Knee Implants

Question 1

What is biomechanics?

Answer 1

The study of the structure and function of biological systems by means of the methods of mechanics.

Question 2

What are the 3 load bearing bones of the knee joint?

Answer 2

Femur, tibia, patella

Question 3

What are the 2 compartments of the knee joint?

Answer 3

Tibial Femoral

Patella Femoral

Question 4

What are the static stabilizers in the knee joint?

Answer 4

Ligaments

Question 5

What are the dynamic stabilizers in the knee joint?

Answer 5

Muscles

Question 6

What are the 4 ligaments in a knee joint?

Answer 6

Anterior Cruciate Ligament
Posterior Cruciate Ligament
Medial Collateral Ligament
Lateral Collateral Ligament

Question 7

How many degrees of freedom in the knee joint? What are they?

Answer 7

6.
Rotation: flexion-extension, varus-valgus, internal-external
Translation: anterior-posterior, medial-lateral, compression

Question 8

What are the common conditions that lead to knee replacement? (2)

Answer 8

Osteoarthritis.

Rheumatoid Arthritis

Question 9

What is rheumatoid arthritis?

Answer 9

Autoimmune disease that affects cartilage, can cause inflammation and then degradation.

Question 10

What are some of the non-pharmacological treatments before a total knee replacement? (5)

Answer 10

Patient education.
Use of assistive devices.
Weight loss.
Physical therapy.
Occupational therapy.

Question 11

What are some of the pharmacological interventions before a knee replacement? (4)

Answer 11

NSAIDs
Glucosamine sulphate
Intra-articular corticoteroids
Intro-articular hyaluronic acid

Question 12

What do cortical steroids do that are bad?

Answer 12

Affect proteoglycan production

Question 13

What are the 3 operative treatment operations for the knee?

Answer 13

Arthroscopy - minimally invasive procedure to shave off worn cartilage.
Osteotomy - wedge from tibia removed
Knee replacement

Question 14

What are the 2 types of knee replacement?

Answer 14

Partial - unicondyle replaced

Total - both condyles and tibial plateau are replaced

Question 15

What are the 2 classifications of knee replacements?

Answer 15

Unconstrained and constrained (hinged)

Question 16

What are the 3 types of unconstrained design?

Answer 16

Cruciate retaining/sparing
Cruciate substituting
Mobile bending prothesis

Question 17

What is Wolff’s Law?

Answer 17

Decreasing strain leads to thinning of compact bone and loss of spongy bone - which increases fragility. Increasing strain results in thickening of compact and spongy bones - which increases bone strength.

Question 18

Which knee operative treatment is better for younger people and why?

Answer 18

Osteotomy is better for younger people because knee replacements only last 10-15 years and osteotomys are good for physically active people with good bones.

Question 19

What are some indications for surgery? (2)

Answer 19

Cartilage breaks down, bones start to rub against each other causing pain.
Bony spurs form around joint and ligaments start to weaken.

Question 20

What is the screw hole mechanism of the knee joint?

Answer 20

Medial condyle is bigger than lateral. Therefore knee tries to spin around in a similar way that a cone would with a small circle at one end and a bigger circle at the other. This leads to an instantaneous axis of rotation, allowing the knee to rotate and translate.

Question 21

What would happen if the knee was perfectly symmetrical?

Answer 21

It would only rotate and not translate.

Question 22

Name the three key unique features of the knee.

Answer 22

Polycentric joint.
Instantaneous axis of rotation.
Rotates and translates.

Question 23

What do the post and metal bar do in a knee replacement?

Answer 23

Mimic the function of the PCL.

Question 24

What are the three main criteria for materials used in TKR?

Answer 24

Biocompatible
Duplicate the knee structures they are intended to replace.
Able to retain strength and shape for a long time.

Question 25

Name the six materials used for TKR.

Answer 25

``` Stainless steel Cobalt chromium alloys Titanium Alloys Tantalum Zirconium Alloys UHMWPE ```

Question 26

What does UHMWPE stand for?

Answer 26

Ultra High Molecular Weight Polyethylene

Question 27

Name the two types of combination materials used for TKR and the reasons why they aren't used.

Answer 27

Ceramic = too fragile to endure the heavy stress and weight. | Metal on metal = increasing failure rate, patients report loosening, breakage, fracture, pain, stiffness etc.

Question 28

Name the three types of materials used for TKR fixation.

Answer 28

Cemented (PMMA). Cementless. Hybrid.

Question 29

What is PMMA?

Answer 29

Bone cement - Polymethylmethacrylate.

Question 30

What does cementless fixation rely on?

Answer 30

New bone growing into the surface of the implant for fixation. They are textured or coated so that the new bone actually grows into the surface of the implant.

Question 31

What is hybrid fixation?

Answer 31

Femoral component is inserted without cement as other design features (grooves) are used for better bone growth around replacement. Tibial and patellar components are inserted with cement. This allows for the plastic insert to be removed while the stem remains cemented into the tibia.

Question 32

What is the best material design for TKR?

Answer 32

Metal on plastic.

Question 33

What are the three basic parts of a TKR?

Answer 33

Femoral element: metal Tibial element: flat metal surface with plastic spacer Patellar Piece: rounded polyethylene cap

Question 34

What does TKR look like today?

Answer 34

There are more than 150 implant designs on the market, the majority of which are condylar replacements.

Question 35

What is TKR made of today?

Answer 35

Femoral component: cobalt chrome alloy Tibial tray: cobalt chrome or titanium Tibial bearing component: UHMWPE Patellar component: UHMWPE

Question 36

What are the four technical goals of knee replacement surgery?

Answer 36

1. Restoration of mechanical alignment. 2. Preservation of the joint line. 3. Balanced ligaments 4. Maintaining or restoring a normal Q - angle.

Question 37

What is the Q-angle?

Answer 37

The angle between the longitudinal axis of the tibia and the line of action of force of quad muscle.

Question 38

Why is the Q-angle important?

Answer 38

A greater Q angle applies a greater torque on the knee joint. Women have greater Q angles which leads to 4x as many ACL injuries.

Question 39

What is the difference between proximal and distal?

Answer 39

``` Proximal = towards head. Distal = away from head. ```

Question 40

What is a varus deformity?

Answer 40

Distal to midline. Genuvara. Ankles come in towards midline and knee sticks out.

Question 41

What is a valgus deformity?

Answer 41

Distal away from midline. Genuvalga. Ankles away from midline and knees towards.