William B Kurtz | Leg Length Guide

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Leg Length Measurement in Total Hip Replacement

patent pending

The main concept about this leg length measurement guide is that by inserting the femoral component prior to cutting the femoral neck, the surgeon can use the femoral component as a reference guide. The surgeon only needs to insert a marker into the ilium at a known distance from the femoral component. This device requires using a stem with a modular neck such as the Profemur by Wright Medical although other modular stems could be used.

Once the stem is inserted into the femur, the leg length device is attached to the femoral component directly in line with the femoral axis. Because the leg length device is in line with the femoral axis, any error between measurements would be minimized and the same leg position that was used for the initial measurement can easily be reproduced for every additional measurement.

The leg length device allows a synthes 7.3 mm cannulated sleeve to be inserted through the leg length device at 5,6,7, or 8 cm above the shoulder of the femoral implant. Typically, the 5 cm opening is used. The cannulated sleeve is inserted until it abuts the ilium. A guide pin is inserted through the cannulated sleeve and into the ilium bone. The cannulated inner sleeve is removed and the cannulated drill is inserted into the ilium over the guide pin and then removed. The 50 mm cannulated screw is then inserted into the ilium over the guide pin.


Cannulated sleeve insertion	Intra-operative fluoro xray of screw in ilium	screw insertion into ilium 90° from femoral axis

The initial leg length measurement is already determined by which 5,6,7, or 8 cm opening is used. The initial total offset still needs to be determined by measuring the distance from the cannulated screw head to the femoral axis (a.k.a. leg length guide). This is accomplished with a stylus that fits into the cannulated screw and stops when the larger diameter of the stylus abuts the head of the screw (as shown below). The amount of the stylus that extends beyond the leg length guide is measured so that it can be recreated at the end of surgery by selecting the appropriate length and angled modular neck and head. If the third picture below measured the pre-operative offset and the fourth measured the post-operative offset, then the total offset would have been decreased 1 cm between the two measurements, and perhaps a head neck combination that increased the total offset 1 cm should be used.


Stylus entering cannulated screw	Stylus abuts screw head	Pre-operative offset	Post-operative offset

The leg length can easily be measured by comparing the location of the stylus on the post-operative measurement to whichever opening was used in the leg length device for the insertion of the screw. Again, the surgeon can measure the leg length and offset with trial components and then select whichever head and neck combination that best recreates leg length and offset.


Pre-operative leg length	Post-operative leg length has been increased 1 cm

The leg position (abduction/adduction, flexion/extension, internal rotation/external rotation) for a second measurement can be restored to the same position as the initial measurement by ensuring that the stylus is perpendicular to the leg length guide. The cannulated sleeve can be inserted into one of the other openings to help visualize when the stylus is perpendicular to the leg length guide. The picture on the left demonstrates a situation where the leg has not been restored to the same position because the axis of the cannulated screw (i.e. the stylus) is not perpendicular to the leg length guide. The picture on the right demonstrates proper restoration of the leg position.


Incorrect restoration of leg position	Correct restoration of leg position

Multiple trials and measurements may be preformed without any error of loosening because the attachment of the leg length device and stylus are metal on metal attachments and will not deform or change with time. The picture below shows a total hip replacement with trial head and neck components.

trial reduction with stylus inserted into cannulated screw

Pearls and Pitfalls:

The surgeon must be careful with sudden movements of the leg while the stylus is inserted through the leg length device and into the cannulated screw so that the leg length device does not accidental bend the stylus or dislodge the cannulated screw. The surgeon must also make sure that the leg is not flexed during the insertion of the cannulated screw into the ilium. The screw needs to be inserted into the superior acetabulum and should not be inserted in the posterior acetabulum near the sciatica nerve. It is also only necessary to drill the outer cortex of the ilium with the cannulated drill. The screw should be inserted at least 2-3 cm, but does not need to be fully seated into the bone. A proud screw will be easier to see and feel. The 5 cm opening should be used for most cases.

If the surgeon is concerned about restore the center of rotation of the hip joint as well as leg length and offset, then a trial reduction should be performed immediately after the femoral neck osteotomy and before the acetabulum is reamed. By selecting a trial femoral head with the same diameter as the native femoral head, the surgeon can determine which trial neck and head components accurately recreates the femoral length and offset. The surgeon will also know how much acetabular bone can be removed (decreased acetabular offset) by the surgeon and still be able to recreate the normal total offset. If the surgeon is already at the maximum femoral offset before any acetabulum is reamed, then any additional decrease in acetabular offset might result in an inability to completely restore offset. After the acetabulum is reamed and before the acetabular component is inserted, an additional trial reduction can be performed using a femoral head with the same diameter as the last acetabular reamer. If the same length trial head and neck that recreated the femoral offset is used, then the surgeon can calculate the amount of acetabular reaming and any translation of the center of rotation.

The unique aspects and advantages of this technique are as follows:

1) The device measures both the leg length and offset with improved accuracy because the measurements are taken near the hip joint and in line with the femoral axis.

2) The device can be removed and reinserted during the surgery so it is not in the way during the case. The metal attachment sites guarantee a reproducible measurement. The device is compatible with minimally invasive incisions (I use this device with a 8 cm incision on patients).

3) The device ensures the leg is in the exact same position for both the initial and final measurements.

4) The device can be used before acetabular reaming to determine how much acetabular bone can be reamed and still allow the surgeon to recreate the pre-operative hip position.

This same leg length device can easily be incorporated into a pinless navigation system for hip replacements. For more information about this concept, please email me.

Please feel free to contact me if you have any questions regarding this procedure or would like to obtain the necessary equipment to perform this procedure. I can be reached via email at kurtzwb@tnortho.com or by phone at 615-329-6600.