As part of the complex network of soft tissues that stabilize the knee, the medial patellofemoral ligament attaches the inside part of the kneecap (or patella) to the long bone of the thigh, also called the femur. Injury to this ligament can occur when the patella dislocates or subluxes due to trauma experienced during athletics or an accident, as a result of naturally loose ligaments—most frequently seen in girls and women—or due to individual variations in bony anatomy. People with these injuries are described as having patellar instability.
Historically, although some patients benefitted from surgery to tighten the damaged ligament, as recently as ten years ago, many individuals with damage to the MPFL had few treatment options beyond immobilization and rehabilitation. Today, however, MPFL reconstruction, a surgery in which a new medial patellofemoral ligament is created to stabilize the knee and help protect the joint from additional damage, offers an excellent treatment option for people who have experienced more than one dislocation.
In the healthy knee, the bones that make up the patellofemoral joint move smoothly against one another as the joint is flexed or extended. The patella glides in a groove or trochlea of the femur. The MPFL plays a particularly important role in keeping the patella on track and acting as a sort of leash that restrains movement of the patella.
When patellar dislocation occurs, soft tissues are damaged as the patella “jumps” the track and then comes forcibly back into place. Because the bone essentially always dislocates toward the outside part of the leg, the ligament on the inside of the knee—the MPFL—is torn.
Left untreated, an injured MPFL can heal. However, it does so in a looser, lengthened position, setting the stage for subsequent dislocations and more damage to the cartilage in the knee. While pain, swelling, and disability from dislocation are significant in themselves, the greater concern with dislocation is injury to the cartilage that covers the ends of the bones where they meet in the joint. Once cartilage damage occurs, the patient is at high risk of developing patellofemoral arthritis, a significantly more difficult condition to treat. For this reason, it’s never advisable to allow dislocations to continue occurring.
At the Hospital for Special Surgery (HSS), patients with patellar instability undergo thorough assessment that includes a physical examination and patient history. Magnetic resonance imaging (MRI) is also a part of this evaluation, as it provides critical information on the condition of the cartilage in the patellofemoral joint and helps determine whether the patient is a candidate for MPFL or a bony procedure, such as tibial tubercle transfer. Often, these images can be obtained on the same day as an initial visit.
Although non-operative treatment does not have a significant role in the treatment of patellar instability, if the patient has experienced a single dislocation without a cartilage injury on MRI he or she will be treated with short term immobilization and physical therapy. Almost all candidates for MPFL reconstruction have dislocated their knee more than once, and in some cases may have experienced multiple dislocations. (MPFL may be performed in a patient who has had single dislocation, but only in the presence of other problems in the knee that also require surgical intervention.)
Patients undergoing MPFL reconstruction receive regional anesthesia—an spinal block that numbs the lower half of the body—and sedation. During the procedure, the orthopedic surgeon replaces the injured ligament with a tendon, taken from the patient’s hamstring or donor tissue, and creates a new ligament. Arthroscopy is used to visualize the area, and the reconstruction is completed through two small incisions. The entire surgery takes about an hour and patients return home the same day, with their knee stabilized in a brace.
MPFL reconstruction produces excellent results and is associated with a very low rate of complications, which includes rare fractures, infections or blood clots. Moreover, the procedure can be performed safely in children with open growth plates, the area where bone grows, whereas, surgical approaches that change bone alignment are not appropriate in young patients. With no alternative available, in the past, children were sometimes placed in a brace, but remained at risk for additional dislocations until reaching skeletal maturity, when surgical reshaping of the bone (osteotomy) might be considered.
Orthopedic surgeons at the Patellofemoral Center also perform MPFL reconstruction on patients who have failed other, less successful surgeries in the past to address the condition. These may include arthroscopy—minimally invasive surgery in which torn tissue in the patellofemoral joint is “cleaned up”; a lateral release, in which the ligament on the outside part of the patellofemoral joint is loosened, and/or a medial imbrication, a procedure in which the surgeon tightens the MPFL by taking a “tuck” in it, similar to tightening a garment. Those who undergo MPFL reconstruction as a revision surgery generally experience a considerable improvement in stability of the patellofemoral joint.
Although lateral release alone is not an effective surgical option for patellar instability, this procedure may be done in conjunction with an MPFL reconstruction to address other anatomical issues in the joint and to restore balance in the knee. Tubercle tibial transfer or osteotomy, may also be done in conjunction with an MPFL, in patients who have significant mal-alignment of the bones in the patellofemoral joint. This bony procedure is advised when the patient has an anatomical abnormality in which the patella tendon attaches to the tibia in such a way that there is a severe pull on the patella sideways or laterally. In rare cases, people with patellar instability may be candidates for an MPFL repair rather than reconstruction when the MPFL has pulled a small piece of bone off the inside part of the kneecap.
Immediately following MPFL reconstruction, patients can bear weight on the affected leg, which is placed in a brace that is worn for 6 weeks, this keeps the leg straight during walking. During recovery, a continuous passive motion machine (CPM) is used at home to avoid scar tissue and stiffness from developing in the joint as the ligament heals. The CPM machine moves the patellofemoral joint without the use of a patient’s muscles. Once the Quad, the major muscle in the thigh, is strong enough to support the joint—usually at about 6 weeks after surgery—the patient can begin physical therapy. Other measures that can help speed recovery from MPFL reconstruction include devices that provide electric stimulation to the muscles around the knee and Game Ready®, a machine that compresses and cools the leg, thereby reducing swelling and pain. (Insurance does not presently cover the cost of these devices.)
At four to seven months after MPFL reconstruction, most people can generally return to sport or play. Those considering the surgery should be aware than recovery times may vary and can be dependent on individual anatomy, capacity to heal and general health prior to surgery.
Summary by Nancy Novick