Dislocation of patella (subluxation), PF disorder

Dislocation of patella (subluxation), PF disorder

Mitsutoshi Hayashi

Mitsutoshi Hayashi

Doctor of Medicine, specialist in the Japanese Society of Rehabilitation Medicine, specialist in the Japanese Society of Orthopaedic Surgery, specialist in the Japanese Society of Rheumatology, staff to strengthen JOC, and sports physician certified by the Japan Sports Association

Dislocation of patella (subluxation), PF disorder

Dislocation of patella (subluxation) is sports disorder in which the patella deviates (dislocates) from the patellofemoral joint; they occur frequently in athletes and in women.

Disease Overview


Dislocation of patella (subluxation) is a sports disorder of the knee that results when the patella escapes from the patellofemoral joint (dislocates) during jump landing, such as with knock-knees or knee being extended. Symptoms such as knee pain, lack of force on the knees, and stiffening of the knees (giving way) may develop, impairing not only sports, but also activities of daily living. Other causes include many other factors, such as birth defects affecting the patellofemoral joint.

Cause and disease mechanism

Functional anatomy

One of the alignment indices of the lower extremities, an increase in the Q angle (normally less than 15 degrees ), which is the angle between the traction of the quadriceps muscle and the patellar tendon, is problematic. Dynamically, the patellofemoral joint exerts vertical lateral traction (vastus lateralis quadriceps muscles) on the patella from knee extension to flexion, making the patella more prone to lateral dislocations (Fig.). This may be caused by weakness of the vastus medialis muscles to stop the movement, relaxation of the medial joint capsule, or stiffness of the lateral joint capsule with strong (unbalanced) traction by the vastus lateralis muscles. Statically, the patellofemoral joint is more likely to be dislocated, when the lateral articular surface of the femur is shallow, because the shape of the patella is flat like a bun and poor compatibility with patellofemoral joint. Other triggers include strained knees, generalized joint laxity, X legs, flatfoot, high patella, and small patella.

Figure) Functional anatomy: In knee valgus, the patella is laterally displaced (left leg).

Functional anatomy

Functional Anatomy: In knee valgus, the patella is laterally displaced (left leg).

Cause of Event

Adolescent women are more likely to develop this because of the female sex hormones that cause soft tissues to relax (the joints are more likely to loosen).

Injury mechanism

The first dislocation often occurs when the front of the knee is struck in sports or traffic accidents (direct external force), and the second and subsequent dislocations tend to occur repeatedly due to unaided muscular force (indirect force) by sports, etc. The disease is often bilateral and requires checking both sides (including X-rays).


Severe knee pain, swelling, joint hematomas, gait disturbances, and limited knee mobility are evident when the patella is dislocated. Aching pain (called "anterior knee pain") on the front surface of the knee joint, or spontaneous pain on the medial side of the patella, and tenderness (due to traction on the medial joint capsule) are common. However, pain outside the dislocation is less common. The presence of patellar instabilities and instabilities referred to as the "apprehension sign" (deflecting the patella laterally), is a key indicator. Continued repeated dislocations and subluxations lead to the complications of chondromalacia and osteoarthritis of the patellofemoral joint. If the dislocated patella is broken, a piece of bone moves like a mouse and causes pain in another part of the body.


Laboratory Findings

X-rays show that the patella is dislocated lateral to the femoral articular facet, and subluxation does not result in complete dislocation, and it may be trapped or displaced lateral to the femur (Photo 1). If forces are strong, a dislocated fracture may result in the presence of a piece of bone and cartilage. Incompatible patellofeniral joint can also be seen. MRI (Photo 2) shows cartilage degeneration, incompatibility of articular surfaces (even on CT), interposition of surrounding soft tissues, and hydroarthrosis.


Photos 1, 2
Left: X-ray image (axial map): The patella is subluxated and laterally changed. Joint surface incompatibility is seen.
Right: MRI: Poor joint congruence with signal change of the articular surface and joint edema (white)

Popular sports

It often occurs in football (soccer), basketball, and rugby as well as gymnastics.

Age and gender predilection

It occurs predominantly in adolescent girls. As people age, the joints become stiff, and the tendency to dislocate decreases on its own after age 30.

Treatment and rehabilitation


Dislocations require immediate closed reduction (in a medical facility). After reduction, a cast or brace may be needed for about 3 weeks. Be aware that early return to sport can lead to chronic joint loosening, which can lead to recurrence. Daily preventive measures include wearing a support brace called a dynamic patellar brace with a band attached to the outside of the patella to prevent dislocations (Photo 3). Taping is also used to prevent lateral forces in the same way. If frequent dislocations and severe pain do not improve with conservative treatment, surgery may be performed. Doctors may perform endoscopic procedures, such as sewing the medial joint capsule and cutting the lateral joint capsule.

Dynamic patellar brace

Photo 3) Dynamic patellar brace: Patella lateral with pads to control dislocation

Standard rehabilitation

While limiting the knee in genu valgum, strengthen muscles of the vastus medials lightly and stretch the vastus lateralis. Check the form of running and jumping with attention to riding an exercise bike with bow-legs, and cutting and twisting movements when returning to play.

Yoshizumi Iwasaki

Yoshizumi Iwasaki

NATA certified athletic trainers, certified athletic trainers from the Japan Physical Education Association, and chairman of the Japan Core Conditioning Association (JCCA)

Trainer Edition


Dislocation of patella (subluxation) is more likely to occur when the knee is often too medial when the person is likely to step down, land, or fall, it is necessary to improve active alignment (orientation of the joint in motion) of hip joint, knee, and ankle correctly and consciously. Although corrective measures are being taken to re-educate basic movements and improve the form, the person may use visual feedback, such as videos, because people often have habitual knee-in and are unaware of it. This starts with awareness of movement with correct alignment.
People with very specific morphologic features are less likely to be able to prevent them. Braces and tape may be needed. Knee-only approaches are often inadequate, and the foot and hip joint should be checked. Sometimes shoes and insoles need to be changed.

On-site evaluation and first aid

On-site evaluation recognizes the dislocation at first sight. If the dislocation remains firm, the person should be transported to the hospital with the current status maintained as much as possible. It is important to start icing immediately, immobilize the entire leg, and transfer the patient to the nearest medical facility as soon as possible.
As an air splint provides too much compression on the affected area, we will need to devise ways of stabilizing without applying direct pressure by utilizing daily items. Ideally, vacuum splint (negative pressure fixture) are available. In the hospital, the doctor repositions the area. Common sports scenes allow immediate closed reduction in a health-medical setting. However, in emergencies, such as in mountain accidents, the knee is slowly extended in a hip joint flexion position. There is a significant chance of reduction, but it generally should not be done because it is very painful and may cause fracture during reduction. Any patellar dislocation, including spontaneous reduction, is likely to damage soft tissue, which should be examined.


When surgery is done or experience prolonged swelling in conjunction with severe damage of soft tissue, start recovery exercise of range of motion first. CPM (passive joint movement) is used at a relatively early stage in the hospital. Initially, at home, active knee flexion and extension exercises are performed with the patient lying on his back or face down. Correct active alignment should be preferred to forcibly increasing the range of motion.
Weight bearing is permitted at a relatively early stage, but isometric techniques are used to strengthen vastus medialis strength. The knee can be encouraged by changing the orientation of the hip joint or ankle or by tapping the area to be stressed, because the person does not apply force to a difficult area.
In Western sports (particularly Eastern Europe), EMG (electromyogram) may be used to target the oblique head of the vastus medialis to contract. It goes without saying that it can be used to increase the strength of the entire vastus medialis , voluntary contractions during electrical contractions can help smooth muscle re-education. SLR (straight leg raising) is also performed, but it is important to note that some angles can lead to loss of force from the vastus medialis.

Dislocation of patella (subluxation) 1

A closed kinetic approach is taken as soon as loading is permitted. Make sure to perform standing position (posture) with equal weight on both legs, walking, standing on one leg while being conscious about alignment. Large mirrors can be used in a room. Knee extension exercises in a standing position should be performed before entering the squat. Slowly extend the knee with the knees gently flexed, with particular attention to prevent the knees from going in. While straightening the knee, instruct the person to focus on the muscles above the inside of the knee.

Dislocation of patella (subluxation) 2

Once the knee is extended in an upright position and can be bent to the depth of a quarter squat (1/4 squat), proceed to perform quarter squat on a mini-trampoline, or a half-squat in a position while holding a handrail.
If the person recovers further, he/she may proceed to a single-leg squat or forward lunge with weight relief, but always make sure to be aware of alignment and confirm that the vastus medialis is contracting without being knee-in.

One-leg standing exercises on BOSU systems are intended to achieve coordination of the muscles surrounding the knee joint.
The ultimate goal of reconditioning is to allow jumping, landing, and running without feeling unstable or painful, so rhythmic stabilization is an essential subject. The final phase of conditioning requires training with awareness of dynamic alignment, in which the knee flexion/extension axis cannot be shifted during side steps or directional changes.

One-leg standing exercises on BOSU systems are intended to achieve coordination of the muscles surrounding the knee joint.

The ultimate goal of reconditioning is to allow jumping, landing, and running without feeling unstable or painful, so rhythmic stabilization is an essential subject. The final phase of conditioning requires training with awareness of dynamic alignment, in which the knee flexion/extension axis cannot be shifted during side steps or directional changes.

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