Acute Patella Dislocation

Acute Patella DislocationPatella Dislocation Skyline

 

Mechanism

 

1. Direct lateral blow to patella

- usually with knee partly flexed and quadriceps relaxed

 

2.  Indirect low energy injury

 

Epidemiology

 

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

 

Pathology

 

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

 

15-20%

- more likely in those predisposed to instability

 

Reduction technique

 

Conscious sedation

- knee extended

- medial force on patella

- usually reduces easily

- splint

 

Examination

 

Haemarthrosis post reduction

- investigate further

 

Xray

 

AP / Lateral / Skyline

- examine carefully for loose body

 

Knee Xray Loose Body

 

CT

 

Shows loose body and origin

 

MRI

 

Demonstrates

- 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

 

Management

 

Non operative

 

Options

 

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

 

Operative

 

Indications

- loose body

- management of OCD Lesions

- +/- early MPFL repair

 

Arthroscopy

 

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

 

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

 

Issue

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

 

Results

 

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

 

Problem

 

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

 

Medical epicondyle avulsion

- over medial epicondyle

- divide deep fascia

- elevate VMO

- identify MPFL

- repair using bone anchors

 

MPFL repair medial epicondyle

 

Arthroscopic technique

 

Pass spinal needle medial to patella

- insert 1 PDS

- retrieve laterally with loop retriever

- repeat multiple times

- mini - incision and tie from outside in