Anterior Cruciate Ligament Tears and Their Treatment: arthroscopic and minimally-invasive surgery for ACL reconstruction

Edited By: Christopher J. Wahl, M.D., Suzanne L. Slaney, PA-C, ATC, MMS
Last updated Friday, October 20, 2006

Review of the condition

Characteristics of anterior cruciate ligament - acl - tear

There are several mechanisms that can cause injury to the ACL. Direct contact forces, such as those experienced in a motor vehicle accident, can cause ACL disruption.  However, the ACL is most commonly injured by indirect, noncontact mechanisms such as vigorous cutting, landing, or twisting motions.  An example of this would be an athlete who suddenly decelerates from running and makes a sharp cutting motion or when a skier catches their ski in the snow causing a rotational force at the knee.

At the time of ACL injury, individuals will experience a sudden severe knee pain and possibly hear or feel a “popping” sensation in their knee.  Patients will have a difficult time bearing weight on the injured leg because of an unstable “giving out” sensation in the knee.  Usually within the first few hours after the injury, the knee will become significantly swollen and the range of motion will typically decrease due to the limiting effects of pain and swelling.

A completely torn ACL will never heal back to it pre-injury “normal” state even after conservative treatment such as rehabilitation.  The ACL is contained within the joint and covered with a thin layer of tissue (synovium).  This synovial tissue is in contact with synovial joint fluid in the knee.  In order for healing to occur, a collection of blood must form and clot around the ligament, but once the ligament and synovial tissue are torn, the ligament will be bathed in synvoial joint fluid.  The blood is not able to collect, as it is diluted and “washed” away by the joint fluid; therefore healing is unable to occur.  In addition, even with a partially torn ligament, the mechanical function of the knee may be altered after an ACL tear such that the normal path of motion of the knee is altered (like swing with one of the chains broken).  It is very difficult for the ligament to resume a normal length and function in this setting.

Types

ACL injuries can be classified by the amount of damage to the ligament (partial or complete disruption). Injury to the ACL is usually a complete disruption, classifying it as a Grade III complete tear.

• Grade I Sprain - There is some stretching and micro-tearing of the ligament. The ligament is intact.  The joint remains stable.  These injuries rarely require surgery.
• Grade II Sprain (Partial Disruption) - There is some tearing and separation of the ligament fibers.  The ligament is partially disrupted.  The joint is moderately unstable.  Depending on the activity level of the patient and the degree of instability, these tears may or may not require surgery. 
• Grade III Sprain (Complete Disruption) - There is total rupture of the ligament fibers.  The ligament is completely disrupted.  The joint is unstable.  Surgery is usually recommended in young or athletic persons who engage in cutting or pivoting sports. 

Additionally, injury can be classified by the presence or absence of associated damage to other structures in the knee (isolated or combined). Combined injuries may involve damage to the menisci, stabilizing collateral ligaments, or other knee structures.  Figure 1.

• Meniscus - The medial and lateral menisi are “cushions” between the tibia and femur that act as a shock absorber and distribute stresses placed on the knee joint.  Additionally, this structure helps stabilize the knee. A meniscus tear typically occurs with twisting motions such as pivoting.

• PCL - The posterior cruciate ligament “crosses” behind the ACL and restrains the tibia from moving backwards (posterior) on the femur.  Traumatically, this ligament is commonly injured by striking the upper tibia, causing the tibia to move backwards, thereby stretching or tearing the PCL.  An example of this would be striking the upper tibia on the dashboard during an automobile accident.  In athletics, a PCL will tear during a hyperextension or extreme hyperflexion injury (like falling onto the shin with the knee bent and foot pointed).

• MCL - The medial collateral ligament provides stability to the inside aspect of the knee.  This ligament is commonly injured when a medially (inward) directed force is applied to the outside of the knee, forcing the knee to twist in and the foot to twist out.  Injury to this structure is common, but if it is an isolated partial disruption injury then it can typically be treated with physical therapy and bracing.

• LCL - The lateral collateral ligament imparts stability to the outside aspect of the knee.  Isolated LCL injuries are infrequent, but when injured it is commonly due a lateral (outside) force applied to the inside of the knee.  

It is not uncommon to hear the term “unhappy triad” associated with an ACL injury. This describes an ACL injury associated with a concomitant MCL injury and medial meniscus tear.  This triad usually occurs when the ACL has been torn for a long time (‘chronic tear’).  It is more common to tear the lateral (outside) meniscus after an ‘acute’ ACL tear.

Similar conditions

ACL injuries are usually not subtle and most individuals will know exactly when the injury occurred. There are conditions in the knee that can mimic a sense of instability, some operative and others non-operative:

• Isolated collateral ligament injury - Severe injury to any of the knee ligaments (ACL, PCL, MCL, LCL) can result in a sense that the knee does not behave normally.

• Meniscal tear - A torn fragment of the meniscal cartilage can become temporarily “trapped” in the joint, and produce a sense of “giving way” or “instability”.

• Arthritis/articular cartilage injury - A flap of cartilage, or a loose fragment of cartilage or bone in the knee will produce “locking” or “giving way” that may be likened to “instability”.

• Patellofemoral joint instability/dislocation - Dislocation of the kneecap off the front of the femur can often mimic the “pop” that is heard when an ACL injury occurs, and can result in pain, inflammation, and a sense of instability.  This problem can frequently be treated non-operatively after the kneecap is re-located.  In cases where the problem recurs, surgery may be warranted.

• Patellofemoral joint pain - Pain behind the kneecap from cartilage softening or wear will often manifest as a sense of “giving way” or temporary instability.  This problem is almost always treated non-operatively.

Incidence and risk factors

The ACL is not the most commonly torn ligament of the knee joint, but because it does not heal (unlike the medial collateral ligament (MCL) or posterior cruciate ligament (PCL)); tears of the ACL frequently require surgical treatment.

This injury is particularly common in athletic individuals who participate in sports that involve twisting, cutting, jumping, and sudden decelerations. These activities overload the strength and stability of the ligament, leading to an ACL tear.

This injury is predominant in female athletes.  It is believed that women are at greater risk than men because anatomical differences put women at a mechanical disadvantage.  Some of the distinctions being reviewed include having a wider pelvis, greater “knock-kneed” alignment, delayed muscle reaction, and decreased muscle force.  Additionally, hormones may play a role in ACL injuries in women.  The change in hormone levels may influence the amount of laxity (looseness) in the ACL which predisposes it to disruption.

Diagnosis

Medications

There are no medications that can be used to heal a disrupted ACL. However, some medications such as non-steroidal anti-inflammatory drugs (NSAIDs) will help ease the pain or symptoms related to the meniscus deficient knee.

• The risks associated with the medication
• The possible interactions with other drugs
• The recommended dosage
• The cost

Exercises

After visiting the orthopaedic physician, it might be advised that the patient meet with a physical therapist to increase the knee range of motion, decrease the amount of swelling, and maintain muscle control. Physical therapy and at home exercises will become part of the patients daily routine, whether the patient has the ACL reconstructed or not.

In rare cases or in sedentary individuals, there may be a role for non-operative treatment and rehabilitation.  Non-operative treatment should be considered in:

• Patients with partial injuries and/or relatively stable knees on examination, who can perform their expected activities of daily living without difficulty
• Patients who were not capable of walking prior to the injury
• Patients who can not undergo surgery safely

Possible benefits of arthroscopic anterior cruciate ligament (acl) reconstruction

The ACL is vital for “normal” knee function and surgical reconstruction can successfully restore this function.

The overwhelming majority of patients who undergo arthroscopic ACL reconstruction to address knee instability will have a successful result.  This success is seen in patients who can participate in not only daily life activities but also in demanding physical activities such as competitive sports. 

Surgery for Anterior cruciate ligament - ACL - tear at the University of Washington

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