Marie Askenberger1,2, Per-Mats Janarv1,3, Throstur Finnbogason1,4, Elizabeth A Arendt5. 1. Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden. 2. Section of Pediatric Orthopaedic Surgery, Karolinska University Hospital Solna, Stockholm, Sweden. 3. Capio Artro Clinic, Stockholm, Sweden. 4. Section of Pediatric Radiology, Karolinska University Hospital Solna, Stockholm, Sweden. 5. Department of Orthopaedic Surgery, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA.
Abstract
BACKGROUND: The incidence of primary lateral patellar dislocation (LPD) in children aged 9 to 14 years is 0.6 to 1.2 per 1000. Causation is assumed to be multifactorial, including anatomic variants of the patellofemoral (PF) joint that result in a higher risk of LPD. No publication has compared the morphology of the PF joint and anatomic patellar instability risk factors (APIFs) in a primary LPD population versus controls, defining children by skeletal maturity. PURPOSE: To characterize the PF morphology and APIFs (trochlear dysplasia, abnormal lateral patellar tilt, elevated tibial tubercle-trochlear groove [TT-TG] distance, patella alta) through magnetic resonance imaging (MRI) measurements in skeletally immature children with and without a primary LPD and to identify (potential) distinctive differences between these 2 groups. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A prospective series of 103 skeletally immature children aged 9 to 14 years with an MRI-confirmed primary LPD were matched with a control group of 69 children. The PF morphology and APIFs were assessed during a 2.5-year period with standardized MRI using sagittal and axial views. RESULTS: In the LPD group, 79% had 2 to 4 APIFs compared with 7% in the control group. All major measurements of trochlear dysplasia were significantly different between the 2 groups. The mean central condylar height was significantly higher in the LPD group compared with the control group, resulting in a lower trochlear depth (2.3 vs 4.5 mm, respectively) and higher sulcus angle (156.7° vs 141.1°, respectively). The LPD group had significantly higher values of patellar height, Caton-Deschamps index (1.33 vs 1.15, respectively), lateral patellar tilt (21.1° vs 8.5°, respectively), and TT-TG distance (13.9 vs 9.8 mm, respectively) compared with the control group. The main divergent APIF was trochlear dysplasia (defined as trochlear depth <3 mm), seen in 74% of the LPD group compared with 4% of the control group. Elevated TT-TG distance as a single APIF was never present in the LPD group; patellar tilt was only seen in the LPD group. The most common APIF in the control group was patella alta (36%). CONCLUSION: There was a significant difference in mean values of all established APIFs between the children with a first-time LPD and the controls. Trochlear dysplasia was the main APIF, and together with lateral patellar tilt (≥20°), they had the strongest association with LPD.
BACKGROUND: The incidence of primary lateral patellar dislocation (LPD) in children aged 9 to 14 years is 0.6 to 1.2 per 1000. Causation is assumed to be multifactorial, including anatomic variants of the patellofemoral (PF) joint that result in a higher risk of LPD. No publication has compared the morphology of the PF joint and anatomic patellar instability risk factors (APIFs) in a primary LPD population versus controls, defining children by skeletal maturity. PURPOSE: To characterize the PF morphology and APIFs (trochlear dysplasia, abnormal lateral patellar tilt, elevated tibial tubercle-trochlear groove [TT-TG] distance, patella alta) through magnetic resonance imaging (MRI) measurements in skeletally immature children with and without a primary LPD and to identify (potential) distinctive differences between these 2 groups. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A prospective series of 103 skeletally immature children aged 9 to 14 years with an MRI-confirmed primary LPD were matched with a control group of 69 children. The PF morphology and APIFs were assessed during a 2.5-year period with standardized MRI using sagittal and axial views. RESULTS: In the LPD group, 79% had 2 to 4 APIFs compared with 7% in the control group. All major measurements of trochlear dysplasia were significantly different between the 2 groups. The mean central condylar height was significantly higher in the LPD group compared with the control group, resulting in a lower trochlear depth (2.3 vs 4.5 mm, respectively) and higher sulcus angle (156.7° vs 141.1°, respectively). The LPD group had significantly higher values of patellar height, Caton-Deschamps index (1.33 vs 1.15, respectively), lateral patellar tilt (21.1° vs 8.5°, respectively), and TT-TG distance (13.9 vs 9.8 mm, respectively) compared with the control group. The main divergent APIF was trochlear dysplasia (defined as trochlear depth <3 mm), seen in 74% of the LPD group compared with 4% of the control group. Elevated TT-TG distance as a single APIF was never present in the LPD group; patellar tilt was only seen in the LPD group. The most common APIF in the control group was patella alta (36%). CONCLUSION: There was a significant difference in mean values of all established APIFs between the children with a first-time LPD and the controls. Trochlear dysplasia was the main APIF, and together with lateral patellar tilt (≥20°), they had the strongest association with LPD.
Entities:
Keywords:
children; knee; patellar dislocation; patellofemoral anatomy; pediatric sports medicine
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