First Time Patella Dislocation

Acute patella dislocations form a 2-3% of acute knee injuries. The patient gives history of a fixed foot twisting injury and giving way with the patella lying over the lateral side. Sometimes as the patient extends the knee the patella relocates spontaneously. More often there is history of relocation by a physiotherapist or Paramedic. Occasionally the pivoting episode during ACL injury may be mistaken as patella dislocation. Haemarthrosis is extremely common in both Patella dislocations and ACL injury.


Most of the literature is retrospective. In such studies diagnosing the first episode can be non-specific as most patients don’t present to A&E with a dislocated patella The natural history after patellar dislocation including recurrence dislocation rate is not clear Hence there is confusion about who would benefit from surgery The incidence of osteochondral injuries is as high as 71% and only 1/3rd are picked up on radiographs. There is no clear indication as to which group of patients would benefit from surgery

Applied Anatomy

There are two restraints to lateral patellar dislocation

  • bony constraint due to patella-trochlear congruity
  • soft tissue restraint.

Three layered arrangement of medial retinaculum described by Warren and Marshall Layer 1- superficial medial retinaculum and Medial Patellotibial ligament Layer 2- Medial patellofemoral ligament (MPFL) and Superficial MCL Layer 3- Medial patellomeniscal ligament

In full extension the soft tissue restraints are the only stabilisers and there is no constraint offered by the trochlea. The guiding role of the femoral groove prevailed over soft-tissue action through most of the range of motion (Heegaard, CORR 1994)

The MPFL courses from supero-posterior to the medial femoral epicondyle to the super medial two thirds of the patella. Its fibres fuse with the under surface of the Vastus Medialis tendon. The MPFL is variable in cadaveric specimens. Total length and width of the MPFL was 58.8 +/- 4.7 mm and 12.0 +/- 3.1 mm (Nomura) The MPFL contributes 41-80% of the restraining force to lateral patellar dislocation.

The influence of Vastus Medialis Obliquus on lateral patellar dislocation is less clearly understood. VMO does offer passive restraint but varies in angle of insertion. Contraction of VMO can increase joint reaction force but it is questionable if it can counter the deficiency of passive restraints.


The risk is highest amongst females 10-17 years of age. A lot of patients have a prior history of instability. The cause of dislocation is usually multifactorial. The recurrent dislocation rate varies from 15% (Macnab), Fithian 17%, Buchner 26% to Cofield 50%. Fithian showed that in patients with previous instability symptoms, the risk of recurrent dislocation is 49%. Patients with hyperlaxity, dysplasia of trochlea and altered patella height are at high risk of dislocations.


History is important, as most patellae have been reduced by the time they present to A & E.

  • Clear history of dislocation
  • Haemarthrosis
  • Tenderness medial retinaculum and or femoral attachment of MPFL
  • Apprehension to lateral patella displacement
  • Bruise medial edge of patella

Previous History- previous subluxations, patello femoral pain or arthritis Previous activity level Hyperlaxity- Beighton and Horan score (JBJS 1969) Score of 4/9 or more is significant.


Xray AP, True Lateral with knee flexed 30 degrees and Skyline patella at 30 degrees. Routine MRI is not indicated but one should have a high suspicion for osteochondral injuries and/or significant medial stabiliser disruption and obtain MRI in these situations.


Findings on MRI after first time patella dislocation are

  • MPFL rupture in one or more sites in more than 80%.
  • Tear of inferior fibres of VMO
  • Impaction injury to inferomedial patella
  • Contusions of lateral femoral condyle
  • Intra-articular loose bodies
  • MCL injury not uncommon

Management of the first time patella dislocation

Non operative treatment

Non-operative treatment is the primary method of treatment for most first time patella dislocations. Different methods and duration of immobilisation have been reported. There is general agreement that 3 weeks of immobilisation with the knee in extension is sufficient. The author recommends a removable splint worn full time for 3 weeks but it is important to perform intermittent static quadriceps exercises during this period.

Role of surgery

Presence of Osteochondral fractures

Osteochondral fractures are seen in up to 71% of MRIs after first time dislocation and less than 1/3rd are picked up on plain radiographs. Nomura in their arthroscopic study shoed that 95% of their 39 consecutive knees had articular cartilage injuries to the central and medial aspect of patella and 12 knees had damage to the lateral femoral condyle. Stanitski reported that only a third of the osteochondral injuries seen at arthroscopy are seen on xrays. It does not still mean that a majority of patella dislocations need surgery as we don’t know the natural history of such articular damage. Fractures usually occur at the inferomedial aspect of patella or of the lateral femoral condyle. Lateral femoral condyle bruising is seen in 80% of MRI scans after patella dislocation. Picture shown shows classical location of osteochondral fracture off patella that has been fixed with bio-absorbable pins.

Significant disruption of medial stabilisers

Role of MPFL repair Presence of bruising over the antero-medial aspect of the knee would suggest substantial disruption of the medial stabilisers and warrant investigations and potential MPFL repair. Patella avulsion fractures can be seen on skyline xrays and similarly lateral subuluxation that may indicate surgery. MRI scans suggest that single or multiple location MPFL injury can be identified in more than 50% of patients. There is controversy as to MPFL rutures more commonly at the patella or femoral end but it appears that Patellar end rupture is more common (Guerrero, Elias). At arthroscopy one may identify a bare medial edge of patella (Picture). Haemorrhage and oedema at the inferior edge of VMO can be seen on MRI and also at surgery. Christiansen showed that delayed primary repair at the adductor tubercle may not be beneficial though it may improve subjective patella stability score. Silanpaa has reported that the incidence of recurrent dislocation is significantly lower in the surgically treated group.


  • Fithian DC, Paxton EW, Stone ML, Silva P, Davis DK, Elias DA, White LM.Epidemiology and natural history of acute patellar dislocation. Am J Sports Med. 2004 Jul-Aug;32(5):1114-21.
  • Hawkins RJ, Bell RH, Anisette G.Acute patellar dislocations. The natural history.Am J Sports Med. 1986 Mar-Apr;14(2):117-20.
  • Noyes FR, Bassett RW, Grood ES, Butler DL Arthroscopy in acute traumatic hemarthrosis of the knee. Incidence of anterior cruciate tears and other injuries. J Bone Joint Surg Am. 1980 Jul;62(5):687-95, 757
  • DeHaven KE.Diagnosis of acute knee injuries with hemarthrosis. Am J Sports Med. 1980 Jan-Feb;8(1):9-14
  • Heegaard J, Leyvraz PF, Van Kampen A, Rakotomanana L, Rubin PJ, Blankevoort L. Influence of soft structures on patellar three-dimensional tracking. Clin Orthop Relat Res. 1994 Feb;(299):235-43.
  • Nomura E, Horiuchi Y, Kihara M Medial patellofemoral ligament restraint in lateral patellar translation and reconstruction. Knee. 2000 Apr 1;7(2):121-127
  • Nomura E, Inoue M, Osada N.Anatomical analysis of the medial patellofemoral ligament of the knee, especially the femoral attachment. Knee Surg Sports Traumatol Arthrosc. 2005 Oct;13(7):510-5.
  • Elias DA, White LM, Fithian DC.Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology. 2002 Dec;225(3):736-43.
  • Guerrero P, Li X, Patel K, Brown M, Busconi B Medial patellofemoral ligament injury patterns and associated pathology in lateral patella dislocation: an MRI study. Sports Med Arthrosc Rehabil Ther Technol. 2009 Jul 30;1(1):17
  • Arendt EA, Fithian DC, Cohen E.Current concepts of lateral patella dislocation.Clin Sports Med. 2002 Jul;21(3):499-519. Review Christiansen SE, Jakobsen BW, Lund B, Lind M.Isolated repair of the medial patellofemoral ligament in primary dislocation of the patella: a prospective randomized study. Arthroscopy. 2008 Aug;24(8):881-7
  • Steiner TM, Torga-Spak R, Teitge RA Medial patellofemoral ligament reconstruction in patients with lateral patellar instability and trochlear dysplasia. Am J Sports Med. 2006 Aug;34(8):1254-61.
  • Buchner M, Baudendistel B, Sabo D, Schmitt H .Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clin J Sport Med. 2005 Mar;15(2):62-6
  • Nam EK, Karzel RP.Mini-open medial reefing and arthroscopic lateral release for the treatment of recurrent patellar dislocation: a medium-term follow-up. Am J Sports Med. 2005 Feb;33(2):220-30.
  • Mäenpää H, Lehto MU. Patellar dislocation. The long-term results of nonoperative management in 100 patients. Am J Sports Med. 1997 Mar-Apr;25(2):213-7.
  • 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. J Bone Joint Surg Am. 2009 Feb;91(2):263-73
  • Palmu S, Kallio PE, Donell ST, Helenius I, Nietosvaara Y.Acute patellar dislocation in children and adolescents: a randomized clinical trial. J Bone Joint Surg Am. 2008 Mar;90(3):463-70
  • 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 Orthop Scand. 1997 Oct;68(5):419-23
  • 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 Orthop. 2005 Oct;76(5):699-704
  • Buchner M, Baudendistel B, Sabo D, Schmitt H.Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clin J Sport Med. 2005 Mar;15(2):62-6
  • Stanitski CL, Paletta GA Jr .Articular cartilage injury with acute patellar dislocation in adolescents. Arthroscopic and radiographic correlation. Am J Sports Med. 1998 Jan-Feb;26(1):52-5
  • Nomura E, Inoue M, Kurimura M.Chondral and osteochondral injuries associated with acute patellar dislocation. Arthroscopy. 2003 Sep;19(7):717-21. Review.