Thou hast enlarged my steps under me, that my feet did not slip. Job often complained that God "hedged in his steps" (Job 3:23) and "fenced up his way" (Job 19:5), so that he had no liberty of movement.
David enumerates among the blessings which he receives of God, the freedom which he enjoys (comp. Psalms 31:8). He is at liberty to go where he likes. and also his footsteps "do not slip." This is rather an independent clause than a consequence.
Translate, and my ankles slip not.