Anterior Cruciate Ligament (ACL) Tear Symptoms & Treatment

Overview

The anterior cruciate ligament (ACL) is one of the four major ligaments of the knee. It runs through the center of the knee joint and connects the femur (thigh bone) to the tibia (shin bone), providing critical stability.

The ACL:

• Prevents the tibia from sliding too far forward
• Controls excessive rotation of the knee
• Helps maintain overall knee stability during movement

When the ACL is injured—whether through a partial ACL sprain or a complete ACL ligament tear—the knee may become unstable, especially during physical activity.

What causes Anterior Cruciate Ligament (ACL) Tear?

An anterior cruciate ligament tear occurs when the ligament is overstretched or torn, either partially or completely. ACL injuries are among the most common knee injuries in athletes, particularly in sports that involve cutting, jumping, and rapid changes in direction.

Most ACL injuries occur without direct contact, making them one of the most common non-contact knee injuries. In many cases, athletes feel symptoms immediately after injury.

What Causes an Anterior Cruciate Ligament (ACL) Tear?

Most ACL injuries occur due to non-contact mechanisms, although direct trauma can also cause an ACL ligament tear.

1. How the Injury Occurs

An ACL tear typically occurs when the knee is forced into:

• Sudden deceleration
• Twisting or pivoting motions
• Hyperextension (over-straightening)

These movements place excessive stress on the ACL, leading to a sprain or tear.

2. Common Everyday Causes

• Slipping or falling awkwardly
• Sudden directional changes while walking or running
• Missing a step while going downstairs

3. ACL Tears Are Common in These Sports

Sports that place high rotational and impact stress on the knee increase the risk of ACL ligament tears, including:

• Basketball
• Football
• Gymnastics
• Lacrosse
• Volleyball
• Skiing
• Rugby
• Snowboarding
• Soccer
• Softball
• Wrestling

Athletes in these sports are particularly prone to ACL tears due to repetitive cutting and jumping movements.

Symptoms

You may have an ACL injury if you experience one or more of the following ACL tear symptoms after a knee injury:

• Immediate swelling caused by bleeding inside the joint
• A popping sensation or sound at the time of injury
• Pain, often felt deep within or along the outside of the knee
• A feeling that the knee is unstable or “gives out” during movement

Mild injuries may present as an ACL sprain, while severe symptoms often indicate a complete ACL ligament tear.

Associated Knee Injuries with ACL Tears

ACL tears are frequently associated with injuries to other structures in the knee, including:

• Medial Collateral Ligament (MCL) tear – affects inner knee stability
• Lateral Collateral Ligament (LCL) tear – affects outer knee stability
• Meniscus tear – causes locking, catching, or deep knee pain

These combined injuries can worsen symptoms and prolong recovery if not properly treated.

Non-operative treatment

Initial treatment for an ACL injury focuses on reducing swelling and restoring knee motion.

Conservative Treatment Options Include:

• Rest and activity modification
• Icing the knee regularly
• Wearing a knee brace for stability
• Physical therapy to regain strength and motion

Patients with a partial tear or ACL sprain, and those who do not participate in high-demand sports, may successfully manage their condition without surgery.

Rehabilitation Exercises

A structured exercise program helps restore strength and control.

(Refer to the PDF Exercise Program below)

Knee ACL Injury

Surgical Treatment

Surgery is often recommended for athletes or individuals with a complete ACL ligament tear, especially if knee instability persists.

Goals of ACL Surgery:

• Restore knee stability
• Prevent further damage to cartilage and meniscus
• Allow safe return to sports and activity

ACL reconstruction replaces the torn ligament using a tendon graft.

Common Graft Options

Allograft

A donor tendon that allows for smaller incisions and quicker early recovery.

Bone–Patellar Tendon–Bone Graft

Uses a portion of the patellar tendon with bone attachments for strong fixation, but it may cause more postoperative knee pain.

Hamstring Graft

Uses hamstring tendons and typically results in less kneecap pain and smaller incisions.

ACL reconstruction is performed using arthroscopic techniques with small incisions and specialized instruments.

In select cases, a newer approach known as ACL repair may be considered instead of traditional reconstruction. This technique involves repairing the patient’s original ligament rather than replacing it with a tendon graft. ACL repair is less commonly performed and is only suitable in specific situations, such as when the ligament has torn cleanly from the bone and treatment is initiated soon after the injury. While this approach may allow for a faster recovery in carefully selected patients, it is not appropriate for most ACL tears.