ACL Injuries

What is an ACL?

Simply put, an anterior cruciate ligament (ACL) connects the bottom of the femur (thighbone) to the top of the tibia (shinbone). It is one of four ligaments in the knee and is responsible for stability, forward movement of the lower leg and preventing rotational stress. Not only is the ACL the weakest of the four ligaments in the knee, too much stress can cause it to tear.

How does the ACL get injured?

Direct contact ACL injuries occur from an on-field or on-court collision. Non-contact ACL injuries are usually the result of a quick pivot, unbalanced landing or acceleration of speed followed by a sudden stop. Sometimes, the non-contact ACL injury can be exacerbated by overuse, when an athlete continues to play one sport year round without a break. Experts are most concerned about the rising number of non-contact ACL injuries, which account for nearly 70 percent of all ACL injuries.

Who gets an ACL injury?

Anyone can get an ACL injury, but the most susceptible are those involved in sports that require pivoting, jumping, decelerating and turning quickly, such as skiing, basketball, football, lacrosse, volleyball, cheerleading, soccer and gymnastics.

Females are at greater risk than males. The American Academy of Orthopaedic Surgeons (AAOS) reports that female athletes are up to 10 times more likely to sustain an ACL tear than their male counterparts. This is because higher levels of estrogen in women actually weaken the tendons by relaxing the fibers, making them more susceptible to tears. Since girls typically have wider hips than boys, there is a smaller notch for the ligament to connect to the femur, which restricts movement. Girls are also more likely to land on their feet with knees straight, as opposed to bent, which increases pressure on the joints. With more girls playing sports since the inception of Title IX in 1972, there has been at least a 10-fold increase in the number of injuries sustained by females.

What are the symptoms of an ACL injury?

Many patients are only too aware of their injury. There is usually intense pain, a telltale pop or snap, a loose feeling in the joint and an inability to put weight on the affected limb. However, there are instances in which the extent of the injury is less severe. Some ball players have been known to play with a damaged ACL, but that is an exceptional situation. Any lack of stability in the knee should be followed up with an MRI to assess damage. The risk of permanent injury, arthritis and total knee replacement is too great not to check for signs of a torn ligament.

How prevalent is it?

ACL injuries are extremely common among both professional and amateur athletes.

About 400,000 people in the U.S. are treated for ACL injuries every year. Medical professionals nationwide are seeing a significant uptick in the number of ACL injuries every year. Physicians in Philadelphia documented a 400 percent increase in ACL patients in a 10-year time period. From 2009 to 2013, the number of MOR patients with ACL injuries doubled. The number of ACL injuries in young people under age 25 tripled in that same five-year period. That's why Midwest Orthopaedics at Rush (MOR) physicians are concerned about what they call an epidemic of ACL injuries.

With more emphasis on competitive sports and more young people engaged in these activities year-round, the numbers are going up.

To counter these accelerated rates of injury and to reduce stress on the joints, more cross training should be emphasized. Longer breaks between activities and exercises to improve balance and core strength around the knee joints can further lessen the likelihood of an ACL tear in people involved in rigorous competition.

ACL Research

One of the injuries most feared by athletes at all levels (and their fans) is tearing the anterior cruciate ligament, also known as known as an ACL tear. Midwest Orthopaedics at Rush physicians are at the forefront of research efforts to prevent, treat, and help patients recover from this devastating injury.

What is the treatment?

In order to avoid collateral damage, including meniscus tears and degenerative joint disease in the future, reconstructive surgery should typically be performed. This also provides stability and function in the knee. MOR knee surgeons use either an allograph (from a cadaver) ligament or an autograph (the patient's own tissue usually from the knee cap tendon or the hamstring) for the repair.

In most cases, the surgery is performed using arthroscopic surgery, as opposed to an open incision. Arthroscopic surgery allows the surgeon to visualize the area using a tiny camera inserted through a very small incision. This eliminates a greater risk of complications during and after the operation. The surgery is usually performed under a local anesthetic. The physician will make tiny tunnels in the bone to pull the new tissue through to replace the old ACL. They then secure it to the bone with screws or other devices. As it heals, the bone tunnels fill in. This secures the new ligament.

Post-surgery, the knee is braced for one to four weeks. A patient may have to use crutches in the first week of recovery. MOR knee physicians typically prescribe medication, to help with post-operative pain. An intense but gradual regimen of rehabilitation is typically recommended.

The goal is to strengthen the joints and regain a full range of motion. At the end of therapy, an assessment of the patient's ability to return to sports is made. The MOR Department of Rehabilitation provides a Functional Sports Assessment (FSA) to help determine if a patient is fully ready to return to his/her sport.

More than 600,000 patients have reconstructive surgery at Midwest Orthopaedics at Rush every year — and that number is growing. Midwest Orthopaedics at Rush physicians treat the highest number of ACL patients, among physician groups in the Midwest. 

Not long ago, a torn ACL would end the careers of many athletes. But today, ACL reconstruction is usually very successful. Research by MOR physicians shows a high percentage of athletes return to play following ACL reconstructive surgery. Recent improvements in surgery and rehabilitation have resulted in less pain and stiffness, fewer complications and quicker recovery times.

About the Functional Sports Assessment (FSA)

The knee surgeons at MOR recommend ACL patients complete an FSA to identify potential weaknesses and risk of further injury before they return to play. The FSA identifies the functional sports level of an athlete after surgery and rehabilitation. It is one of the first rehab centers in the country to offer this kind of thorough analysis. The FSA includes a series of movements, including single leg hops, triple leg hops, crossover hops, six meter timed hops, resisted single leg squats, lateral agility and pivoting moves, drop to jumps and deceleration from a sprint. These activities are monitored to determine the level of success an injured athlete will have when he or she returns to a chosen sport. This requires a doctor's prescription and includes a 30-minute consultation as a follow up to review the results and receive a recommended course of action. A written copy of the assessment is also provided.

For information regarding the Functional Sports Assessment, contact Donna Williams at 312.432.2513 or

Can ACL injuries be prevented?

While it is difficult to prevent an ACL injury from occurring, the chances of an injury happening can be lowered by performing training drills that emphasize power and agility and by improving muscular reactions with jumping and balance drills. MOR physicians emphasize that pre-conditioning before practices or games is always a good idea. Building core strength through spot exercises can reduce the stress on these joints. Taking breaks, playing multiple sports and not specializing too early are other good preventative measures.

It's also important to wear the right protective gear for the sport. This includes supportive shoes to keep legs properly aligned. Shin guards and kneepads offer additional protection especially for contact sports. It's important to warm up before and cool down after rigorous play.