Anterior Cruciate Ligament Reconstruction Surgery

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Understanding ACL Injuries (pdf)


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UW Health's Sports Medicine doctors in treat a wide range of common athletic injuries, including anterior cruciate ligament (ACL) reconstruction.


Anterior cruciate ligament (ACL) injuries affect men and women across a wide age range and at all levels of athletics.


About the Anterior Cruciate Ligament (ACL)


There are four main ligaments that stabilize the knee. The ACL is located in the center of the knee along with the posterior cruciate ligament (PCL). The ACL is responsible for stabilizing knee rotation that occurs during cutting and pivoting activities. The ACL is also a secondary restraint to knee hyperextension.


The ACL stabilizes the knee joint in two ways.

  • First, the ligament acts as a passive restraint to excessive movement through its connection to the tibia and femur.
  • Second, the ACL has mechanically sensitive nerve receptors, called proprioceptors, which sense the position of a joint. When a joint starts to exceed its normal range or speed of movement these proprioceptors will send a signal to the brain and spinal cord, which in turn stimulates the appropriate musculature to assist with stabilizing the joint.

Mechanism of Injury 


An ACL injury usually occurs without contact from another player. The most common form of non-contact injury is a deceleration injury. An athlete often plants their foot on the ground to cut or change directions, and the ACL cannot withstand the force placed on it, so it tears. This causes the knee to buckle or give out. The ACL also can be torn if the knee is forcefully hyperextended while landing from a jump.


Although less common, contact ACL injuries occur. A common contact injury occurs when an athlete is hit from the side at the knee with the foot planted on the ground. These injuries often involve more than one ligament. 


Research studies have attempted to determine what factors contribute to an increased injury risk, but ACL injuries are multi-factorial and cannot be isolated to a single cause.


Diagnosis of an ACL Injury 


There are several ways to diagnose an ACL injury. A thorough history of how the injury occurred is important to know, but the physical examination is often the most reliable and least expensive method of diagnosis. A sports medicine physician, physical therapist or athletic trainer will assess the knee’s laxity, compared to the uninjured knee, using a Lachman’s test and an anterior drawer test. They will also test the rotational stability component with a test called the pivot shift test. This test attempts to reproduce the athlete’s sensation of buckling or giving out.


A magnetic resonance imaging (MRI) scan can visualize soft tissue and is a relatively accurate test in predicting an ACL tear. A KT-1000 is a device that measures the laxity or looseness in the uninjured knee compared to the injured knee. In a diagnostic arthroscopy, a surgeon looks inside the knee with a camera to determine an injury. This is the most definitive test but also the most expensive and invasive.


Consequences of an ACL Injury


When treating an ACL injury, the key is controlling the instability of the knee. Repeated instability not only hinders athletic performance, but more importantly increases the risk of further injury to the cartilage and other ligaments of the knee. Cutting and pivoting activities (common in sports like football, soccer, basketball and volleyball) are the most stressful for the ACL and therefore are the activities most likely to reproduce the instability in an athlete with a torn ACL.


Treatment Options for an ACL Injury


The choices for treatment should be individualized and should take into account the age, activity level and the desire to return to sports which require significant amounts of cutting and pivoting or other high-speed movements.

  • One form of conservative treatment is to modify the athlete’s sports participation. This involves discontinuing sports involving cutting and pivoting, such as soccer and basketball. These sports could be replaced by sports that do not involve cutting and pivoting, such as swimming or running.
  • Another form of conservative treatment is rehabilitation. Rehabilitation for an ACL injury focuses on improving an athlete’s proprioception and reactive muscular stabilization. For sports such as basketball, soccer and football, rehabilitation alone may not be enough to prevent instability. If instability persists, the athlete must undergo surgical reconstruction of the ligament to return to these sports.
  • Surgical reconstruction involves replacing the torn ACL with a graft. The graft choices include using a portion of the patellar tendon, quadriceps tendon, or hamstring tendons. A fourth option is the use of an allograft (or tissue from a cadaver).



Following surgery these athletes will undergo four to seven months of physical therapy. The post-operative physical therapy can be divided into five phases.

  • During the first phase, the rehabilitative goals include improving range of motion, decreasing swelling, normalizing the walking pattern and increasing strength.
  • In phase two, the goal is to focus on restoring proper body alignment and control with basic movements, such as squats, lunges and single leg balance. This phase continues to build lower extremity and core (trunk) strength.
  • In phase three, the focus shifts to developing good movement control with impact activities and more complex movements, such as a lunge with a rotational component.
  • Developing movement control and eliminating apprehension while cutting and pivoting is the primary goal of phase four. At this time there is also more focus on single leg impact and push off with change of direction.
  • The final phase transitions the athlete from performing intense cutting and pivoting activities in a controlled environment to an environment that more closely replicates their sport.

Although most athletes can return to sports, an ACL injury causes a significant amount of time lost from sports. Recent research has shown a decreased risk of injury is associated with balance and proprioceptive training, but it is very unlikely that ACL injuries can be totally prevented in high demand sports.