A prosthetic elbow includes a fixed member structure and a powered gearbox mechanism housed in a housing structure for rotating the forearm portion to varying angular positions. The powered gearbox mechanism includes a motor attached to the housing structure, a planetary frictional drive connected to a motor shaft of the motor and the housing structure, and a strain wave gear set having an input driven by the planetary fictional drive and an output attached to the fixed member structure, where the powered gearbox mechanism is configured to convert an output of the motor into a rotation of the housing structure relative to the fixed member structure, thereby causing the rotation of the forearm portion to varying angular positions relative to the upper arm. The fixed member structure and the housing structure each are connected to one of a forearm portion and an upper arm portion and rotatable relative to one another about an axis of rotation of the forearm portion.