A simple distal interlocking aid for intramedullary nails.

AY Bonshahi, A Cowey, R Vhadra 
 Department of Orthopaedics and Trauma, Royal Bolton Hospital, Minerva Road, Farnworth, Bolton BL4 0JR, UK.

Correspondence Address:
A Y Bonshahi
Department of Orthopaedics and Trauma, Royal Bolton Hospital, Minerva Road, Farnworth, Bolton BL4 0JR, UK.

Full Text

Distal locking of intramedullary nails can be problematic. We present a simple technique to aid freehand locking of an intramedullary nail.

::   Technique

A Steinmann pin is pushed through the spout of a 50 ml bladder syringe as shown [Figure:1]. With the plunger withdrawn the syringe can be used as a radiolucent handle to hold the Steinmann pin against the bone through a nick in the skin. The image intensifier is centered on the screw hole so that it appears as a perfect circle. Initially the tip of the Steinmann pin is placed with some angulation in the centre of the hole. With a few seconds of continuous screening it is possible to angulate the pin to the correct trajectory for the nail hole so that it appears as a dot within the nail hole [Figure:2]. This confirms that the entry point and orientation of the pin are correct. With some hammering the position of the pin is secured and this acts as a punch to guide the drill.

::   Discussion

Locking an intramedullary nail makes the construct more stable and stops rotation of the nail within the bone. The proximal locking is usually done with a jig but nail deformation during intramedullary insertion makes using a jig inaccurate for the distal screws.[1] Most nail systems require a freehand technique for the distal locking which can take 50% of the total screening time.[2] Other methods of aiding distal locking have been described in the literature and include proximally mounted targeting device or laser devices.[3], [4] The proximally mounted device is specific to the type of nail used. It is not as versatile as free hand locking devices, which can be applied to more than one locking nail system. There are a few commercially available hand held radiolucent devices to aid free-hand distal interlocking.[5] The advantages of our device in comparison to the commercial devices are that it is cheap, readily available and easy to use.

The two main reasons for failure in distal locking are incorrect entry point on the bone and wrong orientation of the drill. If either of these two factors is wrong, then the drill will not go through the nail hole. An inaccurate entry point also compounds the problem as the rounded end of the drill bit often slips and it is then difficult to place another drill hole next to the earlier one. Inaccurate distal locking leads to premature failure with breakage of the nail through the nail hole, breakage of the screw or the breaking of the drill bit within the bone.

Our experience has shown that this technique allows quick and accurate distal locking with minimal time taken for screening. In the hands of the senior author (RV), the time taken to distally lock the two screws (from start of screening to insertion of second screw) is 12.5 minutes (range 8-19.2 mins, N=10). The procedure combines the benefit of radiolucency with a trocar technique thereby avoiding slippage of the drill bit. It is also cheap and the materials required are readily available.

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