Knee Stability and the ACL


Knee Stability and the ACL

The ACL (anterior cruciate ligament) is the primary stabilizer of the knee, and the most commonly injured ligament in the knee complex. The ACL can be found in the center of each knee joint, connecting the shin bone (tibia) to the thigh bone (femur). A function of the ACL is to prevent the tibia from moving forward in relation to the femur.
Injury to the ACL can cause a feeling of instability, resulting in the knee buckling or giving way particularly during twisting and cutting motions.


ACL: Mechanism of Injury


Individuals who participate in activities requiring a quick change in direction (such as soccer and basketball) are at an increased risk to sustain an injury to the ACL. There are multiple components that can increase one’s risk of an ACL injury. Regarding anatomical differences between men and women, women typically have a wider pelvis which creates a less optimal femur position (relative to the shin bone) and can place additional mechanical forces on the ACL. Men and women can also have varying muscular strength and flexibility affecting the position of the knee and ACL during activities. An injury to the ACL can occur due to contact or without contact (traumatic and non-traumatic). A direct blow force to the knee, a sudden stop hyperextending and/or twisting the knee will translate force through the ACL, and possibly causing injury. One’s playing surface, and the interaction with the shoe (slips and “catches”) can also have an affect on the strain placed on the ACL.


ACL: Signs and Symptoms


- Feeling that knee is buckling or giving out; instability
- Hearing or feeling a “pop” at the time of injury
- Swelling or effusion (fluid in the joint)
- Pain located deep inside knee, or in the back of the knee joint
- Decrease in knee function and motion
- High calf pain


ACL: Evaluation and Diagnosis


An injury to the ACL can be assessed during a clinical evaluation by a physician, surgeon, physical therapist or athletic trainer. Based on the results of the examination an MRI may be ordered by the physician to take a better look at the ligament, and other surrounding structures.


Ligament injuries are classified into one of three categories:


Grade 1: Mild
- There is an injury to the ligament, but there are few disruptions to the ligament fibers. Generally the ligament is still providing good stability to the joint and may only be sore to physically stressing it.


Grade 2: Moderate
- The ligament is disrupted partially. There may be some instability (joint looseness) associated with this tear.


Grade 3: Severe
- Complete and total disruption of the ligament causing instability.


ACL: Treatment


Depending of the extent of the injury, and any associated injuries, your physician or surgeon may recommend a knee immobilizer brace immediately to prevent knee movement and facilitate healing. It is advisable to follow the R.I.C.E. acronym (Rest, Ice, Compression, and Elevation) to aid in the reduction of pain and swelling. Ice should be administered for 15-20 minutes at a time, and should not be re-applied until your skin return to normal temperature. For more details on R.I.C.E. <click here>


ACL: Surgical Reconstruction


A surgical intervention may be necessary to repair the damaged ACL. The need for surgical reconstruction will depend on the extent of the injury, and the patient’s outcome goals and activity level. An individual with plans to return to competitive athletic activities will more than likely require a surgery to reconstruct the injured ligament. In comparison, an individual who is able to function with the knee instability resulting from the injury may not need surgical intervention. In the non-surgical case, physical therapy to train all the muscles surrounding the knee to help stabilize may be a very effective approach.


While a surgeon cannot successfully repair the injured ACL due to its healing capabilities, a replacement ACL can be surgically inserted. Tendon has proven to be the most effective tissue to replace the ligament with as it too is very fibrous and can provide stability to connecting bones. A tendon graft, known as an autograph, can be harvested from another part of the patient’s body (hamstring or patella tendon) or a cadaver tendon from an organ donor (allograft) can surgically replace the injured ACL. The new ACL graft will be inserted through the thigh bone connecting to the shin bone, and anchored appropriately.


ACL: Surgical Rehabilitation


An average rehabilitation time for recovery from an ACL surgery is 4-6 months. Please keep in mind that this time frame varies depending on the individual’s nature of the initial injury, surgical complications, and compliance with post-surgical treatment. After reconstructive surgery physical therapy will be prescribed to increase the range of motion in the knee joint, begin regaining strength of the muscles in the involved leg, advancing balancing and coordination, and returning to life, work, and sport activities. Wearing a brace after surgery will be based on the recommendations of the attending surgeon. In many cases, with surgeon approval, return to sport can occur in the 12 month range.


ACL: Pre-surgical Rehabilitation


Your surgeon may recommend attending a course of physical therapy prior to your surgery. The goal of physical therapy would be to decrease pain and swelling, and increase range of motion and strength. This is a great opportunity to prepare your knee for surgery, and gain an understanding of the exercises you will be performing during the post-surgical rehabilitation stage.


If you need assistance in dealing with an ACL injury, please locate the nearest ProEx Physical Therapy Sports Medicine Specialist at http://proexpt.com/content.php?l=66


*** Resources: MGH, AOSSM, NATA

Knee Stability and the ACL