The medial patellofemoral ligament is a part of the complex network of soft tissues that stabilize the knee. The MPFL attaches the inside part of the patella (kneecap) to the long bone of the thigh, also called the femur.
Together, the patella and femur compose the patellofemoral joint.
Injury to the MPFL can occur when the patella dislocates or becomes subluxated (partially dislocated) due to a 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.
MPFL reconstruction is a surgery in which a new medial patellofemoral ligament is created to stabilize the knee and help protect the joint from additional damage.
It offers an excellent treatment option for people who have experienced more than one dislocation. The procedure is relatively new. Historically, although some patients benefitted from surgery to tighten the damaged ligament, as recently as around 2006, many individuals with damage to the MPFL had few treatment options beyond immobilization and rehabilitation.
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 trochlea (groove) of the femur. The MPFL plays a particularly important role in keeping the patella on track (that is, in this groove) by acting like a leash that restrains the patella's movement.
When patellar dislocation occurs, soft tissues are damaged as the patella “jumps” the track and then comes forcibly back into place. Because the kneecap dislocates toward the outside of the leg, the ligament on the inside of the knee (the MPFL) gets torn.
Left untreated, an injured MPFL can heal on its own. However, when left alone, the ligament heals in a loosened, lengthened position. This causes instability that makes it easier for the patella to become dislocated again in the future. This, in turn can cause damage to the cartilage in the knee. While the pain, swelling and disability associated with a dislocated kneecap are problems in themselves, the greater concern is subsequent injury to the cartilage that covers the ends of the bones where they meet in the knee joint. Once this cartilage is damaged, you are put at a high risk of developing patellofemoral arthritis, a significantly more difficult condition to treat. For this reason, it always advisable to get treatment that will help prevent further dislocations of the kneecap.
Watch this animation video to understand how MPFL reconstruction surgery works.
At the Patellofemoral Center at HSS, patients with patellar instability undergo a thorough assessment that includes a physical examination and review of the patient's medical history. A magnetic resonance imaging (MRI) is also performed to help the doctor understand 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 nerve block that numbs the lower half of the body – and sedation. The orthopedic surgeon then replaces the injured ligament with a portion of a tendon taken either from the patient’s own hamstring or from donor tissue. An arthroscope is used to view the surgical area, and the ligament reconstruction is conducted using 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 has a very low rate of complication. Rare complications can, however, include fractures, infections or blood clots. The procedure can be performed safely in children with open growth plates (the area where bone grows), as opposed to surgical approaches that change bone alignment and which 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 they reached skeletal maturity, at which time a surgical reshaping of the bone (osteotomy) would become an option. Today, MPFL reconstruction is a safe option for children and teenagers.
In rare cases, people with patellar instability may be candidates for a surgical repair of their MPFL, rather than a complete MPFL reconstruction, such as when the MPFL has pulled a small piece of bone off the inside part of the kneecap.
Orthopedic surgeons at the Patellofemoral Center also perform MPFL reconstruction on patients who have had other, less successful surgeries to address the condition. Such prior surgeries may include:
Although a 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 problems 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 procedure is recommended for patients who have an anatomical abnormality in which the patella tendon attaches to the tibia in such a way that there is a severe sideways pull on the patella.
Those who undergo MPFL reconstruction as a revision surgery generally experience a considerable improvement in stability of the patellofemoral joint.
Immediately following MPFL reconstruction, patients can bear weight on the affected leg, which is placed in a brace that is worn for six weeks. The brace 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 quadriceps (the major muscle in the thigh) is strong enough to support the joint, the patient can begin physical therapy. This is usually about six weeks after surgery. Other measures that can speed up recovery 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 may not cover the cost of these devices.)
Most people can generally return to sport or play sometime between 4 to 7 months after MPFL reconstruction. If you are considering the surgery, be aware than recovery times may vary and can be dependent on your individual anatomy, capacity to heal and general health prior to surgery.
Summary by Nancy Novick