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7Poller screw (blocking screw)

General considerations

The concept of a poller screw is based on the principle that the malalignment induced by oblique, proximal and distal fractures can be counteracted by the nail-directing effect of the screw. Therefore, its position should aim to counteract the anticipated displacement of the fracture. Most often, it is therefore inserted in the short side in the distal fragment. If there is a wide canal, two screws can be inserted, one on either side of the path of the nail. It is technically challenging to insert the poller screw in the exactly correct position. On one hand, the screw should prevent reaming in the undesired location. On the other hand, it should not impede the reaming process, or nail insertion.

It is better to insert the poller screw prior to reaming and, in cases of unreamed nailing, prior to nail insertion, in order to provide adequate contact between the nail and the screw. If the poller screw is inserted after reaming, the path of the nail is already set and the poller screw may not function. A small fracture screw, or a locking screw, can be used as a poller screw, depending on the local anatomy.

The reaming process in the presence of the poller screw must be performed very carefully in order not to damage the reamer tip.

The most frequent indication for poller screws is an oblique fracture which would tend to shift when the axial knee blow technique is used to close any fracture gap, or when the patient is mobilized.

See also: Stedtfeld HW, Mittlmeier T, Landgraf P et al (2004) The Logic and Clinical Applications of Blocking Screws. J. Bone Joint Surg. Am. 86:17-25, 2004.