Chana Femoral Neck Targeting Device for Hip Resurfacing
An easy to use, accurate targeting device has been developed for both open and minimally invasive hip resurfacing. This allows precise placement of a guide wire into the centre of the femoral neck in both antero posterior and lateral planes.

The Device
The device is suitable for open and anterior posterior surgical approach and also posterior minimally invasive approach, for hip resurfacing.



1.Handle 2.Screw mechanism 3.Parallel guide tunnels 4.Guide sleeves to take various diameter wires 5. Femoral neck footplate with long horizontal rod 6. Femoral footplate with spikes 7.Srewdriver 8.Repositioning jig

Concept
The device relies on the fact that shoot through lateral X-rays of femoral head and neck will show the anterior and posterior cortices of the femoral neck are parallel.

A line drawn equidistant from the anterior and posterior cortices will find the central axes of the femoral neck in the lateral projection.

Method
Once the femoral head is dislocated from the acetabulum, the minimum anteroposterior diameter of the femoral neck is measured using a calliper. (Fig.1) Radius of the minimum anteroposterior diameter is calculated. Two guide sleeves, to take appropriate size guide wire are screwed onto the parallel guide tunnels in the device.

Two guide wires are inserted through the guide sleeves and the distance between the pointed ends of the guide wire is adjusted using the screw mechanism. One revolution of the screw mechanism in a clockwise direction moves the guide wires closer to each other by one millimetre. Similarly one revolution in an anti-clockwise direction diverges the guide wires by one millimetre.

The distance between the guide wire tips is set to the anteroposterior radius. The long horizontal bar of the footplate (5) is engaged through the hole in the device and is locked into position using the butterfly nut. It is noted that the top guide wire is parallel to the horizontal long arm of the footplate. The top guide wire, when advanced through the guide sleeve, lies parallel and just below the small footplate with its two spikes (6).

The superior and inferior head-neck junction is marked on the dislocated head. (Fig.2)

Midpoint of the femoral head is marked on the femoral head. Another superoinferior midpoint is marked posteriorly on the middle of the femoral neck, using a marker pen or diathermy. Another such midpoint is marked at the base of the neck posteriorly. All three midpoints are joined to give the midline on the anteroposterior projection of the femoral neck. The femoral neck is positioned in the horizontal plane by rotating the femur. The spiked femoral footplate is placed on the posterior cortex of the femoral neck, in line with the marked mid-line on the posterior aspect of the femoral neck.

With the handle of the device held vertically, the guide wire through which the inferior guide sleeve is power driven into the femoral head and neck. This will give accurate position of the guide wire in the mid anteroposterior and superoinferior planes of the femoral neck.

The device is removed and the guide wire is left in situ. The femoral notch guide is slipped over the guide wire and rotated circumferentially onto the neck at the head-neck junction to make certain that no notching will occur. If however notching is deemed to occur, the repositioning guide jig is secured on the targeting device.

The screw mechanism must be rotated clockwise fully until it stops rotating any further. The repositioning jig can then be secured onto the targeting device using the screwdriver. The top guide wire repositioning sleeve is inserted over the guide wire in the femoral head neck. The guide wire repositioning sleeve can be rotated circumferentially round the guide wire to find the most appropriate point. A second wire is placed onto the inferior guide repositioning sleeve. The initial guide wire is removed and a further check is made to make certain that notching does not occur.

In case of a large posterior femoral head osteophyte the femoral footplate 5 will catch the osteophyte preventing footplate 6 from lying on the femoral neck posteriorly. In this case a shallow trough is made into the posterior femoral osteophyte in line with the posterior mid line to allow 6 to rest on the femoral neck. The trough is shallow and will be removed when the peripheral cut of the femoral head is made.

Supplier:
Comis Orthopaedics Ltd
15 Aspen Court, Bessemer Way, Rotherham, South Yorkshire, S60 1FB
Tel/Fax: +44 (0) 1709 367 700
E-mail: info@comisorthopaedics.com