![LEG LENGTH DISCREPANCY [ANISOMELIA]This is the term used to describe inequality in the length of the two limbs comparati...](https://img3.findhealthclinics.org/924/453/232984539244537.jpg)
14/03/2023
LEG LENGTH DISCREPANCY [ANISOMELIA]
This is the term used to describe inequality in the length of the two limbs comparatively.
Leg length discrepancy can be categorized into two based on where the main source of the leg length difference can be traced as;
1. TRUE LEG LENGTH DISCREPANCY
2. APPARENT LEG LENGTH DISCREPANCY.
β’TRUE LEG LENGTH DISCREPANCY
True leg length discrepancy, also known as structural leg length discrepancy is a leg length difference which occurs due to difference in the length of the bones; either from the femur or the tibia.
Many compensation patterns can be associated with true leg length discrepancy. These may involve;
1. Pronation; Hip or knee flexion on the longer leg
2. Supination; Hip and knee extension on the shorter leg.
If there is no such compensation, the anterior superior iliac spine and or the posterior superior iliac spine will be lower on the shorter leg resulting in the development of functional scoliosis. As a result, stance time is decreased on the shorter side as well as walking speed or velocity but cadence is increased while step length is decreased.
Many factors can cause true leg length discrepancy. This is to say that, the factors will affect the bony length in a way that will account for one being longer or shorter than the other. These will include; Bony diseases or displasia, neurological conditions, Infections affects the growth plate of the bone.
β’APPARENT LEG LENGTH DISCREPANCY
This is also know as a functional leg length discrepancy. The inequality in the length of the limb in this case has no structural trace, but may be due to an altered mechanics. The length of the bones may be normal but other problems relative to soft tissues may account for the length inequality.
Actually, as we have understood from definition, a leg length inequality which occurs with normal bony lengths will be attributed to different etiology. Often many soft tissue problems may account for apparent leg length discrepancy. Commonly, hip adduction or flexion contracture and or pelvic obliquity.
Despite having these clear ways to identify either two discrepancies, there is a very reliable and sensitive way to establish that, a particular leg length inequality is structural or functional. This brings us to the methods of assessment.
ASSESSMENT OF LEG LENGTH DISCREPANCY
There are different ways clinicians can assess LLD.
Either of the two types of LLD have a specific method used by clinicians to rule them out. This can be done simply by using measuring tape or tape measure and having some landmarks on the body as your references. However, without using measuring tape, there is also another method clinicians can use to determine the limb length inequality and also know which bone is having the problem as in the case of true leg length discrepancy.
In that case, the patient is made to lie in supine. With the knees bent 90 degrees with the feet being flat on the table. clinician then ask the patient to lift the pelvis up so that the buttocks are lifted off the treatment table.
As soon as the pelvis is lifted, if there is height difference in the knees, the tibia is longer on the side where the knee lies superiorly(Figure 4A).
If one of the knees lies more anterior with respect to the other knee however, then it indicates that the femur is extremely longer on that limb(Figure 4B)
If the knees are fully aligned, then the next step is for the examiner to extend the knees passively for another unique and simple testing technique using the tape measure.
In the assessment using the tape measure, the clinician measures from the anterior superior iliac spine (ASIS) to the medial malleolus of both limbs for true leg length discrepancy testing
On the other hand, clinicians measure from either the xiphoid process of the sternum or the umbilicus to the medial malleolus of both limbs for functional leg length discrepancy.
In both cases, the values obtained from the measurement taken from both limbs will then be compared and the differences determined. When the difference is either 1-2cm, it will be considered normal. However, when the difference exceeds 2cm or as mostly regarded, if it greater than 2.5 cm, it will be regard abnormal and treatment may be required.
Leg length discrepancy must be taken serious as far as lower back pain, scoliosis and other spinal problems are concerned. There is a close relationship between low back pain and leg length inequality greater than 9mm according research.
Many authors over the years have noted that, leg length inequality may one way or another contribute to the development of low back especially if the difference is greater than 9mm.
Actually, one must be able to distinguish a leg length which may be normal and that which may be considered abnormal by considering certain figures. Many clinicians consider leg length difference of about 1cm and 2cm as normal. Having any of these figures may not pose any secondary problem and may require little to no treatment. However, when the difference is greater than 2.5 cm, it must be treated serious because this difference may be most likely to poses compensations that may threaten the body mechanics and result to other secondary problems.
Moreover, we must also treat leg length discrepancy with keen attention whenever we are handling total hip arthroplasty. Leg limb inequality is the commonest complication of total hip
arthroplasty. More importantly information regarding LLD are up next. Kindly stay tuned for it.
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