Patellar Instability

The knee can be divided into three compartments: patellofemoral, medial and lateral compartment. The patellofemoral compartment is the compartment in the front of the knee between the kneecap and thighbone. The medial compartment is the area on the inside portion of the knee, and the lateral compartment is the area on the outside portion of the knee joint. The patella attaches with the femur bone and forms a patellofemoral joint. The patella is protected by a ligament which secures the kneecap from gliding out and is called as medial patellofemoral ligament (MPFL). Patellofemoral instability means that the patella (kneecap) moves out of its normal pattern of alignment. This malalignment can damage the underlying soft structures such as muscles and ligaments that hold the knee in place. Patellofemoral instability can be caused because of variations in the shape of the patella or its trochlear groove as the knee bends and straightens. Normally, the patella moves up and down within the trochlear groove when the knee is bent or straightened. Patellofemoral instability occurs when the patella moves either partially (subluxation) or completely (dislocation) out of the trochlear groove. A combination of factors can cause this abnormal tracking including anatomical defects, malalignment, improper muscle balance, and patellofemoral arthritis. Some of the causes for patellar dislocation include a direct blow or trauma, twisting of the knee while changing the direction, muscle contraction, and congenital defects. It also occurs when the MPFL is torn. If your kneecap is only partially dislocated (subluxation), your physician may recommend non-surgical treatments, such as pain medications, rest, ice, physical therapy, knee-bracing, and orthotics. If the kneecap has been completely dislocated, the kneecap may need to be repositioned back in its proper place in the groove. Surgical treatment is recommended for those individuals who have recurrent patella dislocation. This may include a reconstruction of the MPFL to provide proper stability to the patella. Surgical treatment may also be recommended if a kneecap instability event leads to a loose fragment of bone or cartilage in the knee.

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