Nonoperative treatment after first-time patellar dislocation has been considered as the standard of care in patellar instability management. However, recurrent instability following first-time patellar dislocation has been reported in 15% to 44% of patients. Among patients who do not have re-dislocation, some may continue to have functional limitations including persistent pain, partial giving-way episodes (subluxation) or inability to return to sports.
In the absence of appropriate treatment, patients with continued recurrent instability may develop progressive chondral damage affecting the patellofemoral joint, leading to worse long-term outcomes. Recent studies have attempted to identify risk factors to predict failure of nonoperative treatment. Patients with these risk factors may benefit from surgical stabilization after first-time patellar dislocation to prevent long-term morbidity.
Shital N. Parikh
In principle, this concept is similar to a Bankart repair after first-time shoulder dislocation in the adolescent age-group (age-based stratification) to prevent subsequent dislocations and bone attrition, or ACL reconstruction in skeletally immature patients to prevent recurrent instability and the progression of chondral and meniscal injuries. In a randomized controlled study that compared nonoperative treatment to medial patellofemoral ligament (MPFL) reconstruction after first-time patellar dislocation in 41 knees, Bitar and colleagues found MFPL reconstruction was more effective (average Kujala score 88.9 and no re-dislocation) than nonoperative treatment (average Kujala score 70.8 and a 35% re-dislocation rate).
The etiology of patellar instability is multifactorial and therefore, identification of high-risk patients who are more prone to recurrent instability is complex. In a landmark study, H. Dejour and colleagues identified four risk factors that contribute to patellar instability including trochlear dysplasia (present in 85% of patients with patellar instability), increased patellar tilt (83%), patella alta (24%) and increased tibial tubercle–trochlear groove (TT- TG) distance greater than 20 mm (56%) as compared to presence of these factors in control knees of only 3% to 6.5%. Other risk factors that have been shown to contribute to patellar instability include hyperlaxity, coronal plane malalignment (genu valgum) and rotational lower-limb malalignment (femoral anteversion, external tibial torsion). The pattern of MFPL tear can also predict recurrence. Based on a 7-year nonoperative follow-up study, Sillanpaa and colleagues identified 15 of 35 patients with femoral-sided MPFL avulsion on MRI had recurrent instability compared to two of 18 patients with medial-sided tears in other location. In another study, Lewallen and colleagues reported a 69% recurrence rate in skeletally immature patients with trochlear dysplasia (33 out of 48 patients) compared with a 38.4% recurrence rate in the entire cohort (76 out of 198 patients).
Recently, a prediction model has been proposed to help estimate the risk of recurrent dislocation after nonoperative treatment of first-time patellar dislocation. Based on multivariate analysis of 222 knees with first-time patellar dislocation, Jaquith and Parikh identified four risk factors (skeletal immaturity, history of contralateral patellar dislocation, trochlear dysplasia and patella alta with a Caton Deschamps Index of greater than 1.45). These risk factors were based on patients’ history and lateral knee radiograph, so as to simplify its application during the initial patient encounter. As per the prediction model, presence of all four risk factors had an average risk of recurrence of 88%; presence of three risk factors had an average risk of recurrence of 75%; presence of two risk factors had an average risk of recurrence of 54%; presence of a single risk factor had an average risk of recurrence of 30%; and absence of all risk factors had a risk of recurrence of about 14%.
Due to the retrospective nature of the study, several other risk factors (like hyperlaxity, lower limb malalignment and MRI-based factors) were not included in the development of the prediction model. In the future, inclusion of these risk factors and prospective validation of the model would help to strengthen the level of evidence to better predict the risk of recurrence after first-time patellar dislocation. Such a prediction model would help to counsel patients and facilitate the decision-making processes related to optimal treatment choices following first-time patellar dislocation.
Shital N. Parikh, MD, is an associate professor in the Department of Orthopaedic Surgery at Cincinnati Children’s Hospital and University of Cincinnati. He is a board-certified pediatric orthopedic surgeon specializing in pediatric sports medicine and patellofemoral disorders. He can be reached at email@example.com.
Disclosure: Parikh reports no relevant financial disclosures.