Make no mistake this can be a serious injury. This is not as common as the ACL injury in athletes but an ACL injury must be ruled out and that can be done with a number of different tests. Surgery is not indicated unless the injury is recurrent and is usually a last resort.

Treatment for this injury obviously depends on how severe the injury is, but special care is taken to strengthen the Vastus Medialis of the Quad Muscle structure. This muscle helps to place a medial pull on the patella, reducing the lateral, dislocating force.

Here is a little anatomy and physiology from the Athletic Advisor:

The Dislocated Patella

The patella (knee cap) is a sesamoid bone. A sesamoid bone is one that is encased in tendon or ligament. The patella is located inside the quadriceps tendon. The patella acts as a fulcrum to increase the strength of the quad muscle. It is held in place by the quadriceps tendon above, the patellar tendon below, and very thin ligaments on either side. The patello-femoral joint is formed by the patella and trochlear groove of the femur.

Due to the twisting nature of sports, the patella can dislocate (come out of joint) with an awkward twist of the femur (thigh) on the tibia (shin). A twisting motion causes the patella to shift to the side. Usually, the patella moves laterally (to the outside). This occurs because the quadriceps muscle contracts to maintain the stability of the body. The shin has shifted so that the line of pull of the quads causes the patella to shift laterally. The patella is pulled laterally because it wants to remain in line with the muscle.

The patella can dislocate more easily in some people than others. Individuals with a greater "Q-angle" are at a greater risk for patellar dislocations. The "Q-angle" is formed by envisioning a circle around the patella, the line of pull of the quad muscle forms the tail of the "Q." If the tail of the "Q" is more than 25 degrees off of the center of the quad-patella-patellar tendon line of pull, it is considered an abnormally high "Q-angle."

This places the patella at a greater risk to slide off of the femur. The quad-patella-patellar tendon mechanism wants to form a straight line when the quad muscle contracts, due to this, the patella is pulled laterally. This places a person with a high "Q-angle" at a greater risk for patellar dislocations.

Another risk factor for patellar dislocations is a malformed patella or trochlear groove (the groove located between the two heads of the femur) . The back side of the patella should have a peak, like an inverted mountain top. The trochlear groove should look like the valley between mountains. If either the mountain or the groove are not large enough, the patella is more prone to dislocate.

This is demonstrated by the x-ray. The back side of the patella is flat. This accounts for the sideward lean of the patella. This patella is prone to dislocate and is partially dislocated or subluxed in the x-ray. X-rays are necessary to rule a fracture of the patella. In some cases the mountain peak of the patella will be "knocked off" when it impacts with the femur. This piece of bone can cause severe damage to the joint if it is not properly addressed.

The retinaculum is the band of connective tissue that attaches to the medial and lateral structures of the knee joint, including the patella and patellar tendon. In a patellar dislocation this is either stretched or torn. Most surgeons I have discussed this with pretty much agree that this is usually a tear and not a stretch of the retinaculum. The amount of stress placed upon the tissues during this injury usually result in a some sort of a tear.

The "Sunrise" view of the Knee
Images from Kyle Palmer, MD

Non-surgical treatment of the dislocated patella is as follows:

• Patients will usually be required to keep the knee stabilized for up to six weeks. The doctor will prescribe either a brace or splint to prevent further damage.
• After the splint or brace is removed, physical therapy will be initiated to restore strength and correct alignment problems or muscle imbalances that may have contributed to the dislocation.
• The goal of therapy is to re-establish a full range of motion in the knee with proper alignment or tracking of the patella.
• Ongoing therapy rehabilitates the quadriceps and hamstrings, the muscles surrounding the knee which add strength and stability to the joint.
• Therapists may recommend changes in activity and specialized bracing to support the knee during movement or while it is under stress.

Surgical Treatment

Image and Text from RONALD P. GRELSAMER, MD

Reconstruction of the medial patello-femoral ligament (MPFL). This procedure has been designed for the patient whose kneecap dislocates (completely slips out of the trochlear groove). Operations go in and out of favor, and this one is currently in vogue. Since the MPFL helps keep the kneecap in its groove, it is logical to repair or reconstruct this ligament when the kneecap has dislocated. But repair only makes sense if the ligament was normal to begin with. In many patients it is stretched out even before it tears, so simple repair doesn't create a normal MPFL.

Reconstruction implies that the surgeon is creating a ligament from scratch, and this means taking a ligament from some other part of the knee or using a synthetic material. I tend to recommend this to patients who’ve undergone a simpler procedure that has failed.

Other procedures include:

The Hauser Procedure - A Distal transfer of the tibial tuberosity. In situations where the patella is riding high (patella alta) consideration can be given to lowering it. This can be done by osteotomizing the tibial tuberosity, freeing it up on three sides (medial, lateral, and distal), removing a portion of the tuberosity at its lower end, and transferring the remainder of the tuberosity distally into the underlying bony bed.

The Fulkerson Procedure - This osteotomy most likely unloads the disto- lateral aspect of the patella and loads its supero-medial aspect. The advantage of this osteotomy is that with one cut both medialization and elevation can be obtained. No bone graft is needed (though it can be added for increased elevation). The disadvantage is that one loses correction relative to one-plane osteotomies.

The Maquet Procedure - Anterior elevation of the tibial tuberosity. The Maquet procedure is usually combined with a lateral release. Sorting out the benefits of the lateral release from those of the tuberosity elevation is therefore difficult.

The Elmslie-Trillat Procedure - By transferring the tibial tuberosity medially, one decreases the quadriceps (Q) angle. Accordingly one decreases the bowstring effect of the quadriceps mechanism, and, most significantly the tendency of the patella to move laterally when the quadriceps contracts.