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Transient Patella Dislocation
Kirkland W. Davis, MD, FACR; Andrew Sonin, MD, FACR; Donna G. Blankenbaker, MD, FACR
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KEY FACTS

  • Terminology

    • Imaging

      • Top Differential Diagnoses

        • Pathology

          • Clinical Issues

            • Diagnostic Checklist

              TERMINOLOGY

              • Abbreviations

                • Transient patella dislocation (TPD), lateral femoral condyle (LFC), medial femoral condyle (MFC), vastus medialis obliquus (VMO)
              • Synonyms

                • Transient patellar dislocation, patella dislocation, patella subluxation, transient dislocation of patella
              • Definitions

                • Lateral dislocation of patella out of femoral trochlear groove due to twisting/pivoting injury of knee
                • Usually transient: spontaneous relocation typical
                • Pertinent anatomy: medial patellofemoral ligament (MPFL) = sheet of collagen attaching to superior 1/2 of patella, MFC just above origin of medial collateral ligament
                  • Primary soft tissue restraint against lateral patella dislocation
                  • Medial retinaculum attaches to lower 1/2 of patella
                • Trochlear sulcus angle: angle between medial and lateral facets, measured at deepest point ~ 2 cm above joint
                • Trochlear dysplasia = abnormally flat sulcus angle, > 145°
                  • Usually easy to "eyeball" measurement as normal or abnormal

              IMAGING

              • General Features

                • Radiographic Findings

                  • CT Findings

                    • MR Findings

                      • Ultrasonographic Findings

                        • Imaging Recommendations

                          DIFFERENTIAL DIAGNOSIS

                            PATHOLOGY

                            • General Features

                              • Staging, Grading, & Classification

                                CLINICAL ISSUES

                                • Presentation

                                  • Demographics

                                    • Natural History & Prognosis

                                      • Treatment

                                        DIAGNOSTIC CHECKLIST

                                        • Consider

                                          • Image Interpretation Pearls

                                            • Reporting Tips

                                              Selected References

                                              1. Aicale R et al: Combined medial patellofemoral and medial patellotibial reconstruction for patellar instability: a PRISMA systematic review. J Orthop Surg Res. 15(1):529, 2020
                                              2. Grimm NL et al: Traumatic patellar dislocations in childhood and adolescents. Orthop Clin North Am. 51(4):481-91, 2020
                                              3. Jiang B et al: Evaluation of risk correlation between recurrence of patellar dislocation and damage to the medial patellofemoral ligament in different sites caused by primary patellar dislocation by MRI: a meta-analysis. J Orthop Surg Res. 15(1):461, 2020
                                              4. McMahon CJ et al: The extensor mechanism: imaging and intervention. Semin Musculoskelet Radiol. 21(2):89-101, 2017
                                              5. de Oliveira V et al: Medial patellofemoral ligament anatomy: is it a predisposing factor for lateral patellar dislocation? Int Orthop. 38(8):1633-9, 2014
                                              6. Reagan J et al: MPFL reconstruction: technique and results. Clin Sports Med. 33(3):501-16, 2014
                                              7. Sillanpää PJ et al: Medial patellofemoral ligament avulsion injury at the patella: classification and clinical outcome. Knee Surg Sports Traumatol Arthrosc. 22(10):2414-8, 2014
                                              8. Torabi M et al: MRI evaluation and complications of medial patellofemoral ligament reconstruction. Clin Imaging. 39(1):116-27, 2014
                                              9. Zhang GY et al: Evaluation of medial patellofemoral ligament tears after acute lateral patellar dislocation: comparison of high-frequency ultrasound and MR. Eur Radiol. 25(1):274-81, 2014
                                              10. Earhart C et al: Transient lateral patellar dislocation: review of imaging findings, patellofemoral anatomy, and treatment options. Emerg Radiol. 20(1):11-23, 2013
                                              11. Camanho GL et al: Conservative versus surgical treatment for repair of the medial patellofemoral ligament in acute dislocations of the patella. Arthroscopy. 25(6):620-5, 2009
                                              12. Kapur S et al: Acute knee dislocation: review of an elusive entity. Curr Probl Diagn Radiol. 38(6):237-50, 2009
                                              13. Kitamura K et al: Avulsion-tear type medial patellofemoral ligament injury with a small bony fragment in lateral patellar dislocation. J Trauma. 66(1):271-3, 2009
                                              14. Le Corroller T et al: Transient medial patellar dislocation: injury patterns at US and MR imaging. Skeletal Radiol. 38(5):519-23, 2009
                                              15. Nietosvaara Y et al: Acute patellar dislocation in children and adolescents. Surgical technique. J Bone Joint Surg Am. 91 Suppl 2 Pt 1:139-45, 2009
                                              16. Andrish J: The management of recurrent patellar dislocation. Orthop Clin North Am. 39(3):313-27, vi, 2008
                                              17. Christiansen SE et al: Isolated repair of the medial patellofemoral ligament in primary dislocation of the patella: a prospective randomized study. Arthroscopy. 24(8):881-7, 2008
                                              18. Colvin AC et al: Patellar instability. J Bone Joint Surg Am. 90(12):2751-62, 2008
                                              19. Panagopoulos A et al: MPFL reconstruction for recurrent patella dislocation: a new surgical technique and review of the literature. Int J Sports Med. 29(5):359-65, 2008
                                              20. Robinson RJ et al: Wii knee. Emerg Radiol. 15(4):255-7, 2008
                                              21. Feibel RJ et al: Irreducible lateral patellar dislocation: the importance of impaction fracture recognition. J Emerg Med. 33(1):11-5, 2007
                                              22. Sanders TG et al: MRI of osteochondral defects of the lateral femoral condyle: incidence and pattern of injury after transient lateral dislocation of the patella. AJR Am J Roentgenol. 187(5):1332-7, 2006
                                              23. Elias DA et al: Imaging of patellofemoral disorders. Clin Radiol. 59(7):543-57, 2004
                                              24. O'Reilly MA et al: Sonographic appearances of medial retinacular complex injury in transient patellar dislocation. Clin Radiol. 58(8):636-41, 2003
                                              25. Sanders TG et al: Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr. 25(6):957-62, 2001
                                              26. Sonin AH et al: MR imaging appearance of the extensor mechanism of the knee: functional anatomy and injury patterns. Radiographics. 15(2):367-82, 1995
                                              27. Kirsch MD et al: Transient lateral patellar dislocation: diagnosis with MR imaging. AJR Am J Roentgenol. 161(1):109-13, 1993
                                              Related Anatomy
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                                              Related Differential Diagnoses
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                                              References
                                              Tables

                                              Tables

                                              KEY FACTS

                                              • Terminology

                                                • Imaging

                                                  • Top Differential Diagnoses

                                                    • Pathology

                                                      • Clinical Issues

                                                        • Diagnostic Checklist

                                                          TERMINOLOGY

                                                          • Abbreviations

                                                            • Transient patella dislocation (TPD), lateral femoral condyle (LFC), medial femoral condyle (MFC), vastus medialis obliquus (VMO)
                                                          • Synonyms

                                                            • Transient patellar dislocation, patella dislocation, patella subluxation, transient dislocation of patella
                                                          • Definitions

                                                            • Lateral dislocation of patella out of femoral trochlear groove due to twisting/pivoting injury of knee
                                                            • Usually transient: spontaneous relocation typical
                                                            • Pertinent anatomy: medial patellofemoral ligament (MPFL) = sheet of collagen attaching to superior 1/2 of patella, MFC just above origin of medial collateral ligament
                                                              • Primary soft tissue restraint against lateral patella dislocation
                                                              • Medial retinaculum attaches to lower 1/2 of patella
                                                            • Trochlear sulcus angle: angle between medial and lateral facets, measured at deepest point ~ 2 cm above joint
                                                            • Trochlear dysplasia = abnormally flat sulcus angle, > 145°
                                                              • Usually easy to "eyeball" measurement as normal or abnormal

                                                          IMAGING

                                                          • General Features

                                                            • Radiographic Findings

                                                              • CT Findings

                                                                • MR Findings

                                                                  • Ultrasonographic Findings

                                                                    • Imaging Recommendations

                                                                      DIFFERENTIAL DIAGNOSIS

                                                                        PATHOLOGY

                                                                        • General Features

                                                                          • Staging, Grading, & Classification

                                                                            CLINICAL ISSUES

                                                                            • Presentation

                                                                              • Demographics

                                                                                • Natural History & Prognosis

                                                                                  • Treatment

                                                                                    DIAGNOSTIC CHECKLIST

                                                                                    • Consider

                                                                                      • Image Interpretation Pearls

                                                                                        • Reporting Tips

                                                                                          Selected References

                                                                                          1. Aicale R et al: Combined medial patellofemoral and medial patellotibial reconstruction for patellar instability: a PRISMA systematic review. J Orthop Surg Res. 15(1):529, 2020
                                                                                          2. Grimm NL et al: Traumatic patellar dislocations in childhood and adolescents. Orthop Clin North Am. 51(4):481-91, 2020
                                                                                          3. Jiang B et al: Evaluation of risk correlation between recurrence of patellar dislocation and damage to the medial patellofemoral ligament in different sites caused by primary patellar dislocation by MRI: a meta-analysis. J Orthop Surg Res. 15(1):461, 2020
                                                                                          4. McMahon CJ et al: The extensor mechanism: imaging and intervention. Semin Musculoskelet Radiol. 21(2):89-101, 2017
                                                                                          5. de Oliveira V et al: Medial patellofemoral ligament anatomy: is it a predisposing factor for lateral patellar dislocation? Int Orthop. 38(8):1633-9, 2014
                                                                                          6. Reagan J et al: MPFL reconstruction: technique and results. Clin Sports Med. 33(3):501-16, 2014
                                                                                          7. Sillanpää PJ et al: Medial patellofemoral ligament avulsion injury at the patella: classification and clinical outcome. Knee Surg Sports Traumatol Arthrosc. 22(10):2414-8, 2014
                                                                                          8. Torabi M et al: MRI evaluation and complications of medial patellofemoral ligament reconstruction. Clin Imaging. 39(1):116-27, 2014
                                                                                          9. Zhang GY et al: Evaluation of medial patellofemoral ligament tears after acute lateral patellar dislocation: comparison of high-frequency ultrasound and MR. Eur Radiol. 25(1):274-81, 2014
                                                                                          10. Earhart C et al: Transient lateral patellar dislocation: review of imaging findings, patellofemoral anatomy, and treatment options. Emerg Radiol. 20(1):11-23, 2013
                                                                                          11. Camanho GL et al: Conservative versus surgical treatment for repair of the medial patellofemoral ligament in acute dislocations of the patella. Arthroscopy. 25(6):620-5, 2009
                                                                                          12. Kapur S et al: Acute knee dislocation: review of an elusive entity. Curr Probl Diagn Radiol. 38(6):237-50, 2009
                                                                                          13. Kitamura K et al: Avulsion-tear type medial patellofemoral ligament injury with a small bony fragment in lateral patellar dislocation. J Trauma. 66(1):271-3, 2009
                                                                                          14. Le Corroller T et al: Transient medial patellar dislocation: injury patterns at US and MR imaging. Skeletal Radiol. 38(5):519-23, 2009
                                                                                          15. Nietosvaara Y et al: Acute patellar dislocation in children and adolescents. Surgical technique. J Bone Joint Surg Am. 91 Suppl 2 Pt 1:139-45, 2009
                                                                                          16. Andrish J: The management of recurrent patellar dislocation. Orthop Clin North Am. 39(3):313-27, vi, 2008
                                                                                          17. Christiansen SE et al: Isolated repair of the medial patellofemoral ligament in primary dislocation of the patella: a prospective randomized study. Arthroscopy. 24(8):881-7, 2008
                                                                                          18. Colvin AC et al: Patellar instability. J Bone Joint Surg Am. 90(12):2751-62, 2008
                                                                                          19. Panagopoulos A et al: MPFL reconstruction for recurrent patella dislocation: a new surgical technique and review of the literature. Int J Sports Med. 29(5):359-65, 2008
                                                                                          20. Robinson RJ et al: Wii knee. Emerg Radiol. 15(4):255-7, 2008
                                                                                          21. Feibel RJ et al: Irreducible lateral patellar dislocation: the importance of impaction fracture recognition. J Emerg Med. 33(1):11-5, 2007
                                                                                          22. Sanders TG et al: MRI of osteochondral defects of the lateral femoral condyle: incidence and pattern of injury after transient lateral dislocation of the patella. AJR Am J Roentgenol. 187(5):1332-7, 2006
                                                                                          23. Elias DA et al: Imaging of patellofemoral disorders. Clin Radiol. 59(7):543-57, 2004
                                                                                          24. O'Reilly MA et al: Sonographic appearances of medial retinacular complex injury in transient patellar dislocation. Clin Radiol. 58(8):636-41, 2003
                                                                                          25. Sanders TG et al: Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr. 25(6):957-62, 2001
                                                                                          26. Sonin AH et al: MR imaging appearance of the extensor mechanism of the knee: functional anatomy and injury patterns. Radiographics. 15(2):367-82, 1995
                                                                                          27. Kirsch MD et al: Transient lateral patellar dislocation: diagnosis with MR imaging. AJR Am J Roentgenol. 161(1):109-13, 1993