Patella (kneecap) Dislocation

The patella, also known as the kneecap, is the structure at the front of the knee that connects the muscles of the anterior thigh to the leg, allowing for forceful contractions that propel human beings in walking, running, and jumping.  The alignment of the patella can impact its function. In cases in which there are anatomical features that reduce the stability of the patella in its groove (trochlea) on the femur (thigh bone) the  kneecap can dislocate.  The bone, cartilage, and soft tissue restraints of the patella can be injured during such an event.

When someone injures the patella there will often be a pop felt or heard, and in some cases there will be an obvious deformity of the knee in which the patella is positioned at the lateral side of the knee.  In many cases the patella will spontaneously relocate with knee extension, and the cause of the pain and instability noted after the injury can be mistaken for other injuries, such as ACL tear. Initial treatment sometimes requires relocation of the kneecap, bracing, and pain management. Rehabilitation is initiated when pain and swelling is controlled, utilizing bracing for athletic activity.

The stabilizing ligament of the patella, the medial patellofemoral ligament (MPFL) is often stretched or torn with a dislocation.  For this reason a person that suffers this injury is often placed in an immobilizer or patella stabilizing brace to allow for the ligament to heal. X-rays are often normal after a dislocation, but occasionally there can be an associated fracture.  Imaging such as MRI is performed to identify the soft tissue injuries and to identify the degree to which there was damage to the stabilizing ligament (MPFL) and retinaculum.  At times there will be  injury to cartilage of the patella or occult fracture. In circumstances where a dislocation causes damage to the articular cartilage of the patella or trochlea, a surgery may be needed to remove a loose body and/or repair the damaged cartilage.  Additionally the medial patellofemoral ligament (MPFL) can be repaired or reconstructed.

A big question to answer when someone dislocates their patella is whether this event is an isolated trauma which causes a tear that can heal, or if it is the heralding event of a more chronic problem in which alignment is abnormal and puts a person at increased risk of repeated dislocations.  The decision to perform surgery for this injury is a complex one with concerns such as skeletal immaturity, alignment of bony restraints, and isometry of MPFL graft.  A discussion that is essential in the care setting for people that have suffered this injury involves an understanding of the family history, injury or anterior knee pain of the opposite knee, overall joint stability, and evaluation of bony and soft tissue structures.  In many circumstances rehabilitation and bracing can allow healing and may help to prevent re-injury in anatomically stable patients.   Some athletes might even return to their sport within the same season after this injury.  In other circumstances there may be confounding factors such as trochlear dysplasia (abnormal groove for the kneecap), hypermobility (loose connective tissue), patella alta (abnormally long patella tendon), or abnormal alignment of the patella and the trochlea (>20 mm TT/TG).  In those cases a surgery, even after just one instability episode can be considered and pursued even in younger, skeletally immature patients.

For our patients that suffer this injury, bracing and rehabilitation is initiated, imaging ordered and reviewed, and engagement in a shared-decision making conversation is employed to review the risks and benefits of surgery versus non-operative treatment.

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