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