First ray range of motion:
• first metatarsal head is griped with the thumb and forefinger of one hand while the thumb and forefinger of the other hand grips the lessor metatarsal heads
• the subtalar joint is held approximately neutral and the midtarsal joint is pronated (by everting the forefoot on the rearfoot)
• the dorsiflexion and plantarflexion excursion of the first metatarsal head relative to the second is noted
No normal range of motion is known, but generally considered that there should be about 5mm in each direction (10mm in total). Greater than 15mm could be considered hypermobility.
If dorsiflexion is greater than plantarflexion dorsiflexed first ray/metatarsus primus elevatus.
Sources of error:
• STJ not neutral or MTJ not pronated
• first ray plantarflexion is needed if the first metatarsophalangeal joint is to dorsiflex (add Roukis et al ref)
• a dorsiflexed first metatarsal is a primary aetiological factor in hallux abducto valgus and hallux limitus
• a correlation between mobility of the first ray and dynamic function has been shown
Transverse plane range of motion of the first ray:
Normally no motion is available in the transverse plane – may get some in hallux abducto valgus.
To determine this, the hallux is griped by the hand and a retrograde force is applied through the hallux in an attempt to abduct the first ray (increase intermetatarsal angle). A distraction/pulling force is applied to the hallux while a force is applied to the lateral aspect of the first metatarsal head to attempt to decrease the first intermetatarsal angle.