A needle assembly (26) for delivering a dermal filler comprises a cannula (30) and a hub (42) having a distal end (46) and a proximal end (50) matable with a distal end (22) of a syringe (12). The hub (42) has an inner bore disposed therein, the inner bore comprising a hub retention cavity (80) extending from the proximal end (50) of the hub (42) and including a stepped interior surface, and a cannula retention section extending towards the distal end (46) of the hub (42). The stepped interior surface of the hub retention cavity (80) includes a step (88), wherein a section of the stepped interior surface extending distally from the step (88) towards the cannula retention section is smaller in diameter than a section of the stepped interior surface extending proximally from the step (88), the inner bore thereby decreasing in diameter along the stepped interior surface to a proximal end of a cannula retention surface of the cannula retention section. The inner bore does not increase in diameter from the hub retention cavity (80) to a distal end of the cannula retention section. The cannula retention section has a constant diameter, and the cannula retention surface is mated against an outer surface of the cannula (30) to secure the cannula (30) within the cannula retention section.
