Reporting a weightbearing foot series can be a daunting process if you are inexperienced and often results in the films being left for somebody else to report. This article attempts to demystify the whole process by providing a structured approach to their reporting.
The weightbearing foot series will usually be composed of a weightbearing DP foot radiograph and a weightbearing lateral foot radiograph with possible additional views as directed by an orthopaedic surgeon or if the radiographers need to highlight an area of pathology.
It is important that alignment is assessed using weightbearing radiographs because the functional position of the bones of the foot is needed. If the radiographs have been performed on a nonambulatory child, simulated weightbearing can be achieved with a plastic board.
It is worth considering that the foot in composed of three sections:
- hindfoot: the talus and calcaneus
- midfoot: the navicular, cuboid and cuneiforms
- forefoot: the metatarsals and phalanges
During the assessment of the radiograph, you should consider alignment, but not forget to review the bones and joints, especially looking carefully for tarsal coalition. It's always worth thinking about bone density too - making a handy A, B, C, D:
Splitting the foot into three sections allows the relationship of the tibia, hindfoot, midfoot and forefoot to be assessed.
The talus has no muscular attachments and is held at the base of the tibia by a complex set of ligamentous attachments. Assessment of the hindfoot therefore relies on reviewing the alignment of the talus and calcaneus.
This is best assessed on the DP radiograph using the talocalcaneal angle. The mid-talar axis should intersect the 1st metatarsal base and the mid-calcaneal axis should intersect the 4th metatarsal base.
In hindfoot valgus there is an increase in the talocalcaneal angle and an apparent medially displaced talus secondary to abduction of the rest of the foot. In hindfoot varus there is decrease of the talocalcaneal angle with relatively parallel mid-talar and mid-calcaneal axes.
Assessment of talar position should be made on the lateral view. The talus may be relatively vertically orientated in hindfoot valgus because of loss of calcaneal support, or be vertical in congenital vertical talus.