Patellar dislocation

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Definition/Description[edit | edit source]

A patellar dislocation occurs by a lateral shift of the patella, leaving the trochlea groove of the femoral condyle. This mostly occurs as a disruption of the medial patellofemoral ligament.[1]

patella dislocation

Clinically Relevant Anatomy[edit | edit source]

The patellofemoral joint makes part of the knee joint. The articular surfaces consist of the patella and the trochlear surface of the femoral condyles. The articular cartilage on the medial facet is thicker than on the lateral facet, with the lateral facet bigger than the medial.[2] It has an anterior projection on the lateral femoral condyle, lateral to the patellar groove. This prevents lateral dislocation of the patella. [2][3] The patellofemoral articulation depends on the function of the quadriceps as it increases the angle of pull of the patellar tendon, improving the mechanical advantage of the quadriceps in knee extension.[4]


The suspension and movement of the patella is provided by passive and active stabilizers:[4]

  • Passive stabilizers: Tensor fascia lata, patellar ligament, knee capsule, patellofemoral ligament (medial and lateral), menisco patellar ligament (medial and lateral)
  • Active: Quadriceps, patellar ligament, retinaculum

The medial patellofemoral ligament is the primary stabiliser (53-67%) against lateral displacement/dislocation of the patella. It is situated deep to the vastus lateralis muscle, ranging from the posterior aspect of the medial femoral condyle to the superomedial part of the patella, vastus medialis and quadriceps tendon.[1]

Epidemiology/Etiology[edit | edit source]

Epidemiology[edit | edit source]

The incidence of acute primary patellar dislocations are 2-3%.[5][6] Patellar dislocations are often associated with athletes[7][8], and is most common in females in the second decade of life.[9] Redislocation rates after conservative management are estimated between 15 and 44%.[1]

Aetiology[edit | edit source]

Primary patellar dislocation is defined as traumatic disruption of the previously uninjured medial peripatellar structures.[5][6] It often results from a non-contact injury to the knee.

Predisposing factors include both morphological and functional patellofemoral disorders:[9][10][11]

  • Ligament laxity (can lead to atraumatic dislocations)[1]
  • Reduced osseous constraint form the lateral femoral condyle
  • Imbalance between stronger lateral tissues (e.g. lateral retinaculum and vastus lateralis), which are able to overcome weaker medial structures, especially the medial patellofemoral ligament and the distal vastus medialis
  • Biomechanical issues such as femoral and tibial rotation, and pes planus
  • Patella alta
  • Genu recurvatum
  • Increased Q Angle
  • Patellar hypermobility

Mechanism of Injury[edit | edit source]

  • Non-contract: Twisting of the leg, with internal rotation of the femur on a fixed foot and tibia
    • Often associated with valgus stress (strong lateral force then dislocates the patella)[8]
  • Traumatic: A direct blow to the knee (lateral or medial)[10]

Clinical Presentation[edit | edit source]

One of the common findings related to acute, primary, traumatic patellar dislocations is hemarthrosis of the knee, caused by rupture of the medial restraints of the patella.[12] Medial swelling will also be prominent.[9] Patellar dislocations often reduce spontaneously when the knee is extended.[1]

Main complaints from the patient will include:[9]

  • Pain
  • Instability of the knee
  • Locking of the knee after the trauma

Differential Diagnosis[edit | edit source]

[9][11]

Diagnostic Procedures[edit | edit source]

  • X-rays; To exclude associated fractures (osteochondral, avulsion); subluxation will be seen on a lateral view
  • CT: To measure tuberosity tibia-trochlea groove distance
  • MRI: To differentiate degree of tear; to rule out osteochondral fractures
    • Indicated in young patients with primary dislocations[1]

[13]

Outcome Measures[edit | edit source]

[14]

Physical Examination[edit | edit source]

  • History:[1]
    • Instability (giving way) of the knee after jumping/twisting with severe onset of pain
    • Feeling of moving/popping out
    • Immediate swelling
  • Observation:
  • Measure Q Angle
  • Special tests:[9][11]
    • Patella apprehension test
    • Patella tracking assessment
    • Patellar hypermobility

Medical Management[edit | edit source]

Conservative Management[edit | edit source]

Indication:

In cases where the patella was not relocated spontaneously, it can be done under regional anaesthesia.[1] Conservative management after reduction include:

  • Immobilization for 6 weeks (cylinder cast/back slab/knee range of motion brace)[18]
  • Medication:
    • Supplements like glucosamine and
    • NSAID’s

Conservative treatment is the most common treatment after primary patellar dislocation.[13]

Surgical Management[edit | edit source]

Surgical management is done arthroscopically, with or without surgical repair of the torn retinaculum or immediate patellar realignment [10][19]

Indications:[20][21][22]

  • Recurrent/chronic dislocation[23]
  • Patellofemoral symptoms
  • Associated osteochondral fracture or major chondral injury
  • Substantial disruption of the medial patellofemoral ligament)- vastus medialis obliquus-adductor mechanism
  • Laterally subluxated patella on the plain Mercer-Merchant view with normal alignment on the contralateral knee
  • Failed conservative management

Surgical stabilization significantly reduces the redislocation rate of primary traumatic patellar dislocation in the young adult population[24], but is associated with a higher risk of patellofemoral joint osteoarthritis.[25] Initial post-operative management consists of pain management, physiotherapy and cryotherapy .

Types of Surgery[edit | edit source]

  • Lateral release: Release of tight lateral retinaculum to allow more medial tracking of the patella.
    • Indication: Mild patellar instability
  • Medial patellofemoral ligament reconstruction / proximal realignment
    • Balance the patellar tracking to more natural (medial) alignment
    • Often done with a lateral release
    • Indication: Severe patellar instability
  • Distal realignment / anteromedialisation
    • Transferring of the tibial tubercle (where the patellar tendon attaches to the tibia). The bony attachment of the tendon is moved more medially to allow the patella to track normally
    • Used in conjunction with the lateral release and/or the medial patellofemoral ligament reconstruction.
    • Indication: Severe patellar instability

Physiotherapy Management[edit | edit source]

Goals:

  • Improve function
  • Prevent further dislocation:
    • Taping: Lateral reinforcement will reduce the movement of the patella (to prevent dislocation)[9]

Physiotherapy modalities include:[9][10][26]

  • Prevention of re-dislocation:
    • Taping: Lateral reinforcement will reduce the movement of the patella (to prevent dislocation)[9]
    • Bracing
    • Reassurance and behavioural modification[27]
  • Improve range of motion:

Resources[edit | edit source]

Clinical Bottom Line[edit | edit source]

Primary acute patellofemoral dislocations should be managed conservatively with immobilization and rehabilitation, as the majority of these patients will do well without surgery. A MRI is necessary to assess for osteochondral lesions, as they are associated with a poor prognosis if not addressed. Surgical management would be considered in cases with recurrent dislocations, or when it is associated with patellofemoral symptoms.

References[edit | edit source]

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Frobell R, Cooper R, Morris H, Arendt, H. Acute knee injuries. In: Brukner P, Bahr R, Blair S, Cook J, Crossley K, McConnell J, McCrory P, Noakes T, Khan K. Clinical Sports Medicine: 4th edition. Sydney: McGraw-Hill. p.626-683.
  2. ↑ 2.0 2.1 Matthijs O, Van Paridon-Edauw D, Winkel D. Hoofdstuk 2 knie. Manuele therapie van de perifere gewrichten. 1e uitgave. Houten. Bohn Stafleu Van Loghum bv. 2004. pp.220–235.
  3. ↑ Bijl GVD (Jr), De Graaf CG, De Ridder PA. In: Actief en passief bewegen in de gewrichten der extremiteiten. De tijdsstroom, 1975. p.126.
  4. ↑ 4.0 4.1 Egmond DL, Schuitemaker R. De knieregio. In: Mink AJF, Rer Veer HJ, Vorselaars JACTh. Extremiteiten manuele therapie in enge en ruime zin. 1e uitgave. Houten. Bohn Stafleu Van Loghum bv, 2006. p.559–628.
  5. ↑ 5.0 5.1 Atkin DM, Fithian DC, Marangi KS, Stone ML, Dobson BE, Mendelsohn C. Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med 2000;28:472–479.
  6. ↑ 6.0 6.1 Kirsch MD, Fitzgerald SW, Friedman H, Rogers LF. Transient lateral patellar dislocation: diagnosis with MR imaging. AJR Am J Roentgenol 1993;161:109–113.
  7. ↑ Ficat RP, Hungerford DS. Disorders of the patello-femoral joint. Williams & Wilkins, 1977.
  8. ↑ 8.0 8.1 Hughston JC, Walsh WM, Puddu G. Patellar subluxation and dislocation. WB Saunders Company, 1984.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 Meeusen R. Praktijkgids knieletsels. Cursus. Vrije Universiteit Brussel, 2011.
  10. ↑ 10.0 10.1 10.2 10.3 Skinner HB, Barrack RL, Bedmar MS, Clarson GD. Sports medicine. In: Reinhardt S, Nogueira I, Boyle PJ. Current diagnosis en treatment in orthopedics. 2nd edition. McGraw-Hill: United States of America, 2000. p.125–175.
  11. ↑ 11.0 11.1 11.2 Beeton KS. The knee. Manual therapy masterclass: the peripheral joints. Churchill Livingstone. Elsevier, 2003. p.54–55.
  12. ↑ Tsai CH, Hsu CJ, Hung CH, Hsu HC. Primary traumatic patellar dislocation. Journal of orthopaedic surgery and research 2012;7(1):21.
  13. ↑ 13.0 13.1 Hohlweck J, Quack V, Arbab D, Spreckelsen C, Tingart M, Lüring C, Rath B. Diagnostic and therapeutic management of primary and recurrent patellar dislocations-analysis of a nationwide survey and the current literature. Zeitschrift für Orthopädie und Unfallchirurgie 201;151(4):380-8.
  14. ↑ Paxton EW, Fithian DC, Lou Stone M, Silva P. The reliability and validity of knee-specific and general health instruments in assessing acute patellar dislocation outcomes. The American journal of sports medicine 2003;31(4):487-92.
  15. ↑ Nikku R, Nietosvaara Y, Aalto K, Kallio PE. Operative treatment of primary patellar dislocation does not improve medium-term outcome: a 7-year follow-up report and risk analysis of 127 randomized patients. Acta orthopaedica 2005;76(5):699-704.
  16. ↑ Arendt EA, Fithian DC, Cohen E. Current concepts of lateral patella dislocation. Clinics in sports medicine 2002;21(3):499-519.
  17. ↑ Buchner M, Baudendistel B, Sabo D, Schmitt H. Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clinical Journal of Sport Medicine 2005;15(2):62-6.
  18. ↑ Van Gemert JP, de Vree LM, Hessels RA, Gaakeer MI. Patellar dislocation: cylinder cast, splint or brace? An evidence-based review of the literature. International journal of emergency medicine 2012;5(1):45.
  19. ↑ Castelyn P. Acute knee injuries, diagnostic and treatment managment proposals. Vub University press, 2001. p.42-43.
  20. ↑ Fithian DC, Paxton EW, Cohen AB. Indications in the treatment of patellar instability. The journal of knee surgery 2004;17(01):47-56.
  21. ↑ Koskinen SK, Rantanen JP, Nelimarkka OI, Kujala UM. Effect of Elmslie-Trillat and Roux-Goldthwait procedures on patellofemoral relationships and symptoms in patients with patellar dislocations. The American journal of knee surgery 1998;11(3):167-73.
  22. ↑ Stefancin JJ, Parker RD. First-time traumatic patellar dislocation: a systematic review. Clinical Orthopaedics and Related Research 2007;455:93-101.
  23. ↑ Weber AE, Nathani A, Dines JS, Allen AA, Shubin-Stein BE, Arendt EA, Bedi A. An algorithmic approach to the management of recurrent lateral patellar dislocation. JBJS 2016;98(5):417-27.
  24. ↑ Sillanpää PJ, Mattila VM, Mäenpää H, Kiuru M, Visuri T, Pihlajamäki H. Treatment with and without initial stabilizing surgery for primary traumatic patellar dislocation: a prospective randomized study. JBJS 2009;91(2):263-73.
  25. ↑ Smith TO, Song F, Donell ST, Hing CB. Operative versus non-operative management of patellar dislocation. A meta-analysis. Knee Surgery, Sports Traumatology, Arthroscopy 2011;19(6):988-98.
  26. ↑ Smith TO, Davies ., Chester R, Clark A, Donell ST. Clinical outcomes of rehabilitation for patients following lateral patellar dislocation: a systematic review. Physiotherapy, 2010;96(4):269-81.
  27. ↑ Smith TO, Chester R, Clark A, Donell ST, Stephenson R. A national survey of the physiotherapy management of patients following first-time patellar dislocation. Physiotherapy, 2011;97(4):327-38.
  28. ↑ Smith TO, Chester R, Cross J, Hunt N, Clark A, Donell ST. Rehabilitation following first-time patellar dislocation: a randomised controlled trial of purported vastus medialis obliquus muscle versus general quadriceps strengthening exercises. The Knee,2015;22(4):313-20.
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