Skip to content

Member Log In

Traumatic Patellar Dislocation

Traumatic patellar dislocation
Objectives
  1. Describe mechanism of injury of patellar dislocation
  2. Discuss the role of anatomic variations in the patellofemoral joint to vulnerability to acute patellar dislocation
  3. Discuss factors predisposing to recurrent dislocation following an initial acute dislocation
  4. Describe the incidence of osteochondral fracture accompanying acute patellar dislocation
  5. Describe preferred treatment for acute patellofemoral dislocations
  6. Describe treatment for recurrent patellofemoral dislocation

Discussion point
  1. How can one find such disparity in results of operative and nonoperative treatment?

Discussion
Acute patellar dislocations are relatively common in children. There is reasonable agreement that there are predisposing anatomic features rendering some children more vulnerable. Ultrasonographic analysis of the trochlea has revealed that the actual cartilaginous trochlea is more shallow in children sustaining dislocation than normal, and more shallow than the plain radiograph might indicate. There is also increased awareness over the past two decades of the importance of the medial patellofemoral ligament, extending from the medial femoral epicondyle to the superomedial patella. This ligament lies deep to the vastus medialis muscle. MR imaging can reveal a tear of this ligament. Surgical treatment of acute patellar dislocation which does not address this component of the pathology may have a higher failure rate. Traumatic dislocation of the patella is almost always lateral, following an indirect mechanism of injury. The knee is flexed, with the tibia externally rotated, and the quadriceps forces in this position are concentrated over the lateral femoral condyle. Osteochondral fractures of the patella, which may be avulsion fractures medially or shear fractures laterally, and/ or of the lateral femoral condyle occur in about 40 % in children. Conservative management, consisting of immobilization of the knee for comfort, followed by quadriceps strengthening, carries a failure rate of 25-50%. A family history of patellar dislocation implies a worse prognosis. An increasing emphasis is placed on early operative management, which would include not only an arthroscopic assessment of chondral integrity, but an open repair of the medial patellofemoral ligament, which is arthroscopically inaccessible. Results of this approach are still preliminary.

References
  1. Ahmad CS, Shubin Stein BE, Matuz D, Henry JH. Immediate surgical repair of the medial patellar stabilizers for acute patellar dislocation. Am J Sports Med 2000; 28: 804-08.
  2. Boden BP, Pearsall AW, Garrett WE, Jr., Feagin JA, Jr. Patellofemoral instability: Evaluation and treatment. J Am Acad Ortho Surg 1997; 5: 47-57.
  3. Garth WP, Jr., Pomphrey M, Jr., Merrill K. Functional treatment of patellar dislocation in an athletic population. American Journal of Sports Medicine 1996; 24( 6): 785-91.
  4. Irwin LR, Bagga TK. Quadriceps pull test: an outcome predictor for lateral retinacular release in recurrent patellar dislocation. Journal of the Royal College of Surgeons of Edinburgh 1998; 43( 1): 40-2.
  5. Maenpaa H, Lehto MU. Surgery in acute patellar dislocation--evaluation of the effect of injury mechanism and family occurrence on the outcome of treatment. British Journal of Sports Medicine 1995; 29( 4): 239-41.
  6. Maenpaa H, Lehto MU. Patellar dislocation. The long-term results of nonoperative management in 100 patients. American Journal of Sports Medicine 1997; 25( 2): 213-7.
  7. Maenpaa H, Huhtala H, Lehto MU. Recurrence after patellar dislocation. Redislocation in 37/ 75 patients followed for 6-24 years. Acta Orthopaedica Scandinavica 1997; 68( 5): 424-6.
  8. McManus F, Rang M, Heslin DJ. Acute dislocation of the patella in children. A natural history. Clin Orthop 1979; 139: 88-91.
  9. Muhle C, Brinkmann G, Skaf A, Heller M, Resnick D. Effect of a patellar realignment brace on patients with patellar subluxation and dislocation. Evaluation with kinematic magnetic resonance imaging [see comments]. American Journal of Sports Medicine 1999; 27( 3): 350-3.
  10. Nietosvaara Y, Aalto K, Kallio PE. Acute patellar dislocation in children: incidence and associated osteochondral fractures. Journal of Pediatric Orthopedics 1994; 14( 4): 513-5.
  11. Nietosvaara Y, Aalto K. The cartilaginous femoral sulcus in children with patellar dislocation: an ultrasonographic study. Journal of Pediatric Orthopedics 1997; 17( 1): 50-3.
  12. Nikku R, Nietosvaara Y, Kallio PE, Aalto K, Michelsson JE. Operative versus closed treatment of primary dislocation of the patella. Similar 2-year results in 125 randomized patients. Acta Orthopaedica Scandinavica 1997; 68( 5): 419-23.
  13. Sallay PI, Poggi J, Speer KP, Garrett WE. Acute dislocation of the patella. A correlative pathoanatomic study. American Journal of Sports Medicine 1996; 24( 1): 52-60.
  14. Vainionpaa S, Laasonen E, Silvenoinen T, al. e. Acute dislocation of the patella: A prospective review of operative treatment. J Bone Joint Surg (Br) 1990; 72: 366-69.
  15. Warren LF, Marshall JL. The supporting structures and layers on the medial side of the knee. An anatomic analysis. J Bone Joint Surg (Am) 1979; 61: 58-62.

See Also

Physician Education

Annual Meeting

Annual Meeting Location May 16-19, 2012 in Denver, CO

Meeting Archives

Past Annual Meeting Location

Parents & Patients

Patient photos

Find a doctor