A prosthetic implant utilizes lateral retaining structures as part of the interior surface of the implant to more effectively secure and retain the implant while reducing the overall size and mass of the implant. In one embodiment, the prosthetic implant is provided with one or more T-shaped members extending from the inner surface of the implant, with the cross-member of the T-shaped member forming the laterally retaining structure that mate with a correspondingly shaped channel formed in the bone and are inserted into that channel at one or more oversize locations along the channel. In another embodiment, the prosthetic implant is provided with one or more retentions apertures in a projection structure extending inwardly from the inner surface of the implant that are laterally secured with a force fitted cross pin inserted through the retention aperture.