Assumed to be a more valid representation of rearfoot function, as it takes into account how much compensatory movement is occurring at the midtarsal joint (more motion occurs at the talonavicular joint than the subtalar joint when the subtalar joint is pronated and supinated). Navicular drift measures the transverse plane motion of the navicular as the foot moves from it relaxed position to its defined subtalar joint neutral position (first proposed by Menz, 1998). Navicular drop measures the sagittal plane motion of the navicular as the foot moves from it relaxed position to its defined subtalar joint neutral position (first proposed by Brody , 1982).
Navicular drop = amount of ‘arch’ flattening
Navicular drift = amount of medial talo-navicular bulging
• small mark with pen is placed on most medial aspect of navicular tuberosity
• patient is placed in their relaxed ankle and base of gait
• a business card or something similar is used to mark the height of the navicular from the ground
• the foot is then place in its defined subtalar joint neutral postion
• the height of the mark on the navicular is again marked on the card
• the difference (either measured or observed) between the two marks is the ‘navicular drop’
• the business card is now placed flat on the ground and the shaft of the pen held vertically against the medial side of the navicular while the foot is still in its defined subtalar joint neutral position. The pen is used to mark this position on the business card
• the foot is now place in its relaxed position and the position is again marked on the card with the shaft of the pen held vertically against the navicular
• the difference (either measured or observed) between the two marks is the ‘navicular drift’
• observe or measure the magnitude of navicular drift and drop, as well as the ration between the two measurements
• the relaxed position of the navicular drift and drop could be measured in the single limb stance positions
If measured and used for research – will need to control for foot length – larger feet will have larger amounts of navicular drift and drop.
Cross check navicular drift with MTJ oblique axis clinical determination.
• results of reliability studies are mixed. Poor reliability reported by Vinicombe et al (2001) and Picciano (1993) and good reliability reported by Mueller et al (1993) and Sell et al (1994).
• reliability may be dependant of the prominence of the navicular tuberosity (ease of finding same point at subsequent measurement)
• reliability of navicular drop and drift measurements are also dependant on reliability of finding the defined subtalar joint neutral position, which has been shown to not have good reliability
• measure of the amount of compensation in the midfoot for proximal or distal variation during static stance
• Brody (1982) considered that greater than 1cm of navicular drop represented excessive pronation.
• very few studies using these measurements have controlled for foot length
• the ratio between the two measurements may be more important than the magnitude of any one of them. Could be assumed that they should be about the same
• ratio between two may be important for orthoses prescribing and prognosis. A greater amount of compensatory motion in the sagittal plane, as indicated by navicular drop being greater than navicular drift, may be more effectively controlled by something under the foot (eg arch support). A greater amount of compensatory motion in the transverse plane, as indicated by navicular drift being greater than navicular drop, may be less effectively controlled by an orthoses under the foot (eg may need medial flanges on orthoses).