BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of a first part of the adapter,
FIG. 2 shows a perspective view of a second part of the adapter,
FIG. 3 shows a perspective view of a bioabsorbable screw,
FIG. 4 shows a perspective view of an exploded assembly comprising parts of the system of the invention,
FIG. 5 shows a perspective view of the system of the invention,
FIGS. 6-8 and 10 and 11 show cross-sectional views of a torque limiting junction,
FIG. 9 shows a perspective view of an adapter (a partial view),
FIG. 12 shows schematic views of possible modifications of the system according to the invention,
FIG. 13 shows a perspective view of an adapter (a partial view),
FIG. 14 shows a view of the adapter of FIG. 13 in extended position,
FIG. 15 shows a perspective view of the system of the invention,
FIG. 16 shows a view of the system of FIG. 15 in extended position, and
FIG. 17 shows a top view of a head of a polymeric screw.
DETAILED DESCRIPTION
An example of the first part of the adapter is shown in FIG. 1. The head of the first part comprises a hexagonal slot 1 that fits the AO/ASIF hexagonal screw driver. The first part 32 is also formed in the shape of an AO/ASIF metallic screw head so that it fits the screw holding sleeve 2. In the middle of the first part 32, there are ridges 3 that form part of the torque-limiting element. The sequential ridges 3 are on the periphery of a shaft 34. The ridges 3 are shaped so that they allow torsion in the clockwise direction when the maximum torque to the clockwise direction is exceeded, but grip the counterpart when the first part is turned in counterclockwise direction (in this case, the polymeric screw is screwed to the clockwise direction and screwed off in the counterclockwise direction). In this case, the ridges incline in the counterclockwise direction, i.e. in the screwing-off direction. The end portion 4 of the first part is formed so that it attaches firmly to a recess 8 in the counterpart.
The counterpart of FIG. 1, i.e. the second part 33, is shown in FIG. 2. There is a cavity 5 of the same form as in FIG. 1 so that the ridges 3 fit inside the part. There are four bending walls 6 that allow the torque-limit to function with the clockwise torsion. The four bending walls are separated with four slots 7. The counterpart, i.e. the first part 32, fits the recess 8 in the middle of the second part 33. The other end of the part has two forks 9 that fit the bioabsorbable screw head. Small tabs 10 allow the part to attach firmly to the screw so that the adapter only comes off with a bending motion.
The polymeric screw 31 is shown if FIG. 3. The head 11 of the screw is formed to fit the adapter by two cuts 12 in both sides of the head. Flutes 13 that fit the tabs of the adapter attach the screw to the adapter. The screw comprises threads 14 and a core 15 underneath the threads below the head 11.
There is an exploded assembly of the screw-adapter combination in FIG. 4. The different parts are positioned in their proper places before the assembly. The built up adapter-screw is shown in FIG. 5.
The FIG. 6 shows one modification of the torque-limiting part of the adapter. The shaped pinion 16 allows rotation in the clockwise direction and prevents it in counterclockwise direction (in this case, the polymeric screw is screwed to the clockwise direction and screwed off in the counterclockwise direction). The teeth of the pinion incline in the counterclockwise direction, i.e. in the screwing-off direction. The walls 17 around the pinion 16 restrict the rotation. The slots 18 allow the walls 17 to bend, and with the proper torque, allow the pinion 16 to turn.
In FIG. 7 there is another modification of the torque-limiting part of the adapter. The shaped pinion 20 is shaped so it can bend walls 21 around it. The slots 22 allow bending of the walls 21 with the proper torque. The counterclockwise rotation is prevented by the blades 24 of the pinion 20 and the walls 21. The blade 24 have a rounded edge and a rectangular edge. The rounded edges of the blades 24 allow the rotation when necessary but the rectangular edges prevents the rotation.
FIG. 8 shows still another modification of the torque-limiting part of the adapter. On the shaft 34 of the first part of the adapter there are blades 36 which have rounded edges and incline in the screwing-off direction. The shape of the blades allows the rotation in the clockwise direction and prevents it in the counterclockwise direction (in this case, the polymeric screw is screwed in the clockwise direction and screwed off in the counterclockwise direction). In this case, the blades have rounded edges. Walls 35 keep the blades 36 in their position but when the torsional force is high enough the walls 35 bend and allow the rotation. In the current modification, the walls 35 are individual columns as shown in FIG. 9.
FIG. 10 shows blades 37 which are formed on the shaft 34 and walls 36. The blades comprise a rounded edge and a rectangular edge. The function of the adapter is the same as described also in connection with the other figures.
FIG. 11 shows blades 38 which are formed on the shaft 34 and walls 39. The blades have rounded edges and incline in the screwing-off direction. The function of the adapter is the same as described also in connection with the other figures.
FIG. 12 shows different modifications of the instrument-adapter-screw junctions. The screw 25 can be attached to the adapter 26 with a male or female connection. Simultaneously the instrument 27 can be attached to the adapter 26 with a male or female connection.
FIGS. 13 and 14 show still another modification of the torque-limiting part of the adapter. The first element comprises a laterally rotating pinion 40. The pinion 40 comprises blades 41 which become larger towards the periphery of the pinion 40.
The second element comprises walls 42 whose upper side is bevelled in the screwing direction. The walls 42 are placed radially and their height becomes smaller towards the center of the second part. The underside of each blade is stepped so that the walls will grip the steps 43 of the blades 41 when the screw is screwed off.
The first element also comprises a shaft 44 which is compatible with a hole 45 in the second element. When the shaft 44 is placed in the hole 45 the torque-limiting junction is accomplished.
FIGS. 15 and 16 show a modification of the system of the invention. The system comprises the first part 32 of the adapter but the second part is omitted. The first element of the first part 32 comprises fingers 50. The head of the polymeric screw 11 has cutting-ins 51 which serve as the second element. The fingers 50 and the cutting-ins 51 form counterparts. The fingers 50 bend outwards when the maximum torque in the screwing-in direction is exceeded. However, the screw 31 may still be screwed off if desired.
FIG. 17 shows the head of the polymeric screw 31 shown in FIGS. 15 and 16. The periphery of the head comprises the cutting-ins 51 so that teeth 52 are formed therebetween. The teeth 52 incline in the screwing off direction.
A skilled person can readily construct other modifications in addition to those shown in FIGS. 1-17 after seeing the principle of this invention. Further, it is possible to use both left-handed screws or right-handed screws and a skilled person will understand how to modify the adapter according to the screw to be used.
Patent Application
20070274800
