The influence of medial and lateral placement of orthotic wedges on loading of the plantar aponeurosis - An in vitro study

Background: Repetitive trauma and overuse of the plantar aponeurosis are be lieved to be causal factors of plantar fasciitis, Therefore, it is importan t to know how an orthosis influences loading of the plantar aponeurosis, Th e aim of this study was to quantify strain in the plantar aponeurosis in ca daveric feet with the use of various combinations of orthotic wedges. Methods: An in vitro test that simulated static stance was used to determin e the loading characteristics of the plantar aponeurosis. A differential va riable reluctance transducer was operatively implanted into the plantar apo neurosis of nine fresh-frozen cadaveric lower limbs. Each specimen was moun ted in an electromechanical testing machine that applied an axial load of a s much as 900 newtons to the tibia. Eight different combinations of test co nditions, in which wedges (each with a 6-degree incline) were or were not p ositioned under the medial and lateral aspects of the forefoot and hindfoot , were evaluated, with the plantigrade foot used as a neutral control. Results: Each of the test conditions that involved a wedge under the forefo ot resulted in strain that was significantly different from that in the neu tral control. A wedge under the lateral aspect of the forefoot decreased st rain in the plantar aponeurosis, and a wedge under the medial aspect increa sed strain (p < 0.05), The test conditions that involved a wedge under the hindfoot but not under the forefoot resulted in strains that were not signi ficantly different from those in the neutral control (p > 0.05), Conclusions: A wedge under the lateral aspect of the forefoot transmits loa ds through the lateral support structures of the foot, locking the calcaneo cuboid joint and decreasing strain in the plantar aponeurosis, A wedge unde r the medial aspect of the forefoot transmits loads through the medial supp ort structures of the foot, which produces a truss-like action that increas es strain in the plantar aponeurosis. Clinical Relevance: Orthotic wedges seem to be effective in controlling the load-path pattern in the foot. The results of the tests involving a wedge under the lateral aspect of the forefoot were noteworthy, as the potential of such a wedge for reducing strain in the plantar aponeurosis was not prev iously known, The data suggest that an orthotic wedge under the lateral asp ect of the forefoot thus may be effective for the treatment of plantar fasc iitis.