PT Tip of the Month

Anterior Cruciate Ligament (ACL) Tears

The Anterior Cruciate Ligament or ACL is a ligament which helps to stabilize the knee joint. More specifically, it stabilizes the tibia (lower leg) from sliding forward at the femur (upper leg).

Mechanism of Injury

The ACL is the most frequently injured and repaired ligament within the knee and can be injured both by contact and non-contact mechanisms. The most common mechanism of an ACL contact injury involves a blow to the outside of the knee. This type of mechanism commonly results not only in an injury to the ACL, but also the Medical Collateral Ligament (MCL) and medial meniscus. This type of injury, in which all three structures are damaged, is called the “unhappy or unholy triad.” As stated previously, the ACL can also be injured through non-contact means. This most commonly occurs as result of excessive rotation forces through the knee with a planted foot.1, 2


Treatment for this type of injury is very important for ligament injuries because non-treatment can lead to chronic instabilities and long term changes within joint if not adequately monitored and managed.2 In most cases the ACL will need to be surgically repaired, but for some patients the ACL can be treated non-surgically.2, 3, 4 There are many considerations to make before deciding the best avenue for care.2

Surgical Care
Surgery is indicated for the following reasons:

  • Patients with a high level of function
  • Presence of additional pathology (i.e. meniscus tears)
  • Pre-existing condition of the joint articular surfaces (i.e. osteoarthritis)
  • Potential for re-injury
  • Complete acute tear or chronic insufficiency of the ACL, causing abnormal joint motion and instability or buckling
  • Partial tears that result in limitations or functional activities in active individuals
  • Non-successful conservative management
  • Most recreationally active patients with acute isolated ACL injuries will have surgery to repair the injured ligament

The most common type of surgery performed is arthroscopic surgery which utilizes grafts of other tissue in place of the ACL. The grafts are most commonly harvested from the patient through the patella tendon or hamstring tendon. Grafts can also be taken from donor tissue or made synthetically.1, 2



Types of Grafts



Patella Tendon

- More tensile strength
- Faster healing time

- Increased risk of patella
   femoral pain


- Decreased risk of
   patella femoral pain

- Less tensile strength
- Residual Hamstring 

Donor ACL

- ACL tissue can be
   replaced with an actual

- Risk of disease
   transmission and tissue
- Decreased Graft Strength
  due to the sterilization

The initial post-op treatment will focus to protect the healing graft and control pain and joint effusion while regaining range of motion. The patient will wear a knee immobilizing brace for approximately 8 weeks post-operation. Later in the recovery, treatment will focus on regaining functional abilities through therapeutic exercise.2

Nonoperative management
Studies show that approximately 1/3 of patients can return to previous levels of function with a torn ACL without surgical intervention. Theses patients develop what is known as dynamic, or muscular, stability. Dynamic stability is created within the knee through increased muscular action and coordination, which takes the place of the compromised ACL.3 The main focus of non-operative treatment, revolves around rest, joint protection and exercise. Shortly following the injury, treatment will involve decreasing pain and swelling and increasing range of motion within limits of pain. After this initial phase, treatment will focus on regaining range of motion, balance, gait and strengthening muscles that stabilize the knee joint.2


Studies show about 96-98% of people who have surgery for an ACL injury will return to their previous level of function. Studies of non-surgical treatment of an ACL injury, reveal between 70-79%3, 4 of patients who are eligible for nonoperative care return their prior level of function after 1 year following the original injury and 72%4 after 10 years following the injury. Rehabilitation programs following an ACL injury will expect a return to sport or prior level of function between 6 months to 1 year, where as patients who can be treated non-surgically usually return to their prior level of function within 2 months to 1 year.3-4


  1. Magee, David J. Orthopedic Physical Assessment. 4th edition. 2006
  2. Kisner, Carolyn. Therapeutic Exercise: Foundations and Techniques. 4th edition.
  3. Moksens et al. Individuals with an anterior cruciate ligament-deficient knee classified as noncopers maybe candidates for nonsurgical rehabilitation. Journal of Orthopedic. 38:10. 2008
  4. Hurd et al. A 10 year perspective trial of a patient management algorithm and screening examination for highly active individuals with anterior cruciate ligament injury. The American Journal of Sports Medicine. 36: 48. 2007.
33 Pond Avenue, Suite 107B Brookline, MA 02445 Tel: (617) 232-PAIN (7246) Fax: (617) 232-5196
1208B VFW Parkway, Suite 202 West Roxbury, MA 02132 Tel: (617) 325-PAIN (7246) Fax: (617) 325-7282