Procedure
- The patient stands upright with knees maximally extended and the feet beside each other.
- Stand behind the patient once you have told them what you are about to do.
- Place one or more planks of different thicknesses (0.5, 1 or 2 cm) underneath the shortest leg [Figure 51].
Figure 51
Pay attention to:
- Whether the pelvis (iliac crests and superior posterior iliac spines) reaches a horizontal position (with knees extended).
- Assess how many cm of heel elevation is required to reach a horizontal pelvic position. For this, inspect/palpate the pelvis both on the ventral and dorsal sides (eyes at pelvis level).
Interpretation
If the creases of the knees are of equal height following the correction, the length difference has been localised in the lower leg. If the buttock folds are of equal height following the correction, but the knee folds are not, the length difference has been localised in the upper leg. If the pelvic tilting is still present, this may be caused by an asymmetric pelvis.
This method has an inter-observer variance of 0.5 cm. X-ray measurement is far more reliable. Corrections of leg length differences of between 1 and 2 cm are often achievable using conservative measures (for example heel elevation). In principle, the complete difference, as measured using the plank test, is corrected. Leg length differences of 1 cm are often only corrected in runners.