total knee arthroplasty

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

Intraoperative Fractures

1.  Shaft fracture from IM rod

2.  Posterior condylar fracture

Management

- assess stability

- ORIF if needed

Incidence

10%

Requirements

70^o  swing phase

80^o climb up stairs

90^o climb down stairs + sit down in chair

100^o low chair

NHx

Stiffness usually subsides at 6-8/52

- generally improves out to 3/12

- slow improvement for up to next 9/12

Arterial injury

Incidence

0.05%

Types

1. Thrombosis

- most common scenario

- tourniquet with atherosclerosis

- indirect damage to vessel

- femoral or popliteal

2.  Embolisation

- atherosclerosis again

- blue toes syndrome post operatively

3.  Vessel transection

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 

Preoperative

Identify high risk groups

- immunocompromised

- diabetes

- RA

- malnutrition

Urine screen

- check for and treat UTi

Groin, nose, axilla swabs

- for MRSA

- if positive, treat

- need 3 consecutive free swabs

3 x chlorhexidine preoperative showers in 8 hours

Admit day of surgery

- check skin for lesions