Patella

Problems

 

Instability / Maltracking

Fracture

Loosening or failure of component

Patella Clunk Syndrome

Extensor Mechanism Rupture

 

Incidence

 

PFJ complications 5%

 

PFJ Instability / Maltracking

 

Effect

 

Catastrophic wear

Component loosening

Pain

Fracture

 

Aetiology

 

1.  Component Malposition / Malalignment

 

A.  Internal rotation of the femoral or tibial component

- increases the Q angle

 

 

B.  Medialisation of femoral component

 

C.  Axial Malalignment

- valgus > 10^o

 

D.  Lateralisation of patella button

 

E.  Overstuffing of the patella femoral joint

- tightens the lateral retinaculum

 

2.  Poor patellofemoral Component design

 

A.  Poorly designed trochlea / patella

 

 

B.  Hinged or constrained knee

- normally get IR with early flexion 

- this medialises tibial tuberosity

- constrained TKR don't do this and have a lateral vector

 

3. Soft tissue balancing

 

Tightness of lateral retinaculum in long standing valgus

- at end of OT should track centrally without any external pressure 

- no tilt

- otherwise lateral release +/- patella resurfacing

 

 

Investigation

 

Examination

- Assess tracking

Xray

- skyline views

- lateral tilt / subluxation

 

 

CT

- rotational profile of the components

 

Management

 

Non-Operative

- VMO exercises

- often unsuccessful

 

Acute trauma

- patella has been tracking centrally since OT

- not since acute trauma

- immediate capsular repair is indicated

 

Surgical options

 

1.  Lateral release + Patella resurfacing

 

2.  Tibial tuberosity transfer +/- MPFL reconstruction

 

 

Barber et al Arthroscopy 2008

- 91% successul in eliminating instability in 35 knees

- used Elmslie Trillat

 

3.  Revision

 

Options

- medialise patella component

- revise malrotated components

 

Patella Fracture

 

 

Incidence

 

Uncommon

- 0.1% Primary

- 0.6% Revision

 

Causes

 

1.  AVN

 

Disruption of patella blood supply

- patella turndown

- medial approach and lateral release

 

 

2.  Excessive / asymmetric patella resection

- at least 15 mm native patella must remain

 

3.  Large central hole

- increases strain more than small peripheral holes

 

4.  Anterior patella perforation

- more common with inlay

 

5.  Increased PF strain

- oversized or anterior femoral component

- oversized patella component

- patella baja

 

Management

 

Non-Operative

 

Indications

- extensor mechanism intact

- patella component stable

 

 

Treatment

- immobilse for 6 weeks then progressive ROM

 

Operative

 

Indications

- loose component or ruptured extensor mechanism

 

Treatment

A.  Patella ORIF if component stable

B.  Removal component if unstable + Patella ORIF

 

Patella Component Loosening

 

Incidence

 

Cemented patella

- < 2%

 

Uncemented higher

- 0.6% - 11.1%

 

Associations

 

Metal backed designs

Uncemented

Fracture / AVN of patella

Excessive bone removal

 

Management

 

A.  Remove and leave

 

B.  Revision

- need > 10 mm bone left

 

C.  Patellectomy

 

Patella Clunk Syndrome

 

Symptom

 

Clunk with knee extension

- as patella exits groove at 30-45° extension

 

Complain of symptoms when rising from chair or climbing stairs

 

Pathology

 

Fibrous nodule at junction of posterioraspect of patella and quadricep tendon

- with flexion enters trochlear groove and gets trapped as go back into extension

- usually due to entrapment at superior flange of femur

- inflammation and a synovial proliferation

 

Causes

 

Increased incidence in PS knees

 

Newer designs

- deeper patella groove

- more posterior femoral box

 

Investigation

 

Can visualise nodule on ultrasound

 

Management

 

Arthroscopic debridement

 

Dajani et al J Arthroplasty 2010

- good result in 15 knees

 

Rupture of Extensor Mechanism

 

Incidence

 

0.17-2.5%

 

Causes

 

Usually post operative, insidious and due to a vascular insult

 

Lateral release - devascularises tendon

Closed MUA of knee

Osteotomy of tibial tuberosity

Revision TKR

 

Prevention with surgical technique is imperative

 

Effect

 

Debilitating extensor lag

- can be about 50^o

- operation improves this to about 20^o

 

Can predispose to knee dislocation / post jump

 

Operative Management

 

1.  Primary repair with autograft / allograft reinforcement

- staples, wire reinforcement

- hamstring reconstruction (leave attached distally)

- achilles tendon allograft

- Lars ligament reinforcement

 

Usually left with extensor lag

 

 

2.  Chronic rupture / failed repair

 

Must deal with patella baja

- combine repair with proximalization of tibial tuberosity

 

 

3.  Revise to constrained prosthesis if required

- PS component

- loss of mechanical advantage of quads

- extensor lag

- anterior translation of femur on tibia once the PCL stretches