Causes and Risk Factors for Dislocated Kneecaps

Kneecap dislocation is commonly caused by traumatic injury or by placing an excessive amount of pressure on the knee joint. The injury is more common in women, and is one of the more common injuries sustained by athletes.

Common Causes of a Dislocated Kneecap

The injury can occur as the result of one or a combination of the following:

• Direct trauma to the knee. When the knee joint collides with another person or object with great force, trauma to the joint can cause the kneecap to dislocate.

• Excessive pressure from movement. When an athlete is moving at high speeds in one direction and has to quickly change direction with his or her leg planted, the knee joint sustains a great deal of pressure. In cases where the pressure is too much, the kneecap may dislocate.

• Female gender.¹Tsai C, Hsu C, Hung C, Hsu H. Primary traumatic patellar dislocation. Journal of Orthopaedic Surgery and Research. 2012. Available at: http://www.josr-online.com/content/7/1/21. Accessed August 14, 2015. Women have been shown to be at a higher risk for kneecap dislocation than men. It is thought that this risk may may be because women tend to have wider hips, causing the thigh bones slant inward and join the knee at more of an angle.

• Weak leg muscles. Individuals who have weak leg muscles or an imbalance in strength of their respective legs may put unneeded pressure on their knee joint, increasing the risk of patellar dislocation.

• Height. Athletes who are exceptionally tall may have an increased risk of patellar dislocation.

• Misaligned or elevated patella. If an athlete’s patella is misaligned or sits unnecessarily high on the femoral groove, that individual may have an increased risk of sustaining a dislocated kneecap.

• Prior injury. Having previously suffered a kneecap dislocation or another traumatic injury that has weakened the knee joint may increase the likelihood of sustaining a kneecap dislocation.²Lewallen L E. First-Time Patellofemoral Dislocation: Risk Factors for Recurrent Instability. - PubMed - NCBI. Ncbinlmnihgov. 2015. Available at: http://www.ncbi.nlm.nih.gov/pubmed/25633361. Accessed July 28, 2015.

  See About Acute Patellar Injuries

• Excess weight. Individuals who are severely overweight or obese are more likely to sustain a kneecap dislocation, and a dislocation can occur even without the presence of traumatic injury or excess force. In what is known as a low-velocity kneecap dislocation, the knee is overwhelmed by the weight of carrying the body and dislocates.³Werner, BC, Gawthmey FW Jr, Higgins ST, Hart JM, Miller MD. Ultra-low velocity knee dislocations: patient characteristics, complications and outcomes. American Journal of Sports Medicine. 2014, Feb. Available at: http://www.ncbi.nlm.nih.gov/pubmed?cmd=historysearch&querykey=6. Accessed August 14, 2015.

While many types of knee injuries are unavoidable, it is possible to somewhat lessen the risk through a combination of maintaining a healthy body weight, wearing the protective gear, and avoiding high trauma situations.