How ACL and PCL Injuries Differ

Differences in Symptoms, Causes, Diagnosis, and Treatment

Mature woman in gym holding painful knee

Barry Austin / Digital Vision / Getty Images

In This Article
Table of Contents

The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are two major ligaments in the knee that work together to provide stability. They are also common sites of serious tears, particularly in athletes.

Although ACL and PCL injuries may initially appear to have similar symptoms such as knee instability and pain, the ligaments have unique characteristics that make them differ in terms of who is affected, extent of injury, and treatment guidelines.

Anatomy

The ACL and PCL are two major ligaments that crisscross within the joint, allowing the knee to flex and extend without sliding back and forth. The ACL prevents the tibia from sliding forward along the femur, while the PCL prevents the tibia and femur from sliding backwards.

Together they provide stability for the knee joint, preventing it from moving from side-to-side while at the same time allowing it to flex and extend. The ACL prevents the tibia from sliding forward along the femur, while the PCL prevents the tibia and femur from sliding towards each other.

The other two ligaments of the knee, the medial collateral ligament (MCL) and lateral collateral ligament (LCL). These run along the outside of the knee and prevent the knee from bending sideways.

Symptoms

The symptoms of ACL injuries and PCL injuries are essentially the same: pain, swelling, and knee instability. Where they tend to differ is the extent of the injury and the severity of symptoms.

Because it's smaller and weaker than the PCL, the ACL is more likely to sustain a complete tear. When this occurs, there may be an audible "pop" at the moment the ligament ruptures. ACL damage can extend to adjacent structures, including other ligaments as well as the crescent-shaped pad of cartilage known as meniscus that serves as a cushion between the bottom of the thigh bone and top of the shin bone.

The pain from an ACL tear usually will be more severe than that of a PCL tear. There also may be significant (or total) loss of range of motion of the knee. Swelling from an ACL tear tends to develop slowly, over the course of 24 hours.

Most PCL injuries are partial tears. Swelling is likely to happen almost immediately, but there will be relatively less pain, if any. Fewer than 20% of knee ligament injuries involve the PCL.

Causes

Both ACL tears and PCL tears can result from a sports mishap. The ACL is most likely to be injured during a sudden stop or rapid change in direction—movements that are typical in activities like soccer, basketball, football, and downhill skiing. Landing awkwardly from a jump can also damage the ACL. The risk of a sports-related ACL tear is increased for people who are in poor physical condition, have ill-fitting footwear (or ski binding), and play on slippery artificial turf.

Being a woman also is a risk factor for ACL tears. Female athletes are two to seven times more likely to injure their ACL than are men due to a number of anatomical and biomechanical differences between the two sexes.

PCL tears typically occur when the knee is bent, such as during a fall with the knee pointed downward or in car accident in which the bent knee jams into the dashboard. A hard blow to the shinbone just below the knee, as might happen in football or soccer, also can injure the PCL, as can a misstep on an uneven surface.

Diagnosis

To diagnose a torn ACL or PCL, a doctor will start with a physical exam, looking for certain signs and symptoms of injury.

With an ACL tear, the knee will be tender to the touch along the joint line and it will be difficult, if not impossible, to flex the knee. There also may be spasms and guarding of the hamstring muscles at the back of the thigh.

A tell-tale sign of a PCL tear is a backward, sagging position of the knee as it is bent. The kneecap may be able to slide even further back when the knee is bent more than 90 degrees.

Once a tear is suspected, the diagnosis can be confirmed with an X-ray (which is able to show complete ruptures) or magnetic resonance imaging (which is better able to visualize ligaments and other soft tissues).

Treatment

Treatment for ACL and PCL injuries essentially is the same, but will differ depending on the severity, or grade, of the injury:

  • Grade 1: The ligament is slightly stretched but the knee is stable.
  • Grade 2: The ligament has become loose or is partially torn.
  • Grade 3: There is a complete rupture of the ligament.

Depending on the grade, the injury may be treated with the RICE protocol: rest, ice, compression, and elevation. Physical therapy is often recommended to regain joint strength and range of motion. Complete tears may require arthroscopic surgery and ligament reconstruction.

The only true difference between the treatment of ACL and PCL injuries is the likelihood of surgical intervention. Since ACL tears are more likely than not to be complete, the course of treatment tends to be far more extensive.

Not everyone with a complete ACL rupture will need surgery. People who are largely inactive or are older often can manage with a knee brace or assisted mobility device after an ACL tear.

On the other hand, most PCL injuries can heal on their own without surgery and may require only crutches and a knee immobilizer to prevent knee movement during recovery.

Was this page helpful?
Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Canale ST, Beaty JH. (2012) Campbell's Operative Orthopaedics (12th Ed). Maryland Heights, Missouri: Mosby/Elsevier.

  2. Marieswaran M, Jain I, Garg B, et al. A Review on Biomechanics of Anterior Cruciate Ligament and Materials for Reconstruction. Appl Bionics Biomech. 2018;2018:4657824. doi:10.1155/2018/4657824

  3. Cimino F, Volk BS, Setter D. Anterior Cruciate Ligament Injury: Diagnosis, Management, and Prevention. Am Fam Physician. 2010 Oct 15;82(8):917-922.

  4. Lee BK, Nam SW. Rupture of Posterior Cruciate Ligament: Diagnosis and Treatment Principles. Knee Surg Relat Res. 2011 Sep;23(3):135-41. doi:10.5792/ksrr.2011.23.3.135

  5. Salzler MJ, Chang J, Richmond J. Management of Anterior Cruciate Ligament Injuries in Adults Aged >40 Years. J Am Acad Ortho Surgeons. 2018 Aug;26(16):553-61. doi:10.5435/JAAOS-D-16-00730

Additional Reading