Such bone screw arrangements are used for the fixation of bones or bone fragments, particularly in the case of bone fractures, in such a way that the bone screw arrangement adjusts in a dynamic manner to changing conditions during the healing process by changing its length.  An example of use would be the treatment of slipped capital femoral epiphysis (SCFE). 
A bone screw arrangement with variable length is disclosed in Document WO 8906940 A1.  In the prior art arrangement, provision is made of an anchoring screw configured as a bone screw, which is axially displaceably received in a guide formed in the interior of a guide screw.  In this manner it is possible for the bone screw arrangement, to change its overall screw length in response to bone growth, for example, when the bone screw arrangement is positioned in a human or animal body.  As the overall length changes, a guide element formed at the head end on the anchor screw is guided in the axial direction in the guide.  The guide element formed on the anchor screw is configured with a, hex head, which is interlockingly received in the guide on the guide screw such that the anchor screw turns conjointly with the guide screw as the latter is turned. 
Document DE 10 2005 007 674 A1 relates to an orthopedic fixation system.  In using the system, a bearing sleeve is screwed into a bone plate.  In its interior the bearing sleeve receives a bearing screw, which has a bone thread on its distal end.  A head of the bearing screw is freely movable in the axial direction in the interior of the bearing sleeve until the head reaches an annular step, which forms a distal stop for the head.  The annular step prevents the bearing screw from extending any further. 
Document DE 692 11 561 T2 concerns a device for inserting an, implant.  The implant comprises a sleeve, into which a bolt portion is screwed.  In each relative position, the sleeve and the bolt portion are secured against relative axial displacement by an outer thread on the bolt portion and an inner thread on the sleeve engaging with one another. 
Document US 20040127900 A1 concerns a bone plate arrangement in which a bone plate has a plurality of through-holes in which a corresponding bone screw is screwed during the implanting process. 
A bone screw arrangement is described in Document US 20050143735 A1, in which a screw shank is inserted in a compression portion in such a way that the outer thread on the screw shank ultimately cooperates with the inner thread on the compression portion. 
Document U.S. Pat.  No.  2,801,631 also discloses a bone screw arrangement in which a bolt portion has a bone thread on its end.  In use, the bolt portion is screwed into a sleeve.