The anterior cruciate ligament (ACL), together with the posterior cruciate ligament (PCL), forms the “X” structure at the middle of the knee joint, providing stability to the knee during movements.
The ACL runs diagonally in front of the shinbone, going upward, backward, and to the side, attaching itself to the broad end of the thigh bone[femur]. Its position allows it to resist excessive forward sliding of the shinbone and provides stability during rotational motions.
- 1 ACL Injury and Classification
- 2 ACL Tear Signs and Symptoms
- 3 Causes of ACL Injury
- 4 Diagnosis
- 5 Treatment and Home Remedies
- 6 Prevention
ACL Injury and Classification
ACL injuries commonly happen in combination with damage to other knee structures, including cartilages, meniscus, and other ligaments. Ligamental injuries are called sprains.
ACL injuries are classified into three grades based on the severity of injury:
Grade 1 ACL Sprain
There is only mild damage to the ACL, and only a slight stretch can be observed. The ACL is still able to provide stability to the knee joint.
Grade 2 ACL Sprain
There is partial damage or tear to the ACL. Considerable stretching or looseness of the ACL can be observed. This type is rare.
Grade 3 ACL Sprain
There is complete or almost complete tear/damage to the ACL. The ACL can be seen as completely torn and split in two, making it unable to support the knee joint. This is the most common injury to the ACL.
ACL Tear Signs and Symptoms
An injury to the ACL is usually accompanied by a “pop” sound followed by the feeling like the knee giving out. One might not be able to give weight to the injured knee. Other symptoms include:
Pain and Swelling
Some may experience pain accompanied by swelling within 24 hours after injury. This may resolve on its own, but lack of proper management during return to function may damage other structures of the knee joint.
The area in the knee joint may feel painful when touched.
Limited Range of Motion
One may not move the injured knee to its full motion resulting in difficulty in walking.
The injured knee feels “wobbly” and unable to support the body during walking.
Causes of ACL Injury
ACL injuries can be caused by contact or non-contact mechanisms. A blow to the outer side of the knee is the most common contact mechanism leading to injury not only to the ACL but also to the medial collateral ligament (MCL) and medial meniscus of the knee (also known as the “unhappy triad” or “Blown knee”).
This usually occurs in work-related accidents or automobile accidents. Meanwhile, the most frequent non-contact mechanism involves sudden and forceful rotation movement, which can be seen during basketball and soccer.
Rotation motions involve landing incorrectly from a jump, sudden stop when running, and rapid change in direction.
Studies have shown that female athletes are more likely to injure their ACL than male athletes and that non-contact mechanism in females is likely to result in complete tears.
Some propose that it is due to females’ lower extremity anatomy, such as having smaller ACL size and the leg’s anatomical alignment. Others inferred that it is due to hormonal factors, particularly estrogen, and the differences between male and female athletes’ physical conditioning, muscle strength, and dynamic control of their muscles.
Physical Examination and Medical History
A physician will inquire about the symptoms felt at the time of injury, the current symptoms being experienced, and the activity being performed that resulted in the injury.
A physical exam may involve assessing the range of motion of the injured knee [compared with a healthy knee], ability to balance, and gait pattern. It may also include evaluating other structures within the knee joint since ACL tears are almost always associated with damage to other parts of the knee.
An X-ray will not show if there is damage to the ACL; however, this is usually done to check for the presence of bone fractures.
Magnetic Resonance Imaging (MRI)
Although this is not mandatory to diagnose an ACL, this will provide a clearer view of the knee joint’s ACL and related structures.
Treatment and Home Remedies
Home remedies for an ACL tear are not encouraged as damage to the ACL is usually complete, requiring a trained physician to examine and treat it thoroughly. Self-medication and treatment might result in further damage to a partially torn ACL or damage to other structures, especially when the individual performs high-impact activities.
However, first aid treatment can be done to manage the pain and swelling, such as giving rest to an affected leg to prevent further injury, applying ice every 2 hrs for 15 to 20 mins, followed by wrapping the elastic bandage around the knee and elevating the leg in a lying position by placing pillows under the knee.
Treatment varies depending on the patient’s symptoms, the sprain’s grade, daily activities, occupation, age, condition of the growth plates for pediatric patients, and the patient’s goals.
Partial ACL tears and acute tears are usually managed conservatively through adequate rest, joint protection [wear brace or use crutches], and proper exercise. During the acute stage, treatment is directed towards improving the range of motion, obtaining balance control, strengthening the muscles that stabilize the knee joint, and gait training.
An intensive rehabilitation program might be needed by younger, active patients to improve dynamic neuromuscular control and return to high-impact activities.
Patients with complete tears who are young and active and wish to go back to performing high-joint load activities, including sports, work, or recreational activities, are good candidates for surgical management.
The factors that affect the decision for surgical reconstruction of the ACL include the level of instability being felt by the individual, the presence of damage to other structures, the level of function the individual wishes to return to, and the possibility of ACL re-injury.
Several factors are associated with an ACL injury. It does not only occur to athletes, but it can happen to anyone. Studies have shown that proper strength, balance, and flexibility training are ways to prevent ACL injury.
Prepare and Train Your Body
Proper warm-up and stretching before working out goes a long way in preventing injuries. Proper body mechanics and alignment during exercises must also be done to ensure that the right muscles are being targeted. Other structures, including ligaments that support the joint, will not be subjected to excessive stress.
Studies have shown that athletes who train and condition their bodies all year round are less likely to become injured because they have better neuromuscular control, improved feed-forward mechanism, and increased reaction speed.
Strengthen and Improve Flexibility of Leg Muscles
Strengthening the muscles surrounding and supporting the knee joint is important for ensuring that there will not be undue stress to the ligaments within the knee joint, including the ACL.
The thigh muscles and the buttocks are of particular importance as they work together during leg motions, especially during high-impact activities.
Perform Low-Impact Exercises
Older individuals, people with a previous injury to the knee, and those who are at risk for ACL injuries because of other factors are encouraged to perform low-load exercises to prevent excessive stress to the knee joint.
References:American Academy of Orthopedic Surgeons. (n.d.). ACL injury: does it require surgery? Retrieved
March 26, 2021, from https://orthoinfo.aaos.org/en/treatment/acl-injury-does-it-require-surgery/#:~:text=The%20anterior%20cruciate%20ligament%20(ACL,football%2C%20skiing%2C%20and%20soccer.
J EXP ORTOP 5, 22 (2018). https://doi.org/10.1186/s40634-018-0137-5
from https://www.hopkinsmedicine.org/health/conditions-and-diseases/acl-injury-or-tearKisner, C. & Colby L. (2007). Therapeutic Exercise: Foundations and Techniques.F.A. Davis and Company Stanford Children’s Health. (n.d.). Tips for preventing an ACL knee ligament injury. Retrieved
March 26, 2021, from https://www.stanfordchildrens.org/en/topic/default?id=tips-for-preventing-an-acl-knee-ligament-injury-1-2256