Anterior/Posterior Cruciate Ligaments

Last updated date: 08-Jul-2023

Originally Written in English

Anterior/Posterior Cruciate Ligaments

Anterior Cruciate Ligaments


The anterior cruciate ligament (ACL) is one of two cruciate ligaments in the human knee (the other being the posterior cruciate ligament). Because they are crossed, the two ligaments are also known as "cruciform" ligaments.

Because of its anatomical position in the quadruped stifle joint (analogous to the knee), it is also known as the cranial cruciate ligament. The word cruciate means "cross." The ACL crosses the posterior cruciate ligament to form a "X," hence the name. It is made of a strong, fibrous material that aids in the control of excessive motion. This is accomplished by restricting joint mobility.

The anterior cruciate ligament is one of the four major ligaments of the knee, accounting for 85 percent of the restraining force against anterior tibial displacement between 30 and 90 degrees of knee flexion. The ACL is the most commonly injured of the four ligaments found in the knee.

The ACL originates deep within the distal femoral notch. Its proximal fibers protrude from the medial wall of the lateral femoral condyle. The anteromedial and posterolateral bundles of the ACL are named after where they insert into the tibial plateau. The tibial plateau is a critical weight-bearing region on the tibia's upper extremity. The ACL connects to the tibia in front of the intercondyloid eminence, where it merges with the anterior horn of the medial meniscus. 


Anterior Cruciate Ligaments

Anterior Cruciate Ligaments

The ACL's function is to resist anterior tibial translation and internal tibial rotation, which is necessary for rotational stability. This function prevents anterior tibial subluxation of the lateral and medial tibiofemoral joints, which is required for the pivot-shift phenomenon to occur. The ACL contains mechanoreceptors that detect changes in movement direction, knee joint position, and changes in acceleration, speed, and tension.

The presence of altered neuromuscular function as a result of diminished somatosensory information is a key factor in instability following ACL injuries. Athletes who participate in sports that require cutting, jumping, and rapid deceleration must have a stable knee in terminal extension, which is the screw-home mechanism. 


Clinical significance

An ACL tear is one of the most common knee injuries, with over 100,000 tears occurring in the United States each year. The majority of ACL tears occur as a result of a non-contact mechanism, such as a sudden change in direction that causes the knee to rotate inward. As the knee rotates inward, the ACL is put under additional strain because the femur and tibia, the two bones that articulate together to form the knee joint, move in opposite directions, causing the ACL to tear.

Most athletes require ACL reconstruction surgery, which involves completely removing the torn or ruptured ACL and replacing it with tendon or ligament tissue from the patient (autograft) or from a donor (allograft). Conservative treatment has poor outcomes in ACL injury because the ACL is unable to form a fibrous clot because it receives the majority of its nutrients from synovial fluid, which washes away the reparative cells and makes fibrous tissue formation difficult.

The patellar ligament and the hamstrings tendon are the two most common sources of tissue. The patellar ligament is frequently used because bone plugs are extracted from each end of the graft, which aids in the integration of the graft into the bone tunnels during reconstruction. The procedure is arthroscopic, which means that a small camera is inserted through a small surgical cut. The camera sends video to a large monitor, allowing the surgeon to see any ligament damage. In the case of an autograft, the surgeon makes a larger incision to obtain the required tissue.

This is not necessary in the case of an allograft, in which material is donated, because no tissue is taken directly from the patient's own body. The surgeon drills a hole to form the tibial and femoral bone tunnels, which will allow the patient's new ACL graft to be guided through. After pulling the graft through the bone tunnels, two screws are inserted into the tibial and femoral bone tunnels. Recovery time is usually between one and two years, but it can be longer depending on whether the patient chose an autograft or an allograft.

A week or so after the injury, the athlete is usually misled by the fact that he or she is walking normally and not in much pain. This is risky because some athletes are resuming some of their activities, such as jogging, which, if done incorrectly or with a twist, could damage the bones because the graft has not yet completely integrated into the bone tunnels. In order to avoid complications and ensure a proper recovery, injured athletes must understand the significance of each step of an ACL injury. 


Causes of Anterior cruciate ligament injury

The anterior cruciate ligament can be injured in several ways:

  • Changing course quickly
  • abrupt halting
  • Running at a slower pace
  • Incorrectly landing from a jump
  • A football tackle, for example, is an example of direct contact or collision.

Several studies have found that female athletes in certain sports have a higher incidence of ACL injury than male athletes. This may be due to differences in physical conditioning, muscular strength, and neuromuscular control. Other possible causes include differences in pelvic and lower extremity (leg) alignment, increased ligament looseness, and estrogen's effects on ligament properties.



Posterior Cruciate Ligaments Symptoms

When your anterior cruciate ligament is injured, you may hear a "popping" sound and feel your knee give out from under you. Other common symptoms include:

  • Pain and Swelling: Your knee will swell within 24 hours. If the swelling and pain are ignored, they may resolve on their own. However, if you try to return to sports, your knee will most likely be unstable, and you risk causing further damage to your knee's cushioning cartilage (meniscus).
  • Full range of motion is lost.
  • Tenderness along the line of the joint
  • Discomfort while walking


Nonoperative treatment of the ACL

Although ACL reconstruction is the most common treatment for an ACL tear, it is not the only option for individuals. Some people may find that completing a nonoperative rehabilitation program is more beneficial. Individuals who will continue to engage in physical activity that involves cutting and pivoting, as well as those who will no longer engage in those activities, are both candidates for the nonoperative route.

When comparing operative and nonoperative approaches to ACL tears, there were few differences between the two groups, with no significant differences in knee function or muscle strength reported by the patients.

The primary goals of ACL tear rehabilitation (rehab) are to regain adequate functional stability, maximize full muscle strength, and reduce the risk of reinjury. Nonoperative treatment typically consists of three phases: the acute phase, the neuromuscular training phase, and the return to sport phase. During the acute phase, rehab focuses on the acute symptoms that occur immediately after the injury and cause impairment.

The use of therapeutic exercises and appropriate therapeutic modalities is critical during this phase to aid in the repair of the injury's impairments. The neuromuscular training phase focuses on the patient regaining full strength in both the lower extremity and core muscles. When the patient regains full range of motion, no effusion, and adequate lower extremity strength, this phase begins.

The patient completes advanced balance, proprioception, cardiovascular conditioning, and neuromuscular interventions during this phase. The patient focuses on sport-specific activities and agility during the final, return to sport phase. During the phase, a functional performance brace is recommended to aid in stability during pivoting and cutting activities.


Operative Treatment of the ACL

ACL Operative Treatment

Anterior cruciate ligament surgery is a complex procedure that necessitates orthopedic and sports medicine expertise. When discussing surgery, many factors should be considered, including the athlete's level of competition, age, previous knee injury, other injuries sustained, leg alignment, and graft selection.

The bone-patella tendon-bone graft, the semitendinosus and gracilis tendons (quadrupled hamstring tendon), the quadriceps tendon, and an allograft are the most common graft types. Despite extensive research into which grafts are the best, the surgeon typically selects the type of graft with which he or she is most comfortable. The reconstruction should last if properly rehabilitated. In fact, 92.9 % of patients are pleased with their graft selection.

Prehabilitation is now an essential part of the ACL reconstruction procedure. This means that the patient should exercise prior to surgery to maintain factors like range of motion and strength. Prehab improved function based on a single leg hop test and self-reported assessment; these effects were sustained 12 weeks postoperatively.

In order to recover from the reconstruction, postsurgical rehabilitation is essential. It usually takes 6 to 12 months for a patient to return to his or her pre-injury life. The rehabilitation process is divided into four stages: graft protection, range of motion improvement, swelling reduction, and regaining muscle control.

Depending on the needs of the patients, each phase includes a different set of exercises. For example, while the ligament heals, a patient's joint should not be used for full weight-bearing; however, the patient should strengthen the quadriceps and hamstrings by performing quad sets and weight shifting drills. Phase two would necessitate full weight-bearing and the correction of gait patterns, so core strengthening and balance exercises would be appropriate.

In phase three, the patient begins running and can do aquatic workouts to help with joint stress reduction and cardiorespiratory endurance. Phase four includes multiplanar movements, which improves a running program as well as the beginning of agility and plyometric drills. Finally, depending on the patient, phase five focuses on sport- or life-specific motions.

According to one study, children under the age of 14 who had ACL reconstruction early on fared better than those who had delayed surgery. However, in adults aged 18 to 35, patients who had early surgery followed by rehabilitation fared no better than those who had rehabilitative therapy followed by a later surgery.

This would imply that many patients who do not have instability, buckling, or giving way after a course of rehabilitation can be managed nonoperatively, but the study was limited to outcomes after two years and did not include serious athletes. Patients who participate in sports that require significant cutting, pivoting, twisting, or rapid acceleration or deceleration may be unable to do so without ACL reconstruction.


Posterior Cruciate Ligaments

Posterior Cruciate Ligaments

The Posterior Cruciate Ligament (PCL) is one of the four major ligaments of the knee that works to keep the tibia on the femur stable. It begins on the anterolateral aspect of the medial femoral condyle near the intercondylar notch and ends on the posterior aspect of the tibial plateau.

The Posterior Cruciate Ligament prevents the tibia from moving posteriorly on the femur. The PCL, to a lesser extent, resists varus, valgus, and external rotation forces. It is roughly 1.3 to 2 times as thick and roughly twice as strong as the anterior cruciate ligament (ACL) and, as a result, is less commonly injured.

The posterior cruciate ligament (PCL) functions similarly to the anterior cruciate ligament (ACL) (ACL). It connects the tibia's posterior intercondylar area to the femur's medial condyle. This configuration enables the PCL to withstand forces that push the tibia posteriorly relative to the femur.

Because they are located deep within the knee joint, the PCL and ACL are intracapsular ligaments. They are both wrapped in the synovial membrane, which separates them from the fluid-filled synovial cavity. The PCL gets its name from its attachment to the tibia's posterior portion. 



The PCL is found within the knee joint, where it helps to stabilize the articulating bones, particularly the femur and tibia, during movement. It extends from the lateral edge of the medial femoral condyle and the roof of the intercondyle notch to the posterior of the tibia, just below its articular surface, at a posterior and lateral angle. 



Although each PCL is a unified unit, it is divided into anterolateral and posteromedial sections based on its attachment site and function. The PCL rotates during knee joint movement, so that the anterolateral section stretches in knee flexion but not in knee extension, and the posteromedial bundle stretches in extension but not in flexion.

The PCL's function is to keep the femur from sliding off the tibia's anterior edge and to keep the tibia from displacing posterior to the femur. The posterior cruciate ligament is found in the knee. Ligaments are strong bands of connective tissue that connect bones. The PCL, like the anterior cruciate ligament, connects the femur to the tibia. 


Clinical significance

posterior sag test

Direct blows to the flexed knee, such as the knee hitting the dashboard in a car accident or falling hard on the knee, are common causes of injury, both of which displacing the tibia posterior to the femur.

The posterior sag test, which, unlike the drawer test, does not use active force, is another test for posterior cruciate ligament injury. Rather, the person lies supine with one leg held by another, with the hip flexed to 90 degrees and the knee flexed to 90 degrees.

One of the tests used by doctors and physiotherapists to detect PCL injury is the posterior drawer test. Patients suspected of having a PCL injury should always be evaluated for other knee injuries that frequently occur in conjunction with a PCL injury. Cartilage/meniscus injuries, bone bruises, ACL tears, fractures, posterolateral injuries, and collateral ligament injuries are examples of these.

There are four different grades of classification in which medical doctors classify a PCL injury:

  • Grade I, the PCL has a slight tear.
  • Grade II, the PCL ligament is minimally torn and becomes loose.
  • Grade III, the PCL is torn completely and the knee can now be categorized as unstable.
  • Grade IV, the ligament is damaged along with another ligament housed in the knee (i.e. ACL).


Posterior cruciate ligament injury

Posterior cruciate ligament injury

The lateral femoral condyle has been removed in this medial view of the flexed knee to reveal the structure of the PCL. Excessive flexion in the form of hyperflexion causes tensile stress on the anterolateral bundle of the ACL, which leads to ACL injury, because the anterolateral bundle is stretched and the posteromedial bundle is relaxed during flexion.

The PCL's function in this position is to prevent posterior tibial movement as well as tilting or shifting of the patella. The laxity of the two sections, however, makes the PCL vulnerable to injury during hyperflexion, hyperextension, and in a mechanism known as a dashboard injury.

When this viscoelastic behavior is combined with sudden hyperflexion and hyperextension, the PCL deforms or tears. The third and most common mechanism, the dashboard injury mechanism, involves the knee being struck in the back during knee flexion toward the space above the tibia. These mechanisms occur as a result of excessive external tibial rotation and falls that cause a combination of tibial extension and adduction, known as varus-extension stress, or as a result of the knee being flexed.



An extreme anterior force applied to the proximal tibia of the flexed knee causes PCL injuries. Dashboard injuries, which occur when the knee is forced into the dashboard during a motor vehicle collision, are a common cause. The PCL can also be injured as a result of falling forward onto a flexed knee. Football, skiing, soccer, and baseball are the most common sports in which PCL injuries occur. A rotational hyperextension injury to the knee joint is a less common cause of damage.



Anterior/Posterior Cruciate Ligaments Evaluation

Plain X-rays should be used for initial imaging. Include ipsilateral standing AP, 45-degree flexion weight-bearing, and merchant patellar views alongside contralateral views to look for associated fractures, arthritis, joint effusion, and the 45-degree flexion view may show positive sag compared to the contralateral knee.

MRI is the gold standard for assessing a PCL injury. It has been reported that its accuracy ranges from 96 percent to 100 percent. It can also detect concomitant injuries like meniscal, ligamentous, posterolateral joint capsule, popliteus, medial collateral ligament, and posterior oblique ligament tears.

Increased signal within the PCL substance or disruption in the continuity of the ligament fibers on T1- and T2-weighted sagittal MRI images suggest acute injury. Posterior tibial translation can be seen in chronic PCL injuries. On MRI, posterior translation of 8 mm has the potential to heal with the restoration of ligament continuity.



The PCL has the potential to heal on its own. Even if the PCL does not heal normally, surgery is rarely required. Physiotherapy is usually used to strengthen the muscles around the knee; these muscles usually provide adequate stability even in the absence of a functional PCL. Only if there are persistent symptoms or if there are other injuries in the knee will ligament reconstruction be required.

Ligament reconstruction is used to replace a torn PCL with a new ligament, which is usually a graft taken from a host cadaver's hamstring or Achilles tendon. An arthroscope allows for a thorough examination of the entire knee joint, including the patella, cartilage surfaces, meniscus, ligaments (ACL & PCL), and joint lining. The new ligament is then screwed to the bone of the thigh and lower leg to keep it in place. Because of its placement and technical difficulty, surgery to repair the posterior cruciate ligament is contentious.

When the PCL is injured, it can heal on its own without surgery if it is a Grade I or Grade II injury. PCL injuries classified in these categories can have their recovery times shortened by engaging in certain rehabilitative exercises.

Operative surgery is usually required or recommended for Grades III and IV. Grafts are used to treat PCL injuries that require surgical intervention. There are various methods for grafts, such as the tibial inlay or tunnel method.



The anterior and posterior cruciate ligaments are important knee joint stabilizers. Although they have a similar appearance, they have slightly different properties and complement each other's function.

The ACL is located in front of another ligament known as the posterior cruciate ligament (PCL). The cruciate ligaments get their name from the fact that they form a cross within the knee as they run from the thigh to the shin bone. Your ACL, along with the other ligaments in your knee, keeps your knee stable and keeps your thigh and shin bones from moving out of place.

The posterior cruciate ligament (PCL) is located just behind the anterior cruciate ligament (ACL) inside the knee (ACL). It is one of several ligaments that attach the femur (thighbone) to the tibia (shinbone) (shinbone). The posterior cruciate ligament prevents the tibia from shifting backward in relation to the thigh bone.

A powerful force is required to injure the posterior cruciate ligament. A bent knee hitting a dashboard in a car accident or a football player falling on a bent knee are two common causes of injury. Furthermore, damage to the PCL can occur as a result of a severe twisting injury or a contact injury during sports.