Review of the biomechanics of the knee joint

Question 1

What is the main 2 features that are difficult to combine when considering knee replacement?

Answer 1

Acceptable range of motion of the natural joint

Sufficient stability

Question 2

What is a total condylar design?

Answer 2

Surface replacement which achieves stability through its shape

Question 3

What is hemi-arthroplasty?

Answer 3

Joint surfaces of only one compartment of the knee are replaced

Question 4

What is the function of the ACL?

Answer 4

Resists posterior subluxation of the femur

Question 5

What is the function of the PCL?

Answer 5

Resists anterior subluxation of the femur

Question 6

What is the function of the LCL?

Answer 6

Resists adduction of the joint

Question 7

What is the function of the MCL?

Answer 7

Resists abduction of the joint

Question 8

What is the function of the posterior capsule?

Answer 8

Resists hyperextension

Question 9

How are the ACL and PCL named?

Answer 9

According to their attachments to the tibia not the femur

Question 10

How does the centre of rotation move as the knee flexes?

Answer 10

Moves posteriorly (as does the point of surface contact between femur and tibia)

Question 11

How do the medial and lateral compartments of the tibial plateau differ?

Answer 11

Medial = slightly concave
Lateral = slightly convex

Question 12

How do you calculate the circumference of a circle?

Answer 12

πd

Question 13

What limits the rolling distance in knee motion?

Answer 13

Cruciate ligaments

Question 14

What are the 2 types of motion of the knee?

Answer 14

Sliding and rolling

Question 15

What are the main type of external forces that act on the knee joint?

Answer 15

Compressive (due to the weight of the body)

Question 16

Why are the forces at the contacting femoral/tibial surfaces much higher than body weight?

Answer 16

Combined effects of gravitational forces, contacting forces of the muscles and balancing loads of the ligaments

Question 17

Roughly what force goes through the knee joint under normal daily activities? (compared to body weight)

Answer 17

2 to 6 times body weight

Question 18

What vertical forces go through the knee joint?

Answer 18

Ground reaction forces (1 BW)
Quad force via patella ligament (3 BW)

Resultant joint reaction force = 4 BW

Question 19

Which ligament is most important when walking downstairs?

Answer 19

PCL (prevents femur sliding forwards over tibia)

Question 20

What is thr rough magnitude of the horizontal component of GRF and what direction does it act?

Answer 20

About 5% BW - medial

Question 21

How are low magnitude sideways medial reaction forces managed?

Answer 21

Quadriceps muscles

Question 22

As horizontal force increases, in activities more strenuous than normal walking how are these controlled?

Answer 22

Hamstrings (increases the joint reaction force)

Question 23

Eventaully as horizontal force increases and muscles do not have the strength to maintain contact what happens?

Answer 23

Lateral side loses contact
All the load is taken by medial condyle
Stability of the joint then relies on LCL

Question 24

What are the design implications due to the high load acting on the medial compartment of the knee?

Answer 24

Tibial component needs to be able to transfer high medial compartment loads on its upper surface to the underlying bone without causing high compressive stresses which could cause the bone to fail

Question 25

What is likely to happen if the knee is subjected to excessive axial loads?

Answer 25

Meniscal tear