Fracture of one or more sesamoids of the foot

Understanding sesamoid fracture

Definition of Sesamoids

A sesamoid bone, also known as a sesamoid, is defined as a small, rounded bone, interposed within a joint capsule, where it facilitates movement by amplifying responsiveness within the tensegrity structure.

The metatarso-phalango-sesamoid joint of the hallux or first ray (MTPS) includes the head of the first metatarsal, the base of the first phalanx, and the sesamoids, so named by analogy to sesame seeds. They are small, very dense, robust bones, embedded in a complex capsulo-ligamentous system, important in the biomechanics of the foot.

The shape of the sesamoids is variable; usually there are two sesamoids, a medial sesamoid and a lateral sesamoid, also called the tibial sesamoid and the fibular sesamoid.

Sesamoid injuries can be traumatic, microtraumatic, or degenerative. More rarely, injuries are inflammatory, metabolic, or infectious.

Treatment of sesamoid pathologies can be, depending on the extent, medical or surgical.

The effectiveness of medical treatment can take a long time to assess, and the indication for surgical treatment must be carefully considered, as inappropriate surgical interventions on the sesamoids can potentially cause residual deformities of the hallux, painful stiffness, loss of strength in the flexor hallucis longus muscle (FHL), and pain with chronic disability.

Anatomy of the Sesamoids

Embryology

Sesamoids first appear as condensed tissue islands at 8 weeks in utero; they become completely cartilaginous by 12 weeks and will remain cartilaginous throughout the fetal period.

The two sesamoids are regularly present under the head of the first metatarsal. The lateral, or fibular, sesamoid appears first at three months, followed by the medial, or tibial, sesamoid, which can be bipartite.

Sesamoids can also be present under the metatarsal heads of the metatarso-phalangeal joints of the lateral rays. Ossification centers of the sesamoids are visible from age 11 in boys and 9 in girls. The fibular sesamoid ossifies first.

Vascularization

A medial branch of the first plantar metatarsal artery supplies the tibial sesamoid. The main branch of the first plantar metatarsal artery continues distally along the lateral edge of the sesamoid, which it supplies.

Arterial vascularization enters the sesamoids at their proximal, plantar, and distal levels. The first plantar metatarsal artery is the main nourishing artery for the tibial and fibular sesamoids.

The vascularization of the fibular sesamoid is fragile; this must be taken into account when choosing the surgical approach and the incision location.

Anatomical Variations

The shape, partition, and consistency of the sesamoids may vary.

• Shape: Sesamoids are symmetrical in only 15 % of cases. The tibial sesamoid is ovoid, 12 to 15 mm long and 9 to 11 mm wide. The fibular sesamoid is circular and measures 9 to 12 mm in length and 7 to 9 mm in width. In 15 % of cases, the fibular sesamoid is larger than the tibial sesamoid. Sesamoids vary in thickness and articulate with the plantar surface of the first metatarsal head, which is grooved by two tracks separated by a longitudinal crest called the crista. When well developed, the crista stabilizes the centering of the sesamoids under the metatarsal head from 0° to 30° dorsiflexion of the hallux, or big toe.
• Partition: Sesamoid bones can be single-fragment or multi-fragmented. Partition is more common in the tibial sesamoid. Bipartition is the most frequent, referred to as bipartite sesamoid. A bipartite, tripartite, or quadripartite sesamoid will be longer than a normal sesamoid. Partition of a sesamoid represents a point of weakness, as the various fragments are separated by interposed fibrous tissue. Partition is much less common in the fibular sesamoid. Partition anomalies are bilateral in 25 % of cases, but not necessarily symmetrical. Bipartition is seen in nearly a third of hallux valgus cases. In the population free of hallux valgus, the frequency of bipartite sesamoids is 15.2 %. In cases of congenital or juvenile hallux valgus, significant pronation of the first ray and metatarso-phalangeal dysplasia can explain excessive stress on the sesamoids and a possible failure of fusion of the ossification centers.
• Consistency: Absence of one or both sesamoids is exceptional and called sesamoid agenesis. Sesamoids can be hypotrophic, in the shape of rice grains, and are then often bi- or tripartite.

Functional Role of the Sesamoids, Biomechanics of the Phalango-Sesamoid Apparatus (APS)

The metatarso-phalango-sesamoid joint consists of 2 joints: the first ray metatarso-phalangeal joint (MTP1) and the metatarso-sesamoid joint (MSJ). The MTP1 behaves like a hinge joint according to a fixed transverse axis of rotation in flexion/extension. Up to 30° dorsiflexion, the sesamoids are thus stabilized by the inter-sesamoid crest or crista. Beyond 30° dorsiflexion, the MTP1 acts as a condyloid joint as the crista no longer contributes to stabilization. The joint is then actively stabilized by capsulo-ligamentous and muscular tightening.

The metatarso-phalango-sesamoid joint is a spheroidal joint, allowing flexion/extension, varus/valgus, and pronation/supination. It allows for cushioning and absorption of body weight, stabilizes the tendon of the flexor hallucis longus muscle (FHL), and the first ray to increase its propulsive efficiency during walking via the windlass effect. It also allows inversion of the foot by the windlass effect during hallux dorsiflexion.

During walking, the deltoid ligament complex (ankle) and spring ligament (plantar calcaneonavicular ligament) initiate foot locking while stabilizing the ankle. During walking in the flat foot phase, the tendon of the posterior tibial muscle pushes the medial malleolus forward, causing external rotation of the lower leg segment. This external rotation is transmitted to the talar head, locking the talo-navicular joint and increasing the propulsive efficiency of the Suro-Achilleo-Plantar complex.

The hallux, bearing weight on the ground, experiences a supination force due to the reaction from the ground. The first metatarsal, connected to the inverting foot, undergoes dynamic pronation due to forward movement in gait; it pronates around the lateral sesamoid, allowing alignment of the metatarsal and phalangeal axes along the path of the FHL. This counter-rotation mechanism enables ligament tightening and muscle locking, stiffening the joint for propulsion and limiting valgus and dorsiflexion of the MTP1.

During gait, valgus stresses on the hallux are constant and can destabilize the metatarso-phalangeal and metatarso-sesamoid joints.

Retraction of the posterior muscle chains, especially the gastrocnemius or calf muscles, dysfunctions of the posterior tibial muscle, injuries to the ankle deltoid ligament, and injuries to the spring ligament impede external rotation of the talus, thus the midfoot remains in eversion.

Capsulo-ligament injuries, sesamoid injuries, and muscle weakness allow excessive dorsiflexion of the MTP1, making it unstable.

The concept of biotensegrity can explain the phenomenon of reversible cyclic deformation of the foot. The sesamoids are directly connected to the bones of the leg, ankle, and foot through aponeurotic, ligamentous, muscular, and tendinous connections. The sesamoids can be seen as a convergence node of various muscle, tendon, and ligament structures, allowing, due to their density, for instant transmission of energy and movement, and adaptation to significant stresses that enable instantaneous modifications of the foot's shape.

Causes and risk factors

Sports activities and overuse

Sesamoid fractures often occur due to intense physical activity, particularly with improper footwear and in the context of a rapid increase in sports training intensity. High-impact sports, such as football, basketball, or dance, can excessively strain the area of the foot where the sesamoids are located. Here are some points to keep in mind: 

• Repetitive movements : Frequent actions, such as jumping or running, can fatigue the sesamoids and increase the risk of fracture or necrosis.
• Inappropriate footwear : Wearing poorly adapted shoes can create excessive pressure on the sesamoids, contributing to injuries.
• Sudden intensity change : Suddenly switching from light training to intense activity without proper preparation can overload the sesamoids.

Associated pathologies and predispositions

Certain health conditions can also increase the risk of sesamoid fractures: 

• Biomechanical considerations : Posture issues, hindfoot misalignment, or high-arched feet with increased pressure under the head of the first metatarsal, increase the pressure on the sesamoids.
• Osteoarthritis : Patients who suffer from osteoarthritis of the big toe, or from hallux rigidus, may experience painful arthritic lesions of the metatarso-sesamoid joint.
• Muscle weakness : Insufficient muscle strength in the feet and legs can reduce the ability to absorb shocks, increasing the risk of injury.

By taking these factors into account, it is wise to adopt preventive practices to reduce the risk of sesamoid injuries, especially for athletes and active individuals.

Symptoms and Diagnosis

Clinical analysis

The clinical analysis begins with the patient interview, followed by the physical examination. The diagnosis of a sesamoid pathology of the hallux is suspected during the interview, clarified by the physical examination, and confirmed by imaging tests.

The interview aims to determine the location of symptoms, the mode of onset of pain (sudden or progressive), the timing of pain (mechanical and/or inflammatory), whether it is unilateral or bilateral, and its type (burning, electric shocks), as well as the presence of a limp. Looking for a traumatic factor is important—even a minor trauma, which patients may not remember, can cause painful symptoms that are potentially highly disabling in cases of sesamoid lesions. Work activity, sports practices, as well as footwear habits should be evaluated, especially when microtraumatic pathology is suspected. It is also essential to specify the patient's general medical history, such as the presence, duration, and management of neuropathy, chronic autoimmune or metabolic inflammatory diseases (gout, diabetes).

Finally, the analysis of different therapeutic measures already undertaken and their respective effectiveness must be taken into account, both for diagnosing sesamoid lesions and for treatment.

Physical examination begins with analysis of the patient's gait, barefoot, in order to observe the walk, the gait angle, and evaluate the alignment of the hindfoot and lower limbs overall. It looks for the presence of an avoidance limp. The morphology of a foot can only be assessed while walking; even a weight-bearing X-ray does not allow precise diagnosis of a flexible flat foot, for example, since an antalgic inversion position can make it look like a cavus foot on X-ray, with an elevated first ray. The exam looks for any leg length discrepancy, and assesses the condition of the skin in search of vascular or nerve issues.

The signs and factors of excessive pressure under the forefoot are systematically looked for :

• Contraction of the posterior muscle chains, particularly the gastrocnemius muscles
• Plantar hyperkeratosis
• Hypotrophy or atrophy of the plantar fat pad
• Deficient action of the flexor hallucis longus

The sesamoids cannot truly be palpated, but it is possible to compress each sesamoid with a digital maneuver. Stretching the plantar fascia may reproduce the pain. The shape of a sesamoid can be determined if it is hypertrophic or pointed, especially in cases of atrophy of the plantar fat pad.

Imaging tests for sesamoid pathology

• X-ray is an essential complement to the clinical exam. X-rays are taken while standing, bilaterally and comparatively, with three views. Radiological analysis allows the practitioner to assess the shape, partition, and density of the sesamoids, as well as the presence of joint narrowing and osteophytes. It is essential for analyzing associated deformities such as hallux valgus, hallux rigidus, or arthrosis, and for assessing the centering of the sesamoids under the crista. Precise analysis of the sesamoids requires a CT scan.
• CT scan allows a more precise study of bone structure (millimetric slices). CT of the foot is performed without injection of contrast product, and allows assessment of the trabecular structure of the sesamoids, possible fractures, and evaluation of whether they are recent or old. Osteonecrosis of the sesamoids and the vitality of fragments can be assessed by CT scan.
• “Weight-bearing CT” allows reconstructions while standing and in all planes of the ankle and the entire foot, and helps evaluate the position of the bones in the kinematic chain. This is also possible with weight-bearing cone beam, which enables analysis of joint displacements.
• MRI provides assessment of all tissues, and can show a fracture, osteonecrosis, or inflammation of the sesamoids. It is very useful in traumatic pathology to analyze potential associated cartilaginous, capsulo-ligamentous, and tendon injuries related to a sesamoid injury.
• Ultrasound allows dynamic analysis of capsulo-ligamentous and musculoskeletal structures, as well as soft tissues adjacent to the sesamoids. It is useful for assessing associated injuries.

Sesamoid pathologies of the hallux

Traumatic Pathologies

• Fractures of the sesamoids often go unnoticed at the beginning, and the diagnosis is generally made late at the chronic stage. Non-displaced fractures are managed with functional treatment. Displaced fractures show an interfragmentary gap, in which case the treatment is surgical.
• Turf Toe is a combination of injuries that may include a sesamoid fracture, capsular and ligamentous lesions, tendon and muscle injuries, as well as cartilage damage of the metatarsophalangeal joint.
• Sesamoid pseudarthrosis, or lack of fracture healing, may become asymptomatic or remain painful.

Microtraumatic Pathologies

Fatigue fractures or stress fractures cause pain that appears suddenly or gradually, and bearing weight on the first ray is then painful. Certain morphotypes favor forefoot overpressure such as hallomegaly with a relatively long first metatarsal, and a high-arched foot.

Necrotic Pathologies

Osteonecrosis and osteochondritis are very rare, difficult to diagnose, thought to originate from probable defects in bone vascular perfusion, known as Renander's disease for the sesamoids, and are part of the group of growth osteochondroses.

Arthritic Pathologies

Metatarso-sesamoid osteoarthritis may be secondary to traumatic, microtraumatic or degenerative causes. This is the most common involvement, and is often asymptomatic when isolated. It may be either symptomatic or not when associated with involvement of the metatarsophalangeal joint, especially in hallux valgus.

Inflammatory Pathologies

Chronic inflammatory diseases, such as rheumatoid arthritis, result in global joint involvement, called arthritis. Hallux involvement therefore concerns the metatarsophalangeal and metatarso-sesamoid joints. A subsesamoid bursitis may be present; it is generally large and should not be confused with a rheumatoid nodule, which is a tissue mass always larger than its estimated size by palpation.

Infectious Pathologies

Infection of the sesamoids can be associated with a plantar perforating ulcer in diabetics, and is then frequently associated with neighboring infectious osteoarthritis. Hematogenous bacterial grafting results in a rather subacute or chronic osteomyelitis. Direct bacterial inoculation is always possible through injury or puncture.

Hallux Valgus and Sesamoid Involvement

Hallux valgus corresponds to metatarsophalangeal and metatarso-sesamoid joint instability. Pronation of the first metatarsal can be significant in congenital and juvenile forms of hallux valgus, thereby increasing pressure on the sesamoids, mainly the tibial sesamoid, and thus promoting metatarso-sesamoid osteoarthritis. In longstanding forms of hallux valgus, up to 50% metatarso-sesamoid cartilage lesions are observed intraoperatively, which may explain some postoperative painful stiffness.

Treatment of sesamoid lesions

There are two types of treatment for managing sesamoid pathologies: functional medical treatment and surgical treatment. Functional treatment is always offered as the first option, except in cases of displaced fracture or infectious pathology of the sesamoids.

Functional, non-surgical treatment

Functional treatment may combine several methods, including:

• Partial or total offloading of the forefoot. Immobilization and offloading may be achieved with a plaster cast insole.
• Taping of the hallux constraining the metatarsophalangeal joint of the hallux in plantar flexion, which helps to limit dorsal flexion and offload the metatarso-sesamoid joint.
• The rigid orthosis, custom-molded, maintains the joint in plantar flexion.
• The corrective orthopedic insole with an offloading cup under the sesamoids.
• Rehabilitation measures with strengthening of the intrinsic foot muscles and the flexor hallucis longus, stretching of the posterior muscle chains especially the gastrocnemius muscles, and physiotherapy treatments.

Surgical treatment

This remains rare, it is tailored to the lesions to be treated and is offered in case of failure of functional treatment.

• Osteosynthesis is for displaced, non-comminuted fractures of the sesamoids. It can be performed percutaneously under fluoroscopic guidance, or via surgical approach, and consists of stabilizing the fracture with surgical hardware.
• Thinning is for prominent, hypertrophic, pointed sesamoids, generally in a context of hypotrophy or atrophy of the plantar fat pad. Thinning can be performed percutaneously by milling the sesamoid under fluoroscopic guidance to guide the bur and avoid injuring the plantar aponeurosis.
• Sesamoid resection or sesamoidectomy. This is the most commonly performed surgical procedure. The resection may be partial or total, involving the entire tibial or fibular sesamoid. Sesamoidectomy is not trivial, as the risk of mechanical complications is significant if the fibrous envelope of the sesamoids is injured: metatarsophalangeal deviation, claw toe deformity of the hallux, weakness of plantar flexion of the first phalanx of the hallux, and lateral transfer metatarsalgia.
• Metatarsophalangeal arthroscopy is an interesting technique for the treatment of sesamoid lesions, especially for sesamoidectomy.
• Metatarsophalangeal arthroereisis. This procedure consists of temporarily blocking the metatarsophalangeal joint in a neutral position or slight plantar flexion to offload the sesamoids, mainly in cases of pseudarthrosis.

Prevention of Sesamoid Fractures

Practical tips and exercises

Preventing injuries related to sesamoid fractures is essential to keep your feet in great shape. Here are some simple tips to incorporate into your daily routine:

• Strengthen your feet: Practice exercises such as toe curls and arch work. These movements will not only improve your muscle strength, but also the stability and agility of your foot.
• Choose suitable shoes: Opt for models that provide good support and comfortable cushioning. Footwear should be specifically adapted to the physical activity you practice.
• Vary your physical activity: Alternate types of exercises to avoid overuse injuries. Consider including low-impact activities, such as swimming or cycling, in your routine.

Warm up before activity and stretch afterwards

Before starting your sports activities, take the time to warm up properly beforehand, and stretch thoroughly afterwards, to reduce the risk of injuries. Here are some steps to follow:

• General warm-up: Spend 5 to 10 minutes doing light aerobic exercises. This will help raise your body temperature and prepare your muscles for exertion.
• Targeted stretching: Pay special attention to the muscles in your feet and ankles. Stretching your calves and hamstrings is important after exercise.
• Progress gradually: Gradually increase the intensity of your physical activity to give your body time to adapt.

Incorporating these practices into your routine will help reduce the risk of sesamoid fractures while promoting foot health.

Conclusion

Sesamoid pathologies are mainly traumatic and microtraumatic; they can also be part of a chronic inflammatory disease, metabolic disorder, or infectious pathology.

The imaging assessment, guided by the clinical examination, varies depending on the suspected pathologies. CT scan is essential in chronic pathology to evaluate the sesamoid bone structure.

Functional treatment should always be attempted in cases of traumatic and microtraumatic pathology, over a sufficiently long period to achieve results.

Arthroscopy is probably the best surgical technique for treating sesamoid pathologies as well as potentially associated intra-articular lesions.