The Quadratus plantae (Flexor accessorius) muscle. Do you have foot pain ?
(*There are two pictures here on the blog. Move your cursor over to the side of the photo and you will see that you can toggle between the photo and anatomy pic).
This is a great, but highly overlooked, muscle. The QP acts to assist in flexing the 2nd to 5th toes. Equally important is its effect of offsetting the oblique pull of the long toe flexor group (flexor digitorum longus). It has two heads, medial and lateral. The medial head is attached to the calcaneus, while the lateral head originates from the lateral border of the calcaneus, in front of the lateral process of the calcaneal tuberosity and the long plantar ligament.
The fact that we just love, and one that we believe is often overlooked is the acute angle at which the muscle heads attach into the tendons of the flexor digitorum longus (see picture) and has a rather dramatic alignment effect on the lateral 3 digits (since the line of pull on the long flexor tendons to these 3 digits is most dramatically changed by the purely posterior pull of the Quadratus Plantae. As you can see in this stripped down anatomy picture, without the QP pulling on the tendons of the FDL to these 3 lateral toes, those toes will have to curl medially and gently flex (*see the photo, a classic presentation!) By having a competent and active QP that oblique line of pull of the FDL /long flexors is rearranged to be more of a pure posterior pull and you will not see this classic lateral 3 digit curl and medial drift. This action is accentuated in a cavus foot type, where the pull of the FDL will be accentuated, due to the mechanical advantage afforded it and relative adduction of the forefoot with respect to the rear foot.
In the photo you can see a classic representation of a deficient Quadratus Plantae, in this case the patients lateral head was dramatically weaker than the medial, but both were weak. So, summary time….if you know your anatomy, know your biomechanics, and if you can test the muscle bundles specifically……..then you can see why form follows function (and in this case, why form has followed dysfunction). As we always say, “ya gotta know your stuff”, and you have to test what you suspect……there are other things that could also do this……so, let your eyes gain info, let your brain process and prove or disprove the information.
we are…….the gait guys !