Sesamoiditis

**Sesamoiditis** is inflammation of the **sesamoid bones** — two small, oval, pea-sized bones (each about 10-15mm) that are embedded within the **flexor hallucis brevis tendon** on the bottom of the foot, directly beneath the **first metatarsophalangeal (MTP) joint** (the big toe joint). **What Are Sesamoid Bones?** Sesamoid bones are unique — they are NOT connected to other bones by joints. Instead, they are embedded within tendons, similar to the kneecap (patella). Everyone has two sesamoid bones under each big toe: - **Medial (tibial) sesamoid** — on the inner side; larger; more commonly affected (90% of cases) - **Lateral (fibular) sesamoid** — on the outer side; slightly smaller **Their Critical Functions:** 1. **Act as a pulley** — they increase the mechanical advantage of the flexor hallucis brevis muscle, enhancing push-off power during walking and running 2. **Absorb pressure** — they absorb up to **300% of body weight** during walking and up to **800%** during running at the ball of the foot 3. **Protect the tendon** — they prevent the flexor tendon from being compressed against the metatarsal head **Why They Get Injured:** The sesamoids bear enormous repetitive forces. During normal walking, they absorb 50% of body weight with each step. During running, jumping, or dancing en pointe, these forces multiply dramatically. When the load exceeds the bones' capacity to remodel, inflammation develops (sesamoiditis), and with continued overload, stress fracture can occur. Sesamoiditis exists on a spectrum from mild inflammation to stress fracture to avascular necrosis (loss of blood supply). Distinguishing between these is important because treatment intensity differs. A **bipartite sesamoid** — a naturally divided sesamoid present in 10-30% of people — can be mistaken for a fracture on X-ray, so comparison views of the opposite foot are helpful.

The pathophysiology of sesamoiditis involves **mechanical overload** of bones designed to withstand significant but not unlimited repetitive forces: **The Biomechanical Basis:** During the **push-off phase** of gait (toe-off), the first MTP joint extends (big toe bends upward) and the sesamoids are compressed between the metatarsal head above and the ground below. The forces involved are substantial: - **Walking**: 50% of body weight on the sesamoids per step - **Running**: 200-300% of body weight - **Jumping/landing**: Up to 800% of body weight - **Ballet en pointe**: Near-total body weight concentrated on the sesamoids When these forces exceed the bones' capacity for remodeling and repair, a spectrum of injury develops: **Stage 1 — Sesamoiditis (Bone Stress Reaction):** The bone marrow becomes edematous (swollen) from microdamage that outpaces repair. This is the "overuse inflammation" stage — the bone is stressed but intact. Rest and offloading allow full recovery. **Stage 2 — Sesamoid Stress Fracture:** Continued overload causes a crack in the sesamoid bone. Unlike a bipartite sesamoid (smooth, rounded edges), a stress fracture shows irregular, sharp-edged separation. MRI or bone scan differentiates the two. **Stage 3 — Avascular Necrosis (AVN):** If the sesamoid's blood supply is disrupted (from fracture, prolonged inflammation, or vascular insufficiency), the bone tissue dies. AVN causes persistent pain and may require surgical removal. **Risk Factor Contributions:** - **High arches (pes cavus)**: Rigid foot that doesn't absorb shock well → increased sesamoid loading - **High heels**: Shift body weight forward onto the ball of the foot → chronic sesamoid overload - **Tight calf muscles**: Limit ankle dorsiflexion → the foot compensates by increasing MTP joint extension → more sesamoid compression - **Thin shoe soles**: No cushioning between the sesamoids and the ground - **Bony anatomy**: A prominent or plantarflexed first metatarsal concentrates more force on the sesamoids

Treatment follows a **conservative-first approach** that succeeds in 90-95% of cases: **Phase 1: Acute Management (Weeks 1-4)** - **Activity modification** — Reduce or stop activities that load the sesamoids (running, jumping, dancing, high heels). Cross-train with swimming or cycling. - **Offloading** — The cornerstone of treatment: - **Dancer's pad/sesamoid pad**: A felt or gel pad with a U-shaped or oval cutout positioned under the ball of the foot to shift pressure AWAY from the sesamoids. This is the single most effective intervention. - **Stiff-soled shoe or rocker-bottom shoe**: Limits big toe extension, reducing sesamoid compression during push-off - **Carbon fiber footplate insert**: Provides rigid support to limit MTP joint motion - **Ice** — 15-20 minutes after activity; ice massage particularly effective for this localized area - **NSAIDs** — Ibuprofen or naproxen for 1-2 weeks during acute inflammation - **Taping** — Low-Dye taping or sesamoid taping to limit big toe extension **Phase 2: Rehabilitation (Weeks 4-12)** - **Calf stretching** — Tight calves increase forefoot loading; stretch 30 seconds, 3 reps, 3-4 times daily - **Big toe range-of-motion exercises** — Gentle flexion/extension within pain tolerance to prevent stiffness - **Intrinsic foot muscle strengthening** — Towel curls, marble pickups, short-foot exercises to support the first ray - **Gradual return to activity** — 10% per week increase in loading activities **For Sesamoid Stress Fracture:** - **Walking boot or hard-soled post-operative shoe** for 4-6 weeks — complete sesamoid offloading - **Non-weight-bearing or limited weight-bearing** if pain is severe - Healing time: 6-12 weeks (sesamoids heal slowly due to limited blood supply) - Follow-up imaging (MRI or CT) to confirm healing before return to activity **Phase 3: If Conservative Treatment Fails (3-6 Months)** - **Corticosteroid injection** — Peritendinous injection near (not into) the sesamoid. Provides temporary relief. Risk: tendon weakening, fat pad atrophy. Maximum 2-3 injections. - **Custom orthotics** — Rigid orthotic with built-in sesamoid offloading and metatarsal support - **Extracorporeal shockwave therapy (ESWT)** — Emerging evidence for chronic sesamoiditis **Phase 4: Surgery (Rarely Needed — 5-10%)** - **Sesamoidectomy** — Surgical removal of the affected sesamoid bone. Reserved for failed conservative treatment or avascular necrosis. - Medial sesamoidectomy: 85-90% good outcomes. Risk: hallux valgus (big toe drifting outward) if not properly managed - Lateral sesamoidectomy: Higher risk of hallux varus (big toe drifting inward) - Recovery: 6-8 weeks in a walking boot, then gradual return over 3-6 months - Important: Push-off strength may be slightly reduced after sesamoidectomy **Prognosis:** - 90-95% resolve with conservative treatment - Sesamoid fractures heal in 6-12 weeks with proper immobilization - Avascular necrosis has a less favorable prognosis and often requires sesamoidectomy