The extension (6) has grip portions (7) and coupling portion (8) for connecting the extension to the handle portion of a bone lever or the retractor. The coupling portion comprises C-shaped cross section, which is intended to surround the handle portion of a bone lever or retractor. The clearance of C-shaped cross-section is decreased towards the free end of the coupling portion. The extension is made of stainless steel and titanium. The extension made of fibers such as carbon fiber reinforced plastic.
