Bisection of lower one third of posterior aspect of leg.
Patient is standing in angle of base of gait and the foot is manipulated into the defined STJ neutral position (as the reference postion).
Tibial position is defined as the angle that the bisection on the posterior aspect of the leg makes with vertical. Root et al (1971) believe the bisection should be vertical whereas McPoil et al (1988) and Astrom & Arvidson (1995) found 6-8 degrees of tibial varum in a healthy population.
The angle will be greater if the subtalar joint is in a pronated position rather in it defined neutral postion.
May be more valid to determine tibial position in single limb stance position.
McPoil et al (1988) have shown the measurement of tibial position to be reliable, but there comparison to x-rays, shows that the measurement is more appropriately measuring tibio-fibular position and that the position was best measured in the RCSP and not NCSP.
Clinical use –
• if tibia is more in varus foot will have to pronate more at the subtalar joint to become flat on the ground (this compensation is a risk factor for pathology, but the foot looks relatively ‘normal’ as the STJ has not pronated past vertical).
• if tibia is more in valgus may cause a greater pronatory or supinatory moment to foot