A bone-stiffness measuring instrument comprises a set or kit of readily assembled and adjusted components, namely a goniometer (16), a light-weight load cell (15), and a small computer package (22), adapted to continuously respond to the outputs of the load cell and goniometer and to display and/or record (i.e., store) measured stiffness data; plus hardware in duplicate, namely, a bone-screw clamp (18, 20) and bracket for fixed reference to bone-screws that are externally exposed on each of the respective sides of the fracture (following removal of an external fixator), a stiff arcuate arm member of radius at least twice the diameter of the fractured bone, and a goniometer-end mount. The arcuate arm member is adjustably fixed to the bracket for bone-screw reference, and the goniometer-end mount is also adjustably fixed to the arcuate arm member, with a releasably lockable-ball-joint connection for adjusted orientation of an end mounting to the goniometer.