In the May 2004 Instructional Course Lecture, "Soft-Tissue Balancing
of the Hip. The Role of Femoral Offset Restoration"
(2004;86:1078-88), by Charles
et al., text was inadvertently omitted from the section entitled "Limb
Length" on page 1085. The text should read:
There are several methods with which limb length can be measured
radiographically. Two of the more common techniques will be described.
The first method consists of drawing a horizontal line through two points
located at the inferior aspect of the ischial tuberosities. Alternatively, a
horizontal line can be drawn between the inferior aspects of the acetabular
tear-drops, which may be more reliable points of reference than the ischia.
The teardrop is a more discrete anatomic structure, and therefore its vertical
position is not affected as much by rotation of the pelvis27. A
vertical line is then extended perpendicularly from the horizontal reference
to the estimated center of each femoral head. The difference in length between
the two vertical lines ("A" — "B") represents an
estimate of the limb-length discrepancy. Alternatively, two lines can be drawn
through the center of the lesser trochanter of each femur and parallel to the
ischial line. The net difference in height between the lesser trochanter and
ischium or femoral head and ischium is then measured. Finally, all
measurements should be reduced by a factor of approximately 20% to account for
the enlargement of the osseous anatomy on the radiographs28.
Therefore, in this example, increasing the neck length in the affected right
hip by the distance "A" — "B" and then
multiplying this value by 0.80 (to account for the 20% magnification) should
equalize the limb lengths (Fig. 9).
It is important to note that, although radiographs are useful adjuncts for
determinations of limb lengths, radiographic measurements should be adjusted
on the basis of the findings of the relevant clinical examination. For
example, a unilateral adduction contracture will result in a perceived
increase in limb length on the affected side, whereas a fixed flexion
contracture tends to result in an overestimation of any shortening that may be
present. Furthermore, patients with fixed pelvic obliquity tend to have
overcorrection or undercorrection as a result of an alteration in the relative
positioning of the osseous landmarks used for templating and determinations of
limb lengths. Accordingly, one of the most important questions that the
clinician should ask the patient is what is his or her perceived limb-length
discrepancy (if any)3.