Question

1. Implants can be positioned in soft or hard tissue (i.e.: arthroplasty vs. vascular stent). Discuss what design challenges you might face for implants in two different locations in relation to the material properties of each location – name and discuss at least 1 property for each location.

Answer 1

Arthoplasty is an operation to construct a new mobile joint .

The following indications include:

1. Advanced osteoarthritis or RA of hip, knee, shoulder.

2.Tuberculous arthritis of hip

3. Rarely to correct deformity, eg: hallux valgus.

Types of arthoplasties :

1. HEMIARTHOPLASTY: This means replacing only one side of a joint. For instance the head of femur is replaced with an artificial component while the acetabulum is left as it. It is indicated in situations where only one half of the joint is affected, eg; fracture neck of femur in elderly. A variety of prostheses are used it could be monopolar or bopolar.

2. TOTAL JOINT REPLACEMENT: Both the components of joint are replaced-- eg; the head as well as acetabulum are replaced in total hip replacement operation.

TOTAL KNEE REPLACEMENT: In the knee replacement only the damaged articular surface is sliced off to prepare the bones end to take the artificial components which ' cap' the ends of the bones.

The implants and the procedure in this total knee replacement include:

a) A U- shaped femoral component to 'cap' the prepared lower end of femur.

b) A tibial base plate to cover the cut flat surface of upper end of tibia.

c) A plastic tray inserted between the above two metallic components.

d) A patellar button made of polyethylene to replace the damaged surface of patella.