The Science of Metatarsalgia
Metatarsalgia represents a symptom complex rather than a specific diagnosis, describing pain under the metatarsal heads in the forefoot. This mechanical overload syndrome occurs when weight-bearing forces exceed the tissues' adaptive capacity, leading to inflammation and pain in the plantar structures of the forefoot. The normal forefoot functions as a complex lever system during push-off, with forces distributed across all five metatarsal heads. The central metatarsals (second and third) typically bear the greatest loads due to their length and position in the transverse arch. When this load distribution becomes pathological, excessive pressure concentrates under one or more metatarsal heads. Several pathophysiological mechanisms contribute to metatarsalgia development. Primary metatarsalgia results from anatomical variants like elongated metatarsals or plantarflexed positioning that increase localized pressure. Secondary metatarsalgia develops from other conditions that alter forefoot mechanics, including hallux valgus, hammer toes, or first ray insufficiency that causes load transfer to the lesser metatarsals. The plantar fat pad plays a crucial role in shock absorption and pressure distribution. With aging, this fat pad undergoes atrophy and displacement, reducing its protective effect. Repetitive loading can accelerate this process, particularly in high-impact activities or when combined with inappropriate footwear. Inflammatory changes occur in response to excessive mechanical stress, affecting the joint capsules, surrounding soft tissues, and skin. Chronic inflammation can lead to synovitis of the metatarsophalangeal joints, plantar plate tears, and development of hyperkeratotic lesions (calluses) that further concentrate pressure points.
Contributing Factors
Normal forefoot biomechanics depend on coordinated function of the metatarsal parabola, transverse arch, and windlass mechanism. During the propulsive phase of gait, the metatarsal heads contact the ground sequentially, with forces distributed according to metatarsal length and position.
The first metatarsal typically bears 30-40% of forefoot load, while the lesser metatarsals share the remainder. This distribution depends on proper first ray function, adequate plantar flexion strength, and normal hallux mechanics. When first ray insufficiency occurs (from hallux valgus, arthritis, or functional weakness), load transfers excessively to the central metatarsals.
Transverse arch collapse represents a common biomechanical dysfunction contributing to metatarsalgia. As the arch flattens, the metatarsal heads spread apart and lose their coordinated load-sharing mechanism. This creates focal pressure points under individual metatarsal heads, particularly the second and third.
Calf muscle tightness significantly impacts forefoot loading by limiting ankle dorsiflexion during midstance. This forces earlier heel rise and prolonged forefoot contact time, increasing the duration and magnitude of metatarsal loading. The resultant compensatory changes can overload the forefoot structures.
Footwear choices dramatically affect forefoot biomechanics. High heels shift body weight forward, increasing forefoot loading by up to 75%. Shoes with inadequate cushioning or support fail to attenuate impact forces, while narrow toe boxes compress the transverse arch and alter normal pressure distribution patterns.
Intrinsic foot muscle weakness contributes to metatarsalgia by reducing the foot's natural shock absorption capacity. These muscles help maintain the transverse arch and provide dynamic stabilization during loading. When weakened, they cannot effectively distribute forces, leading to concentrated pressure under individual metatarsal heads.