ACL Injuries | Florida Orthopaedic Institute
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ACL Injuries

An anterior cruciate ligament (ACL) sprain or tear is one of the most common knee injuries. High demand sports like soccer, football, and basketball have a higher incidence of ACL injuries.

An injury to the anterior cruciate ligament may need surgery to regain full function of the knee, depending on the severity of your injury, your activity level, and other factors.

ACL Injuries


The knee is a hinged joint made up of four main parts: bones, cartilage, ligaments, and tendons. The thighbone (femur), shinbone (tibia), and kneecap (patella) meet to form the knee joint. The kneecap helps protect the front of the joint.

ACL Injuries

Ligaments connect bones to one another and keep the knee stable. The knee has four primary ligaments, of two types:

  1. Collateral Ligaments – on the sides of the knee, controlling the sideways motion of the knee and braces it against unusual movement.
    • Medial collateral ligament (MCL) on the inside
    • Lateral collateral ligament (LCL) on the outside
  2. Cruciate Ligaments – located inside your knee joint, controlling the back and forth motion of the knee.
    • Running diagonally in the middle of the knee, the anterior cruciate ligament (ACL) prevents the shinbone (tibia) from sliding out in front of the thighbone (femur) and provides rotational stability.
    • The posterior cruciate ligament (PCL) mirrors the ACL, but is attached to the back of the knee, crossing the ACL in an X.

The weight-bearing surface of the knee is covered by a layer of articular cartilage. Between the cartilage surfaces of the thighbone and shinbone on either side of the joint are the medial meniscus and lateral meniscus. They act as shock absorbers and work with the cartilage to reduce stress between the shinbone and the thighbone.

ACL Injuries


Your anterior cruciate ligament can be injured in several ways:

  • Rapidly changing direction
  • Deceleration coupled with cutting, pivoting or sidestepping moves
  • Suddenly stopping
  • Slowing down while running
  • Awkward or incorrect landings from a jump
  • Out of control play
  • Direct contact or collision (like a football tackle)

The majority of ACL injuries occur through non-contact – a smaller percent are from direct contact with another player or object.

Female athletes tend to have a higher incidence of ACL injuries than males in certain sports. This may be due to differences in physical conditioning, muscular strength, and neuromuscular control, differences in pelvis and lower leg alignment, increased looseness in ligaments, and the effects of estrogen on ligament properties.

Half of ACL injuries happen when there is damage to other structures in the knee, such as the meniscus, articular cartilage, or other ligaments. There can also be bruising of the bone beneath the cartilage surface. Magnetic resonance imaging (MRI) scans can help to see these additional injuries. Football players and skiers commonly injure the ACL, the MCL, and the medial meniscus – nicknamed the “unhappy triad.”

An injury to a ligament is called a sprain and is graded on a severity scale.

Grade 1 Sprains – The ligament is mildly damaged. It has been slightly stretched but can still to help keep the knee joint stable.

Grade 2 Sprains – The ligament is stretched to the point where it becomes loose. Also referred to as a partial tear of the ligament. Partial tears are rare – most ACL injuries are complete or near complete tears.

Grade 3 Sprains – The ligament is split into two pieces, and the knee joint is unstable. Commonly called a complete ligament tear.


When the anterior cruciate ligament is injured, typical symptoms include:

  • A “popping” noise
  • The knee gives out from under you
  • Loss of range of motion
  • Tenderness along the joint line
  • Discomfort while walking
  • Pain with swelling. Within 24 hours after the injury, the knee swells. Sometimes, the swelling and pain resolve on their own. You risk causing further damage to the cushioning cartilage (meniscus) of your knee if you return to sports, as your knee may be unstable.


Your Florida Orthopaedic Institute physician checks all the structures of your injured knee and compares them to your non-injured knee during a physical examination. Most ligament injuries can be diagnosed with a thorough physical examination of the knee. They will also ask you about your symptoms and medical history.

Other tests that help your doctor confirm a diagnosis include X-rays and MRI scans. Although X-rays don’t show injuries to your anterior cruciate ligament, they can show whether the injury is associated with broken bones. MRI scans (Magnetic Resonance Imaging) create a better image of your soft tissues like anterior cruciate ligaments.

Your physician may also perform a Lackman Test which tests the movement of the knee. The test helps identify the anterior cruciate ligament’s integrity and gauge instability in various directions.


Treatment for an ACL tear depends upon the patient. Young athletes involved in agility sports usually need surgery to safely return to them. Less active and older individuals may not need surgery.


Torn ACLs do not heal without surgery, but nonsurgical treatment may be effective for patients who are older or have very low activity levels. Non-surgical healing varies from patient to patient and depends on their activity level, the degree of injury and knee instability.

A positive outcome for partially torn ACLs without surgery is possible, with the recovery and rehabilitation period typically lasting at least three months. Some patients with partial ACL tears may still have instability symptoms. Comprehensive clinical follow-up and physical therapy help identify patients that have unstable knees from partial ACL tears.

ACL Injuries

Without surgical intervention, complete ACL ruptures have a much less favorable outcome. After a complete ACL tear, some patients have instability during walking or other normal activities. Athletes are usually unable to take part in sports that involve cutting or pivoting movements, but there are a few who can participate without any symptoms of instability. It all depends on the severity of the original knee injury and the physical demands of the patient.

Secondary damage to the meniscus, articular cartilage or other ligaments can occur in patients who have repeated episodes of knee instability. With chronic instability, a majority of patients have meniscus damage 10 or more years after the initial injury. Articular cartilage lesions increase in patients who have a 10-year-old ACL instability.

With progressive physical therapy and rehabilitation, most knees can be restored to a condition close to their pre-injury state. Patients have to learn how to prevent instability and may need to use a hinged knee brace.

These types of isolated ACL tears have better nonsurgical success:

  • Partial tears with no instability symptoms
  • Complete tears with no symptoms of knee instability during low-demand sports, and patients who are willing to give up high-demand sports
  • Those with light manual work or sedentary lifestyle
  • Children whose growth plates are still open

If the overall stability of the knee is intact, your Florida Orthopaedic Institute physician may recommend these nonsurgical options:

BRACING. Protects your knee from instability. You may also be given crutches to keep you from putting weight on your leg to further protect your knee.

PHYSICAL THERAPY. A rehabilitation program can be started as soon as the swelling goes down. Specific exercises can restore function to the knee and strengthen the leg muscles supporting it.


Your physician may recommend knee arthroscopy if your condition does not respond to nonsurgical treatments and you have pain. Surgery to rebuild an anterior cruciate ligament can be done with an arthroscope using small incisions, and the procedure is less invasive. There is less pain from surgery, less time spent in the hospital, with quicker recovery times.

Knee arthroscopy can also relieve painful symptoms of many problems that damage the cartilage surfaces and other soft tissues surrounding the joint. Other arthroscopic procedures for the knee include:

  • Torn anterior cruciate ligament reconstruction
  • Removal of inflamed synovial tissue
  • Removal of loose fragments of bone or cartilage
  • Removal or repair of a torn meniscus
  • Treatment of knee infection (sepsis)
  • Treatment of kneecap (patella) problems
  • Trimming of damaged articular cartilage


With combined injuries (ACL tears in combination with other injuries in the knee), your Florida Orthopaedic Institute physician will usually recommend surgery.


To surgically repair the ACL and restore knee stability, the ligament must be reconstructed as most ACL tears cannot be stitched (sutured) back together. ACL repairs done this way generally fail over time. The torn ligament is replaced with a tissue graft to act as a framework for a new ligament to grow on.

Grafts are obtained from several sources. If they come from the patient, they are called autografts. Grafts are often taken from the patellar tendon, which runs between the kneecap and the shinbone (patellar tendon autograft). Hamstring tendons at the back of the thigh (hamstring tendon autograft) and quadriceps tendons (which runs from the kneecap into the thigh and called a quadriceps tendon autograft) are also common sources of grafts. Cadaver grafts (allografts) are also used and taken from the patellar tendon, Achilles tendon, semitendinosus, gracilis, or posterior tibialis tendon.

Your Florida Orthopaedic Institute surgeon will review the advantages and disadvantages of various graft sources to help determine which is best for you.

Because regrowth takes time, it can take six months or more before an athlete can return to sports after surgery.


Rehabilitation plays a vital role in getting you back to your daily activities, whether your treatment involves surgery or not. Physical therapy programs help regain knee strength and motion.

Following surgery, physical therapy focuses initially on returning motion to the joint and surrounding muscles, followed by a strengthening program to help protect the new ligament. Strengthening exercises gradually increase the stress across the ligament. For athletes, the final phase of rehabilitation is designed to create a functional return to their particular sport.

Active adult patients whose jobs involve pivoting, turning or heavy manual labor should consider surgical treatment, as well as those who actively play sports. Activity, not age, typically determines surgical consideration.

Your surgeon may delay ACL surgery in young children or adolescents until they are closer to skeletal maturity. They may also change the ACL surgery technique to decrease the risk of growth plate injury and bone growth problems.

In combined injuries, surgical treatment may be necessary as it generally produces better outcomes. Almost half of meniscus tears are repairable and can heal better if the repair is done along with the ACL reconstruction.

All Florida Orthopaedic Institute surgeons are fellowship trained, which adds additional expertise in their specialty. They stay current on the latest ACL treatments and research and can talk to you about all your ACL repair options.

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