You will find zero articles about foot and ankle biomechanics and orthotics in the NEJM. Look at foot and ankle specific journals such as Foot and Ankle International (FAI), Journal of Foot and Ankle Surgery (JFAS), Foot and Ankle Specialist (FAS), Clinics in Podiatric Medicine and Surgery (Clinics), Foot and Ankle Clinics (FAC), and also the foot/ankle sections of Journal of Bone and Joint Surgery (JBJS)/American Journal of Sports Medicine (AJSM). There are also some classic textbooks out there such as Normal and Abnormal Function of the Foot by Root and Weed, among others.