Mensuration in the lower limb
Measurement is an important part of the clinical examination of the lower limb. Unfortunately, students find difficulty in carrying this out accurately and still greater difficulty in explaining the results they obtain, yet this is nothing more or less than a simple exercise in applied anatomy.
First note the differences between real and apparent shortening of the lower limbs. Real shortening is due to actual loss of bone length — for example, where a femoral fracture has united with a good deal of overriding of the two fragments. Apparent shortening is due to a fixed deformity of the limb (Fig. 148). Stand up and flex your knee and hip on one side, imagine these are both ankylosed at 90° and note that, although there is no loss of tissue in this leg, it is apparently some 2 ft (60 cm) shorter than its partner.
Umbilicus to medial malleolus
Fig. 148 Apparent shortening—one limb may be apparently shorter than the other because of fixed deformity; the legs in this illustration are actually equal in length but the right is apparently considerably shorter because of a gross flexion contracture at the hip. Apparent shortening is measured by comparing the distance from the umbilicus to the medial malleolus on each side.
- Fig. 149 Measuring real shortening—the patient lies with the pelvis 'square' and the legs placed symmetrically. Measurement is made from the anterior superior spine to the medial malleolus on each side.
Anterior superior iliac spine to medial malleolus
Anterior superior iliac spine to medial malleolus
If there is a fixed pelvic tilt or fixed joint deformity in one limb, there may be this apparent difference between the lengths of the two legs. By experimenting on yourself you will find that adduction apparently shortens the leg, whereas it is apparently lengthened in abduction.
To measure the real length of the limbs (Fig. 149), overcome any disparity due to fixed deformity by putting both legs into exactly the same position; where there is no joint fixation, this means that the patient lies with his pelvis 'square', his legs abducted symmetrically and both lying flat on the couch. If, however, one hip is in 60° of fixed flexion, for example, the other hip must first be put into this identical position. The length of each limb is then measured from the anterior superior iliac spine to the medial malleo-lus. In order to obtain identical points on each side, slide the finger upwards along Poupart's inguinal ligament and mark the bony point first encountered by the finger. Similarly, slide the finger upwards from just distal to the malleolus to determine the apex of this landmark on each side.
To determine apparent shortening, the patient lies with his legs parallel (as they would be when he stands erect) and the distance from umbilicus to each medial malleolus is measured (Fig. 148).
Now suppose we find 4 in (10 cm) of apparent shortening and 2 in (5 cm) of real shortening of the limb; we interpret this as meaning that 2 in (5 cm) of the shortening is due to true loss of limb length and another 2 in (5 cm) is due to fixed postural deformity.
If the apparent shortening is less than the real, this can only mean that the hip has ankylosed in the abducted, and hence apparently elongated, position.
Note this important point: one reason why the orthopaedic surgeon immobilizes a tuberculous hip in the abducted position is that, when the hip becomes ankylosed, shortening due to actual destruction at the hip (i.e.
The lower limb
The lower limb
Fig. 150 (a) Nelaton's line joins the anterior superior iliac spine to the ischial tuberosity— normally this passes above the greater trochanter. (b) Bryant's triangle—drop a vertical from each superior spine; compare the perpendicular distance from this line to the greater trochanter on either side. (There is no need to complete the third side of the triangle.)
true shortening) will be compensated, to a considerable extent, by the apparent lengthening produced by the fixed abduction.
Having established that there is real shortening present, the examiner must then determine whether this is at the hip, the femur or the tibia, or at a combination of these sites.
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