Glossary of Terms
Absolute discrepancy
The difference between the measured lengths of the long and short legs.
Apparent length
The length of the leg a s measured form the umbilicus to the medial malleolus.
In assessing patients with leg length discrepancy it is important to have available blocks of calibrated thickness. These can be placed under the heel of the short leg to simulate the effect of corrective treatment.
Computerized tomography
A radiological technique in which a spectrum of x-ray views is analyzed mathematically to produce a three dimensional representation. It can be used to measure leg length discrepancy.
A surgical procedure which results in the arrest of growth in a physis.
Functional leg length discrepancy
An asymmetry which makes the patient with equal leg lengths function as if a leg length discrepancy were present.
Growth inhibition
The percent slowing of the growth of the short leg compared to the long. It is calculated by determining the amount of growth of both legs over the same period of time, calculating the difference, and dividing the result by the growth of the long leg.
Growth rate
This term is used in a somewhat unusual way by Pedipod/LLD. 'Rate' usually is expressed with respect to time, but Pedipod/LLD, except when using the Menelaus method, ignores the passage of time and considers only skeletal maturity. Since skeletal maturity is so difficult to measure accurately, this concept is only valid when comparing the 'rate' of one leg to that of the other.
In the context of leg length measurement magnification occurs in radiological techniques in which the x-ray beams passing through the measurement points are divergent. This results in the absolute measurement on the x-ray being greater than that in the limb.
In the context of leg length discrepancy maturity is the state reached when the growth plates of the tibia and femur have closed.
Normal growth rate
The normal growth rate of the long leg is assumed to be the rate determined from all data gathered before the first operative procedure on that leg.
A radiological technique for measuring the lengths of the legs. In this technique a radiopaque ruler is placed on the table and the hips, knees and ankles are exposed separately on a 14 X 34 inch film
Pelvic Obliquity (1)
The difference in the heights of the two iliac crests, expressed in centimeters, with the patient standing with the knees extended, the legs together, and weight on both heels.
Pelvic Obliquity (2)
The angle between the longitudinal axis of the trunk and the perpendicular to the transverse axis of the pelvis.
Pelvic Obliquity (3)
The angle between the top surface of L5 and the transverse axis of the pelvis.
Real length
The length of the leg as measured from the anterior superior iliac spine to the medial malleolus.
Regression coefficient
A number which expresses how closely the relationship between two sets of data can be described by a straight line. The regression coefficient for data which is perfectly linear is 1.
A radiological technique for measuring the lengths of the legs. This technique is similar to the orthoroentgenogram except the film is moved beneath the patient between exposures so that the exposures of the hips, knees and ankles all appear on one 14 X 17 inch film.
Scout film
A preliminary lateral view use in computerized tomography to position the transverse sections. The CT software can be used to measure true distances on this view.
Skeletal age
An estimate of chronological age based on the x-ray appearance of the skeleton. In the context of leg length discrepancy it is an estimate of the patient's stage of maturation.
Straight Line Graph
A special graph originally designed as part of a graphic method for representing growth data in a manner to facilitate analysis and prediction. Its principle feature is that the growth lines of the legs can be represented as straight lines.
Swing phase
The phase of gait beginning with toe off and ending with foot strike.
A radiologic technique for visualization of the legs which can be used for leg length measurement. It is a single antero-posterior exposure of the legs on a 14 X 34 inch film with a 72 inch tube to film distance.
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