Knee Injuries: ACL Tear

Your knee has four major ligaments making the complex structure of your joint: the ACL, PCL, MCL, and LCL. Your ACL, or anterior cruciate ligament, connects your femur and shin bone (tibia). This ligament prevents your tibia from sliding too far forward. The ACL provides structure to your knee. In sports such as soccer, basketball, football and skiing, damage the ACL can result from sudden stops, rapid changes in direction and landing jumps. 

Additionally, car accidents often cause knee injuries. ACL injuries occur in auto accidents when the knee is forced to twist which can result in stretch or tearing of the ligament. Injuries may also be caused by impacts to the knee, and twisting or hyperextension of the leg. Often times, knees collide with interior parts of the car such as the dashboard, door, window or even the roof of the vehicle. This trauma resulting from the impact between the car’s interior and your knee can result in ligament tears and other soft tissue damage. Depending upon the degree or grade of damage, injury to the ACL may result in mild pain, rupture or loss of joint stability.


  • Loud Pop or Popping Sensation in the Knee
  • Severe Pain
  • Inability to Continue Physical Activity
  • Rapid Swelling
  • Reduced Range of Motion
  • Joint Tenderness
  • Feeling of Knee Instability or Giving Way
  • Difficulty or Pain While Walking

Sprain Grades

Grade 1: The knee is still able to bear weight and complete range of motion. However, the ligament has been slightly stretched. 

Grade 2: The ACL becomes loose and sustains a partial tear making the knee unstable on occasion. 

Grade 3: Your ACL tears completely making your knee unstable and unable to bear weight. 

Risk Factors

  • Gender
  • Participating in sports such as soccer, basketball, and skiing
  • Poor Physical Condition
  • Improperly fitting footwear

Additionally, people who sustain an ACL injury are at a higher risk of developing osteoarthritis.

Risk Factors For Women

Women have slightly different anatomy that puts them at a higher risk. The space between the femur and the tibia is more narrow in women than men. Due to the narrower space, the ACL can be pinched and weakened as the knee repetitively cinches on this ligament. 

Women have wider pelvises than men. This increases the angle in which the femur and the tibia meet. Due to this difference in angle, the amount of the ACL is pinched increases with any twisting motions that a woman makes. Therefore, the ACL becomes more likely to be damaged.

Female muscles tend to be more elastic than men’s and this decreases the protection that the hamstring muscles can provide. Additionally, hormonal changes during monthly cycles may also affect muscle elasticity. Furthermore, female muscles contract a millisecond slower than males which increases the risk of damage from jumps. 

When to See a Doctor

Seek immediate care if you notice any signs or symptoms of an ACL injury. 

Nonsurgical Treatment Options

If you have a torn ACL, there will not be a nonsurgical option available for you. However, nonsurgical treatment may benefit the elderly and those with sedentary lifestyles. The key determining factor for surgery relies on whether or not your knee joint is stable. These nonsurgical techniques include knee braces, walking on crutches for a period of time, and physical therapy. 

Surgical Treatment

ACL surgery focuses on rebuilding the ACL ligament. Most ACL tears cannot just be stitched back together. The ligament has to be reconstructed with a graft. This graft will act as a scaffold for a new ligament to grow. 

Grafts can often be obtained from the following sources:

  • Patellar Tendon (Kneecap and shin bone tendon)
  • Hamstring Tendon
  • Quadriceps Tendon
  • Cadaver Graft

Each graft source has its advantages and disadvantages. Orthopedic surgeons will be able to help determine which graft source will work best for you and your surgery. 

For the actual procedure, an arthroscope surgery will often be utilized for this process. An arthroscopic surgery will make three incisions. One incision will have a small camera placed inside of the joint so the surgeon can view the interior of the joint on-screen. 


Regardless of whether or not your knee needs surgery, physical therapy programs will help you regain knee strength and motion. If you do need surgery, your physical therapist will first help you with regaining range of motion and muscle function. After your range of motion has been restored, the focus will change to building strength. The final phase is to restore activity to your previous level. 

Rehabilitation may take six to nine months for an ACL tear which requires surgery. Overall, with an ACL injury, there needs to be a balance of pushing yourself and taking it easy in physical therapy. Being too forceful with a graft or damaged ACL can cause the knee to become unstable. However, if exercises are too gentle, the recovery time may be lengthened. 

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