When the podiatrist performs a biomechanical assessment, he has in his mind a model of what should be a normal foot. This is how we recognise when we see abnormality. It is a known fact that most of us have some sort of deviation from the norm, the statistics have shown that up to 85% of us are not perfect as far as our feet are concerned. However whether one has symptoms or not depends on a combination of factors.
There are a number of theories surrounding how we understand the foot. Neither theory is completely right or wrong…but combined create a better understanding of how it all works.
We look at:
- The alignment of the leg to the ground, it should be nearly straight. The most common deviation is Tibial Varum, which is a curvature in the leg bone leading to an excessive lateral heel strike (outerside of the heel).
- The alignment of the heel to the leg, this is the relationship of the calcanues and talus to the leg. It should be about 2 degrees inverted, but it is commonly inverted by 4 degrees and more and this leads to an inverted heel strike. Deviation is referred to as Rearfoot Varus.
- The alignment of the forefoot the the rearfoot, the should be no deviation of the forefoot to the rearfoot, although it is common to have a forefoot that is inverted to the rearfoot leading to a foot that pronates (rolls in) excessively. Deviation is referred to as Forefoot Varus or Forefoot Supinatus
- The position of the rearfoot to the ground on standing, should be vertical. Referred to as Rest Calcaneal Stance Position.
- The flexibility of the calf muscles, that allows the foot to dorsiflex, or allows the leg to move over the foot during normal walking. Most people present with tight calf muscles. Normal measurement would be +10 degrees dorsiflexion on the leg. This is referred to as Ankle Equinus.
- Leg Length Discrepancy (LLD), or Functional Leg length Discrepancy (FLLD). Measuring the legs is not an exact science, but we can get an approximation of the length. In a FLLD, the legs can appear different in length but are not actually different. This can indicate a Pelvic anomaly , muscle imbalances, spasm and pain. Structural LLD where one leg is structurally longer.
- Range of Motion of the Sub-Talar Joint, dictates how much movement there is in the ankle on Inversion and Eversion. (The inward outward motion of the ankle).
The Foot Posture Index
This is a tool that has been developed of late that gives the practitioner several tests to determine a foot type and function. This is being more universally used in order to standardise tests inter professionally so that we can al talk the same language when referring to a patient.
Although I use some of the Foot Posture index information, I do not rely solely on it.