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Patellar Dislocation
Arthur B. Meyers, MD
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KEY FACTS

  • Terminology

    • Imaging

      • Pathology

        • Clinical Issues

          • Diagnostic Checklist

            TERMINOLOGY

            • Abbreviations

              • Transient patellar dislocation (TPD)
            • Definitions

              • Lateral dislocation of patella from direct/indirect injury
              • Dislocation/relocation → shearing, tensile, & compressive forces → injuries of medial patella, lateral femur, & soft tissues
                • Shearing & tensile forces during dislocation → patellar & ligamentous injury
                • Compressive & shearing forces during relocation → femoral & patellar injury
            • Associated Syndromes

              • Syndromes with ligamentous laxity (e.g., Ehlers-Danlos or Marfan syndrome) are predisposed to TPD

            IMAGING

            • General Features

              • Radiographic Findings

                • CT Findings

                  • MR Findings

                    DIFFERENTIAL DIAGNOSIS

                      PATHOLOGY

                      • Staging, Grading, & Classification

                        • Gross Pathologic & Surgical Features

                          CLINICAL ISSUES

                          • Presentation

                            • Demographics

                              • Natural History & Prognosis

                                • Treatment

                                  Selected References

                                  1. Meyers AB et al: Imaging assessment of patellar instability and its treatment in children and adolescents. Pediatr Radiol. 46(5):618-36, 2016
                                  2. Torabi M et al: MRI evaluation and complications of medial patellofemoral ligament reconstruction. Clin Imaging. 39(1):116-7, 2015
                                  3. Ho CP et al: Systematic technique-dependent differences in CT versus MRI measurement of the tibial tubercle-trochlear groove distance. Am J Sports Med. 43(3):675-82, 2015
                                  4. Dickens AJ et al: Tibial tubercle-trochlear groove distance: defining normal in a pediatric population. J Bone Joint Surg Am. 96(4):318-24, 2014
                                  5. Nelitz M et al: Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: surgical technique and clinical outcome. Am J Sports Med. 41(1):58-63, 2013
                                  6. Seeley M et al: Magnetic resonance imaging of acute patellar dislocation in children: patterns of injury and risk factors for recurrence. J Pediatr Orthop. 32(2):145-55, 2012
                                  7. Diederichs G et al: MR imaging of patellar instability: injury patterns and assessment of risk factors. Radiographics. 2010 Jul-Aug;30(4):961-81. Erratum in: Radiographics. 31(2):624, 2011
                                  8. Sillanpää PJ et al: Femoral avulsion of the medial patellofemoral ligament after primary traumatic patellar dislocation predicts subsequent instability in men: a mean 7-year nonoperative follow-up study. Am J Sports Med. 37(8):1513-21, 2009
                                  9. Dirim B et al: Medial patellofemoral ligament: cadaveric investigation of anatomy with MRI, MR arthrography, and histologic correlation. AJR Am J Roentgenol. 191(2):490-8, 2008
                                  10. Morrison W: Imaging of the Knee: In Problem Solving in Musculoskeletal Radiology. Philadelphia: Mosby. 587-633, 2008
                                  11. Amis AA et al: Anatomy and biomechanics of the medial patellofemoral ligament. Knee. 2003 Sep;10(3):215-20. Review. Erratum in: Knee. 11(1):73, 2004
                                  12. Shabshin N et al: MRI criteria for patella alta and baja. Skeletal Radiol. 33(8):445-50, 2004
                                  13. Elias DA et al: Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology. 225(3):736-43, 2002
                                  14. Pfirrmann CW et al: Femoral trochlear dysplasia: MR findings. Radiology. 216(3):858-64, 2000
                                  15. Sanders TG et al: Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury. Radiographics. 20 Spec No:S135-51, 2000
                                  Related Anatomy
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                                  Related Differential Diagnoses
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                                  References
                                  Tables

                                  Tables

                                  KEY FACTS

                                  • Terminology

                                    • Imaging

                                      • Pathology

                                        • Clinical Issues

                                          • Diagnostic Checklist

                                            TERMINOLOGY

                                            • Abbreviations

                                              • Transient patellar dislocation (TPD)
                                            • Definitions

                                              • Lateral dislocation of patella from direct/indirect injury
                                              • Dislocation/relocation → shearing, tensile, & compressive forces → injuries of medial patella, lateral femur, & soft tissues
                                                • Shearing & tensile forces during dislocation → patellar & ligamentous injury
                                                • Compressive & shearing forces during relocation → femoral & patellar injury
                                            • Associated Syndromes

                                              • Syndromes with ligamentous laxity (e.g., Ehlers-Danlos or Marfan syndrome) are predisposed to TPD

                                            IMAGING

                                            • General Features

                                              • Radiographic Findings

                                                • CT Findings

                                                  • MR Findings

                                                    DIFFERENTIAL DIAGNOSIS

                                                      PATHOLOGY

                                                      • Staging, Grading, & Classification

                                                        • Gross Pathologic & Surgical Features

                                                          CLINICAL ISSUES

                                                          • Presentation

                                                            • Demographics

                                                              • Natural History & Prognosis

                                                                • Treatment

                                                                  Selected References

                                                                  1. Meyers AB et al: Imaging assessment of patellar instability and its treatment in children and adolescents. Pediatr Radiol. 46(5):618-36, 2016
                                                                  2. Torabi M et al: MRI evaluation and complications of medial patellofemoral ligament reconstruction. Clin Imaging. 39(1):116-7, 2015
                                                                  3. Ho CP et al: Systematic technique-dependent differences in CT versus MRI measurement of the tibial tubercle-trochlear groove distance. Am J Sports Med. 43(3):675-82, 2015
                                                                  4. Dickens AJ et al: Tibial tubercle-trochlear groove distance: defining normal in a pediatric population. J Bone Joint Surg Am. 96(4):318-24, 2014
                                                                  5. Nelitz M et al: Anatomic reconstruction of the medial patellofemoral ligament in children and adolescents with open growth plates: surgical technique and clinical outcome. Am J Sports Med. 41(1):58-63, 2013
                                                                  6. Seeley M et al: Magnetic resonance imaging of acute patellar dislocation in children: patterns of injury and risk factors for recurrence. J Pediatr Orthop. 32(2):145-55, 2012
                                                                  7. Diederichs G et al: MR imaging of patellar instability: injury patterns and assessment of risk factors. Radiographics. 2010 Jul-Aug;30(4):961-81. Erratum in: Radiographics. 31(2):624, 2011
                                                                  8. Sillanpää PJ et al: Femoral avulsion of the medial patellofemoral ligament after primary traumatic patellar dislocation predicts subsequent instability in men: a mean 7-year nonoperative follow-up study. Am J Sports Med. 37(8):1513-21, 2009
                                                                  9. Dirim B et al: Medial patellofemoral ligament: cadaveric investigation of anatomy with MRI, MR arthrography, and histologic correlation. AJR Am J Roentgenol. 191(2):490-8, 2008
                                                                  10. Morrison W: Imaging of the Knee: In Problem Solving in Musculoskeletal Radiology. Philadelphia: Mosby. 587-633, 2008
                                                                  11. Amis AA et al: Anatomy and biomechanics of the medial patellofemoral ligament. Knee. 2003 Sep;10(3):215-20. Review. Erratum in: Knee. 11(1):73, 2004
                                                                  12. Shabshin N et al: MRI criteria for patella alta and baja. Skeletal Radiol. 33(8):445-50, 2004
                                                                  13. Elias DA et al: Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology. 225(3):736-43, 2002
                                                                  14. Pfirrmann CW et al: Femoral trochlear dysplasia: MR findings. Radiology. 216(3):858-64, 2000
                                                                  15. Sanders TG et al: Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury. Radiographics. 20 Spec No:S135-51, 2000