The symptoms of a kneecap dislocation will vary based upon how the injury occurred as well as the severity of the damage to the knee joint and/or if other knee injuries are also present. In minor cases, it may be possible for an athlete to immediately resume athletic activity. In others, pain and limited mobility will be apparent.

See About Acute Patellar Injuries

Primary symptoms of kneecap dislocation may include:

  • Lack of mobility. If the kneecap dislocates to the outside of the knee, the leg may be stuck in a bent position, making it difficult to move.
  • Knee that gives way. When putting pressure on the affected leg, the knee may give out and be unable to support one's body weight.
  • Repositioning of the patella. In moderate to severe dislocations, the kneecap will not only move away from the knee joint but will fully reposition itself to the outside of the leg.
  • A hyper-mobile patella. In instances where the patella hasn’t moved away from the front of the knee but has dislocated, an individual may be able to move the patella around the front of the knee joint with an extended range of motion. Or the kneecap may simply feel out of place/not lined up. A hyper-mobile kneecap is sometimes referred to as “sloppy knee.”
  • Pain when standing. Kneecap dislocation may cause sharp pain on the front of the knee when an individual tries to stand or put pressure on the knee joint. Over time, the pain in the kneecap will dull, but this is not necessarily indicative of healing.
  • Localized tenderness. The kneecap will usually be painful to touch.
  • Bruising. Bruising may appear on and around the front of the kneecap during the healing process, particularly if the injury was caused by direct impact or blunt force.
  • Swelling. Swelling of the kneecap, also known as “water on the knee,” may occur when fluid is trapped around the kneecap following traumatic injury. This swelling may contribute to an athlete’s inability to move or straighten his or her leg.

Many of the above symptoms are fairly general and may apply to a variety of types of knee injuries. If a kneecap injury is suspected, it’s important to seek diagnosis and treatment immediately in order to avoid further damage to the knee joint and to help minimize the risk of future injury.

Dr. Terry Gemas is an orthopedic surgeon and the founder of Lakewood Orthopaedics and Sports Medicine in Dallas, TX. He specializes in sports medicine and has been in practice for more than 15 years. Dr. Gemas has treated professional athletes and currently serves as the head team physician for several Dallas-Forth Worth area high school, college, and club teams.