The Calcaneo Cuboid Locking Mechanism

Do you know what this is? You should if you treat folks who walk or run!

It is the mechanism by which the tendon of the peroneus longus travels behind the lateral malleolus of the ankle, travels underfoot, around the cuboid to insert into the lateral aspect of the base of the 1st metatarsal and adjacent 1st cunieform. Remember the peroneus longus?

The peroneus (or fibularis) longus arises from the head and upper two-thirds of the lateral surface of the fibula, from the deep surface of the fascia, and from the intermuscular septa between it and the muscles on the front and back of the leg; occasionally also by a few fibers from the lateral condyle of the tibia.  You can see from it attachments that it can influence the entire upper lateral leg.

It’s tendon runs down the fibular shaft, wraps around the lateral malleolus, travels obliquely under the foot, crossing the lateral cuboid (which it everts after midstance to help with supination) crosses the sole of the foot obliquely, and inserts into the lateral side of the base of the first metatarsal and lateral aspect of the 1st cunieform.  

It acts from just prior to heel strike to limit excessive rearfoot inversion, through midstance to decelerate subtalar pronation and assists in stabilization of the midfoot articulations, and into terminal stance and pre swing to lock the lateral column of the foot for toe off and plantar flex the 1st ray (creating a good foot tripod), allowing dorsal posterior shift of the 1st metatarsal-phalangeal joint axis (necessary for dorsiflexion of the hallux (big toe)).

When the peroneus longus contracts, in addition to plantar flexing the 1st ray, it everts the cuboid and locks the lateral column of the foot, minimizing muscular strain required to maintain the foot in supination (the locked position for propulsion). Normally, muscle strength alone is insufficient to perform this job and it requires some help from the adjacent articulations.

In addition, the soleus maintains spuination during propulsion by plantar flexing and inverting rear foot via the subtalar joint. This is assisted by the peroneus brevis and tertius which also dorsflex and evert the lateral column, helping keep it locked. Can you see why the peroneii are so important?

signs of a faulty calcaneo cuboid locking mechanism

• weak peroneus longus, brevis and or tertius
• excessive rear or midfoot pronation
• low arch during ambulation
• poor or low gear “push off”
• subluxated cuboid

The calcaneo cuboid locking mechanism. Essential for appropriate supination and ambulation. Insufficiency, coming to a foot you will soon examine. Make sure to needle those peroneii!!

Here is a quick video on the calcaneo cuboid locking mechanism