Review of the biomechanics of the knee joint Flashcards
What is the main 2 features that are difficult to combine when considering knee replacement?
Acceptable range of motion of the natural joint
Sufficient stability
What is a total condylar design?
Surface replacement which achieves stability through its shape
What is hemi-arthroplasty?
Joint surfaces of only one compartment of the knee are replaced
What is the function of the ACL?
Resists posterior subluxation of the femur
What is the function of the PCL?
Resists anterior subluxation of the femur
What is the function of the LCL?
Resists adduction of the joint
What is the function of the MCL?
Resists abduction of the joint
What is the function of the posterior capsule?
Resists hyperextension
How are the ACL and PCL named?
According to their attachments to the tibia not the femur
How does the centre of rotation move as the knee flexes?
Moves posteriorly (as does the point of surface contact between femur and tibia)
How do the medial and lateral compartments of the tibial plateau differ?
Medial = slightly concave Lateral = slightly convex
How do you calculate the circumference of a circle?
πd
What limits the rolling distance in knee motion?
Cruciate ligaments
What are the 2 types of motion of the knee?
Sliding and rolling
What are the main type of external forces that act on the knee joint?
Compressive (due to the weight of the body)
Why are the forces at the contacting femoral/tibial surfaces much higher than body weight?
Combined effects of gravitational forces, contacting forces of the muscles and balancing loads of the ligaments
Roughly what force goes through the knee joint under normal daily activities? (compared to body weight)
2 to 6 times body weight
What vertical forces go through the knee joint?
Ground reaction forces (1 BW)
Quad force via patella ligament (3 BW)
Resultant joint reaction force = 4 BW
Which ligament is most important when walking downstairs?
PCL (prevents femur sliding forwards over tibia)
What is thr rough magnitude of the horizontal component of GRF and what direction does it act?
About 5% BW - medial
How are low magnitude sideways medial reaction forces managed?
Quadriceps muscles
As horizontal force increases, in activities more strenuous than normal walking how are these controlled?
Hamstrings (increases the joint reaction force)
Eventaully as horizontal force increases and muscles do not have the strength to maintain contact what happens?
Lateral side loses contact
All the load is taken by medial condyle
Stability of the joint then relies on LCL
What are the design implications due to the high load acting on the medial compartment of the knee?
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
What is likely to happen if the knee is subjected to excessive axial loads?
Meniscal tear
