Patellar dislocation and subluxation are injuries to the patella (kneecap) affecting the joint it forms with the femur (thigh bone). A patellar dislocation occurs when the patella is displaced from its normal position and no longer sits in the trochlea. A patellar subluxation occurs when the patella shifts but does not completely dislocate from the trochlea.
What Is Patellar Instability?
The patella is a V-shaped convex bone that sits within a V-shaped concave groove of the femur called the trochlea.
With a patellar dislocation, the patella is displaced from its normal position and no longer sits within the trochlea. With a patellar subluxation, the patella shifts but does not completely dislocate from the trochlea.
A patellar dislocation may cause an obvious deformity and may relocate on its own when the knee is straightened.
Causes and Risk Factors
Patellar dislocation or subluxation can result from:
- A direct blow to the knee
- A twisting or pivoting injury to the lower extremity, such as during a rapid change in direction
- Powerful muscle contraction
- Congenital abnormalities, such as shallow or malformed joint surfaces
- Loose ligaments
- Valgus (knock-kneed) alignment
- A shallow trochlea (patella groove)
Risk factors include:
- Participation in contact sports, including football and soccer
- Sports that require jumping and landing, including basketball and volleyball
- Sports in which cleats are worn
- Loose ligaments
- Wide pelvis
- Valgus alignment (knocked knees)
- Shallow or malformed joint surfaces
- Previous patella dislocation
- Poor physical conditioning, including strength and flexibility
Symptoms
Common signs and symptoms include:
- Severe pain and a feeling of the knee giving way
- Tenderness, swelling, and bruising of the knee
- An obvious deformity when the patella dislocates
- The patella may relocate on its own when the knee is straightened, correcting the deformity
Treatment
After immediate reduction, or repositioning of the bones of the joint, treatment consists of ice and medications to relieve pain.
Reduction can be performed without surgery. However, surgery may be necessary to remove loose fragments of bone or cartilage caused by the dislocation or reduction, or to help prevent further dislocation.
Elevating the injured knee at or above heart level can help reduce swelling. Your doctor may also drain blood from the knee to relieve pain and help recovery.
Recovery focuses on stretching and strengthening the injured, stiff, and weakened joint and surrounding muscles. This may be done with or without the assistance of a physical therapist or athletic trainer.
For patients who continue to experience dislocations, surgery is recommended to rebuild the restraining ligaments.
Recovery and Outcomes
A good prognosis is expected with appropriate reduction and proper treatment.
Potential complications include:
- Associated fracture or joint cartilage injury due to the dislocation or repositioning of the patella
- Damage to nearby nerves or major blood vessels, although this is rare
- Prolonged healing
- Recurrent dislocation
- Excessive bleeding within the knee due to dislocation
- Patella pain and giving way, usually due to inadequate or incomplete rehabilitation
- An unstable or arthritic joint following repeated injury or delayed treatment
When to See Dr. Chudik
If you are concerned about a patellar dislocation or subluxation, continue to experience episodes of dislocation, or your symptoms worsen, schedule an evaluation with Dr. Chudik.
Call 630-324-0402, request an appointment online, or email contactus@chudikmd.com.