Introduction: The purpose of this paper is to demonstrate the biomechanical efficacy of a custom molded UCBL with articulated ankle AFO to functionally brace and conservatively treat posterior tibial tendon dysfunction (PTTD). Methods: Cadaver legs were thawed and a plaster mold of the foot and ankle in neutral position was made. From the mold a custom UCBL foot insert was fabricated and assembled to an AFO with an articulated ankle joint for each leg. Ten Nm dorsiflexion (DF), plantarflexion (PF), varus (VR) and valgus (VL) loads were applied to the cadaver foot and fluoroscopy was used to image the positions of the ankle and subtalar joints before and after simulation of PTTD both with and without the AFO. PTTD Stage 2 was surgically created with a scalpel through a small skin wound. Measures of ankle and subtalar position were made from the fluoroscopic images with Imagpro software. Results: The AFO had minimal effect on sagittal ROM: 47.6° ± 19.8 without; and, 45.5 ° ± 21.6 with the AFO. The AFO controlled coronal plane ROM (P < 0.002): 27.0 ° ± 9.0 without; and, 9.7 ° ± 3.3 with the AFO. The AFO was most effective at reducing VL motion: 19.4 ° ± 8.5 vs. 5.1 ° ± 1.1, compared to VR motion: 7.7 ° ± 2.5 vs. 5.6 ° ± 2.2. Conclusions: The articulated AFO with a custom molded UCBL foot insert is effective at resisting varus - valgus loading at the ankle and subtalar joints, which is critical for the treatment of PTTD. The AFO does allow for near normal flexion - extension movement which is desirable.