A torque transmission apparatus incorporates a differential gear system and a stationary sensor connected to the differential gear system for measuring output torque. The stationary sensor may be connected to a measurement output element of the differential gear system by a torsionally compliant measurement member, wherein the stationary sensor measures torsional deformation of the measurement member. The torsional deformation may be measured directly, or it may be measured following amplification by a gear train. A rotary position sensor may be used as the stationary sensor. Alternatively, the stationary sensor may be connected to the measurement output element of the differential gear system by way of a rigid measurement member, wherein the stationary sensor measures force applied by the measurement member. In this alternative, a force sensor may be used as the stationary sensor.