the knee
- The knee locking
- If the ligament is completely torn, there may not be pain, but the knee will give out.
Sometimes it is possible to suffer an ACL injury and still be able to walk and function. However, if not treated, the knee will repeatedly buckle and may heal incorrectly. Left untreated, an ACL tear can cause the cartilage of the knee to deteriorate and can lead to osteoporosis. If you experience any of the symptoms of an ACL tear, consultation with a physician is important.
Types of Anterior Cruciate Ligament Tears
Not all ACL tears are equal in size and severity. Some tears are minor and require minimal intervention, while more serious injuries necessitate major surgery and extensive rehabilitation. There are 200,000 ACL injuries annually, with approximately half of them requiring surgery.
Of all the Sports induced ACL injuries, the vast majority are not from contact with another athlete. They occur from incorrect movements, lunges and jumping. Female athletes experience more ACL tears than their male counterparts, due to differences in structure, hormones and muscle mass.
Partial ACL Tears
It is possible to strain or partially tear the ACL and recover without surgery. The normal time for complete recovery varies based on the health and level of activity of the patient, but is usually a minimum of three months. It is highly recommended to stay under a doctor’s care during recovery and take advantage of physical therapy to accelerate healing. It is however, possible to have future stability problems after the ligament has repaired itself.
Full ACL Tears
If you suffer a complete ACL tear, there will be extreme discomfort and instability if you attempt to rotate or bend the knee and walking may be impossible. In about 50% of complete ACL tears, other ligaments and tissues are damaged as well, compounding the problem. Common related injuries are lesions of the articular cartilage and damage to the meniscus. If there is damage to multiple ligaments including the ACL, surgery is recommended.
Anterior Cruciate Ligament Injuries in Children
Knee injuries are becoming more prevalent in children with the increase in organized sports teams and events geared towards adolescents and teens. Of those injuries, ACL tears make up a significant amount. Older adolescents and teens experience more tears than younger athletes. However, in younger children, it is common for them to break a portion of the leg bone in addition to tearing the ligaments. Often, the ligament tears with a piece of the bone attached. This is due to skeletal immaturity.
There is also a disparity in the number of teen girls that suffer ACL injuries in comparison to boys. Statistics show girls to be two to eight times more likely to suffer such an injury. As with women, hormonal differences, differences in muscular makeup and bone structure all play a part in the increased risk of injury.
Initial ACL First Aid
If you sustain a knee injury, there are a few immediate things you can do to minimize damage while you wait to be evaluated by a health professional:
- Do not put pressure on the knee. Sit or lie down
- Apply ice to minimize initial swelling and bruising
- Wrap the knee in an Ace bandage or other compression aid to minimize swelling and stabilize the joint.
- Elevate the leg to reduce the pooling of fluids around the joint
- Take a non-steroidal anti-inflammatory pain killer, such as Motrin or Advil
In determining the type and severity of injury, a physician will ask a number of questions and conduct a thorough examination. Your doctor will ask you to recount the accident in detail including the position of your leg, the direct point of impact and the amount of force that was applied to the injured knee. He will also inquire as to whether you have tried to place weight on the injured leg and if it gives out or locks when you do so.
Additionally the physician will conduct a physical examination in which he feels for signs of a tear or fracture. Your doctor may perform the Lachman’s test, which feels for abnormal range of movement in the lower leg bone (tibia), in relation to the upper bone (femur). The doctor will hold the femur still and move the tibia to see if it moves independent of the upper leg. If so, a complete Anterior Cruciate Ligament tear is the probable diagnosis.
There is also the Pivot Shift Test, which evaluates the position of the tibia to the femur when shifted to a thirty degree angle. When the leg is straightened, the tibia protrudes, but returns to normal position when the leg is rotated to a thirty degree angle.
In addition to a physical examination, the doctor may order an x-ray or MRI to evaluate the extent of the damage and the affect on the surrounding tissue and bone. The extent of the damage will help to determine the best treatment options.
Depending on the severity of the injury, there are a number of treatment options:
If the injury is minor, it is possible to recover fully with minimal medical intervention. Wearing a compression bandage or leg brace, minimal movement of the joint and taking anti-inflammatory medicine can often suffice. However, there is the chance of the area remaining sensitive and succumbing to future injuries.
Anterior Cruciate Ligament Reconstruction Surgery
For more serious or complete tears that do not mend on their own, surgery becomes necessary. What used to be a more invasive procedure has become less so with the introduction of arthroscopic surgery. This type of surgery requires much smaller incisions, minimal scarring and less recovery time.
In arthroscopic surgery, the surgeon will insert a tiny scope into the knee to definitively identify the tear and severity of the injury, as well as inspect the surrounding tissue and bone for damage. The goal is to reconstruct any affected bones and ligaments at the same time, minimizing the need for repeated surgeries. In order to perform surgery, a new ACL must be created to replace the one that was damaged. This can be done one of three ways.
Types of Anterior Cruciate Ligament Grafts
Surgery to replace the ACL is usually done four to six weeks from the date of injury. The goal is to provide sufficient time for all swelling to go down and fluids to drain out of the affected area. Also, the doctor will want to see if the tendon heals independently and the patient regains his full range of motion. If surgery is to occur, tissue is needed in order to reconstruct the ACL. This is obtained in one of the following ways:
- Tissue taken from the hamstring tendon of the patient
- Tissue harvested from the patellar tendon of the patient
- Tissue taken from a frozen cadaver
Once the tissue is obtained, it is cut into the proper shape and size to function as an ACL.
Replacing the Anterior Cruciate Ligament
To replace the ACL, a small drill is used to make a hole in the tibia and the femur above in the spots where the new ACL will be placed. A pin is then inserted into the holes with the new ACL attached to one end. That uppermost end of the pin is passed through the hole in the femur, while the lower part is in the hole in the tibia. The ACL is then secured to the femur with one of three types (metal, plastic or calcium) of screw. After ensuring the correct amount of tension in the new ACL, it is also attached to the tibia.
Recovery From ACL Surgery
In order to have the best chance of a full recovery, it is imperative that you follow the rehabilitation plan outlined by your surgeon. The plan will likely include initially staying off of the leg and using ice to minimize swelling. Crutches can be used to get around, but are usually discontinued within a week or two. Some doctors will also recommend a knee brace to ensure minimal movement of the surgical site. Other doctors feel it is better to let the knee heal unrestricted.
Within 1-2 weeks of surgery, a rehabilitation plan will begin to ensure that as the knee heals, full range of motion and strength returns. Rehabilitation occurs in phases and each phase has specific goals and milestones.
Phases of Recovery
Initially, in the early rehabilitation phase, which occurs in the first one to two weeks, therapy will focus on a few basic things:
- The patient will be aided in reducing any residual swelling and pain that remains after surgery.
- The patient will be walked through simple exercises to improve the range of motion.
- The therapist will help you to increase muscular strength and usage.
In the second phase, which occurs in the third and fourth weeks, is very important that the patient exercises caution. Most of the pain from surgery will have dissipated, which may make you overconfident in using the knee. However, resuming normal activity too quickly can cause damage. This phase focuses on low impact exercises, such as:
- Water therapy-exercising and rotating the leg in a pool, which reduces shock and pressure on the muscles and ligaments
- Using a stair master or stationary bike on a low setting to promote muscle use
- Modified squats performed against a wall to work muscles and aid balance
- Practice bending the knee, with a desired range of motion of 100 degrees
- Use a leg press machine on a setting that does not cause pain or stress
At this stage, the patient will be monitored closely to ensure that the muscles and ligaments are responding positively to therapy and are not being overtaxed. Careful evaluation will be done before moving to phase three.
The third phase of rehabilitation, labeled the controlled ambulation phase, usually begins within 4-6 weeks from surgery, given the patient is progressing well. This phase will incorporate all of the exercises and therapies from phase two, but will introduce additional ones to push the use of the knee a bit further. They include:
- Increasing the range of motion of the knee to 130 degrees.
- Mini squats balancing on one leg to increase weight bearing ability
- Exercising the calf muscles to ensure strength and flexibility
- Using a stationary bike, with an increased resistance level
- Mastering up and down stepping movements
- Exercises to help resume normal walking patterns, such as a level and inclined treadmill workouts
- Additional exercises to increase balance and coordination.
At this stage, you may also receive exercises to do at home and permission to engage in additional low-impact activities. The goal of this phase is to slowly return to normal function, without overburdening the healing ligaments.
In the moderate protection phase, which spans weeks 6-8, weights will be added to your exercise routine to gauge and increase the knee’s ability to bear weight and perform under pressure. Additionally, you will now be expected to be able to fully rotate and extend the leg. This phase certifies the knee’s return to normal function, with controlled and moderate weight bearing ability.
Weeks 8-10 is comprised of the fifth phase which incorporates light activity. The patient will be guided through exercises that increase balance, focus on building strength, as well as ensure the patient is able to move around comfortably. Additional exercises will include lunges and resistance training.
Within ten to twelve weeks, “return to activity”, the final phase of rehabilitation begins. The length of this period will vary, depending on the severity of the injury and the patient’s performance goals. For example, a professional athlete may need longer rehabilitation to ensure that he can withstand the rigors of competition. A non-athlete would need to ensure that they can function normally and with ease in their daily activities. To get to this point, the following may be implemented:
- Outfitting the patient with a knee brace that allows normal movement, while providing support
- Jogging on a treadmill at a low speed, with various incline levels
- Exercises and drills that test and improve agility and balance
In addition, the surgeon may perform specific tests to see how the patient responds to a specific set of exercises at a set speed. These are called isokinetic tests and are usually done at the three and six month mark to evaluate patient progress.
While undergoing rehabilitation, it is important to communicate with your health care team. Let them know if you feel that you are doing too much too soon, as that may aggravate the surgery site and delay or inhibit healing. It is important to progress slowly, step by step to full recovery, which may take anywhere from a few months to a year in severe cases.
With any major surgery, there is the risk of complications. While ACL surgery is considered relatively safe, possible complications include:
With any surgery, infection is a concern. However, the risk of infection with ACL surgery is low. However, as a precaution, the patient will be given intravenous antibiotics before and after surgery. Keeping the incisions clean is another way to prevent infection. The patient will receive counseling before being sent home which details proper post-op wound care.
Technically called Deep Venous Thrombosis, blood clots are most common in leg and knee surgeries. Clots can be very dangerous if not caught in time and can potentially travel from the leg to the heart, lungs or brain. In order to prevent this, the following precautionary steps may be taken:
- Gently moving and exercising the leg as soon as possible after surgery to promote proper circulation.
- Blood thinners to prevent the formation of blood clots
- Support hose or pressure stockings to aid circulation
The symptoms of deep venous thrombosis are abnormal pain in the leg, the leg being warm to the touch and swelling. If you experience any of these symptoms post surgery, contact your doctor immediately.
Occasionally, the holes that were drilled into the knee to fit the new ACL are out of alignment. When that happens, there is friction of the ACL against bone when the leg is straightened. While it is possible to resolve this through physical therapy, often additional surgery is required to either widen the area where the ACL was placed, or drill new holes altogether.
Stiffness in the knee joint can occur for a few reasons. These include:
- Surgery that was performed too soon after the accident, not allowing for sufficient range of motion before operating
- An inordinate amount of scarring inside of the knee joint
To combat stiffness, exercises that target the joint and increase range of motion are began soon after surgery. It is critical to your future mobility to keep all physical therapy appointments and perform exercises as directed at home.
Prevention of Reoccurring Tears
To prevent initial and recurrent ACL injuries, implement the following:
- Always warm up before playing sports or beginning an exercise routine, with particular focus on the hamstrings and quadriceps
- When playing sports, observe proper techniques for running, lunging and jumping
- Minimize wear and tear on the knee. If you continue to play sports, try to minimize unnecessary hits, twists and turns
- Wearing a leg brace during sports may be helpful, but has not been proven to reduce injuries
- Harvard Medical School. ACL (Anterior Cruciate Ligament) Injuries: http://www.intelihealth.com/IH/ihtIH/WSIHW000/9339/25426.html#symptoms
- University of Maryland Medical Center. Anterior cruciate ligament (ACL) injury – Overview: http://www.umm.edu/ency/article/001074.htm
- American Academy of Orthopedic Surgeons. ACL Injury: Does It Require Surgery? http://orthoinfo.aaos.org/topic.cfm?topic=a00297
- Seattle Children’s Hospital Research Foundation. ACL Injuries: http://www.seattlechildrens.org/medical-conditions/bone-joint-muscle-conditions/joint-ligament-injuries/acl-injuries/
- National Institute of Health. Anterior cruciate ligament (ACL) injury: http://www.nlm.nih.gov/medlineplus/ency/article/001074.htm
- WebMD. Anterior Cruciate Ligament (ACL) Injuries: http://www.webmd.com/a-to-z-guides/anterior-cruciate-ligament-acl-injuries-topic-overview