A method for strengthening a laminate composite material having layers of fiber mats in the X-Y plane. In one form, the cage includes a plurality of spaced apart walls comprising a biodegradable polymeric material ; an osteoconductive mineral coating on at least a portion of the walls; and a bioactive agent associated with the polymeric material andor the coating. The first weld region includes a first weld formed on the first body part and a first weld formed on the second body part. Mounting the cap 7 on the socket body 3 requires no fastening members such as screws, thereby reducing the number of parts thereof and the number of assembly steps in comparison with those which require fastening members.