A common injury seen in orthopedic surgery, patellar dislocation accounts for about 2% to 3% of knee injuries and is the second most traumatic knee injury after ACL tears in the adolescent and young adult population.

“If somebody has a twisting injury of their knee, the first most likely diagnosis is an ACL [tear],” Beth E. Shubin Stein, MD, sports medicine surgeon and co-director of the Women’s Sports Medicine Center at Hospital for Special Surgery, told Healio/Orthopedics Today. “The second most common diagnosis is patellar dislocation and that is in the second and third decades of life, which is the teens and 20s.”

Whether an adolescent athlete experiences an ACL tear or a patellar dislocation depends on the patient’s anatomy, according to Shubin Stein. She said the most common reason for a patellar dislocation lies in the shape of the patient’s trochlea.

“When [the trochlear] groove or track is not shaped correctly, it can be shallow or it can even be flat, then that person is more likely to sustain a patellar dislocation because the groove is not shaped well,” Shubin Stein, an Orthopedics Today Editorial Board Member, said.

In addition, Shubin Stein said patients with ligamentous laxity, an abnormally high patella or patella alta, or a significantly elevated tibial tubercle-trochlear groove distance can also be at risk for patellar dislocation.

Robert F. LaPrade, MD, PhD, of Twin Cities Orthopedics, said patellar dislocation is more common among teenaged girls compared with boys, which may be due to the types of sports female athletes play.

“A lot of the teenaged girls who do have patellar dislocations do not necessarily have the best overall strength, which puts them at a higher risk to having an ipsilateral patellar dislocation,” LaPrade said.

Despite being a common injury, Vicente Sanchis-Alfonso, MD, PhD, of the department of orthopedic surgery at Hospital Arnau de Vilanova in Valencia, Spain, said there is currently no consensus statement on the treatment of first-time patellar dislocations.

“There are several predictive models that can help us to predict which patients are most likely to redislocate after primary patellar dislocation is treated conservatively,” Sanchis-Alfonso told Healio/Orthopedics Today. “This approach helps us with our decision-making for the optimum treatment of these patients. Moreover, these models can be useful when we want to inform patients and their families about the prognosis after primary patellar dislocation.”

To help determine whether a patient with a primary patellofemoral dislocation should undergo early surgical or nonsurgical treatment, Seth L. Sherman, MD, associate professor of orthopedic surgery at Stanford University, said physicians should perform a focused history and physical examination and obtain weight-bearing X-ray series and an MRI, when possible.

“What we are primarily looking for are osteochondral fractures or loose bodies,” Sherman said. “These would classically require surgery in a first-time dislocator. This is not the area of controversy or debate.”

Patients who have a large bone avulsion fracture of the medial aspect of the patella, an irreducible dislocation or a disruption of the medial patellar stabilizers would also benefit from surgical treatment, according to Sanchis-Alfonso.

In addition to the degree of injury, John P. Fulkerson, MD, professor of orthopedic surgery at Yale University School of Medicine and director of the Yale Patellofemoral Instability Program, said physicians should also look at other factors that may predispose a patient to recurrent dislocation, such as the shape and curvature of the trochlea, extensor mechanism alignment problems, patient age, level of activity, ligamentous laxity, type of sport and patient expectations. When surgery is indicated, a medial quadriceps tendon-femoral ligament or medial patellofemoral ligament reconstruction with use of a tendon graft to stabilize the patella have been found to have a high success rate compared with medial repair, Fulkerson said.

While there may be a role for primary MPFL repair in patellofemoral surgery, Sherman said its use is limited.

“The meat of the matter is that you need to know before you go,” Sherman told Healio/Orthopedics Today. “If you have a patient who has no significant risk factors — so the groove is normal, the height is normal, the vectors are normal, they have a contact injury with a big bone and cartilage piece — you fix that piece and then while you are in there it is possible, if the tissue quality is good, you can do a MPFL primary repair in that patient and they might do well.”

But, he said, patients with common risk factors associated with recurrent dislocation may experience high forces on the MPFL repair, which can lead to stretching over time.

“There is a 20% to 30% stretch and failure rate [with repair]. That rate is obliterated in our data when we are talking about MPFL reconstruction and it is fairly straightforward with low morbidity these days,” Sherman said. “So, we have a low threshold just to do reconstructions and not to take the chance on repair in most patients and, particularly, in all patients with underlying bony risk factors.”

When a patient presents with a primary patellofemoral dislocation with no loose cartilage or bony damage, sources who spoke with Healio/Orthopedics Today noted nonoperative treatment is the standard of care.

“The rate of recurrent instability is 10% or less in people who do not have anatomy issues,” LaPrade told Healio/Orthopedics Today. “Even if they do have anatomy issues, there is still a good chance, better than 50%, that they will not dislocate again with rehabilitation.”

Sherman said when performing nonoperative treatment, physicians should reduce the dislocation by gently bringing the limb into extension. This can be followed by use of a brace for a short time and crutches until the patient is no longer limping.

“If you cannot reduce [the dislocation], you have to go to the OR. However, most of the time it is reduced spontaneously before they get to the emergency room and you need a high index of suspicion,” Sherman said. “It is rare they come in with a bent knee and a fixed dislocation, but it happens.”

Regarding the rehabilitation protocol, LaPrade said the focus of treatment is on range of motion and restoring quadriceps strength.

“Because the kneecap sits in the middle of the quad tendon, it is controlled by the quad strength. It is an important thing to address,” he said. “So, making sure they have appropriate quadriceps strength so they do not go back and have a redislocation is essential to optimize their outcomes with nonoperative treatment.”

Early rehabilitation should also focus on passive stretching, terminal knee extension and quadriceps activation, Sherman said.

“Similar prehabilitation principles that we apply to our ACLs can be used in these patients. You can transition from a big brace to a sleeve or a small patellar stabilization brace over time with quad control,” Sherman said. “Then, basically, it goes from that initial management to our standard functional criteria. So, it is phased rehabilitation from low impact to linear to lateral to sport specific and then testing rigorously in our [physical therapy] gym before returning to sport.”

Fulkerson also said athletes should receive counseling on return to sport.

“Cutting sports put a person at greater risk [of redislocation],” Fulkerson said. “If the person does not require going back to playing vigorous sports involving quick turning and cutting, they are going to have a lower risk of redislocating after nonoperative treatment.”

One of the biggest advantages of surgical treatment of primary patellofemoral dislocations is the reduction in the rate of recurrent dislocation, according to Shubin Stein. She said the rate of recurrent dislocation ranges from 65% to 70% in patients younger than 25 years of age with trochlear dysplasia.

“If we fix them, they have about a 95% chance of not having another dislocation if their growth plates are closed,” Shubin Stein said. “If their growth plates are open, they have about an 85% chance of never having another dislocation.”

However, Fulkerson said that does not mean that a patient cannot still experience recurrent dislocation after surgical treatment.

“These days, the likelihood of [surgical treatment] working is better than it used to be,” Fulkerson told Healio/Orthopedics Today. “In skeletally immature patients, however, the tibial tubercle is usually not moved in order to avoid growth plate injury and this limits options for full correction of a tracking abnormality in such young patients which, in turn, increases risk of redislocation.”

Surgical treatment can also lead to complications, such as patella fracture, stiffness, infection and pain, according to Shubin Stein.

Sherman said return to play timeframes are longer if surgical treatment is selected.

“Obviously, there are other surgical risks that are low, including risk of blood clots, but I think the trade-off here is that you are trying to reduce that relative risk that the kneecap pops out again and I think we can do a nice job of stabilizing the joints with well-done MPFL surgery,” Sherman said.

Another advantage of surgical treatment among patients who have dislodged bone and cartilage in addition to a primary patellofemoral dislocation is it can minimize a patient’s risk of developing arthritis later in life, according to LaPrade.

“The kneecap joint has the most stress in the body so if you have an area of arthritis, it can be difficult for your future occupation, future sports and even with activities of daily living, like squatting or lunging, because you load it so much,” LaPrade said. “So, when [patients] have an arthritis area, addressing it, giving them the best chance to get it to heal, is important. Because of that, most of us would do some type of reconstruction of their medial patellofemoral ligament to minimize the risk of having it dislocate again.”

Shubin Stein said published results have also shown that surgical treatment can lead to better outcomes compared with nonoperative treatment.

“[Patient] outcome measures of how they feel and their ability to return to sport and their quality of life, those all seem to be improved in patients who have surgery rather than patients who do not,” Shubin Stein said. “That is not for everybody, but it is in the studies that are out there right now. The trend is toward better outcome measures.”

Where treatment and outcomes are not as clear is in patients with a primary patellofemoral dislocation who are at high risk for recurrent dislocation, but who do not have loose cartilage or bony damage, according to sources who spoke with Healio/Orthopedics Today. Although the standard of care would dictate that nonoperative treatment would be used in these patients, Sherman said some physicians are advocating for early surgical stabilization in patients with no loose cartilage or bony damage but who have a risk of redislocation greater than 60% or 70%.

“Many of us, more recently, start off with risk stratification. If their other side was treated nonoperatively and did poorly, had a recurrence and needed surgery and they have a first timer on the new knee, they may not want to go through that again and I think the evidence says we can reduce their risk with well-done soft tissue surgery, MPFL reconstruction, in the majority of patients,” Sherman said.

To identify whether these patients should be treated surgically, Shubin Stein and her colleagues are performing the Pediatric and Adolescent Patellar Instability study in which patients with primary patellofemoral dislocations but no loose cartilage or bony damage who are at high-risk for redislocation are randomly assigned to receive surgical or non-surgical treatment.

“This type of study takes a while because it is hard to randomize young patients to surgery or no surgery,” Shubin Stein said. “But there is a push in the community because of the literature that we have to potentially treat these patients with early surgery to reduce their risk of another injury.”

Once patients who need surgery are identified, Sherman said the next step would be to identify whether they need more than an MPFL reconstruction.

“We know this à la carte approach is reasonable in the recurrent instability population, but we do not know that for sure in the first-timers,” Sherman said. “If there are extremes of valgus in a young patient, we will be quick to add guided growth surgery while we do the MPFL, but I think our thresholds are higher to offer things like tibial tubercle or rotational osteotomies or trochleoplasty in the first-timer.”

Fulkerson said 3D prints and analyses can also be used to help better understand the characteristics of the patellofemoral joint. He said 3D prints can help identify whether the structural factors of the knee of a patient with a primary patellofemoral dislocation warrant surgical intervention and, if so, the prints can be used to design and plan a surgery that would lead to optimal results.

“I would say 3D printing gives a huge step forward in understanding patella instability patients, in general, and I think will play an increasingly important role in primary dislocations to the point that we will be able to predict who is likely to dislocate again and who is not as likely to dislocate again,” Fulkerson said.

Although more studies and better consensus are still needed on treatment of primary patellofemoral dislocations, Shubin Stein said physicians will have a clearer answer in the coming years. She and her co-principal investigator Shital N. Parikh, MD, FACS, of Cincinnati Children’s Hospital Medical Center and an Orthopedics Today Editorial Board Member, are running the first multicenter patellar instability study — Justifying Patellar Instability Treatment by Early Results or JUPITER trial — and hope to have data that help answer these and other questions related to patellar instability.

“Unfortunately, we do not have an exact answer is what I usually have to tell my patients,” Shubin Stein said. “But there is a lot of good information that we do have, and I think in the next 5 years or so we will answer this question and others more definitively.”

Sherman said, in the meantime, physicians who treat patients with a primary patellofemoral dislocation should be rigid with imaging and obtain weight-bearing X-rays and MRIs to not only rule out osteochondral fractures and loose bodies, but to be able to risk stratify patients to either surgical or non-surgical treatment.

Fulkerson said patients with a primary patellar dislocation who present with several risk factors for recurrent dislocation should have their patella stabilized with a graft and any specific deficits addressed. However, Sanchis-Alfonso said injury treatment should be personalized to the patient and also be conservative.

“Unfortunately, too many non-surgical treatments are done. I considered that the first episode of lateral patella dislocation should be operated on more frequently. I prefer to speak of non-surgical treatment rather than conservative treatment, because any treatment performed on the patellofemoral joint — surgical or non-surgical — should be as conservative as possible,” Sanchis-Alfonso said. “We should not correct all the anatomic abnormalities that predispose to recurrent dislocation. We should only correct the most significant anatomical risk factors. Treatment for the patellofemoral joint should include whatever is necessary for appropriate treatment — no more, no less.”

Overall, physicians should have an honest discussion with the patient and their family about the patient’s injury and the risks of redislocation and possible cartilage injury, Shubin Stein said.

“It may be that not every patient who is under 25 who has a high risk of dislocation should have surgery,” she said. “If that patient is somebody who likes to play the violin and bike ride, that patient may not need to have surgery and might want to wait and see if they have another dislocation. But somebody who is a high-intensity cutting and pivoting athlete who plays three sports a year, they may need to have surgery because their risk may be different.”

Click here to read the Point/Counter to this Cover Story.

Get the latest news and education delivered to your inbox

© 2022 Healio All Rights Reserved.

Get the latest news and education delivered to your inbox

© 2022 Healio All Rights Reserved.