Torn Anterior Cruciate Ligament

The anterior cruciate ligament (ACL) is a tough band of tissue joining the thigh bone to the shin bone at the knee joint. Anatomically, this ligament is located in the middle of the knee. It is one of four ligaments that runs diagonally through the inside of the knee and provides the knee joint stability. It also prevents the shin bone from sliding out in front of the thigh bone and helps to control the back-and-forth movement of the lower leg. The ACL is the most commonly injured ligament in the knee. ACL injury usually occurs when the knee is hyperextended (straightened) and a pivot occurs simultaneously. The injury may occur with or without contact. When the ACL tears, it unravels like a braided rope and does not heal on its own. Once the ACL is torn, the knee usually becomes unstable.

Cause of a torn ACL

The causes of a torn ACL include:

  • Changing direction rapidly
  • Slowing down while running
  • Landing from a jump incorrectly
  • Stopping suddenly
  • Planting the foot hard into the ground
  • Stiff-legged landing
  • Knee rotating while landing
  • Direct contact or collision, such as a football tackle

Numerous studies have shown that women athletes in sports such as football, basketball and tennis are significantly more prone to ACL injuries than men athletes. The discrepancy has been attributed to differences in knee anatomy, physical conditioning, muscular strength, reaction time of muscle contraction and coordination, neuromuscular control and training techniques. In addition, differences in pelvis and lower extremity (leg) alignment, increased looseness in ligaments, and the effects of estrogen on ligament properties make women more vulnerable to ACL injury.

Symptoms of a Torn ACL

Typical signs and symptoms of an ACL injury usually include:

  • A loud "pop" or a "popping" sensation in the knee
  • A very sudden and intense onset of pain
  • Inability to continue activity due to severe pain
  • Swelling that begins within a few hours
  • Loss of range of motion
  • A feeling of instability or "giving way" with weight bearing
  • Tenderness along the joint line
  • Can’t straighten or bend the knee all the way and the knee feels tight
  • Discomfort while walking
  • Sudden instability in the knee


Treatment of a torn ACL will depend on seriousness of the tear, other injuries to the knee, and the patient’s individual needs. For example, the young athlete involved in agility sports will most likely require surgery to safely return to sports. The less active, usually older individual may be able to return to a quieter lifestyle without surgery. 

Nonsurgical Treatment

A torn ACL will not heal without surgery, but nonsurgical treatment may be effective in older and less active individuals. These individuals are not involved with activities or sports that involve pivoting or cutting. If the overall stability of the knee is intact, surgeons may recommend simple, nonsurgical options such as bracing and physical therapy. 

Surgical Treatment

Most people with a torn ACL will experience instability, a feeling that the knee gives way or feels loose. This instability commonly results in a reduction in activities, especially sports. More importantly, the instability will usually lead to additional damage to the knee if left untreated.

Surgical treatment is often recommended for patients with a torn ACL. These patients experience instability leading to additional damage to the knee if left untreated. The purpose of surgical treatment is to return patients to their original level of activity.

Most ACL tears cannot be sutured (stitched) back together. To surgically repair the ACL and restore knee stability, the ligament must be reconstructed. The underlying concept behind the reconstructive surgery is that a tendon is surgically placed into the knee exactly into the position where the torn ACL was located. The reconstruction of the ACL involves tissue grafting with a piece of tendinous tissue to replace the ACL. This graft acts as scaffolding for a new ligament to grow on. During the grafting, the tendon is fixed to the bone with biodegradable screws. The healing process will then reestablish the blood supply to the tendon, and over the weeks following the surgery this blood supply will bring new cells (fibroblasts) that will repopulate the tendon and a new, functional ACL is formed.

The reconstruction procedure for a torn ACL involves minimally invasive surgery using an arthroscope with small incisions. Arthroscopic surgery is less invasive. The benefits of less invasive techniques include less pain from surgery, less time spent in the hospital, and quicker recovery times. A variety of techniques may be used, and the orthopedic surgeon and patient usually discuss the options available before making a decision as to what type of surgery is performed.

Surgery usually does not occur immediately after the injury, but may be delayed three to four weeks or more. This delay gives the inflammation a chance to resolve, and allows a return of motion before surgery. Performing an ACL reconstruction too early greatly increases the risk of arthrofibrosis, or scar forming in the joint, which would risk a loss of knee motion. Physical therapy and rehabilitation may take six to nine months to return to full activity.