A connector assembly includes a lead or a lead extension, a connector, and a retention assembly disposed in the connector. The connector includes a connector housing defining a port at a distal end of the connector, and a plurality of connector contacts disposed in the connector housing. The port is configured and arranged for receiving a proximal end of the lead or the lead extension. The connector contacts are configured and arranged to couple to at least one terminal disposed on the proximal end of the lead or the lead extension. The retention assembly includes a retention mechanism that can be engaged and reversibly disengaged without the use of tools beyond conventional operating-room surgical instruments.