Definition
Kneecap dislocation occurs when the round-shaped bone covering the knee (patella) moves or slides out of place. The dislocation often occurs toward the outside of the leg.
Causes
Kneecap dislocation often occurs after a sudden change in direction when your leg is planted. This puts your kneecap under stress. This can occur when playing certain sports, such as basketball.
Dislocation may also occur as result of direct trauma. When the kneecap is dislocated, it can slip sideways to the outside of the knee.
Symptoms
Symptoms of kneecap dislocation include:
- Knee appears to be deformed
- Knee is bent and cannot be straightened out
- Kneecap (patella) is dislocated and stuck to the outside of the knee
- Knee pain and tenderness
- Knee swelling
- Sloppy kneecap -- you can move the kneecap too much from right to left (hypermobile patella)
The first few times this occurs, you will feel pain and may be unable to walk. If you continue to have dislocations, your knee may not hurt as much and you may not be as disabled. This is not a reason to avoid treatment. Kneecap dislocation damages your knee joint. It can lead to cartilage injuries and increase the risk of developing osteoarthritis at a younger age. Repeat dislocations will make the condition worse and harder to treat.
When to Contact a Medical Professional
Contact your provider if you injure your knee and have symptoms of a dislocation.
Contact your provider if you are being treated for a dislocated knee and you notice:
- Increased instability in your knee
- Pain or swelling return after they went away
- Your injury does not appear to be getting better with time
Also contact your provider if you re-injure your knee.
Prevention
Use proper techniques when exercising or playing sports. Keep your knees strong and flexible.
Some cases of knee dislocation may not be preventable, especially if physical factors make you more likely to dislocate your knee.
References
Mascioli AA. Acute dislocations. In: Azar FM, Beaty JH, eds. Campbell's Operative Orthopaedics. 14th ed. Philadelphia, PA: Elsevier; 2021:chap 60.
Naples RM, Ufberg JW. Management of common dislocations. In: Roberts JR, Custalow CB, Thomsen TW, eds. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. 7th ed. Philadelphia, PA: Elsevier; 2019:chap 49.
Sherman SL, Hinckel BB, Farr J. Patellar instability. In: Miller MD, Thompson SR, eds. DeLee, Drez, & Miller's Orthopaedic Sports Medicine. 5th ed. Philadelphia, PA: Elsevier; 2020:chap 105.
Version Info
Last reviewed on: 11/7/2024
C. Benjamin Ma, MD, Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery, San Francisco, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.