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Patellar (Kneecap) Instability / Dislocations / Malalignment


What is patellar instability?

The patella (kneecap) is attached by tendons to the femur (thigh bone) and the tibia (shin bone). The patella fits into a grove at the end of the femur called the trochlear groove. When the knee bends or straightens, the patella slides up and down. Patellar instability occurs when the patella moves outside of the trochlear groove.  Patellar instability is almost always due to a dislocation of the kneecap. When the kneecap dislocates it can tear the structures on the inside of the knee, with the medial patellofemoral ligament (MPFL) being the most commonly injured.


What causes patellar instability? 

There are two main causes commonly associated with patellar instability:

  • Acute traumatic injuries – typically the result of a sports-related trauma or direct blow to the knee. may result from a specific injury or trauma, such as a direct blow to the knee. Traumatic dislocations of the kneecap can stretch or rupture the stabilizing structures on the inside of the knee, which can eventually lead to recurrent dislocations of the patella.
  • Chronic subluxations – usually associated with malalignment or anatomic anomalies. Chronic subluxation is considered an atraumatic injury and occurs when the kneecap due to the patient’s anatomy, even during their everyday activities.


What are the symptoms of patellar instability?

  • Sensation of the kneecap slipping or moving with turning or rotating movements
  • Pain in the kneecap, especially with activity or when being palpated
  • Swelling and stiffness in the knee, especially following a traumatic incident
  • Weakness and limited range of motion in the joint
  • Hearing a popping sound when the patella dislocates
  • A change in the knee’s appearance with the knee looking misshapen or malformed


How is patellar instability Diagnosed?

Dr. Potts will want to assess the degree of injury and determine the cause leading up to the patellar instability and/or dislocation. He will perform a thorough medical history review and physical examination to determine the level of instability, and will likely order x-rays to evaluate for patellar alignment and evidence of any bone injury from a previous dislocation. An MRI may be also be ordered to evaluate possible ligament and cartilage damage in the case of a traumatic dislocation. 


What is the treatment for patellar instability and malalignment?

In most cases, patellar instability can be treated without surgery in patients at low risk for recurrent patellar instability. Patients with recurrent instability, dislocations, or malalignment may require surgery to restore the stabilizing ligaments of the knee and correct their anatomy.

The type of surgery required will depend on the cause of the instability. Surgical treatment options often include MPFL reconstruction to rebuild the ligament that holds the patella in place, or tibial tubercle osteotomy (TTO) to realign the patella by relocating the attachment of the patellar tendon just below the knee joint.