Abstract: An adjustable length prosthetic implant includes an implant body and an axially received stem. The stem has a threaded portion and an end portion adapted for mounting with a bone. The implant body includes an end portion adapted for mounting with a bone and a tubular sleeve. The sleeve adjustably receives the stem. An adjustment nut is rotatably carried upon the sleeve for threadably engaging the stem to effect telescopic length adjustment of the stem relative to the sleeve. A jam nut is threaded over the stem and forcibly tightened against the adjustment collar to prevent accidental adjustment of the stem. The female thread formation in each of the adjustment collar and jam nut includes a wedge ramp positioned across the thread root for engaging the thread crest of the corresponding male screw formation on the stem to evenly distribute stresses through the screw formations.