in fig1 , the interspinal prosthesis 1 with the counterpart 6 is shown in the assembled state . the central piece 2 of the prosthesis 1 , with the inner end 7 of the prosthesis 1 , adjoins the counterpart 6 . at the outer end 8 of the prosthesis 1 , the two processes 3 are disposed perpendicularly to the central axis 4 and diametrically opposite to one another . in the embodiment shown here , the processes 3 are constructed as halves of an ellipsoid body . the also radial and diametrically opposite to one another processes 3 of the counterpart 6 are disposed symmetrically to a plane , which is orthogonal to the central axis 4 . three radial cams 17 , which are disposed symmetrically when viewed in the cross - section of the prosthesis 1 parallel to the central axis 4 , protrude at the central piece 2 at the inner end 7 of the prosthesis and engage complementary grooves 18 at the counterpart 6 , function as twisting safeguard between the prosthesis 1 and the counterpart 6 . coaxially with the central axis 4 , the central part 2 includes a depression 5 , which penetrates from the inner end 7 into the prosthesis 1 up to a depth t . the counterpart 6 has a peg 16 , which is constructed to be complementary to the depression 5 and accordingly , during the assembly of the prosthesis 1 and the counterpart 6 , can be introduced into the depression 5 . furthermore , the prosthesis 1 comprises a fixing - in - position bolt 19 with a bolt head 26 , which can be brought into contact with the outer end 8 of the prosthesis 1 . the fixing - in - position bolt can be passed coaxially with the central axis 4 through the prosthesis 1 and locked by means of a slide lock 27 in the peg 16 of the counterpart 6 , so that the prosthesis 1 can be locked detachably with the counterpart 6 . a borehole 20 , coaxial with the central axis 4 , passes through the fixing - in - position bolt 19 and the counterpart 6 , so that the prosthesis 1 and the counterpart 6 can be collapsed radially . fig2 shows a further embodiment of the prosthesis with the counterpart 6 in the assembled state . the depression 5 passes through the prosthesis 1 coaxially from the inner end 7 up to the outer end 8 . during the assembly of the prosthesis 1 and the counterpart 6 , the peg 16 at the counterpart 6 is pushed into the through depression until the inner end 7 of the prosthesis 1 comes up against the processes 3 of the counterpart 6 . moreover , a borehole 20 is drilled through the counterpart 6 between the outer end 15 and the inner end 14 . the coupling means 11 are constructed as a screwed connection , the screw 21 being passed through the depression 5 at the prosthesis 1 and through the borehole 20 at the counterpart 6 from the outer end 8 of the prosthesis 1 up to the outer end 15 of the counterpart 6 and bolted with a nut 22 . in addition , the prosthesis 1 is provided with a hollow space 12 , so that the walls 13 of the hollow space can be collapsed or , by filling the hollow space 12 with a filling material , expanded . the embodiment , shown in fig3 , differs from the embodiments described above in that the peg 16 at the counterpart 6 is passed completely through the depression 5 at the prosthesis 1 , so that the inner end 14 of the counterpart 6 aligns with the outer end 8 of the prosthesis 1 furthermore , the counterpart 6 has several boreholes 20 , which are continuous from the inner end 14 to the outer end 15 and the axes of which extend parallel to the central axis 4 . the cerclage wires 23 , by means of which the interspinal prosthesis 1 and the counterpart 6 are fixed in position , can be passed through these boreholes 21 . the embodiment , shown in fig4 , differs from those shown in fig1 owing to the fact that the coupling means 11 comprise a locking bolt 28 , which can be passed through the borehole 20 , which passes through the prosthesis 1 and the counterpart 6 coaxially with the central axis 4 . the locking bolt 28 , with its head 29 , can be brought into contact with the outer end 15 of the counter part 6 and has , at its tip , radially and elastically deformable cams 31 , which , when the prosthesis 1 and the counterpart 6 are assembled , can be locked in an eccentric relief 30 , the diameter of which is larger than the diameter of the borehole 20 , so that the prosthesis 1 and the counterpart 6 are held together . for introducing the locking bolt 28 into the borehole 20 , the cams 31 can be compressed perpendicularly to the central axis 4 by means of axially disposed slots 32 , so that the locking bolt 28 can be passed through the borehole 20 , while , in the assembled state , the cams 31 spring back elastically and latch into the eccentric relief 30 at the prosthesis 1 . a hole is drilled through the locking bolt 28 coaxially with the central axis 4 , so that a pin 25 can be passed through it , as a result of which a radial deflection of the cams 31 is prevented in fig5 , a further embodiment of the inventive prosthesis 1 with a counterpart 6 is shown . at the outer end 8 of the prosthesis 1 as well as at the outer end 15 of the counterpart 6 , the processes 3 are mounted once again perpendicularly to the central axis 4 and diametrically opposite to one another , the processes 3 in this embodiment having a semicircular cross sectional surface parallel to the central axis 4 . the depression 5 passes through the prosthesis 1 from the inner end 7 to the outer end 8 coaxially with the central axis 4 . in the depression 5 , there is an internal thread 36 with a very large pitch . adjoining the inner end 14 , the counterpart 6 once again has a peg 16 , which has an external thread 33 that is complementary to the internal thread 36 , so that the prosthesis 1 and the counterpart 6 can be fastened detachably to one another by means of this screwed connection . a first saw tooth - like system 34 is mounted at the counterpart 6 between the peg 16 and the processes 3 and can be brought into engagement with a complementary second tooth system 35 at the inner end 7 of the prosthesis 1 during the assembly of the prosthesis 1 and the counterpart 6 so that , due to the asymmetric configuration of the saw tooth systems 34 , 35 , a safeguard is provided against the unintentional detachment of the prosthesis 1 from the counterpart 6 .
a prosthesis for use in maintaining an interspinal space is disclosed . the prosthesis may be provided as first and second substantially symmetrical halves . the first and second halves may each have a coupling portion and a process portion . the coupling portions allow the separate halves to be separately fit within the interspinal space and then connected to form a single prosthesis , eliminating the need for cutting connecting ligaments to allow insertion of the prosthesis . various connection and locking arrangements are disclosed to maintain the halves engaged with each other and the interspinal space .