A difference in leg length of more than 2 cm may be the cause of a limping gait of the child. The compensatory mechanism observed during the examination is a non-structural scoliosis, also referred to as functional or compensatory scoliosis.
Besides a dislocated hip joint, the causes of a difference in leg length are: a congenital abnormality, trauma, an infection, a tumour or paralysis. An apparent difference in leg length may be seen in the case of severe structural scoliosis and, for example, in the case of contractures of the hip, knee and/or ankle. This is observed when the block test is performed as the original difference in leg length remains.
Test For The Presence Of Pelvic Asymmetry Without Any Difference In Leg Length
This test is only useful if the child can already stand and if pelvic asymmetry was noted.
Procedure
- Ask the child to sit on the examination table with the legs dangling.
- Palpate the anterior superior iliac spine (ASIS) with the thumbs and assess at eye level whether these are at the same height.
- If this is not the case there is pelvic asymmetry, which could be a consequence of an adduction contracture or an asymmetric pelvis (e.g. after poliomyelitis) or structural (in particular paralytic) scoliosis.
- If both ASIS are at the same height in this situation, there is pelvic asymmetry due to a different in leg length, and the general leg length test and the block test should be performed.
- In addition, it is important to determine whether the leg that is too short is really too short or whether the other leg is too long. Which part of the leg is too short should also be established.
Test To Compare Span And Height
This test should be performed if you observed a difference in leg length and have corrected this using blocks under the leg that is too short.
Procedure
- The child should stand up straight, with blocks under the leg that is too short so that the pelvis is once again horizontal (the anterior superior iliac spines should be at the same height).
- Measure the height of the child in this position.
- Next, have the child spread their arms as far as possible in the horizontal plane and use a measuring tape to measure the distance between both middle fingers (the arm span).
The shorter leg is too short if the arm span is virtually the same as the body length. The longer leg is too long if the arm span is less than the body length. In other words: the span is normally about the same as the height.