THE FOOT CORE SYSTEM: A NEW PARADIGM FOR UNDERSTANDING INTRINSIC FOOT MUSCLE FUNCTION

In recent years, we have been more aware of the importance of the smaller segments of the foot and the role they play.  We know that the movement and stability of the arch is controlled by intrinsic as well as extrinsic muscles. However, the intrinsic muscles tend to be overlooked in favour of the larger muscles by clinicians, particularly when addressing rehabilitation. This month’s paper reports the importance of the “foot core stability” and how to incorporate this into practice.

Overview:

“Core stability” is a buzz phrase which is understood by clinicians and patients alike in reference to the lumbopelvic-hip region. The importance of core stability is also well understood but not in relation to the foot. For the lumbar region, “proper function of local stabilisers provides a stable base on which the primary movers of the trunk, those with larger cross-sectional areas and moment arms, can act to cause gross motion. When core muscles are weak or are not recruited appropriately, the proximal foundation becomes unstable and malaligned, and abnormal movement patterns of the trunk and lower extremity ensue. This can lead to a variety of overuse lower extremity injuries.” This paper enforces the view that strong local stabilizers are equally important for good foot function.

What it all means:

The arch is controlled by the local stabilisers and global movers of the foot, comparable to the lumbopelvic core.

Key points:

• The local stabilisers of the foot are the plantar intrinsic muscles that both originate and insert on the foot. These consist of 4 layers of muscles.

• Global movers are the extrinsic muscles that originate in the lower leg, cross the ankle and insert on the foot.

• The local intrinsic muscles generally have small moment arms, small cross-sectional areas and serve primarily to stabilise the arches.

• The global muscles have larger cross-sectional areas, larger moment arms, are prime movers of the foot, and provide some stability to the arch.

• There is no gold standard for assessing the function of the intrinsic foot muscles.

• There is some evidence that the “short foot exercise” can improve navicular drop, arch index, balance and chronic ankle instability.

• This exercise is similar to abdominal “drawing in manoeuvre” often prescribed to improve core strength in the lumbar region.

Putting it into practice:

Externally supporting the foot with orthoses is still a treatment method which harnesses great results. However, we shouldn’t forget that this is only part of the bigger picture. Training the intrinsic muscles to function as they are designed is equally important.

• Intrinsic foot muscle test: This has been proposed as a functional assessment of a patient’s ability to maintain a neutral foot posture and medial longitudinal arch height during single limb stance.
  1. Set your patient’s test foot in subtalar neutral with the calcaneus and all the metatarsal heads on the ground. Ask your patient to fully extend their toes.
  2. Ask your patient to lower their toes to the ground and maintain the foot position in single limb stance for 30 seconds.
  3. Look for any changes in navicular height and overactivity of the extrinsic muscles, this will suggest intrinsic weakness.

• Short Foot Exercise: “The foot is ‘shortened’ by using the intrinsic muscles to pull the first metatarsophalangeal joint towards the calcaneus as the medial longitudinal arch is elevated. As the arch raises during this exercise, it is also referred to as ‘foot doming”.
  1. It is important that the patient learns to sense subtalar neutral with the calcaneus and the metatarsal heads on the ground and the toes neither flexed nor extended and then shorten the foot by using the plantar intrinsic muscles only.
  2. This exercise can be progressed from sitting, to standing, to standing on one leg as the patient improves.