Mechanisms of Bunion Development

Introduction

A bunion (Hallux Valgus or Hallux Abducto Valgus) isn’t just a bump, it’s a progressive deformity involving the entire forefoot. It occurs when the first metatarsal drifts inward and the big toe angles outward, creating that familiar prominence at the base of the toe. Over time, this misalignment can affect how we move, balance, and bear load.

Bunions are extremely common, affecting around 23% of adults and over 35% of older adults, with women more frequently affected than men [1]. Beyond discomfort or footwear frustration, bunions alter gait efficiency, foot stability, and even postural alignment. As the foundation of the kinetic chain, compromised foot mechanics can ripple upward-impacting knees, hips, and beyond.

Understanding why bunions develop allows both clinicians and the general public to intervene early, restore better movement, and potentially prevent progression.

Common Myths & Misconceptions

“It’s just genetics.”
Genetic factors such as ligament laxity or certain foot structures can predispose someone to bunions, but genetics alone rarely determine outcome. Many people with a family history never develop bunions, especially if they maintain good mobility and functional control.

“It’s all about shoes.”
Footwear matters, but it’s not the whole story. Narrow toe boxes and high heels accelerate bunion formation by forcing the toes together and increasing forefoot load. Studies confirm a higher prevalence in populations wearing restrictive shoes versus those who go barefoot [2]. However, not everyone who wears fashionable shoes develops bunions. It’s multifactoral - it's the combination of foot structure, loading mechanics, and shoe design that determines risk, they’re the result of mechanical imbalance.

Functional Pronation, Joint Centration & Bunion Progression

The alignment and sequencing of foot motion play a crucial role in bunion development. Contrary to popular belief, many bunions stem not from too much pronation, but from a lack of functional pronation at the right phase of gait.

During normal walking, the foot should pronate smoothly from heel strike through terminal mid-stance, allowing the forefoot to adapt to the ground and distribute load evenly. This controlled pronation is essential for optimal joint centration, the even alignment of bones within their joints, permitting efficient load transfer.

When a person moves with restricted or poorly timed pronation, the first ray often remains elevated and rigid. The medial column fails to load properly, forcing pressure toward the inside edge of the big-toe joint. As the heel lifts, pronation then occurs too late - during propulsion rather than mid-stance, creating shear and torsional stress through the first MTP joint instead of a stable push-off. Over time, this mis-timed loading encourages the big toe to drift laterally while the first metatarsal deviates medially, forming the classic bunion.

This results in late, rigid pronation and excessive shear through the forefoot at toe-off. In Dynamic Neuromuscular Stabilisation (DNS) terms, this reflects a loss of the foot’s centrating strategy: instead of balanced neuromuscular control, compensatory fascial tension dominates. The abductor hallucis, peroneus longus, and plantar fascia lose their coordinated function, leaving the big-toe joint vulnerable to repetitive asymmetric stress.

The development of a bunion isn’t just about bone drift or muscle weakness, it often reflects a densification or stiffness of the deep fascia that alters joint alignment and movement sequencing.

According to the Stecco model, fascia is a three-dimensional continuum that binds and interconnects muscle, tendon and joint systems; when certain fascial “centres of coordination” lose their glide or become fixed, movement becomes compromised.  

In the context of bunion formation:

• A foot that should be adapting via subtle pronation through mid-stance becomes “locked” because fascial layers don’t glide correctly. With the fascia stuck, the first ray fails to centre properly in its joints (subtalar, navicular-cuneiform, first metatarsal). This loss of joint centration leads to uneven load distribution beneath the first metatarsal head.

• As propulsion begins, instead of a smooth roll and toe extension, the fascia’s restricted state forces the motion into a compensatory shift: the first metatarsal is pulled medially, the big toe drifts laterally and the joint capsule gradually deforms under chronic shear.

• The Stecco method posits that specific fascial densification points corresponding to the limited movement can be identified and treated. Once these local fascial restrictions are freed, the foot’s mechanics improve, allowing the first ray to recenter, the hallux joint to extend more fully and the forefoot to withstand ground reaction forces more evenly. 

In essence, it’s not “too much” pronation but rather poorly timed, incomplete pronation, combined with fascial rigidity and non-functional joint centration that perpetuates bunion development. Restoring natural pronation sequencing, improving first-ray mobility, and addressing fascial restriction are critical components of prevention and rehabilitation.

Tendon and Muscle Imbalances

As the bunion progresses, the muscle-tendon system around the big toe changes. The flexor and extensor tendons begin to “bowstring” laterally, increasing the outward pull on the toe [3].

The abductor hallucis, a key stabiliser that helps hold the toe straight, often becomes weak and lengthened, while its counterpart, the adductor hallucis, tightens, drawing the toe further toward the second toe. Imaging studies show a significant reduction in the cross-sectional area of the abductor hallucis in people with bunions, sometimes years before deformity is visible [4].

Meanwhile, the peroneus longus, a crucial stabiliser of the first ray, is often underactive and is inefficient at eccentrically contracting at the right time. When it fails to anchor the first metatarsal, the bone drifts upward and medially, reducing stability. Strengthening and lengthening this muscle can help re-establish forefoot alignment and resist bunion progression.

Limited Big Toe Dorsiflexion (Functional Hallux Limitus)

A common contributing factor is limited great-toe dorsiflexion during weight-bearing. In a healthy gait, the big toe should extend about 60° as the heel lifts. 

When the first MTP joint is stiff, the big toe cannot extend, and the metatarsal is instead forced medially with each step. Over time, this repetitive jamming shifts joint position and worsens deformity. As researcher Clough (2022) describes, insufficient dorsiflexion at the toe causes the proximal phalanx to lever against the metatarsal head, driving the bone inward and advancing hallux valgus [5].

Improving toe mobility and restoring  are essential steps in bunion prevention and treatment.

The Role of Fascial Chains & Whole-Body Mechanics

The bunion is rarely a local problem. Fascial continuity connects the big toe to the calf, thigh, and core - it occurs in multiple planes and every single person fascial restrcitions are differeing. . Limitations in ankle or hip mobility, pelvic rotation, or even diaphragm tension can alter load transfer through the foot.

From a DNS perspective, the bunion reflects a breakdown in global stabilisation patterns. Limited hip internal rotation and/or core control often leads to compensations at the foot. Addressing only the bunion without restoring upstream control is short-sighted. Clinically, improving hip rotation, ankle dorsiflexion, and breathing coordination frequently improves foot loading and bunion symptoms.

Research on Conservative Management

For decades, bunions were considered a surgical condition, but emerging research supports the effectiveness of conservative management, particularly in early to moderate stages.

• Strengthening Works: A study by Kim et al. (2015) showed that participants performing daily toe-spread-out exercises increased abductor hallucis size by 24% and improved their bunion angle by over 3° within eight weeks [6].

• Combined Therapy Yields Greater Gains: Abdalbary (2018) found that combining manual therapy, stretching, strengthening, and toe separators led to an 8° reduction in bunion angle and 30% improved toe strength after 12 weeks [7].

• Night Splints and Spacers: Consistent use of toe spacers or night splints provides modest but meaningful alignment improvements (~4°) and reduced pain [8].

• Insole Therapy: Insoles can be used to faciliate ideal foot function to reduce inefficient loads and stresses to help reduce excessive strain,  though their best outcomes occur when paired with strengthening and footwear modification [9].

Thomas Michaud (2024) summarised it succinctly: “Unlike drugs or surgery, there are no side effects to strengthening your feet.” Early conservative treatment can halt progression, and sometimes even partially reverse the deformity.

Why Early Intervention Matters

Once bunions become rigid, conservative correction is limited. Early management prevents degenerative changes, maintains gait efficiency, and reduces the cascade of secondary problems such as metatarsalgia, hammertoes, knee pain and even pelvic floor issues.

Even mild bunions can compromise propulsion and balance. By restoring pronation timing, joint centration, and muscle balance early, clients can often avoid surgery altogether.

Practical Steps: What You Can Do

For the General Public

1. Choose foot-friendly footwear: Wide toe boxes, minimal heel height, and flexible soles that allow your toes to move.

2. Mobilise daily: Stretch calves and big toes, and spend short periods barefoot to retrain intrinsic control.

3. Strengthen foot muscles: Try the hand and toe spread exercise as a great starting point (available below) and wearing toe separators daily. Small, consistent efforts matter.

For Clinicians

1. Assess movement, not just structure: Observe timing of pronation and push-off patterns.

2. Incorporate DNS and fascial principles: Re-establish joint centration via movement retraining, not just local strengthening.

3. Combine interventions: Use manual therapy, fascial release, toe spacers, and foot intrinsic training for optimal results.

Summary & Call to Action

Bunions aren’t simply caused by bad shoes or bad genes - they’re the result of impaired movement sequencing, fascial restriction, and lost joint centration. Addressing these early can profoundly change outcomes.

For clinicians, this means seeing the bunion not as an isolated toe deformity, but as a sign of system-wide inefficiency. For individuals, it means understanding that restoring functional movement through strength, mobility, and smart footwear, can transform both comfort and performance.

At The Stabilisation Academy, we teach these principles in depth through our Bunion Care Courses -where foot, fascia, and function intersect. If you’d like to learn the practical steps to restore balance and prevent progression, visit www.thestabilisationacademy.com  to learn more.

Health Professionals find out more here with a great active assessment for bunions 👉 Active Bunion Assessment

Those with bunion issues find out more and get your starter exercise here 👉Starter Bunion Exercise

References

1. Nix, S., Smith, M., & Vicenzino, B. (2010). Prevalence of hallux valgus in the general population: a systematic review and meta-analysis. J Foot Ankle Res, 3(21).

2. Puszczałowska-Lizis, E., et al. (2019). Foot deformities in women are associated with wearing high-heeled shoes. Med Sci Monit, 25, 7746–7754.

3. Perera, A. M., Mason, L., & Stephens, M. M. (2011). The pathogenesis of hallux valgus. J Bone Joint Surg Am, 93(17), 1650–1661.

4. Stewart, S., Ellis, R., Heath, M., & Rome, K. (2013). Ultrasonographic evaluation of the abductor hallucis muscle in hallux valgus. BMC Musculoskeletal Disorders, 14(45).

5. Clough, J. (2022). Position of the first MTP joint and the effect on hallux valgus progression. J Int Foot & Ankle Foundation, 1(2).

6. Kim, M. H., Yi, C. H., Weon, J. H., et al. (2015). Effect of toe-spread-out exercise on hallux valgus angle and abductor hallucis CSA. J Phys Ther Sci, 27(4), 1019–1022.

7. Abdalbary, S. A. (2018). Foot mobilization and exercise program combined with toe separator improves outcomes in women with moderate hallux valgus. J Am Podiatr Med Assoc, 108(6), 478–486.

8. Chadchavalpanichaya, N., et al. (2018). Effectiveness of a custom-molded silicone toe separator on hallux valgus. Prosthetics Orthotics Int, 42(2), 163–170.

9. Michaud, T. (2024). Prevent and even reverse bunion formation – without surgery. Dynamic Chiropractic, 42(8).