A seatbelt pretensioning retractor assembly for use in a passenger vehicle, the seatbelt pretensioning retractor assembly comprising: a housing adapted for being mounted to a vehicle structure and having an interior cavity; a tube (52, 152) having an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing; a sprocket rotatably mounted to the housing and fixedly coupled to a spindle adapted for taking up seatbelt webbing during pretensioning, wherein the sprocket has a plurality of vanes; a driving element comprising a plastically deformable polymer rod (53, 153) configured to extend in a longitudinal direction and having a recessed portion defining a recess that extends generally in the longitudinal direction, wherein the plastically deformable polymer rod (53, 153) is disposed within the tube (52, 152) and is translatable through the tube (52, 152) in a first direction toward the sprocket in response to an actuation by the gas generator; a stopper coupled to an end portion of the plastically deformable polymer rod (53, 153); and a seal member disposed between the gas generator and the stopper, wherein the tube (52, 152) includes a projection extending within the tube (52, 152) adjacent to the exit to define a constriction portion that has an opening dimension smaller than an inside dimension of adjacent portions of the tube (52, 152), characterized in that the recess is aligned with the projection in the first direction and the constriction portion is sized to permit the recessed portion of the plastically deformable polymer rod (53, 153) to pass therethrough while preventing the stopper from passing therethrough. a housing adapted for being mounted to a vehicle structure and having an interior cavity; a tube (52, 152) having an arcuate and curved shape having a first end for fluid communication with a gas generator and a second end in fluid communication with the interior cavity of the housing; a sprocket rotatably mounted to the housing and fixedly coupled to a spindle adapted for taking up seatbelt webbing during pretensioning, wherein the sprocket has a plurality of vanes; a driving element comprising a plastically deformable polymer rod (53, 153) configured to extend in a longitudinal direction and having a recessed portion defining a recess that extends generally in the longitudinal direction, wherein the plastically deformable polymer rod (53, 153) is disposed within the tube (52, 152) and is translatable through the tube (52, 152) in a first direction toward the sprocket in response to an actuation by the gas generator; a stopper coupled to an end portion of the plastically deformable polymer rod (53, 153); and a seal member disposed between the gas generator and the stopper, wherein the tube (52, 152) includes a projection extending within the tube (52, 152) adjacent to the exit to define a constriction portion that has an opening dimension smaller than an inside dimension of adjacent portions of the tube (52, 152), characterized in that the recess is aligned with the projection in the first direction and the constriction portion is sized to permit the recessed portion of the plastically deformable polymer rod (53, 153) to pass therethrough while preventing the stopper from passing therethrough.