Description

One of the easiest ways to categorize prosthetic knees is by the number of axes or centres of rotation that the unit has. Prosthetists generally divide knees into two groups; those which have a single pivot and those with multiple pivot points.

The monocentric type of knee works as a simple hinge with one part of the knee rotating about the other using a shared pivot point.

Advantages

  • May feature mechanical, pneumatic or hydraulic control.
  • Lightweight – generally lighter than comparable polycentric knees.
  • Can be made smaller than similar polycentric knees.
  • Durable & robust – mechanical versions have fewer moving parts due to their simplicity.
  • Mechanical versions are relatively inexpensive.
  • May offer stance control, which assists the user to maintain stability when standing.
  • Sometimes features a manual lock to compensate for lack of stance control.
  • Mechanical units use constant friction to regulate the swing speed of the shin section.

Disadvantages

  • Constant friction design does not adapt to different walking speeds.
  • Distance from center of rotation to toe is fixed during swing phase; this increases the risk of stumbling.
  • Bending action does not match the anatomical knee.
  • No geometric lock.
  • May lack stance control, which means that the user must use muscle power to remain stable when standing.
  • Mechanical stance control may be unreliable.
  • May become noisy when wearing.
  • May result in thigh length inequality when used with a very long residual limb.
  • Become less stable as they wear.
  • Amount of flexion is not as great as polycentric knees.
  • Higher wear coefficient for full length cosmetic covers.