We commonly overlook the abductor hallucis muscle in the foot and rarely does it even get recognition or discussion when it comes to any foot pathologies. However, recent literature has demonstrated its importance to the foot, especially to the medial longitudinal arch.1-4 Accordingly, let us examine the anatomy of the abductor hallucis and review how it may be more involved with the pathology we see on a day-to-day basis.
The abductor hallucis muscle originates at the posteromedial aspect of the calcaneus and inserts into the medial sesamoid of the hallux or proximal phalanx.5 The action of the abductor hallucis is to flex and supinate the first metatarsal, invert the calcaneus, externally rotate the tibia, and elevate the medial longitudinal arch.1 It also contributes to the stabilization and supination of the midtarsal joint against the pronating force of ground reaction during propulsion.6
Researchers have demonstrated that the abductor hallucis muscle supports the medial longitudinal arch and recommend strengthening foot intrinsics to prevent overuse injuries in those who present with excessive pronation. Fiolkowski and colleagues demonstrated with electromyography that the intrinsic pedal muscles play an important role in supporting the medial longitudinal arch and controlling pronation during static stance.2 Headlee and colleagues demonstrated that fatigue of the abductor hallucis muscle led to increased navicular drop.3 Fiolkowski and co-workers also confirmed this after witnessing an increased navicular drop by blocking the tibial nerve.2
The abductor hallucis muscle plays an important role in maintaining arch height as well as controlling excessive pronation. Strengthening this muscle can aid in treating and preventing overuse injuries. We should view it no differently than the posterior tibial muscle and tendon.
The question this poses is whether one should rely on external support such as an orthotic device to maintain or support the arch, or whether the focus should be on strengthening the intrinsic muscles of the feet, specifically the abductor hallucis. Jung and colleagues demonstrated that the short foot exercise is a useful exercise in increasing the strength of the abductor hallucis and medial longitudinal arch, more so than toe curls, which also provided a strength increase.4
Something else to consider is muscular tone, which is a measure of a muscle's resistance to stretching while in a passive, resting state. Muscular tone also describes the continuous, partial contraction of muscles while in a passive resting state. For example, when external force acts on a passive muscle, muscles will increase in tension due to the partial contraction, reflexively responding to avoid stretching.7 A weak gluteus medius muscle or thoracic and lumbar muscles can lead to poor posture.
Can we say the same for the abductor hallucis? If significant strength gains occur in the abductor hallucis, will increased muscle tone lead to a more stable structure of the arch? The above studies demonstrate increased support of the medial longitudinal arch during static stance. Knowing the abductor hallucis muscle abducts the hallux would lead one to think that by increasing the muscle’s tone, a reduction in a hallux valgus could result.
It is pretty clear the research demonstrates that strengthening the intrinsic musculature can influence foot structure. We still need to establish the degree of influence and whether this can have a positive effect on treating and preventing injuries.
1. Wong YS. Influence of the abductor hallucis muscle on the medial arch of
the foot: a kinematic and anatomical cadaver study. Foot Ankle Int. 2007; 28(5):617-20.
2. Fiolkowski P, Brunt D, Bishop M, Woo R, Horodyski M. Intrinsic pedal musculature support of the medial longitudinal arch: an electromyography study. J Foot Ankle Surg. 2003; 42(6):327-333.
3. Headlee DL, Leonard JL, Hart JM, Ingersoll CD, Hertel J. Fatigue of
the plantar intrinsic foot muscles increases navicular drop. J Electromyogr Kinesiol. 2008; 18(3):420-425.
4. Jung DY, Kim MH, Koh EK, et al. A comparison in the muscle activity of the abductor hallucis and the medial longitudinal arch angle during toe curl and short foot exercises. Physical Ther Sport. 2011; 12(1):30-35.
5. Kendall FP, McCreary EK, Provance PG, Rodgers MM, Romani WA. Muscles: Testing And Function, With Posture And Pain, fifth edition. Lippincott Williams & Wilkins, Philadelphia, 2005.
6. Mann R, Inman VT. Phasic activity of intrinsic muscles of the foot. J Bone Joint Surg (Am). 1964; 46:469-481.
7. Available at https://www.boundless.com/physiology/muscle-tissue/control-of-muscle-ten...  .