Knee Ligament Injuries


Four main ligament units stabilize the knee: the Anterior Cruciate Ligament (ACL), the Posterior Cruciate Ligament (PCL), the Medial Collateral Ligament (MCL), and the combination of the Lateral Collateral Ligament (LCL) and postero-lateral corner (PLC). Additional contributions from the joint capsule provide further stabilization, however, these four are the main ligaments injured during sporting activities and trauma.


What Do Those Ligaments Do?

  • ACL – prevents the tibia from moving forward
  • PCL – prevents the tibia from moving backward
  • MCL – resists a knock-knee force
  • LCL/PLC – resists a bow-legged and external rotation (turning outward) force

All the ligaments also prevent different and varying degrees of rotation through the knee.

How Are The Ligaments Injured?

The most common ligament injured is the ACL, followed closely by the MCL. These are usually injured during sporting activities, and usually occur after contact or a twisting/pivoting motion without contact. PCL and LCL/PLC injuries usually occur after higher energy injuries such as high-speed collisions or motor vehicle accidents. These ligaments can also be sprained (partially torn), and treatment will depend on the degree of instability symptoms experienced by the patient.

What Are Some Symptoms Of A Knee Ligament Injury?

The most common symptom upon injury is the feeling of a pop in the knee; you or others around can sometimes hear this. The knee will often (but not always) swell on the day of injury and be quite painful to move. The swelling usually decreases over the first week as your motion improves, and most people are able to go on with day-to-day activities at this time. You may note the sensation of instability in the knee and occasional (or frequent) “giving out” during simple movements like sitting and standing, walking, or turning. Knees with multiple structures injured will usually have significantly more instability symptoms. In severe cases the knee can dislocate upon injury – this is an emergency and should be evaluated immediately by emergency medical personell.

How Are The Ligaments Repaired Or Reconstructed?

This depends on what ligaments are torn and the timing of surgery. Injuries to the ACL and PCL require reconstruction – replacement of the torn tendon with a new tendon or ligament graft. This graft can come from the patient (autograft) or from a tissue bank (allograft). The ACL and PCL make up the “central pivot;” these two ligaments are on the inside of the joint and centered between the femur and tibia. Because of the central location within the joint, ACL and PCL injuries are usually reconstructed arthroscopically through a few small incisions. MCL injuries very rarely need surgical treatment; most will heal over the course of 6-12 weeks with protection in a knee brace, depending on the severity of the tear. Injuries to the LCL/PLC complex usually occur in addition to ACL or PCL tears. We typically try to repair these ligaments within 2-3 weeks of injury. If the injury is older than this, we often recommend reconstruction of the ligaments with tendon allograft.

What Is The Recovery Like?

Recovery after an ACL reconstruction is generally a 6-9 month recovery before beginning sporting activities. You are able to walk on the limb with crutches beginning the day of surgery, and therapy to regain motion begins immediately. Strengthening starts by 6 weeks, and light jogging and regaining power begins at 12 weeks. If additional ligaments require treatment, or if you have a meniscus repair, the recovery period slows down depending on exactly what was repaired and reconstructed.

How Do I Know If I Injured A Knee Ligament?

In addition to the symptoms mentioned above, a physical examination by a medical professional comfortable with evaluating and diagnosing knee injuries is extremely important. Plain xrays of both knees, as well as an MRI assist in completing the diagnosis and identifying any associated injuries.

Do I Need My ACL Reconstructed?

Not everyone with an ACL tear needs a reconstruction. There are many patients who are able to regain their motion and strength in the limb and don’t have significant symptoms of functional instability. Patients that we suggest have their ACL reconstructed regardless of instability symptoms are pediatric patients and young adults. The reason for this is to try and prevent repeated and more severe instability episodes that can lead to cartilage and meniscus injuries. If you have torn your ACL (or another ligament in your knee) and have repeated episodes of instability and looseness of the knee that prevent normal daily activity and maintenance of an active lifestyle, you will likely benefit from a reconstructive procedure.

Knee Cap (Patella) Realignment & Stabilization


  • Patella – knee cap
  • Trochlea – the groove on the femur (thigh bone) the patella glides in
  • MPFL – Medial Patello-Femoral Ligament; holds the patella in place
  • Patellar ligament – thick ligament attaching the patella to the tibia (shin bone)
  • Tibial tubercle – bony prominence on the tibia; site of insertion of the patellar ligament

What Is Patella Realignment And Stabilization And What Is It Used For?

Patellar realignment or stabilization is a group of surgical procedures used to change or stabilize the tracking of the patella on the femur as the knee bends. These surgeries are used to treat patellar instability (dislocation of the knee cap), and rarely cartilage injuries of the patella or trochlea.

What Is Patellar Instability?

It is when the patella dislocates or slips out of the trochlea with knee flexion. This can be caused by a traumatic injury to the MPFL, or to a structural abnormality of the trochlea or it’s relationship to the tibial tubercle.

What Are The Symptoms Of These Types Of Injuries Or Problems?

Instability problems of the patella are usually associated with recurrent dislocations of the kneecap or the feeling (apprehension) of dislocation with certain positions. This is the most common indication for a stabilization or realignment procedure. Cartilage injuries can manifest as catching/locking/popping of the kneecap associated with pain.

How Are Patellar Realignment And Stabilization Procedures Done?

This depends on the injured or abnormal structures. If no structural abnormalities of the femur and tibia exist, the MPFL is usually the only structure injured. In this case, the ligament is reconstructed using a tendon graft from either the patient or a tissue bank. Structural abnormalities of the trochlea or it’s rotational relationship to the tibial tubercle require an osteotomy (cutting the bone) to change the underlying abnormality.

What Is The Recovery Like?

Isolated MPFL reconstruction is a same-day procedure, and most people are able to return to school or work in 3-5 days. Weight bearing and activity are limited the first 6 weeks, and advanced rehab starts by week 10-12. If a patellar realignment is done in addition to this, most patients will stay overnight in the hospital. Patients can return to work or school in 1-2 weeks, and weight bearing and activity is limited for the first 6 weeks. Again, higher-level rehab begins at this point. For both procedures, most patients return to sport by the 4-5 month range.

Is A Patellar Realignment Or Stabilization Right For Me?

More than 50% of patients with a first-time patella-dislocation will never have a second episode of instability. If you experience repeated episodes of patella dislocation, or have the feeling of dislocation that limits your ability to remain healthy and active, a discussion with an orthopedist experienced in patellar instability will be quite helpful. As always, a complete series of high quality x-rays including sunrise views and full-length, standing xrays of the lower extremities are required. An MRI scan is also helpful to identify any cartilage lesions that might also require treatment.

For more information, visit the following link:
AAOS Orthoinfo unstable kneecap

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