My Knee “Pops” In & Out of Place! Patellar Instability

by B. Rodney Comisar, MD

What is Patellar Instability?  Patellar instability is the movement of the patella (knee cap) out of the trochlea groove (groove in which the knee cap sits on the bone of the knee). The degree of instability is determined by whether the patella “subluxed” or “dislocated”. A subluxation occurs when the knee cap translates out of the groove slightly and then “pops” back into place. A dislocation results in the patella moving completely out of the groove and staying in that position. The instability may be classified as acute or chronic depending on the frequency of occurrence. Acute instances typically occur predominantly in sports, specifically football, basketball, and volleyball. Young athletes (age 13-20) have the highest incidence rates.  Due to anatomic issues, teenage females are at the highest risk for patella instability.

Mechanism of Injury:  How Does It Happen?  

  • Most Common: Non-contact twisting injury with knee near full extension
  • Direct blow to the knee cap

Symptoms of Acute Instability

  • Pain
  • Deformity
  • Swollen
  • Decreased range of motion (ROM)
  • Tenderness in the area

Your physician or athletic trainer will perform an apprehension test to assess your injury. Your physician may also order an x-ray to rule out a possible fracture of the patella. Initial management of the injury will include, swelling reduction, bracing, and possibly crutches for protected weight bearing. Physical therapy can also be beneficial to recovery. The orthopedic surgeon will determine whether non-surgical or surgical intervention is the best treatment.

After primary acute event, 14-49% recur and become chronic conditions.

Strategies to Decrease Recurrence

  • Activity modification
  • Quad-strengthening
  • Stretching
  • Bracing 
  • Custom orthotics

Does your knee cap pop in and out of place?  Schedule an appointment with Dr. Comisar to evaluate your symptoms.

Dr. Comisar is a board certified, fellowship-trained orthopedic surgeon who specializes in sports medicine related injuries. He has a sub-specialty certification in Sports Medicine. Dr. Comisar offers a full spectrum of sports medicine surgery, including arthroscopy and minimally invasive procedures.  

“I strive to provide comprehensive, state of the art treatment in an environment in which you/one would feel comfortable and confident sending family and friends.”

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