A knee sprain is a stretch, tear or complete rupture of one or more of the knee ligaments.

Knee Injuries

graphic of the knee joint; MassGeneral Pediatric Orthopaedic Service

Photo courtesy of AAOS

What is a knee sprain? A knee sprain is a stretch, tear or complete rupture of one or more of the knee ligaments. Knee ligament injuries are particularly common in sports that involve tackling (football) and/or twisting (basketball). Knee sprains are not as common in children because the ligaments are stronger than the epiphyseal plates (growth plates). Therefore, it is more common for children to sustain growth plate injuries or fractures. X-rays will distinguish the growth plate fractures from the ligament injuries.

What are the ligaments of the knee?

  • The medial collateral ligament (MCL) prevents the knee from buckling inwards (valgus injury)
  • The lateral collateral ligament (LCL) prevents the knee from buckling outwards (varus injury)
  • The anterior cruciate ligament (ACL) prevents the tibia from sliding forward under the femur
  • The posterior cruciate ligament (PCL) prevents the tibial from sliding backward under the femur

Ligament Injuries (Sprains) are classified according to severity:

  • Grade I: mild-the ligament is stretched but only a few fibers are disrupted
  • Grade II: moderate-the ligament is partially disrupted
  • Grade III: severe-the ligament is totally disrupted and there is instability

graphic of an acl tear; MassGeneral Pediatric Orthopaedic Service

How can the ACL tear? The anterior cruciate ligament is frequently injured with forced twisting or hyperextension of the knee. Frequently the ligament is injured in sports when there is sudden stopping and twisting at the knee. In skiing, the ACL is commonly injured when the skier sits back while falling. The modern ski boot is stiff, high, and is tilted forward. The boot thus holds the tibia forward. The weight of the body can quickly shift backwards. When the body rotates away from the weight- bearing ski, the knee is twisted. When force exceeds the strength of the ligament, it fails (tears).

Many researchers are currently investigating the increased incidence of ACL injuries in female athletes. Females are 2-5 times more likely than males to injure their ACL while participating in intercollegiate basketball and soccer. Some researchers believe that the higher incidence in women is caused by the increased used of the quadriceps muscles compared to the hamstrings. Others feel that it is the females' ligamentous laxity and wider pelvis that placed a greater stress on the knee. Finally, there are many studies investigating the role that estrogen/menstrual cycle plays in female ACL injury.

What are the Symptoms of an ACL tear? There will often be a loud, painful pop when the ACL is injured. If the patient tries to stand on the injured leg, the knee may feel unstable and "give way." The knee will usually have a large amount of swelling shortly after the injury (within 1-2 hours). This swelling is called an effusion and is made up of blood in the knee joint. Over the next several hours, pain will often become more severe and the patient will find it difficult to walk.

graphic of an acl tear; MassGeneral Pediatric Orthopaedic Service

How is an ACL tear diagnosed? An ACL injury can often be suspected based on the mechanism of injury. The orthopaedic surgeon will examine the knee and will often obtain x-rays and an MRI (magnetic resonance imaging) study to confirm the diagnosis of and ACL tear. The initial treatments are to use ice to decrease the swelling and use a knee immobilizer and crutches to protect the knee. We will often have patients return to the clinic in 2-3 weeks after the injury to re-examine the knee after the acute swelling and pain has decreased.

When should surgery be performed for a torn ACL? It is always best to wait for the acute pain and swelling to subside prior to having surgical repair of the ACL injury. Surgical repair is usually recommended when the knee is unstable during routine or athletic activity. Surgery is generally recommended in younger patients, as they will frequently have problems with instability and "giving way" of the knee. The unstable knee may lead to a higher incidence of meniscus injuries and arthritis. However, not all ACL tears will need surgical repair/reconstruction. Some older patients will be able to function normally with a torn ACL. Good knee function is more common in patients who are over thirty years old and are inactive in sports.

If a younger child with open growth plates has an ACL injury, the orthopaedic surgeon may recommend waiting for growth the end before surgical repair/reconstruction.

knee injuries and ACL tears; MassGeneral Pediatric Orthopaedic Service knee injuries and ACL tears; MassGeneral Pediatric Orthopaedic Service knee injuries and ACL tears; MassGeneral Pediatric Orthopaedic Service knee injuries and ACL tears; MassGeneral Pediatric Orthopaedic Service

How can ACL injuries be prevented? Although sports accidents cannot be totally prevented, there are many ways to decrease the number of knee injuries. Training and conditioning should be a year-round program. Emphasis should be on strengthening and stretching of the hamstrings and quadriceps muscles. In activities such as skiing, make sure your ski bindings are set correctly by a trained professional so that your skis will release when you fall.

Below are some basic exercises for the knee that are often initially taught by a skilled physical therapist.

PT exercises for knee injuries; MassGeneral Pediatric Orthopaedic Service

Content developed by Erin S. Hart RN, MS, CPNP