An improved uni-compartmental implant has a shaft having a proximal end attached to a head and a distal end, and one or more raised portions spaced apart along the shaft to resist back-out. The length between the head and distal end is preferably less than 50 mm, the distal end of the shaft has a diameter on the order of 2 to 3 mm, the proximal end of the shaft has a diameter on the order of 2 to 4 mm, and the head has a diameter ranging from 4 mm or less to 20 mm or more, making the device suitable for knee arthroscopy and other applications. The shaft and/or raised portions may include a bone-ingrowth or bone-ongrowth surface, and the shaft and/or raised portions may be made of a fiber-metal. The head portion is preferably ceramic, though a chrome-cobalt alloy, titanium, or other bio-compatible material may be used. The head portion may have a bi-convex shape, a piano-convex shape, or a concave-convex shape.