21/08/2025
🦵 Limb Length Measurement
📌 Shortening of the limb is common in hip diseases. Some of the shortening is compensated by the patient by 🔻 tilting the pelvis down on that side, 🦶 plantar flexing the foot, and 🦵 flexing the knee on the normal side.
🩺 While examining for shortening, it is important to note: whether shortening is present; if yes, whether it is true or apparent shortening; and if it is true shortening, whether it is from the hip (supra-trochanteric) or from some other part of the limb.
📐 It is customary to measure the apparent length (the length of the limb with compensatory mechanisms allowed) and true length (the actual length of the limb after removing the compensatory mechanism). Accordingly, after comparing the lengths on the two sides, apparent and true shortenings are calculated.
ℹ️ It is the apparent shortening which concerns the patient i.e., the shortening which remains even after compensation by the body. True shortening is of significance to the clinician for diagnosis, as it is the shortening produced by the disease due to actual destruction or shortening of the bone.
🔄 There may be a situation where all bones and joints are all right, but the limb is 'short'. This will be due to deformity at the hip, and will be called apparent shortening. There will be no true shortening in this situation. On the other hand, there may be true shortening of the bones, but the body, by compensating this shortening, may make the leg appear equal. Hence, there will be no shortening effectively (no apparent shortening), although true shortening is present, and can be detected by unmasking the compensatory mechanism.
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📏 Measurement of Limb Length
📍 Measurement of apparent length (B) : This is simpler to measure. The patient lies supine on the couch, as straight as he can. Both the legs should be parallel and in alignment with the body. Measurement is taken from any fixed point in the midline of the trunk (e.g., Xiphisternum, suprasternal notch etc.) upto the prominent tip of the medial malleolus. No attempt is made to correct any deformity while measuring the apparent length.
📍 Measurement of true length(A) : The patient lies supine. The first step is to check whether the pelvis is square. If yes, the length is measured from ASIS to the tip of the medial malleolus. If the pelvis is not square, the same is done first. As the pelvis is square, the hip deformity will show up. The limb length, from ASIS to tip of the medial malleolus is measured in the deformed position of the limb. When the normal limb is being measured for comparison, it is necessary that it be placed in the position as that of the affected limb. Hence, before measuring the normal limb, the pelvis must be squared, and the limb should be in a position, identical to that of the affected limb.
📍 Leg length measurement in standing position: In a hip without deformity, a quick and accurate method of measuring true shortening is as follows. The patient is asked to stand against a wall, facing the examiner. The pelvis may be tilted due to shortening of the limb. The examiner puts wooden blocks under the foot on the shorter side, one after another, till the ASISs on the two sides are level. The thickness of the blocks is measured. This indicates the amount of true shortening. Similarly, if the affected limb is longer, insert wooden blocks under the foot on the normal side, till the pelvis is square. The height of the wooden blocks indicates true lengthening of the affected limb.
🩻 CT scanogram is the radiological method of accurately measuring the limb length.