Unit 4 - Ankle Joint Replacement Flashcards
Name 3 reasons for lack of success to create a good ankle replacement?
- Less attention due to ankle not being frequently involved in the primary OA process
- Subtalar joint normally also affected so would need to replace this too
- Arthrodesis is available which is normally very successful
What are the main materials used for ankle joint replacement?
Cobalt chrome and HDP
What are the 3 main reasons ankle protheses fail?
- Overload causing subsidence
- Loosening due to poor fixation
- High torques, which can cause interface loosening
What is the normal range of motion in the ankle (tibia-talar) joint?
25-30 degrees in both dorsiflexion and plantarflexion
What motion does the subtler joint enable?
Inversion/eversion
Fore-aft forces that occur at foot-ground contact during walking contribute to producing a shear force at the ankle joint of how much?
About 0.4 - 0.7 body weight
What is the maximum vertical load on the ankle?
5 times body weight
What is the range of motion in the ankle when walking?
Up to 15 degrees in both plantar flexion and dorsiflexion
Name 4 types of congruent shape ankle replacements?
Spherical
Spheroidal
Conical
Cylindrical
Name 2 types of incongruent shape ankle replacements?
Trochlear
Convex-concave
Name 3 problems with the incongruent type ankle replacements?
- High depth of wear than the congruent types
- Higher contact stresses due to a lower contact area than the congruent types
- Less stability than congruent types due to their greater freedom of movement
Name 6 causes of failure in ankle joint?
- Aseptic loosening of a component
- Lateral or medial subluxation of the joint
- Subsidence of the taller component
- Impingement of the joint
- Wound healing problems
- Infection
List 2 trends in modern ankle joint prostheses designs?
- Move towards meniscal bearing
2. Move towards cement less types
List one advantage of meniscal bearing ankle prosthesis over cylindrical bearing design?
Congruence (low wear) yet freedom of movement
