An expandable implantable device sized for occupying space in a cavity formed between small bones in a human hand or foot. Comprising a first smooth surface on which a first small bone may slide. May include an opening extending through the device for promoting fibrotic development through the opening from a direction from both thumb metacarpal and trapezium. An inflation cannula and/or needle may be attached to inflation port and inflation valve for introducing expansion fluid into the device. In some embodiments, an implant is inserted in a deflated mode and positioned so that a thumb metacarpal abuts distal side of the device when expanded, and trapezium abuts a proximal side thereof. At least one of distal side and proximal side include a smooth surface for allowing relative movement of thumb metacarpal or/and trapezium with respect to the device.
