Proximal Plantar Intrinsic Tendinopathy: Anatomical and Biomechanical Considerations in Plantar Heel Pain

Plantar heel pain is often managed through podiatric and physical therapy interventions. Numerous differential diagnoses may be implicated in patients presenting with plantar heel pain; however, symptoms are often attributed to plantar fasciitis. Abductor hallucis, flexor digitorum brevis, and quadratus plantae share proximal anatomic attachment sites and mechanical function with the plantar fascia. Although these plantar intrinsic muscles each perform isolated digital actions based on fiber orientation and attachment sites, they function collectively to resist depression of the lateral and medial longitudinal arches of the foot. Overuse injury is the primary contributing factor in tendinopathy. The close anatomic proximity and mechanical function of these muscles relative to the plantar fascia suggests potential for proximal plantar intrinsic tendinopathy as a result of repetitive loading during gait and other weightbearing activities. To date, this diagnosis has not been proposed in the scientific literature. Future studies should seek to confirm or refute the existence of proximal plantar intrinsic tendinopathic changes in patients with acute and chronic plantar heel pain through diagnostic imaging studies, analysis of lactate concentration in pathologic versus nonpathologic tendons, and response to specific podiatric and physical therapy interventions germane to tendinopathy of these muscles.