1. Ankle DF/PF
   • Relative DF: moves knee joint center forward relative to GRF, promoting LR knee flexion.

   • Relative PF: moves knee joint center backward relative to GRF, promoting knee extension throughout LR, midstance, and terminal stance.

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2. Socket flexion/extension
   Socket flexion/extension is named for the alignment it produces in the most distal residual joint. The prosthetist can align the socket in some "initial flexion" for an individual with short hip or knee flexors.

   In the transtibial (below-knee) socket,

   • socket flexion moves knee joint center anterior relative to GRF, increasing heel lever, thus promoting LR knee flexion.

   • socket extension moves knee joint center posteriorly relative to GRF, promoting knee extension throughout LR and stance.

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3. AP socket position relative to foot:
   While prosthetists usually speak of altering socket position, therapists may more easily envision the effects on gait in terms of changes in foot position. Thus,

   Forward displacement of socket (equivalent to backward displacement of foot):

   • increases heel lever, creating GRF flexor moment at LR.

     This may be desirable for those with transtibial amputations, as it induces a more normal LR knee flexion.

     This is not desirable for those with transfemoral amputations if it renders the knee unstable.

   • decreases toe lever

     The toe-lever's length determines timing of heel rise. A short toe lever causes early heel rise and knee flexion. Premature midstance or terminal stance knee flexion ("drop-off") is undesirable because it can destabilize the person.

   Backward displacement of socket (equivalent to forward displacement of foot):
   • decreases heel lever,

     allows GRF to move anteriorly to knee axis more quickly, and promotes midstance knee extension.

   • increases toe lever,

     which delays heel rise and supports knee extension through a longer portion of stance phase.