Although the term ‘aponeurosis’ is often used to describe the structure of the plantar fascia, this only takes into consideration the unilateral arrangement of the type I collagen fibres while disregarding the multidirectional arrangement of the fibres in its configuration.
While studying the microscopic properties of the plantar fascia, Carla Stecco of the Department of Molecular Medicine at the University of Padua, observed a multilayer configuration of the collagen fibres in proximal-to-longitudinal, vertical, transverse and oblique directions; with the exception of a few elastic fibres, the plantar fascia is predominantly composed of type I collagen.
Originating from the calcaneal tuberosity, the plantar fascia attaches itself distally into the bases of the proximal phalanx in the form of three bands – medial, lateral and central.
The tibial or medial band of the plantar fascia is the least prominent and covers the plantar surface of the abductor hallucis muscle while inserting into the first metatarsal joint. The fibres are in continuity with the dorsal aponeurosis, the inferior extensor retinaculum and the flexor retinaculum of the foot.
The central component is the thickest and originates from the plantar aspect of the medial tuberculum to cover the flexor digitorum brevis muscle before dividing into five longitudinally oriented bands at the mid-metatarsal level. Each band divides further to form tracts that are superficial and deep, proximally to the metatarsal heads.
The lateral band covers the plantar portion of the abductor digiti quinti muscle to continue with the muscle’s fascia. The structure of this band is variable and ranges from fully developed to incomplete with only partial distal extension. At the cuboid level, the lateral band bifurcates into medial and lateral crura.
The mechanical functioning of the plantar fascia plays a pivotal role in supporting and stabilising the medial longitudinal arch by creating tension within the plantar structure to limit the elongation of the arch in weight bearing activities.
Dorsiflexion of the toes during the propulsive phase of gait results in the plantar fascia being wound around the metatarsal heads causing a shortening in the distance between the calcaneus and metatarsals. This increases tension in the fascia and elevates the medial longitudinal arch.
The shape of the arch influences the loading of the fascia, with tension within the plantar fascia being proportional to the span of the arch; this implies that a low-arched structure would result in significant fascial tension causing excessive stress on the plantar fascia.
With a deterioration in the medial longitudinal arch, the posterior tibialis muscle weakens, minimising its efficiency in reducing tension applied to the plantar fascia, causing the ligament to elongate during pronation; this elongation decreases the windlass mechanism effect on the foot, producing microscopic tears within the fascia and leading to plantar fasciitis.
Rehabilitation programmes for the treatment of plantar fasciitis include strengthening exercises to restore the efficiency of the muscles involved in facilitating the windlass mechanism – posterior tibialis, ankle plantar flexors and peroneus longus muscles – in addition to calf stretching exercises.
The use of customised orthotics such as MASS4D® enforces biomechanical control by reducing hyperpronation, supporting the medial longitudinal arch, strengthening the intrinsic and extrinsic muscles and improving range of motion in the joints; all these factors help in decreasing the excessive strain on the plantar fascia, enabling it to function in its optimal capacity.
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