A patella dislocation occurs when the kneecap (patella) pops out of its groove at the end of the thigh bone (femur). A subluxation refers to a partial dislocation where the kneecap slides out of alignment but stays within the joint or quickly snaps back into place. These injuries often happen during sudden changes in direction while the foot is planted or from a direct blow to the knee.
Patients typically experience a sudden, painful event followed by immediate swelling and difficulty using the leg.
Visible Deformity: The kneecap appears shifted toward the outside of the knee.
Intense Pain: Severe pain at the moment of injury, often accompanied by a popping sensation.
Instability: A feeling that the knee is loose, "giving way," or unable to support weight.
Rapid Swelling: The joint may fill with fluid or blood (hemarthrosis) within minutes or hours.
Limited Motion: Difficulty straightening or bending the knee due to pain and displacement.
Tenderness: Significant soreness along the inner edge of the kneecap where ligaments may have stretched or torn.
Physical Examination
Reduction: If the patella is still dislocated, a professional will move it back into its groove.
X-rays: Used to confirm the kneecap is back in place and to look for small bone fragments (loose bodies) that may have broken off during the injury.
MRI: Recommended to evaluate the Medial Patellofemoral Ligament (MPFL) and the health of the joint cartilage.
Management focuses on stabilizing the kneecap and preventing the injury from happening again.
Immobilization: Wearing a brace or splint for a short period to allow the stretched ligaments to heal.
Physical Therapy: Focusing on strengthening the quadriceps (specifically the VMO muscle) and hip stabilizers to keep the kneecap tracking correctly.
Activity Modification: Avoiding pivoting sports or high-impact activities until strength and stability return.
Bracing: Using a specialized "J-brace" or patellar stabilizer during sports to provide lateral support.
Surgical Repair: If there is a cartilage injury or repeat dislocation.