A method and instrumentation is disclosed for gaining access to areas in and around joints for treatment and to provide new implants and instrumentation adapted for the new method. In a transosseous core approach, the joint is entered through a pathway provided in a portion of a joint bone. Such pathway is preferably made by removing a bone core from the bone in or adjacent to the joint, wherever possible without substantially compromising physical integrity and physiological viability of the joint. A route for the transosseous core approach traverses through a more-accessible bone of the joint which can be aligned with a less-accessible bone in order to facilitate treatment of articular surfaces and/or other structures in the joint. Implant modules are provided which can be inserted into the joint through the transosseous pathway and assembled in situ inside the joint to form an implant assembly.