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Patellar instability is the term given to a range of injuries that occur when the patella, or kneecap, is displaced from its intended resting place. Causes include a traumatic dislocation, such as occurs during a sport activity, or a displacement caused by daily activities. The condition affects an average of 7 out of 100,000 individuals in the United States, and is most often diagnosed in individuals in their teens and twenties, particularly adolescent female athletes. Once individuals have experienced an episode of patellar instability, they are at an increased risk of another episode, with 15% to 44% experiencing it again. To treat patellar instability, physical therapists typically prescribe a combination of strengthening exercises to decrease pain and improve function.

Physical therapists are movement experts. They improve quality of life through hands-on care, patient education, and prescribed movement. You can contact a physical therapist directly for an evaluation. To find a physical therapist in your area, visit Find a PT.

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What Is Patellar Instability?

Under normal circumstances, the kneecap (patella) properly rests in a groove (trochlea) at the end of the thigh bone (femur). As the knee bends and straightens, the kneecap should slide up and down, staying in this groove. This function is often illustrated with the groove as a train track and the kneecap as the train. Patellar instability describes a situation when the train, or the kneecap, "comes off of the track." This can occur during movement as the kneecap does not stay in the groove, and/or without movement if the kneecap does not rest properly in the groove.

Patellar instability can be either the result of a specific injury, or may slowly develop over time with daily activities.

An event, such as a direct hit to the knee or changing directions quickly while running (eg, "cutting" during sports activities), can force the kneecap fully out of the groove (patellar dislocation). This is called a traumatic injury and occurs with equal frequency in males and females. Most often, the kneecap returns to its proper place in the groove on its own; however, at times, the kneecap does not return on its own, and assistance from a medical professional is required, using a procedure called a reduction. After either of these situations, the knee will be painful and activity will be limited.

Patellar instability can also be present without a specific injury when the kneecap comes partially out of the groove (subluxation). This is called an atraumatic injury and occurs most often in females. In this situation, the kneecap does not rest and/or stay appropriately in the groove with daily activities. While the kneecap may not come completely out of the groove, the unstable kneecap will still cause knee pain—most commonly while an individual is walking on uneven terrain, negotiating stairs, or rolling over in bed. As these activities are repeated, the knee becomes increasingly irritated and painful.

Patellar instability also may result from a combination of several different variables, both modifiable and nonmodifiable, including abnormalities in:

  • Bone structure. An abnormally shallow or rotated groove (trochlea) does not provide a stable base on which the kneecap can rest.
  • Muscle weakness. The muscles surrounding the hip and knee need to be strong to help control the position of the leg and keep the kneecap stable.
  • Soft tissue malfunction. Ligaments and tendons also work to hold the kneecap in place. In those individuals who are exceptionally flexible, or who have previously experienced an episode of patellar instability, these tissues may stretch more easily, losing their ability to hold the kneecap properly in place. In other cases, the soft tissue on the outside of the knee is too tight, and pulls the kneecap out of its ideal resting place in the groove.
  • Poor movement patterns. Activities, such as running, jumping, and landing with the knee in a bad position makes the kneecap vulnerable for patellar instability.

How Does It Feel?

Individuals with patellar instability will experience pain and other symptoms that can limit their ability to perform desired daily and recreational activities.

With patellar instability, you may experience:

  • Knee pain, particularly when climbing or descending stairs, squatting, running, jumping, or "cutting" during sport activities.
  • Feeling the kneecap shift or slide out of the groove.
  • Feeling fear of instability with aggravating activities, including walking on uneven terrain, landing from a jump, negotiating stairs, or rolling over in bed.
  • Weakness in your leg, as if your knee might give way.
  • Swelling and stiffness in the knee following a traumatic injury.

How Is It Diagnosed?

Your physical therapist will review your medical history and complete a thorough examination of your knee, while also examining other body parts that might contribute to your injured area, most commonly the hip and foot. The goals of the initial examination are to assess the degree of the injury and determine its cause and contributing factors to the injury.

Your physical therapist will assess the strength and mobility of your knee and kneecap, and may watch you walk, step onto a stair, squat, or balance on 1 leg. Your physical therapist will also gently touch the front, side, and back of your knee to determine exactly where it is most painful.

Your physical therapist may also ask questions regarding your daily activities, exercise regimens, and footwear, to identify other contributing factors to your pain.

Imaging techniques, such as X-ray or MRI, are typically not needed to diagnose patellar instability, but may be valuable following traumatic injuries or repeated episodes of instability, in order to evaluate your bone alignment and rule out other knee injuries.

How Can a Physical Therapist Help?

You and your physical therapist will work together to develop a plan to help achieve your specific goals. To do so, your physical therapist will select treatment strategies in any or all of the following areas:

  • Pain. Many pain-relief strategies may be implemented. The most common one is to apply ice to the area. A knee brace is often provided to hold the kneecap in a stable position. Avoiding certain aggravating activities for a period of time might also be recommended.
  • Range of motion. Your knee motion is often limited after an injury. Your therapist will work with you to select exercises that will help regain your motion without hurting your knee.
  • Muscle strength. Improving and balancing the muscle strength in your leg can help control the stability of your kneecap. Based on your specific condition, your physical therapist will design a safe, individualized, progressive program of resistance exercises for you. You may begin by performing strengthening exercises lying on a table, for example, lifting your leg up while lying in different positions. You then may advance to exercises in a standing position, for example, stepping onto a box or balancing on 1 leg. Your physical therapist will choose what exercises are right for you, based on your age, physical condition, and goals.
  • Functional training. Once your pain eases and your strength improves, you will need to safely transition back into more demanding activities. The way you move while performing these activities can significantly affect the stability of your kneecap. To maximize its stability and minimize your risk of repeated injury, it is important to teach your body safe, controlled movements. Based on your own unique movement assessment and goals, your physical therapist will create a series of activities to help you learn how to use and move your body correctly and safely.
  • Patient education. Your physical therapist will work with you to identify and change any external factors causing your pain, such as the type and amount of exercise you do, and your footwear. Your physical therapist will assess all possible factors and recommend improvements, and develop a personal exercise program to help ensure a pain-free return to your desired activities.

Physical therapy promotes recovery from patellar instability by identifying and addressing all modifiable contributing factors, such as any lack of strength, flexibility, or body control. Your physical therapist may also recommend a period of relative rest during which aggravating activities are avoided, then help you slowly resume safe activities, and carefully guide your progression. When patellar instability remains untreated, however, your pain will persist and may worsen, resulting in long-term difficulty performing your desired activities.

When Surgery is Required

In the event of a serious ligament tear (of the medial patellofemoral ligament), caused by either a traumatic injury or repeated episodes of the kneecap coming out of its groove, or cases that do not improve following several weeks of physical therapy, surgery may be required. The goal of surgery is to restore normal kneecap stability. Depending on the condition, the surgeon may use new tissue to reconstruct a damaged ligament, release tight surrounding soft tissue that is pulling the knee off track, or make changes to the bone alignment of the thigh and/or shin bone.

Following surgery, your initial rehabilitation will focus on protecting your healing knee, decreasing pain, and restoring strength. Immediately after surgery, movement of the knee may be limited to help it heal. As time passes, your physical therapist will help guide you through exercises to safely increase your knee motion. Your physical therapist will also address specific factors that caused your knee injury, in order to minimize the risk of further injury. As you progress, your physical therapist will help you systematically reintroduce activities, such as stair climbing, squatting, and desired recreational activities.

Your physical therapist will help guide you through a process that will progressively reintegrate more demanding activities into your routine, without overstraining your knee. Keep in mind that returning to activities too soon after injury often leads to persistent pain, and the condition becomes more difficult to fix.

Can This Injury or Condition Be Prevented?

Maintaining appropriate lower extremity muscle strength and control, and paying particular attention to your movements—especially while climbing stairs, squatting, jumping and landing, or cutting during sport activities—are the best methods for preventing patellar instability.

Physical therapists are experts in understanding which movements place you at highest risk for patellar instability. One of the goals of physical therapy is to teach patients proper movement techniques to keep the knee safe. This is done by watching patients move, and then providing correct exercises to allow the patient to perform these movements safely. For athletes, this may include observing and improving the way you jump, land, pivot and cut. For other patients, this may include observing and improving the way you sit in a chair or climb stairs. Your physical therapist will work with you to identify which movements in your daily activities need to be improved, to minimize your risk of knee injury.

What Kind of Physical Therapist Do I Need?

All physical therapists are prepared through education and experience to treat patellar instability. However, you may want to consider:

  • A physical therapist who is experienced in treating people with patellar instability. Some physical therapists have a practice with an orthopedic or musculoskeletal focus.
  • A physical therapist who is a board-certified clinical specialist, or who completed a residency or fellowship in orthopedic or sports physical therapy. This therapist has advanced knowledge, experience, and skills that may apply to your condition.

You can find physical therapists who have these and other credentials by using Find a PT, the online tool built by the American Physical Therapy Association to help you search for physical therapists with specific clinical expertise in your geographic area.

General tips when you're looking for a physical therapist (or any other health care provider):

  • Get recommendations from family and friends or from other health care providers.
  • When you contact a physical therapy clinic for an appointment, ask about the physical therapists' experience in helping people who have patellar instability.
  • Be prepared to describe your symptoms in as much detail as possible, and describe what makes your symptoms worse.

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The American Physical Therapy Association believes that consumers should have access to information that could help them make health care decisions and also prepare them for their visit with their health care provider.

The following articles provide some of the best scientific evidence related to physical therapy treatment of patellar instability. The articles report recent research and give an overview of the standards of practice both in the United States and internationally. The article titles are linked either to a PubMed* abstract of the article or to free full text, so that you can read it or print out a copy to bring with you to your health care provider.

Ries Z, Bollier M. Patellofemoral instability in active adolescents. J Knee Surg. 2015 April 18 [Epub ahead of print]. Article Summary in PubMed.

Smith TO, Song F, Donell ST, Hing CB. Operative versus non-operative management of patellar dislocation. A meta-analysis. Knee Surg Sports Traumatol Arthrosc. 2011;19(6):988–998. Article Summary in PubMed.

* PubMed is a free online resource developed by the National Center for Biotechnology Information. PubMed contains millions of citations to biomedical literature, including citations in the National Library of Medicine's MEDLINE database.