For the vast majority of young patients who dislocate their kneecap, surgical reconstruction of the affected ligaments can get them back on the court or field in a matter of months, with little risk of re-dislocation or reduction in their level of athletic performance, a new study has found.

Researchers at Hospital for Special Surgery in New York City have found that very few patients who underwent the ligament procedure -- called medial patellofemoral ligament reconstruction (MPFL) -- showed signs of recurrent instability of the kneecap up to two years later. Roughly 85 percent of them also had returned to their sport and were playing at the same level as before their injury.

"At least for right now, ligament reconstruction is a very reliable, highly reproducible way to get people back to their sport," said Beth Shubin Stein, MD, sports medicine surgeon at HSS, who led the study. "But the procedure is not right for everybody." Dr. Shubin Stein presented the findings at the 2018 summer meeting of the American Orthopaedic Society for Sports Medicine.

The MPFL connects the inside part of the kneecap, or patella, to the femur. Dislocation of the patella is a common sports-related injury in the United States, particularly among young athletes. The result of excessive twisting at the knee, patellar dislocations are estimated to occur in about 23 per 100,000 people per year, typically among youth ages 14 to 18.

Although the damaged ligaments often heal over time, the patella tends to be looser than before the injury -- and therefore more vulnerable to another dislocation. Knee instability also is a risk factor for the development of arthritis, as the cartilage prematurely erodes. (Some people have unstable knee ligaments even without a traumatic injury; they also can benefit from MPFL reconstruction.)

Sports medicine surgeons group MPFL injuries into two categories: those involving trauma to the ligament in the setting of a fairly normal knee anatomically, and those who have significant misaligned or misshapen bones in addition to the damage to the ligament from the injury of the dislocation. In the latter cases, extensive surgery is required. For the rest, a simple reconstruction of the ligament -- a short procedure performed with a localized nerve block and sedation -- generally is appropriate. During the operation, surgeons replace the damaged ligament with a tendon harvested from the patient’s own hamstring or a donor. The tendon is threaded through the patella and used to anchor the bony structure to the side of the femur.

[An animated video of the procedure is available here: https://www.hss.edu/conditions_medial-patellofemoral-ligament-reconstruction-mpfl.asp]

Although still relatively new, the MPFL has become the most common way to stabilize dislocated kneecaps, Dr. Shubin Stein said.

The current study and related research will help to identify patients likely to have a successful MPFL reconstruction and those who are likely to do better with a combination of ligament reconstruction and what are known as "bony" procedures -- more complex surgeries that require reshaping the groove or track or realigning the tibia to decrease the forces on the patella that can lead to a dislocation. The recovery period for these operations is between nine and 12 months, compared with four to six months for ligament reconstruction alone, according to Dr. Shubin Stein. Patients who undergo MPFL can bear weight on the affected knee immediately, whereas those who require more intensive surgery may have to stay off the joint for six weeks or longer.

"The goal of the study is to follow these patients and to find out if there are specific features that make their risk of dislocating over time higher — meaning those patients should probably have their bone moved," Dr. Shubin Stein said.

Dr. Shubin Stein presented data on 90 patients in the ongoing study. Patients were between the ages of 14 and 25 and had undergone MPFL at HSS between 2014 and 2017. Of those, 70 were available for assessment at the one-year point of the study; 47 were evaluated at the two-year mark.

One patient experienced a re-dislocated patella 3.5 years after the initial surgery. However, 96 percent and 100 percent of those who reached the one- and two-year points, respectively, were free of patellar instability, according to the researchers.

Patients also expressed a high degree of satisfaction with the MPFL procedure, rating their experience more than 9 on a 10-point scale, on average.

Side effects were rare, occurring in four patients (three at six months; one at one year); none required hospitalization or a second surgery. 

Dr. Shubin Stein and her colleagues are adding patients to their study pool and extending the follow-up time beyond the two-year point to gather more data.