Acute Patella Dislocation

Acute Patella DislocationPatella Dislocation Skyline




1. Direct lateral blow to patella

- usually with knee partly flexed and quadriceps relaxed


2.  Indirect low energy injury




2 Groups of Patients


1.  Patients with no predisposition to patella instability

- traumatic injury

- contact sports


2.  Patients with anatomic predisposition to instability

- atraumatic / minimally traumatic injury

- young / valgus malalignment / ligamentous laxity / malrotation


Associated injuries 


Osteochondral fracture (40-50%)

- LFC or medial facet patella

- patient will have haemarthrosis

- must identify this group, investigate and manage appropriately




Medial Patellofemoral Ligament (MPFL)

- from MFC between femoral epicondyle and adductor tubercle

- to superolateral border patella

- deep to retinaculum / superficial to capsule


Usually tears off femur


Acts as a checkrein to lateral patella subluxation

- will usually be torn in all patients with patella dislocation


Recurrence rate



- more likely in those predisposed to instability


Reduction technique


Conscious sedation

- knee extended

- medial force on patella

- usually reduces easily

- splint




Haemarthrosis post reduction

- investigate further




AP / Lateral / Skyline

- examine carefully for loose body


Knee Xray Loose Body




Shows loose body and origin





- MPFL tear

- cartilage damage

- loose body


Patella Dislocation Chondral Damage Medial Facet PatellaPatella Dislocation MRI MPFL Disruption Patella SidePatella Dislocation MRI Loose Body Notch


Knee Loose Body PFJPatella DIslocation MRI OCD LFC MPFL Patella Chondral Damage




Non operative




1.  First time dislocator with no associated injury

- splint in full extension with lateral patella pad

- reapproximate torn medial structures

- 4 weeks

- then begin VMO exercises +++


2.  Recurrent dislocator

- splint only initially for symptom relief

- early ROM and rehabilitation

- no role for long term splintage





- loose body

- management of OCD Lesions

- +/- early MPFL repair




Assess Patella and Femoral Lesions


1.  Small pieces cartilage

- remove loose bodies

- microfracture if necessary


Patella Dislocation Loose BodyPatella Small Chondral Lesion


2.  Large Osteochondral Fragment

- usually medial patella or lateral femur

- open approach to knee

- reduce and fix with bioabsorbable compression screws / pins


Patella Ostechondral FracturePatella Osteochondral Fracture Fixation


3.  Large Chondral piece with minimal or no bone

- can attempt suture fixation

- need to warn of risk of failure and need for reoperation

- careful monitoring


4.  Large irreparable chondral lesion

- remove loose body

- microfracture / abrasion initially

- if continue to be asymptomatic, consider alternative procedure

- MACI / mosaicplasty


Patella Dislocation Unsalvageable Chondral LesionPatella Dislocation Removal Medial Facet Cartilage


Early MPFL repair


Patella Dislocation MPFL Disruption Patella Arthroscopy



- ? would recurrence rates be reduced with early repair / reconstruction MPFL




Palmu et al JBJS Am 2008

- RCT of early operative treatment in adolescents < 16

- very high rates of recurrence in both groups (70%)

- up to 50% of this group had contralateral patella problems


Silanpaa et al Am J Sports Med 2008

- compared operative and non operative treatment

- all operative patients had arthroscopic repair of medial retinaculum

- equal (20%) redislocation in each group


Christiansen et al Arthroscopy 2008

- RCT comparing non operative to open MPFL femoral repair

- redislocation rates the same in each group


Camanho et al Arthroscopy 2009

- RCT of operative v non operative

- excluded patients with flat trochlea / valgus > 15o / patella alta

- in surgical group determined if injury on patella side or femoral side

- 7 from patella repaired arthroscopically

- 10 from femur repaired open with anchors

- 0/17 in surgical group redislocated

- 8/16 in surgical group redislocated




1.  Can repair MPFL but if anatomically predisposed to instability

- will still redislocate and rerupture MPFL

- exclude valgus / alta / flat patella


2.  If attempting early repair, need to address specific MPFL pathology


Open Technique


Very important to determine if torn from patella or medial epicondyle

- MRI very useful


1. Medical epicondyle avulsion

- over medial epicondyle

- divide deep fascia

- elevate VMO

- identify MPFL

- repair using bone anchors


MPFL repair medial epicondyle


2.  Patella MPFL avulsion


MPFL Patella Avusion