Sesamoid Disorders of the Foot

Sesamoid Complex Anatomy

The hallucal sesamoids are two small ovoid bones embedded within the tendons of flexor hallucis brevis (FHB), located plantar to the first metatarsal head.

Bony Anatomy:

• Tibial Sesamoid (Medial): Typically more elongated, bears greater weight
• Fibular Sesamoid (Lateral): More rounded, bears less load
• Articular Surface: Dorsal surface articulates with plantar metatarsal head crista
• Non-articular Surface: Plantar surface gives attachment to plantar plate and FHB

Soft Tissue Relationships:

Biomechanical Function

The sesamoids serve multiple critical functions in first ray biomechanics:

1. Mechanical Advantage: Increase moment arm of FHB by elevating the tendon away from joint center
2. Load Absorption: Bear 2-3 times body weight during walking, up to 300% during running
3. FHL Protection: Elevate metatarsal head to protect FHL tendon from compressive forces
4. Weight Distribution: Distribute forces across metatarsal head during gait

Windlass Mechanism:

During toe-off, hallux dorsiflexion tightens the plantar fascia, elevating the arch and depressing the first metatarsal head. This dramatically increases force transmission through the sesamoid complex. Any pathology causing sesamoid pain disrupts this mechanism, leading to compensatory gait changes and potential transfer metatarsalgia.

Mechanisms of Sesamoid Pathology

Sesamoid disorders develop through several distinct pathophysiological mechanisms. Understanding these processes is essential for appropriate diagnosis and management.

Overuse and Repetitive Microtrauma:

Sesamoiditis represents an inflammatory response to chronic repetitive loading. During the push-off phase of gait, the sesamoid complex experiences forces up to 300% of body weight. In athletes performing repetitive toe-off activities (ballet, running, jumping), cumulative microtrauma exceeds the tissue's healing capacity, resulting in:

• Bone marrow edema visible on MRI
• Periosteal inflammation
• Soft tissue swelling in FHB tendons and plantar plate
• Bursitis between sesamoid and metatarsal head

Stress Fracture Development:

When cyclical loading exceeds bone remodeling capacity, stress fractures develop through a predictable sequence:

1. Stress Reaction: Increased osteoclastic activity creating microscopic trabecular damage
2. Cortical Disruption: Fracture line appears as bone remodeling fails to keep pace
3. Propagation: Continued loading extends the fracture through cortex
4. Displacement: In severe cases, complete cortical break with fragment separation

The tibial sesamoid is 25 times more susceptible due to increased load-bearing and more variable vascular supply.

Avascular Necrosis Pathway:

AVN develops when blood supply is critically compromised, most commonly from:

• Fracture-related: Distal pole fractures disrupt the proximal vascular pedicle
• Idiopathic: Gradual vascular insufficiency from chronic repetitive trauma
• Post-surgical: Excessive soft tissue stripping during surgery

The pathological sequence follows:

1. Vascular compromise leads to osteocyte death
2. Bone attempts repair but fails due to persistent ischemia
3. Subchondral collapse as necrotic bone cannot support loads
4. Fragmentation and sclerosis as body attempts to revascularize
5. Secondary degenerative changes in metatarsosesamoid joint

Acute Traumatic Fracture:

High-energy axial loading (forced dorsiflexion, direct impact) exceeds bone's ultimate tensile strength, causing immediate fracture. Sharp irregular fracture lines differentiate these from bipartite variants. Displacement depends on magnitude of force and integrity of surrounding soft tissue envelope.

Degenerative Arthritis:

Chronic overload or post-traumatic changes lead to cartilage degeneration in the metatarsosesamoid articulation. Progressive joint space narrowing, osteophyte formation, and subchondral sclerosis follow typical osteoarthritic patterns.

History

A detailed history often reveals the underlying pathology type.

Key Questions:

• Onset: Insidious (sesamoiditis, stress fracture) vs acute (traumatic fracture, turf toe)
• Mechanism: Forced dorsiflexion (turf toe), repetitive push-off (sesamoiditis), single impact (acute fracture)
• Activity: Ballet dancers (relevé position), runners (push-off phase), basketball players (jumping)
• Pain Characteristics: Localized plantar pain worsened by toe-off phase of gait
• Footwear: High heels, cleats, or minimalist shoes increase forefoot loading
• Previous Symptoms: Prior episodes suggest chronic overload or bipartite variant

Physical Examination

Systematic examination localizes pathology and rules out differential diagnoses.

Imaging Protocol

A systematic approach to imaging ensures accurate diagnosis and appropriate treatment selection.

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The surgical options table and the management algorithm both list sesamoid shaving for a plantar prominence with intractable plantar keratosis (IPK), and Richardson's review names "shaving of a prominent tibial sesamoid," but the technique is never described.

• Indication. A painful plantar prominence or intractable plantar keratosis (IPK) under the tibial sesamoid with a preserved metatarsosesamoid joint and no fracture, AVN or arthritis - the problem is mechanical prominence, not intra-articular disease. It is the least destructive surgical option and preserves the whole sesamoid and the FHB.
• Technique (planing). Through a medial or plantar-medial approach the sesamoid is exposed within the FHB without shelling it out. Using a burr or osteotome the plantar (non-articular) half is shaved/planed flush, reducing the prominence while leaving the dorsal articular surface and the FHB attachment intact. Because the FHB is not divided, the flexor mechanism and the medial buttress are preserved - avoiding the hallux valgus and cock-up risks of total excision.
• Aftercare and caveats. Offloading is similar to the non-operative protocol, with an earlier return than after excision. The main risks are inadequate debridement (persistent keratosis), fracture of the thinned sesamoid, or violating the articular surface; shaving does not help if the pain is intra-articular (arthritis or AVN), where excision is required.

Richardson's review lists "partial or complete resection" and the preservation-first algorithm implies it, but the surgical technique section only develops total sesamoidectomy - partial excision is never described.

• What it is. Removal of only the diseased fragment of a sesamoid (typically the smaller, avascular or ununited pole) while retaining the viable fragment and the FHB attachment. It is used for a fractured or symptomatic bipartite sesamoid where one pole is diseased, or for a stress-fracture nonunion of a bipartite sesamoid - most often the proximal-fragment excision described for medial (tibial) sesamoid stress fractures.
• Rationale. By preserving the larger viable pole and the FHB, it maintains more of the flexor lever and the medial/lateral buttress than total excision, reducing the risk of hallux valgus/varus and cock-up deformity while still removing the pain source. It is a middle option between planing and total sesamoidectomy.
• Evidence and caveats. Biedert and Hintermann reported excision of the proximal fragment in young athletes with medial-sesamoid stress fractures, with all patients pain-free and back to full sport within six months. It is only appropriate when one pole is clearly the pain source and the retained pole is viable; if the whole sesamoid is necrotic or arthritic, total excision with FHB repair is required.

Bone Grafting Protocol (Stricter)

For bone grafting procedures, rehabilitation is more conservative:

• NWB strict for 8 weeks in short leg cast
• Radiographs at 6 and 12 weeks to confirm union
• Transition to weight-bearing boot weeks 8-12
• Full weight-bearing by 12 weeks if healed
• Return to sport 6-9 months (slower than sesamoidectomy)

Global Epidemiology

• Population at risk: Predominantly athletes and dancers worldwide. Sesamoid injuries account for roughly 9% of foot and ankle injuries in athletic populations and up to 12% of great-toe injuries.
• Sport distribution (international): Running and sprinting (push-off loading), ballet and dance (relevé), football/soccer and rugby (forced dorsiflexion), basketball and gymnastics (jump landings), and cricket fast bowling (repetitive forefoot impact).
• Bipartite prevalence: 10-30% of the general population; bilateral in around 85%; tibial sesamoid roughly 10 times more likely to be bipartite than fibular.
• Fracture distribution: Tibial-to-fibular fracture ratio approximately 25:1, reflecting greater medial load-bearing.

Side-by-Side Society Guidance

There is no dedicated AAOS or NICE clinical practice guideline specific to sesamoid disorders; recommendations are extrapolated from foot and ankle society consensus, AO Foundation principles, and sports-medicine bodies. Where guidance genuinely differs, it is on the threshold for surgery and choice of preservation vs excision.

Registry and Evidence Notes

• No national joint registry captures sesamoid procedures (they are non-arthroplasty), so the evidence base is systematic reviews of case series rather than registry survivorship data.
• Best available syntheses: Shimozono 2018 (sesamoidectomy, 196 feet), Robertson 2017 (stress-fracture return to sport), and Artioli 2025 (nonunion algorithm).

High- vs Limited-Resource Practice Variation

• High-resource settings: Early MRI and CT for diagnosis; custom orthoses; access to arthroscopic and sesamoid-preserving fixation/grafting; bone stimulators for delayed union.
• Limited-resource settings: Diagnosis often radiograph-based with contralateral comparison films; conservative management with stiff-soled footwear and felt dancer's pads; open sesamoidectomy is the dominant surgical option where preservation techniques or implants are unavailable.

Universal Consent Points for Sesamoidectomy

1. Hallux valgus (after tibial excision) or varus (after fibular excision)
2. Cock-up toe deformity from inadequate FHB repair
3. Transfer metatarsalgia to the lesser rays
4. Neuroma (medial plantar or dorsomedial cutaneous nerve)
5. Loss of push-off power, career-relevant for sprinters and dancers
6. Possible revision surgery
7. Always document a minimum 3-6 month conservative trial and MRI-confirmed pathology, and discuss preservation alternatives in athletes.

The evidence base for sesamoid disorders is composed almost entirely of small case series and systematic reviews of them; no randomised trials and no registry data exist. Several genuine areas of debate remain.