Should primary patellofemoral dislocations be treated surgically?
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Increasing interest in surgical treatment
This is a timely question.
Traditionally, primary patellofemoral dislocations (first-time patellar dislocations) have been treated conservatively. It is still considered the standard of care. This practice has been based on multiple, well-performed, randomized control studies that have shown no significant advantage of surgical treatment when compared with conservative treatment, with the primary outcome being redislocation. However, the surgical treatments used in these studies were focused on medial-sided repairs or imbrication with or without lateral retinacular release or tibial tubercle osteotomy (also known as proximal-distal realignment). With improvement in surgical techniques and clinical success of medial patellofemoral ligament reconstruction, all previous studies have been called into question. Two recent randomized controlled studies comparing MPFL reconstruction and conservative treatment reported significantly lower redislocation rates and better patient-reported outcomes in favor of surgical treatment for primary dislocations.
The results of natural history studies following primary dislocations can be broadly divided in three categories: one-third patients do well and return to preinjury level of function, one-third patients have redislocation and undergo surgical stabilization and one-third patients do not redislocate but continue to have symptoms, including subluxation episodes, anxiety/fear, pain, swelling and functional deficits. Thus, if redislocation is the outcome of interest, two-thirds of patients would do well without surgery. But if functional outcomes are considered, the failure rate of conservative treatment may be higher. The other concern with conservative treatment and continued instability is development or progression of arthritis, though long-term studies have not been able to conclude if patellofemoral arthritis is related to type of treatment.
Since some patients do well with conservative treatment and some don’t, the question then is: which patients with primary dislocation would benefit from surgical treatment? The answer to this question is evolving as risk prediction models have been developed to identify patients who are high risk for failure of conservative treatment. In one study, the presence of four risk factors (skeletal immaturity, contralateral dislocation, trochlear dysplasia and patella alta) conferred a risk of redislocation and failure of conservative treatment of greater than 80%. In this case, surgical treatment could be considered as initial treatment. Other studies identified young age, contralateral dislocation and presence of anatomic risk factors as predictors of failure of conservative treatment. Another scenario when surgical treatment following primary dislocation would be appropriate would be in the presence of an intra-articular osteochondral or chondral fracture. If surgery is required to address the fracture fragment, then concomitant surgical stabilization should be strongly considered.
To summarize, conservative treatment continues to be the standard of care for primary patellofemoral dislocations. However, there is increasing interest and evidence to suggest the beneficial role of surgical treatment in certain subsets of patients. The ongoing prospective cohort study on patellar instability (JUPITER) with more than 2,000 knees enrolled should help better identify these subsets of patients.
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Shital N. Parikh, MD, is a professor of orthopedic surgery at Cincinnati Children’s Hospital Medical Center in Cincinnati and an Orthopedics Today Editorial Board Member.
Not the answer for everyone
As with anything in orthopedics, and really in medicine, there is never a single best answer. The answer to the question of whether primary patellofemoral dislocations should be treated surgically is, it depends. Patellar instability, similar to shoulder instability, occurs via both traumatic and atraumatic mechanisms. For example, a patella dislocation can be the result of a single-time sport-related injury and can also occur just with activities of daily living in the setting of recurrent instability. Many patients have innate risk factors that cannot be modified, leading them to recurrent instability after a single traumatic event. However, others will experience a single-time injury and never experience another subluxation or dislocation. My single absolute indication for surgery after a first-time dislocation includes the presence of an intra-articular loose body. In those patients, surgery involves arthroscopy with loose body removal, and consideration of MPFL reconstruction. That said, not every patient who undergoes arthroscopy for loose body removal undergoes concomitant MPFL reconstruction. This depends on patient-specific factors, including where they are in their athletic season, risk factors for future instability events, and need for concomitant procedures, such as cartilage repair/restoration and/or realignment osteotomy (or trochleoplasty). Some literature can guide us in this regard, but at the end of the day, each patient must be evaluated on an individual basis, as no two patients are quite the same.
Mario Hevesi, MD, and colleagues performed a variety of studies to discuss this issue. One in particular has become helpful in this regard in which the authors present the recurrent instability of the patella (RIP) score. The RIP Score is a point-based system that assigns different point values to patient-specific demographic and radiographic data points, including age younger than 25 years (2 points), skeletal immaturity (1 point), Dejour grade A through D for trochlear dysplasia (1 point) and tibial tubercle-trochlear groove/patellar length of 0.5 mm or greater (1 point). Patients with scores between 4 to 5 points were deemed to be high-risk for recurrent patellar instability. Using the RIP Score, as well as the understanding that chondral lesions can get worse over time in this patient population, I have become more inclined over the years to recommend MPFL reconstruction surgery in higher-risk patients after a single-instability event. While surgery is not the right answer for everyone after a single patellar dislocation event, it certainly is the right answer for some.
Rachel M. Frank, MD, is an associate professor in the department of orthopedic surgery and director of the Joint Preservation Program at the University of Colorado School of Medicine in Denver and an Orthopedics Today Editorial Board Member.
MPFL reconstruction may hold promise
Until recently, surgical treatment of patellar dislocations has been reserved primarily for cases of recurrent dislocation, unless associated with a displaced osteochondral fracture or loose body. The overall rate of recurrent dislocation after a first-time patellar dislocation event has been reported to be 30% to 40%; however, more recent studies have introduced the concept of risk stratification to better assess the patient’s specific risk of sustaining subsequent instability events.
While several clinical prediction models have been described, they share many of the same features, with skeletal immaturity, bilateral symptoms, trochlear dysplasia, patella alta and increased tibial tubercle to trochlear groove (TT-TG) distance comprising risk factors for recurrent instability. With these scoring systems, a high-risk patient could be found to have a greater than 75% probability of redislocating after a first-time event.
Recurrent dislocations can lead to chondral injury and increased risk of osteoarthritis in the patellofemoral joint. Thomas L. Sanders, MD, and colleagues compared patients with first-time patellar dislocations vs. those without and reported that the incidence of patellofemoral arthritis was 14.8% at 20 years vs. 2.9% in the control group, with a hazard ratio of 7.8 in the dislocation group. Jeanna M. Franzone, MD, and colleagues demonstrated that chronicity of patellar instability is associated with an increased likelihood and severity of patellofemoral chondral injuries, highlighting the importance of minimizing the number of dislocations.
While prior studies have questioned the efficacy of surgical outcomes when comparing MPFL repair and conservative management in the setting of first-time patellar dislocations, there is emerging evidence that supports this approach with newer techniques utilizing MPFL reconstruction. In a study of first-time patellar dislocators, Alexandre Carneiro Bitar, MSc, and colleagues compared nonoperative vs. operative treatment with MPFL reconstruction and found the nonoperative group had lower Kujala scores and a greater number of recurrences and subluxations (35%) compared with the surgical group (0%) at 2-year follow-up.
MPFL reconstruction is not without risks, however, with reported complications including stiffness, pain and even patella fracture, yet the long-term consequences of waiting for a subsequent dislocation might not outweigh these risks in patients who have high probability of recurrence. Future studies refining our ability to accurately predict redislocation risk, as well as improving our understanding of clinical outcomes in the surgical management of first-time patellar dislocations, will allow us to appropriately identify and treat first-time dislocators who are at high risk for subsequent reinjury to optimize the long-term function of their knees.
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Miho J. Tanaka, MD, is the director of the Women’s Sports Medicine Program at Massachusetts General Hospital and associate professor of orthopedic surgery at Harvard Medical School in Boston.