The sesamoid bone of the hallux: anatomical definition, pathologies and common symptoms

Definition and anatomy of sesamoid bones

The sesamoid bone is a particular anatomical structure that we will explore together.

What is the sesamoid bone?

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 called by analogy to sesame seeds. These are small, very dense, robust bones, embedded in a complex capsulo-ligamentous system, important for the biomechanics of the foot.

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

Where are the sesamoid bones located?

These small bones are found in several parts of the human body. They are found notably in the foot, more specifically under the big toe, but also in the hands, knees, and wrists.

What are the functions of the sesamoid bones?

The metatarso-phalango-sesamoid joint consists of 2 joints: the first ray metatarsophalangeal joint (MTP1) and the metatarso-sesamoid joint (MSJ).

The MTP1 acts like a hinge with a fixed transverse axis of rotation in flexion/extension, up to 30° of dorsal flexion. The sesamoids are thus stabilized by the intersesamoid crest or crista. Beyond 30° of dorsal flexion, the MTP1 acts like a condyloid joint because the crista no longer contributes to stabilization. The joint is then actively stabilized by tightening of the capsulo-ligamentous and muscular structures.

The metatarso-phalango-sesamoid joint is a spheroidal joint, allowing flexion/extension, varus/valgus, and pronation/supination. It helps cushion and absorb body weight, stabilizes the long flexor of the hallux (LFH) and the first ray to increase its propulsive efficiency for walking via a pulley effect. It also allows foot inversion via the pulley effect during hallux dorsiflexion.

During walking, the deltoid ligament complex (ankle) and spring ligament (plantar calcaneonavicular ligament) initiate the locking of the foot while stabilizing the ankle.

During walking, at the flat foot phase, the tendon of the posterior tibial muscle pushes the internal malleolus forward, causing external rotation of the leg segment. This external rotation is transmitted to the head of the talus, allowing the talonavicular joint to lock, and increasing the propulsive efficiency of the Suro-Achilleo-Plantar complex.

The hallux bearing on the ground undergoes a supination force by the ground reaction. The first metatarsal, attached to the inverted foot, undergoes dynamic pronation due to the step progressing forward; it rotates in pronation centered on the lateral sesamoid, allowing alignment of the metatarsal and phalangeal axes along the LFH path. This mechanism of counter-rotation enables ligament tightening and muscle locking, stiffening the joint for propulsion and limiting valgus and dorsal flexion of the MTP1.

The concept of biotensegrity can explain the phenomenon of reversible cyclic deformation of the foot. The sesamoids are directly connected with the bones of the leg, ankle, and foot through aponeurotic, ligamentous, muscular, and tendinous connections. The sesamoids can be seen as a node of convergence of different muscular, tendinous, and ligamentous structures, which, thanks to their density, instantly transmit energy and movement, and adapt to significant constraints allowing instant changes in the shape of the foot.

Pathologies related to sesamoid bones

Sesamoid bones, although small, can be susceptible to various pathologies. These sesamoid bone problems can cause significant pain and affect mobility. At the Foot Clinic, we have extensive experience in the diagnosis and treatment of these conditions.

Traumatic Pathologies

• Fractures
• Sesamoid fractures often go unnoticed at first. Diagnosis generally occurs later at the chronic stage.
• Non-displaced fractures are treated functionally. Walking is possible depending on the pain, but with a forefoot offloading shoe with a rigid sole to limit tension constraints on the fracture.
• Displaced fractures have more or less significant interfragmentary gaps. These fractures occur in cases of significant trauma with forced and supported dorsiflexion of the big toe, generally in athletes. Treatment is then surgical.
• Turf Toe is a combination of injuries that may include a sesamoid fracture, capsular and ligament lesions, tendon and muscle injuries, as well as cartilage injuries of the metatarsophalangeal joint.
• Pseudarthrosis can become asymptomatic or remain painful.

Microtraumatic Pathologies

Stress fractures or fatigue fractures cause pain that appears suddenly or insidiously; weight-bearing on the first ray is then painful. Clinical examination may identify bursitis under the sesamoids, and palpation of the affected sesamoid usually produces exquisite pain. It is necessary to look for a context of repetitive activity with overuse in sports, professional, or daily life. Poor footwear can also be an aggravating factor, especially when an activity is performed regularly with shoes not suited for it. Certain morphotypes encourage high pressure in the anteromedial forefoot, such as hallomegaly with a relatively long first metatarsal, and a high anteromedial arch.

Necrotic Pathologies

Osteonecrosis and osteochondritis are very rare, difficult to diagnose, and likely originate from vascular perfusion defects in the bone. The pain is mechanical and decreases with rest. Nighttime inflammatory flare-ups are possible.

Arthritic Pathologies

Metatarso-sesamoid osteoarthritis can be secondary to trauma, repeated microtrauma, or degenerative changes. This is the most common condition and is often asymptomatic when isolated. It can be symptomatic or not when associated with the metatarsophalangeal joint involvement, particularly in hallux valgus.

Inflammatory Pathologies

Chronic inflammatory conditions, such as rheumatoid arthritis, cause widespread joint involvement called arthritis. Involvement of the big toe thus concerns the metatarsophalangeal and metatarso-sesamoid joints.

Sesamoid involvement may be isolated or associated with widespread joint pain in the context of microcrystalline arthritis, such as gout and articular chondrocalcinosis.

Infectious Pathologies

Infection of the sesamoids may be associated with a plantar perforating ulcer in diabetics and is frequently associated with neighboring infectious osteoarthritis.

Hallux Valgus and Sesamoid Involvement

Pronation of the first metatarsal can be significant in the congenital and juvenile forms of hallux valgus, thereby increasing pressure on the sesamoids, mainly the tibial sesamoid, thus promoting metatarso-sesamoid osteoarthritis.

Treatment of sesamoid bone disorders

Conservative treatments for the sesamoid bone

Conservative treatments are generally proposed as a first option :

• Partial or total offloading of the forefoot.
• Toe strapping (hallux) constraining the metatarsophalangeal joint of the hallux into plantar flexion to limit tensile stress on the sesamoids.
• The custom-molded rigid orthosis helps keep the joint in plantar flexion.
• The corrective orthopedic insole with a relief cup under the sesamoids.

Surgical options for sesamoid bone pathologies

These remain exceptional and are adapted to the type of lesion to be treated.

• Osteosynthesis is indicated for displaced, non-comminuted fractures of the sesamoids.
• Thinning is indicated in prominent, hypertrophic, pointed sesamoids, generally in the context of hypotrophy or atrophy of the plantar fat pad.
• Sesamoid resection or sesamoidectomy is the most commonly performed surgical procedure. The resection may be partial or total, involving the entire tibial or fibular sesamoid.
• Metatarsophalangeal arthrorisis consists of temporarily blocking the metatarsophalangeal joint in a neutral position or slight plantar flexion to offload the sesamoids, especially in cases of pseudarthrosis.

Physical therapy for the sesamoid bone

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.

Prevention of Sesamoid Bone Disorders

Prevention of sesamoid bone pathologies is important. It is important to take preventive measures, particularly when it comes to choosing footwear and sports activities. Here are some tips to help you.

Appropriate footwear

The choice of footwear is essential for protecting the sesamoid bones. It is preferable to opt for shoes that offer good support and optimal comfort. High heels or shoes that are too tight can put excessive pressure on the sesamoid bones, so it is advisable to avoid them.

Tips for athletes with sesamoid pain

For athletes, preventing sesamoid bone pathologies involves practicing sports in a way that respects the foot. It is recommended to avoid movements that excessively strain these bones, such as repeated jumping or running on hard surfaces. Good running technique and proper warm-up can also help with prevention. The choice of shoes is crucial; it is necessary to have a pair of shoes suited to the physical activity performed.

Activities to avoid in case of sesamoid pathology

Certain activities can worsen an existing sesamoid pathology. For example, high-impact sports such as running or jumping can be harmful. It is therefore advisable to opt for gentler activities, such as swimming or cycling, which put less strain on the sesamoid bones.