CLASSIFICATION OF LATERAL PATELLAR INSTABILITY IN CHILDREN AND ADOLESCENTS Shital N Parikh, MD, FACS,1 Marios Lykissas, MD, PhD2 1 Division of Pediatric Orthopaedics, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229, USA 2Department of Orthopaedic Surgery, University of Ioannina School of Medicine, Ioannina 45110, Greece OBJECTIVES Instability of the patellofemoral joint is a common, often challenging, problem that affects between 7 and 49 people per 100,000. Approximately 2-3% of all knee injuries are due to acute patellar dislocation which occur during sports in 61% of the cases. The highest risk is noted for young individuals in the second decade of life with a prevalence of first-time patellar dislocation of 31 per 100,000. Following non-operative management for first-time dislocation, up to 44% of patients may experience recurrent dislocation and another half may have pain. Previous history of patellar instability, family history of patellar subluxation or dislocation, and female gender have been associated with increased risk of re-dislocation. With the increasing popularity of Medial Patellofemoral Ligament (MPFL) reconstruction as the surgical treatment of choice to address patellar instablity, it is important to differentiate patients that would benefit from MPFL reconstruction from those who would not. This report discusses a classification based treatment algorithm that could be applied to pediatric and adult lateral patellar instability patterns. DISCUSSION METHODS There is significant heterogeneity in the literature related to patellar instability, its causes The proposed classification system was developed based on review of literature and more and its treatment, leading to several different recommendations to manage it. To address than 300 cases of patellar instability treated at Cincinnati Children’s Hospital Medical such a complex issue, the first task is to classify and define each instability pattern (Tables). Center from 2008 to 2015. Once a classification system is agreed upon, then comparative studies can differentiate the pros and cons of different treatment recommendation for each instability pattern. RESULTS Isolated MPFL reconstruction has been increasingly used to stabilize most patterns of Type I (first-time patellar dislocation) and type II (recurrent patellar instability) represent patellar instabilty. Though isolated MPFL reconstruction may suffice to address Type I, II the most common patterns of patellar instability seen in adolescent and young adult and IIIA, many physicians have reported the importance of analysis and surgical correction patients. If surgery is performed for first-time patellar dislocation due to the presence of of contributing factors. For eg: Tibial tuberlce medialization for increased tibial tubercle- osteochondral or chondral fragment (type IA), then simultaneous or staged patellar trochlear groove distance, Tibial tubercle distalization for patellar alta or Trocheloplasty for stabilization procedure should be considered. Medial patellofemoral ligament (MFPL) trochelar dysplasia. Further studies would clarify the need for such ‘a la carte’ procedures. reconstruction may suffice for most type II patellar instability patients, although all factors contributing to patellar instability should be analyzed. Type IIIB and Type IV instability patterns include congenital and developmental patellar Type III (dislocatable) and type IV (dislocated) instability patterns are typically seen in dislocation. These patterns are typically seen in children in the first decade. An extensor children, although if ignored or in asymptomatic patients, presentation maybe delayed. mechanism realignment or quadricepsplasty is frequently required for surgical correction for MPFL reconstruction may suffice as an adequate treatment option for type IIIA but would these patterns. Isolated MPFL reconstruction would fail in such circumstances. most likely not provide adequate stability for type IIIB and type IV instability patterns. In such cases, Quadricepsplasty, osteotomy and / or alignment procedures may be frequently required to stabilize the patella. Voluntary patellar instability could be managed nonoperatively, similar to the management of voluntary posterior shoulder dislocation. Syndromic patellar instability may present as any type, should be recognized, and appropriate referrals should be made, to formulate a multidisciplinary approach for their management..