TKR

Conformity

Definition

Geometric measure of the closeness of the fit of the knee articulation

Concepts

The ideal TKA maximises articular conformity while minimising axial constraint

Highly conforming / Fully congruent

- constant sagittal femoral radius

- large contact areas

- theoretical limitation of flexion to 120^o due to posterior impingement of the tibial component

Philosophy

Need the least amount of constraint necessary to obtain sufficient stability

Increasing constraint

Advantages

- increase stability

Disadvantage

- increase stress at implant host interface

3 Types

1.  Unconstrained

A.  Posterior cruciate retaining

Options

1. Always resurface

2. Never resurface

3. Selectively resurface

Decision Making

Controversial

- literature divided on issue

Historically

- poor outcomes due to poor implant design

- now improved designs

- non resurfacing also improved due to better design and improved techniques in regard to tracking and rotation

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

Intraoperative Fractures

1.  Shaft fracture from IM rod

2.  Posterior condylar fracture

Management

- assess stability

- ORIF if needed

Incidence

10 -15%

Include

- marginal necrosis

- wound slough

- sinus tract formation

- dehiscence

- haematoma

- oozing knee wound

Blood supply

Anterior knee has no muscles to supply vessels directly 

Natural History

Insall 1984 / no prophylaxis

- DVT 70 - 80%

- asymptomatic PE  8 -17%

- symptomatic PE  0.5 -3%

- death  0.2%

- most commonly in calf / 85-90% below trifurcation

THR

- THR only 10-15% below trifurcation

Bilateral DVT in 10-15%

Prophylaxis

Mechanical prophylaxis

- TEDS