What is the most likely cause of discomfort on the plantar aspect of the feet in custom semi-rigid orthoses?

The discomfort on the plantar aspect of the feet when using custom semi-rigid orthoses can be attributed to a lack of relief for the flexor hallucis longus tendon. This tendon plays a crucial role in the flexion of the big toe and is positioned along the plantar surface of the foot. If the orthosis does not provide adequate relief or accommodation for this tendon, it may become irritated and lead to discomfort, especially during activities that involve toe movement or weight-bearing.

The design of custom semi-rigid orthoses must take into account the anatomy and biomechanics of the foot, ensuring that key tendons and muscles are appropriately supported without being excessively compressed. When too much pressure is placed on the flexor hallucis longus tendon, it can create a localized pain or discomfort under the arch or along the plantar surface. Therefore, ensuring that the orthotic design includes the necessary relief for this tendon is essential for patient comfort and effective orthotic function.