Keys To Recognizing And Treating Limb Length Discrepancy
Current Insights On Identifying LLD
The clinical identification of limb length discrepancy is often unreliable and confusing. There is poor to moderate correlation of direct method tape measurements to radiographic techniques in assessing LLDs.8,9 However, tape measurements, when taking the average of several measurements with steel tape, provide dependable clinical data.10
Measure actual limb length from the anterior superior iliac spine to the distal aspect of the medial malleolus with the patient supine. Mark the malleolus point with a felt pen so the reference point is the same in each measurement. Measure apparent limb length from the umbilicus to the medial malleolus. Neither method takes into account asymmetrical functional or structural differences that take place distal to the malleolus (i.e. in the ankle mortise, subtalar joint and the calcaneus in relationship to its height, pitch and fat pad thickness). Combining several methods of clinical assessment may be necessary to accurately determine if a discrepancy is present.
I learned a useful method to clinically assess weightbearing limb asymmetry from the late Richard O. Schuster, DPM, who routinely performed this method as part of his biomechanical examination. With the patient standing against a wall facing the examiner in subtalar neutral position, place a T-square along the superior brim of the right and then the left pelvis, and draw a mark on the wall for each side. Ask the patient to step away from the wall and measure and record the relative difference. Repeat this same procedure with the subtalar joint in a relaxed position. If there is a difference with the subtalar joint in relaxed position and none with the subtalar joint in neutral position, then there is a functional discrepancy. If there is a difference with the subtalar joint relaxed and in neutral position, then it is probably structural in nature.
Palpation of the anterior or posterior superior iliac spine or the superior brim of the pelvis with the patient weightbearing may detect LLDs that are as small as 6 mm.1 Bailey and Beckwith supported the iliac crest drop reliability, reporting that 88 percent of their subjects had a short limb and ipsilateral iliac crest drop.12 Measurement of the relaxed calcaneal stance position should be another method of LLD assessment since differences of 3 degrees or more result in functional asymmetry.13
In any event, measurement or clinical observation of pelvic level does not indicate the location of the discrepancy. Although clinicians primarily employ the Allis sign to detect developmental dysplasia of the hip in newborns and infants, it may help assess relative lengths of the femur and tibia in older individuals. This procedure, also referred to as Galeazzi’s sign, occurs with the patient supine and the knees flexed. In this position, one can easily see the relative height of the tibia (as represented by knee height) and femoral length, which is represented by one knee segment being anterior to the other. Asymmetric thigh folds and buttock creases are also helpful to examine, especially in younger children.
Another method to determine if below-knee discrepancies are present is to have the patient seated with the foot and leg at a right angle and place a carpenter’s level across the knees. The side that the level dips to is the shorter below-knee extremity. Perform this procedure with the subtalar joint relaxed and then in neutral position. One can readily ascertain both structural and functional below-knee discrepancies in this manner.