Matthew Ellington, MD; Albert Pendelton, MD 2018-2019 Pediatric Patellar Instability 1. Epidemiology Matthew Ellington, MD; Albert Pendelton, MD 2018-2019

Epidemiology: Adult vs Pediatric Overall incidence is 6-77 cases per 100,000 persons (1,2,3) Fithian et. al. AJSM 2004

Adult vs Pediatric Peak incidence occurs during adolescence with a rate as high as 31 per 100,000 (4) Median age is 19 with an inter quartile range from 15 to 31 (5) Same study found 0 in patients less than 5, 6 in patients less than 9, and 10 in patients over 10 out of 4,736,759 ER visits (5) Lowest incidence is in patients 30-59 years of age with an average annual risk of 1.5 to 2 per 100,000 (4)

Adult vs Pediatric 56-85% of patients with acute patellar dislocations are less than 20 years of age (4,6,7,8,9) Locked primary dislocations are more common in patients with closed tibial tubercle apophyses (10)

Adult vs Pediatric Active populations have higher risk 69 per 100,000 person-years at risk in active US military personnel (11) Service members < 20 years old were 84% more likely than those at or above the age of 40 to have patellar dislocations (11)

ACL vs Patellar Instability ACL tears occur at a rate of 92-151 per 100,00 person-years in patients from 6-18 (12) This was an annual increase of 2.3% over 20 years Peak incidence occurs in females at age 16 and males at age 17 with rates of 392 and 422 per 100,000 person years respectively (12)

ACL vs Patellar Instability MRI cohort study of 1145 patients (ages 10-64) with traumatic knee hemarthrosis performed in Sweden (13) 52% had ACL tears 41% had meniscal tears 17% had lateral patellar dislocations

Traumatic Hemarthrosis (TH) Olsson et al. reported a 17% rate of lateral patella dislocation (LPD) in a cohort of 1145 patients who underwent MRI with TH in all age groups (ACL tear in 52%) (13) However, in patients less than 16yo, 39% of boys and 43% of girls with TH had LPD, and had an annual incidence of 88/100,000. (13) Wessel et al. reported 8/51 (15%) with LPD in patients less than age 14 with TH (14) Metelic et al. reported 14/21 (67%) pediatric patients with TH had osteochondral fracture of the medial facet of the patella or lateral femoral condyle (16)

Risk Factors: Age and Gender Sex: No difference in the incidence rate between males in female (2.47 (M) vs 2.10 (F) per 100,000 person years. (15) Fithian reported that in patients with a second dislocation, 70% were female (1) and slightly increased incidence in females for first time dislocation (1) Median age of 16-17 years (1,13) Peak incidence between 15-19 years. Over 50% occurring between 10-19 years. (15) Waterman et al. J Knee Surg 2012

Risk Factors: Mechanism of Injury and Race Over half of all patellar dislocations occurred during athletic activity (51%).(15) Basketball: 18% Football: 6.3% Soccer: 6.9% 24% occurred during activities of daily living (15) 37% occurred at a place of recreation and 35% occurred at home, 19% at school. (15) 72% of first time dislocators reported Tegner score greater than 5. (1) No difference between White and African American, but 4 fold increase when compared to Latino and Asian population (1)

Mechanism of Injury Most common mechanism is non-contact valgus-flexion-external rotation mechanism on a plated foot during cutting or pivoting movements. (4,10) Direct blow in 7% (4)

References 1. Fithian DC, Paxton EW, Stone ML, et al. Epidemiology and natural history of acute patellar dislocation. Am J Sports Med 2004; 32:1114–1121 2. Sillanpää P, Mattila VM, Iivonen T, Visuri T, Pihlajamäki H. Incidence and risk factors of acute traumatic primary patellar dislocation. Med Sci Sports Exerc 2008; 40:606–611 3. Nietosvaara Y, Aalto K, Kallio PE: Acute patellar dislocation in children: Incidence and associated osteochondral fractures. J Pediatr Orthop 1994;14(4):513-515. 4. Atkins DM, et al. Characteristics of patient with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med. 2000;28(4):472-479. 5. Porter PS, Salo D. The epidemiology of patellar disloations. Annals of Emergency Medicine. 2008;52(4):S124. 6. Cofield RH, Bryan RS: Acute dislocation of the patella: Results of conservative treatment. J Trauma 17: 526–531, 1977 7. Larsen E, Lauridsen F: Conservative treatment of patellar dislocations: Influence of evident factors on the tendency to redislocation and the therapeutic result. Clin Orthop 171: 131–136, 1982 8. Cash JD, Hughston JC: Treatment of acute patellar dislocation. Am J Sports Med 16: 244–249, 1988 9. Henry JH, Crosland JW: Conservative treatment of patellofemoral subluxation. Am J Sports Med 7: 12–14, 1979 10. Nikku R, et. al. The mechanism of primary patellar dislocation: Trauma history of 126 patients. Acta Orthopaedica 2009;80(4):432-434. 11. Hsiao M, Owens BD, Burks R, Sturdivant RX, Cameron KL. Incidence of acute traumatic patellar dislocation among active-duty United States military service members. Am J Sports Med. 2010;38:1997-2004. 12. Beck NA, Lawrence JTR, Nordin JD, et al. ACL tears in school-aged children and adolescents over 20 years. Pediatrics 2017. 139(3):e20161877. 13. Olsson O, Isacsson A, Englund M, Frobell RB. Epidemiology of intra- and per-articular structural injuries in traumatic knee joint hemarthrosis – data from 1145 consecutive knees with subacute MRI. Osteoarthritis and Cartilage 2016 (24):1890-1897. 14.Wessel LM, Scholz S, Rusch M, Kopke J, Loff S, Duchene W, Waag KL. Hemarthrosis after trauma to the pediatric knee joint: what is the value of magnetic resonance imaging in the diagnostic algorithm? J Pediatr Orthop 2001;21(3):338-42 15. Waterman BR, Belmont PJ, Owens BD. Patellar Dislocation in the United States: Role of Sex, Age, Race, and Athletic Participation J Knee Surg 2012;25:5158 16. Metelic TM, Aronsson DD, Boyd DW jr, LaMont. Acute hemarthrosis of the knee in children. Am J Sports Med. 1995; 23(6):668-71