Acl Tear, Surgery, Symptoms, Causes, Treatment (Anterior Cruciate Ligament)

What You Need To Know About ACL Tears

The anterior cruciate ligament, or ACL, is one of four major knee ligaments. The ACL is critical to knee stability, and people who injure their ACL often complain of symptoms of their knee giving-out from under them. Therefore, many patients who sustain an ACL tear opt to have surgical treatment of this injury.

What is the ACL?

The anterior cruciate ligament, also called the ACL, is one of the four major ligaments of the knee. The ACL prevents excessive motion of the knee joint--patients who sustain an injury to their ACL may complain of symptoms of the knee giving out.

The most often injured portion of the knee is the ACL, or anterior cruciate ligament. This ligament is located in the very middle of the knee and helps it rotate properly. It also keeps the tibia in place. It is one of the four ligaments in the knee that help humans walk, and it works with the posterior cruciate ligament to keep the tibia stable.

A healthy ACL is essential for pain-free walking and running. Because of this, athletes are usually very protective of their knees. That's the reason for shock-absorbing sneakers and other technology to keep the knees safe. A badly torn ACL can end an athletic career.

An ACL can be injured from a blow to the side of the leg, but in non-athletes, most frequently occurs when the knee is twisted, from a sudden stop and reverse move, or from simple overextension of the knee joint. Athletes are often taught how to decrease stress on the ACL through changing the way they move in certain circumstances.

If a person suspects he has injured the ACL, he should ice and elevate the joint, and should seek medical evaluation as soon as practical. If, after the injury, the lower leg or foot turns blue and is cool to the touch, the person should seek immediate medical assistance, since circulation to that leg may be severely impaired. In children, an ACL injury may heal by itself, but this is rarely the case with adults. Depending on the severity of the tear, an adult may be able to live with the injury, but surgery is often required.

ACL surgery is usually done arthroscopically, and the surgeon may elect to reconstruct the ligament with a cadaver ligament, or with one fashioned from part of the patient's patellar ligament. Physical therapy is required for the patient to regain full mobility of the knee, although he or she may not be able to participate in athletic activities at the same intensity as before the injury.

How does an ACL tear occur?

An ACL tear is most often a sports-related injury. ACL tears can also occur during rough play, mover vehicle collisions, falls, and work-related injuries. About 80% of sports-related ACL tears are "non-contact" injuries. This means that the injury occurs without the contact of another athlete, such as a tackle in football. Most often ACL tears occur when pivoting or landing from a jump. The knee gives-out from under the athlete when the ACL is torn.

Female athletes are known to have a higher risk of injuring their anterior cruciate ligament, or ACL, while participating in competitive sports. Unfortunately, understanding why women are more prone to ACL is unclear.

Signs of an ACL tear

The diagnosis of an ACL tear is made by several methods. Patients who have an ACL tear often have sustained an injury to the knee. The injury is often sports-related. They may have felt a "pop" in their knee, and the knee usually gives out from under them.
ACL tears cause knee swelling and pain. On examination, your doctor can look for signs of instability of the knee. These special tests place stress on the ACL, and can detect a torn ligament.

An MRI may also be used to determine if the ligament is torn, and also to look for signs of any associated injuries in the knee.

What causes an ACL tear or injury?

Anterior cruciate ligament (ACL) injuries are caused when the knee is straightened beyond its normal limits (hyperextended), twisted, or bent side to side.

The most common cause of ACL rupture is a traumatic force being applied to the knee in a twisting moment. This can occur with either a direct or an indirect force. In my practice, about half of the cases of ACL rupture occur without contact, i.e., while side-stepping, pivoting or landing from a jump. The other half are associated with some type of contact, whether it be on the football field, on the snow fields or in a motor vehicle accident. Skiing injuries usually occur during a fall in the inexperienced skier, on hired skis when the bindings do not release.

Typical situations that can lead to ACL injuries include:

  • Changing direction quickly or cutting around an obstacle or another player with one foot solidly planted on the ground. (This can happen in sports that put high demand on the ACL such as basketball, football, soccer, skiing, and gymnastics.)

  • Landing after a jump with a sudden slowing down, especially if the leg is straight or slightly bent (such as in basketball).

  • Falling off a ladder, stepping off a curb, jumping from a moderate or extreme height, stepping into a hole, or missing a step when walking down a staircase. Injuries like these tend to be caused by stopping suddenly, with the leg straight or slightly bent.

Inactive people and some older adults who have weak leg muscles may injure their knees during normal daily activities. But they usually injure bones, not ligaments.

When contact causes an ACL injury, it can be from playing a sport, from a sudden and severe accident, or from less obvious contact injuries. In football, receiving a clipping contact injury-in which the bent knee is struck from the outside-can cause an ACL injury.

Basically any athletic or non-athletic related activity in which the knee is forced into hyperextension and/or internal rotation may result in an ACL tear. 

Often those are non-contact activities with the mechanism of injury usually involving:

  • Planting and cutting - the foot is positioned firmly on the ground followed by the leg (and body for that matter) turning one direction or the other. Example: Football or baseball player making a fast cut and changing direction.

  • Straight-knee landing - results when the foot strikes the ground with the knee straight. Example: Basketball player coming down after a jump shot or the gymnast landing on a dismount.

  • One-step-stop landing with the knee hyperextended - results when the leg abruptly stops while in an over-straightened position. Example: Baseball player sliding into a base with the knee hyperextended with additional force upon hyperextension.

  • Pivoting and sudden deceleration resulting from a combination of rapid slowing down and a plant and twist of the foot placing extreme rotation at the knee. Example: Football or soccer player quickly slowing down followed by a quick turn in direction.

The severity of the injury to the knee will depend on:

  • The position of the knee at the time of the injury

  • The direction of the blow

  • The force of the blow

At least half of all ACL tears are associated with other soft tissue injuries in the knee, usually the medical meniscus or medical collateral ligament. When the ACL, medical meniscus and medical ligament are all torn the triad (3 injuries) is known as O'Donohugh's triad.

About 40% of people who who tear the ACL describe a "popping sensation" at the time of injury (which may be the tear of the ACL or of the medical meniscus). The knee usually swells and is painful.

The tear of the ACL can be a partial tear or a complete tear.

Instability or a sensation the knee is "giving out" may be a major complaint following this injury.

The question arises as to whether there is a predisposition in some people to ACL rupture. I have a significant number of patients who have sustained bilateral ACL tears. These patients comprise approximately 15% of the total number of patients sustaining rupture of their ACL. I also have a series of patients in my practice where ACL rupture appears to be familial. I have a number of families where up to four members have ruptured their ACL's. Furthermore, I have recorded two cases of ACL rupture in twins.

Another group of patients, I believe, have agenesis of the ACL. In some cases, when I have explored the knee within 3 to 4 days of their injury, there is minimal ACL tissue present in the notch. It has been well documented that patients with narrow intercondylar notches are more prone to rupture their ACL's. I believe that their notch is narrow because they have a hypoplastic ACL and hence are more prone to rupture.

Another interesting factor is that patients with recurvatum tend to be more likely to rupture their ACL and are more difficult to treat. I have also noticed a significant number of patients having ruptured their ACL who also have instability of the shoulder. I believe both these groups have a generalized ligamentous disorder.

Is Surgery Necessary?

ACL tears do not necessarily require surgery. There are several important factors to consider before undergoing ACL surgery. First, do you regularly perform activities that normally require a functional ACL? Second, do you experience knee instability? If you don't do sports that require an ACL, and you don't have an unstable knee, then you may not need ACL surgery.

There is also a debate about how to treat a partial ACL tear. If the ACL is not completely torn, then ACL reconstruction surgery may not be necessary.

Many patients with an ACL tear start to feel better within a few weeks of the injury. These individuals may feel as though their knee is normal again, but the problems with
instability may persist.

Surgery for an ACL Tear

The usual surgery for an ACL tear is called an ACL reconstruction. A repair of the ligament is rarely a possibility, and thus the ligament is reconstructed using another tendon or ligament to substitute for the torn ligament.

There are several options for how to perform ACL surgery. The most significant choice is the type of graft used to reconstruct the torn ACL. There are also variations in the procedure, such as the new 'double-bundle' ACL reconstruction.

Risks of ACL surgery include infection, persistent instability and pain, stiffness, and difficulty returning to your previous level of activity. The good news is that better than 90% of patients have no complications with ACL surgery.

Post-Surgical Rehab

Rehab is one of the most important, yet too often neglected, aspect of ACL reconstruction surgery. Rehab following ACL surgery focuses on restoring motion and strength, and improving the stability of the joint to prevent future injuries.

While general guidelines exist for ACL rehab, it is critically important that each individual progress through their rehab as their knee allows. Progressing too quickly or too slowly can be detrimental to overall results from surgery, therefore it is important to ensure your therapist and physician are guiding your rehab.

Rationale for Treatment

Rupture of the ACL causes significant short term and long term disability. With each episode of ACL instability there is subluxation of the tibia on the femur, causing stretching of the enveloping capsular ligaments and abnormal shear forces on the menisci and on the articular cartilage. Delay in diagnosis and treatment gives rise to increased intra-articular damage as well as stretching of the secondary stabilizing capsular structures.

Evidence to support this has been documented by research undertaken in my practice over the past 15 years. In 1976 I studied the relationship of anterior cruciate ligament rupture to meniscal pathology in three groups of patients. The first group comprised 100 consecutive patients who had a primary diagnosis of medial meniscal tear. At surgery 40% of these patients had a ruptured ACL. The next group comprised 100 patients who were operated on primarily for a diagnosis of a lateral meniscal tear. At surgery 60% had a ruptured ACL. The final groups comprised 100 consecutive patients who had tears in both menisci at arthroscopy. It was fascinating that 95% of these patients had a ruptured ACL.

Since that time, a number of authors have supported this view that a significant function of the ACL is to protect the menisci and if the ACL is ruptured then meniscal damage will occur.

The long-term outlook for an ACL deficient knee is for the development of significant osteoarthrosis. Evidence to support this view has also been documented in my practice. A series of 100 consecutive total knee replacements demonstrated a 15% incidence of previous ACL rupture. This incidence of ACL rupture is five times higher than that in the general population. Thus it is important to make an early diagnosis of ACL rupture Meniscal injury and long term degenerative damage is to be minimized.

Surgical Techniques

The development of surgery for ACL instability has been proceeding over the last century. Techniques at the turn of the 20th Century used autograft semitendinosus and gracilis with variable results. Xenografts were employed in Germany in 1912, using Kangaroo tail tendon for ACL substitution. However, results were poor due to problems with infection and graft rejection.

It was not until the 1950's when Don O'Donoghue began to aggressively treat knee ligament injuries in American footballers, that a renewed interest in ACL surgery began. Don Slocum from Eugene, Oregon invented the pes plasty in association Bob Larson. This operation was a dynamic tendon transfer attempting to prevent the anterior draw by dynamic muscle contraction. This operation enabled many athletes to return to the sporting arena and I believe that its main function was that it enhanced the proprioceptive control of the knee joint.

With the advent of arthroscopy came renewed research into the anatomy and biomechanics of the normal and injured knee joint. Early anatomical studies finding damage to the lateral capsular ligaments at the time of ACL rupture, caused many of the operative procedures to be aimed at repairing the capsule. Dr. Jack Hughston from Columbus, Georgia, drew the world's attention to the significant of capsular lesions causing knee joint instability.

Following the failure of repair techniques to ensure stability, focus became centered on substitution-type intra-articular reconstructions. Various graft materials have been tried including autograft, allograft, xenograft and artificial ligaments.

Many centers in the world are using allograft patella or Achilles tendon, or allograft anterior cruciate transfers. I have been unhappy to use these techniques, as a rule, because of concerns about sterility and the possible transmission of viruses. In the past, xenografts have been tried and have failed due to infection and failure to be incorporated.

Artificial ligaments made of fibres such as Dacron or Gortex have also been tried with mixed success. There is an unacceptable failure rate within two years due to either mechanical failure or inflammatory synovitis secondary to breakdown products shed for the graft.

A ligament augmentation device (LAD, invented by Kennedy in London) has also been widely used. Most studies, however, have not demonstrated that the use of the LAD has any significant advantage over the patella tendon transfer alone.

The use of autograft reconstructions have so far shown the best long term results. The two most common techniques use either the semitendonosis and gracilis, or the middle third of the patella tendon.

Currently, my preferred surgical technique for the routine case, is one using an isolated mid-third patella tendon graft placed, and secured arthroscopically. This technique has many advantages over the previous types of surgery. The procedure is relatively non-invasive requiring only small incisions. The graft can be placed accurately at the isometric points and the fixation of the bone blocks within the femur and tibia with the interference fit screw technique is very secure. This allows early motion and rehabilitation. There is a low perioperative morbidity and a rapid return to the activities of daily living and employment.

I personally believe that the operation should be performed in the first week following injury when advantage can be taken of the second phase healing factors. Many authors disagree with this approach, stating that there is an increased rate of arthrofibrosis. It is this second phase healing that causes arthrofibrosis, and I feel that with excellent fixation of the graft and accelerated rehabilitation, this arthrofibrosis factor can be utilized to an advantageous effect towards the graft revascularization and regeneration.


Anterior cruciate ligament rehabilitation has undergone considerable changes over the past decade. Intensive research into the biomechanics of the injured and the operated knee have led to a movement away from the techniques of the early 1980's characterized by post operative casting and delayed rehabilitation, to the current early rehabilitation program.

The major goals of rehabilitation following ACL surgery are:

  • restoration of joint anatomy;

  • provision of static and dynamic stability;

  • maintenance of the aerobic conditioning and psychological well being; and

  • early return to work and sport.

These have required the development of an intensive rehabilitation program in which the patient has to take an active involvement.

The graft undergoes physiological changes during its incorporation, as fibroblastic activity changes the biology of the graft to become more ligamentous. The graft is weakest between six and twelve weeks post operatively so programs must be designed to protect the graft during this period. On the other hand investigations into ligamentous healing have shown that progressive controlled loading provides a stimulus for healing which improves the quality of graft incorporation. More over, early immobilization has advantages such as maintenance of articular cartilage nutrition and retention of bone mineralization.

Kinematic research has shown quadriceps contraction causes greatest strain on the anterior cruciate ligament graft between 10° and 45° of flexion. The anterior cruciate ligament graft lacks the normal mechanoreceptors that provide biofeedback in the uninjured knee. All these factors must be taken into account when designing rehabilitation programs.

Our current accelerated rehabilitation program is divided into four phases. In the first one to two weeks the aims of therapy are to decrease pain and swelling, and increase the range of motion of the knee. A post-operative brace is ranged from 30 to 90° and is used until there is adequate quadriceps control. Physiotherapy including CPM is used immediately post operatively. In this early phase there is an emphasis on static contraction of the hamstrings and co-contractions of the hamstrings and the quadriceps. Crutch -walking with partial weight bearing is allowed and the usual modalities are used to reduce pain and swelling.

During the second phase, from two to six weeks, the emphasis is on increasing the range of motion, increasing weight bearing and gaining hamstring and quadriceps control. The patient is usually out of the brace by the third to fourth week. During this phase gait re-education and static proprioception exercises commence. This may include balancing on the affected leg, biofeedback techniques and pool work to maintain conditioning and range of motion.

During the third stage, from six to twelve weeks, emphasis is placed on improved muscular control, proprioception and general muscular strengthening. Proprioceptive work progresses from static to dynamic techniques including balance exercises on the wobble board and eventually jogging on a mini-tramp. The patient should have a full range of motion during this stage and gentle resistance work should be added. By the end of this period the patient should be able to cycle normally, swim with a straight leg kick and be able to jog freely on the mini-tramp.

The fourth phase of rehabilitation from twelve weeks to six months involves the gradual re-introduction of sports specific exercises aimed at improving agility and reaction times and increasing total leg strength.

An athlete who has had a technically well performed early reconstruction of the anterior cruciate ligament followed by an adequate and successful rehabilitation program, should be able to return to the field of his chosen sport between six and nine months.
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