An orthotic is a shoe insert.

Correction of the biomechanics of the foot and ankle can have a strong effect on that of the patella at the knee.
Synonyms:
shoe insert
foot insole
heel support
orthosis
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FORUM DISCUSSIONS
Knee pain caused by custom orthotics?
Can insoles help prevent or ease anterior cruciate ligament knee injury?
CLINICAL PUBLICATIONS
Are foot orthotics efficacious for treating painful medial compartment knee osteoarthritis? A review of the literature. Marks R and Penton L. Int J Clin Pract. 2004 Jan;58(1):49-57.