The anterior cruciate ligament (ACL) is a ligament of the knee that is commonly affected in knee injuries.

Participating in sports that involve a lot of lateral movement, such as basketball and soccer, increases the risk for ACL injury. It is not uncommon for an ACL injury to require surgery, particularly if the injury is severe or if the patient wishes to be highly mobile following the injury.

Anatomy

Knee Joint

The knee joint is the junction between three bones: the thighbone (femur), shinbone (tibia), and kneecap (patella). Ligaments join bones together. Four primary ligaments, two collateral ligaments, and two cruciate ligaments support the knee. The collateral ligaments support side-to-side motion, and the cruciate ligaments support front-to-back and back-to-front movements.

The two collateral ligaments are found on each side of the knee. The medial collateral ligament (MCL) is on the inside of the knee facing the other leg, and the lateral collateral ligament (LCL) is on the outside of the knee, facing away from the body.

The cruciate ligaments lie diagonally across the joint and cross one another in an “X” formation. These ligaments control front-to-back and back-to-front movements, with the anterior cruciate ligament (ACL) located in the front of the knee joint and the posterior cruciate ligament (PCL) located in the back of the knee joint.

The ACL provides the knee with stability during rotational motion and specifically supports the separation of the tibia and femur. The tibia and femur are both covered in articular cartilage, and the cartilage of each is separated by the medial and lateral menisci. These menisci absorb the pressure of weight and motion to minimize stress on the tibia and femur.

Description

When the ACL tears, other structures of the knee are also injured about half the time. Other structures that often endure injuries when the ACL is injured are other ligaments, a meniscus, or articular cartilage.

ACL Tear

Cause

There are a number of ways that the ACL can be injured, but injury generally involves changes in speed or direction of motion. Some of the most common causes for ACL injury are:

  • Altering direction of motion too quickly
  • Halting motion suddenly
  • Landing on the feet off balance

Approximately 70% of all ACL injuries are the result of non-contact mechanisms, though 30% are thought to result from collision with another person or object.

Symptoms

When the ACL tears, it often completely, or almost completely tears. Partial tears are rare. There are a few indicators that suggest that the ACL may be injured. People often hear a pop when the ACL is torn or experience the knee giving out beneath them. Loss of stability of the knee or reduced range of motion can be indicative of ACL injury. Pain and tenderness in the knee are also symptoms of ACL injury.

Swelling occurs within one day of ACL injury. Though it is possible for ACL injuries to resolve without medical intervention, maintaining a high level of activity on an injured ACL can lead to more extensive damage. With the ACL damaged, knee support is compromised, putting other structures of the knee at risk for injury. The menisci are particularly vulnerable once the ACL is injured.

Imaging Tests

Magnetic resonance imaging (MRI) provides high resolution images of soft tissues such as the ACL and is thus a powerful tool for identifying ACL injury. X-rays may also be used in combination with MRI to determine if the injury involves bone fractures. An added advantage of x-rays is that they can reveal any structural abnormalities that could make the patient vulnerable to an ACL injury.

Identifying ACL injuries

Nonsurgical Treatment

Though knee surgery is required to fully heal the ACL, there are scenarios wherein patients may opt out of surgery. For example, elderly patients who are not highly mobile may choose to wear a brace and endure physical therapy if the knee is adequately stable.

Surgical Treatment

Surgery can be performed to fix a torn ACL. Because the ACL cannot be stitched back together, surgery involves reconstruction of the ACL and aims to restore stability to the knee so that the knee functions properly. Young people and athletes will often choose surgical intervention to treat their ACL injuries.

ACL Reconstruction

What happens during the procedure?

ACL Surgery

Dr. Samimi specializes in ACL reconstruction using the most up-to-date minimally invasive techniques. He uses minimally invasive arthroscopic techniques to reduce pain associated with the procedure and hasten recovery time.

Dr. Samimi carefully inserts an arthroscope into the knee through a tiny incision. This scope has a small camera on one end and is attached to a video monitor in the operating room, which allows Dr. Samimi to inspect all the tissues of his patient’s knee. Dr. Samimi then removes the torn tissues using small surgical tools.

Dr. Samimi then prepares a graft to act as a scaffold to support the growth of a new ligament. He attaches this graft to the femur and tibia and then sutures your incisions. The entire process takes approximately 1-2 hours, and the patient can usually go home following the orthopedic surgery. Patients are usually encouraged to do a course of physical therapy after the procedure.

 

ACL repair and reconstruction

 

ACL Graft

Graft Choice

There are a number of different grafts available, and the advantages and disadvantages to each should be considered on a patient-by-patient basis.

Hamstring tendon autograft. Hamstring tendon autografts are employed with the tendons on the inside of the knee. The advantages of this type of graft are that harvesting is technically relatively simple–it requires only small incisions, there is relatively little pain and stiffness associated with this graft, and recovery is faster. The disadvantages of this graft are that it may be limited in strength and may be more susceptible to stretching.

Hamstring Tendon Autograft

Hamstring Tendon Autograft

 

Allografts. Allografts are becoming more popular over time. These grafts are taken from cadavers. Advantages of allografts are that they eliminate the need to harvest tissue from the patient, they provide for strong supportive systems, particular in the Achilles and patellar tendon, and they are associated with reduced surgery time and smaller incisions. Disadvantages of allografts are that they are more highly associated with infections than autografts and may be susceptible to stretching. Allografts are often used in patients for whom prior reconstructive surgery was not effective.

Patellar Tendon and Achilles Allografts

Patellar Tendon and Achilles Allografts

 

Rehabilitation

Rehabilitation is an essential component of therapy following ACL injury. Whether a patient has endured surgery or has opted for non-surgical treatment options, rehabilitation is crucial for regaining strength, stability, and adequate motion in the knee. Because growth occurs during rehabilitation, patience is important. It can take more than 6 months to fully recover from an ACL injury and resume normal activities.

For more detailed information about ACL Reconstruction please visit: AAOS Online Services Fact Sheet – ACL Injury: Does It Require Surgery?