Assumed to represent the centre of the axial load of the lower leg.
Can be very subjective source of error when taking measurements.
• leg rotated to place posterior aspect of calcaneus in frontal plane
• posterior aspect of leg is divided into thirds
• lower third is bisected half way between the medial and lateral aspect of the lower leg by using the medial and lateral ‘horizons’ of the leg as reference points for the bisection
• the line is drawn at a level from above the malleoli and below the soleal muscle belly
Sources of error:
• posterior aspect of calcaneus not in the frontal plane