Tips and Tricks for Removing Problematic Implants: Screws
Difficulties may be encountered in certain cases when removing conventional screws and metal plates and, in particular, locking screws securing plates and internal fixators.
- Use a new screwdriver with undamaged hex tip.
- If a hexagon socket screw is damaged during assembly, it should be replaced before the next stage of the operation.
- In case of locking screws, the correct tightening torque must be applied. Use the correct torque limiter.
- If the locking screws are fixed angle, avoid wrong angulation.
- Use of the available insertion guide and compliance with the instructions in the operating manual are strongly recommended.
- From the outset, only use undamaged, not worn out screwdrivers. From the outset, only use undamaged screwdrivers to prevent stripping of the recess. Check the screwdriver yourself. If the screwdriver blade slips, the internal recess of the hexagon socket screw will be damaged. For this reason, only the best screwdriver is good enough for removal.
- The hexagon socket must be free from any obstruction down to the base of the recess, so that the entire length of the screwdriver tip can be inserted.
If the hexagon socket has been enlarged (rounded corners) (Fig 1):
- Use a tapered, left-hand thread extraction screw (Fig 2). Always use the extraction screw with the biggest possible diameter.
- First, screw the tapered, left-hand thread extraction screw directly into the damaged hexagon socket.
- If this fails to achieve the desired result, or if the extraction screw is not exactly the right size, the hexagon socket can be drilled out slightly oversize (see below) without cutting off the head. A left-hand thread extraction screw of the correct size can then be inserted into the now-cylindrical hole.
- As it is turned in an anticlockwise direction, the extraction screw must cut into the hexagon socket. The diameter and length of the extraction screw must be such that the taper does not project as far as the base of the recess (Fig 3). The extractor pin can then no longer move forward.
If a screw is jammed or damaged to such an extent that it is no longer possible to remove it using an extraction screw:
- The head of the screw must be drilled out in such a way that it is removed from the shaft (Fig 4). The same procedure applies if an instrumentregardless of whether it is a screwdriver or an extraction screwbreaks off inside the hexagon socket (Fig 5).
- Drilling out without a suitable drill bit and tools is a major problem.
- New instruments for drilling out are now available: Carbide drill bits should be used for drilling out. We now have 4.0 mm and 6.0 mm carbide drill bits (Fig 6). Due to production engineering constraints, these drill bits are short. If required, they can be extended with the aid of a screwdriver extension. This ensures that the drill bit is sufficiently long.
- In addition, especially hardened HSS drill bits can be used. In every discussion about the best drill bits for each application, the carbide drill bit has proven to be by far the best and latest all-round drill bit. These carbide drill bits are disposable and are intended for single use. During sterilization they can cause a film of rust to develop.
- The drill suction device is a very helpful instrument in cases of problematic screw removal (both locked and conventional) (see page 44, Drill Suction Device). It allows an efficient aspiration of the drill chips while at the same time cooling and lubricating the drill bit. The lubricating provides the drilling procedure. The drill sleeve provides guidance of the drill and protection of the surrounding soft tissue.
- Can be left in place.
- However, if they have to be removed, an attempt should be made to grasp the shafts of the screws (Fig 7). In addition to conventional pliers, eg, from the extraction kit, individual instruments can also be used. Powerful dentists pliers are suitable for this purpose.
- If this fails to achieve the desired result, the screw shafts must be bored out using a hollow reamer. The inside diameter should be the same as the outside diameter of the screw. Next the hollow extraction bolt (left threaded) should be rotated in an anticlockwise direction. The shaft of the screw must be removed using a left-hand thread extractor pin (Fig 8).
It is very important to apply an orderly forward strategy and to keep to the algorithm. The instruments must be readily at hand.
- Fully expose and clean the hexagon socket or Stardrive.
- Right from the outset, use the best screwdriver.
- If the socket head has been enlarged, immediately select the appropriate tapered left-hand thread extraction screw.
- If this fails to achieve the desired result, or if the extractor screw or threaded rivet breaks off, immediately begin drilling out, using carbide drill bits and the drill suction device.
If these steps are followed, removing a locked or enlarged screw should not pose any problems from either a technical or time point of view.
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