# Biomechanical Effect of 3D-Printed Foot Orthoses in Patients with Knee Osteoarthritis
###### Abstract  
Lateral wedges are a common conservative treatment for medial knee osteoarthritis (OA). However, use of lateral wedges might increase the ankleevers moment. To minimize the risk of ankle symptoms, lateral wedges with custom arch support are suggested. However, the manufacturing process of a custom foot orthosis (FO) is complicated, labor-intensive, and time-consuming. The technology of 3D printing is an ideal method for mass customization. Therefore, the purpose of this study was to develop custom FOs using 3D-printing techniques and to evaluate the effects of 3D-printed FOs in patients with knee OA. Fifteen patients with medial knee OA were enrolled into this study. Kinematic and kinetic data were collected during walking by using an optical motion capture system. A paired-sample \(t\)-test was conducted to compare biomechanical variables under two conditions: walking in standard shoes (Shoe) and walking in shoes embedded with 3D-printed FOs (Shoe + FO). The results show that the first and second peak knee adduction moments were significantly reduced by 4.08% and 9.09% under the Shoe + FO condition. The FOs alter the biomechanical environment in a way that reduces the variables used to infer abnormal loads at the knee and ankle that could result in painful symptoms.  
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walking without a wedge [10; 11; 12]. However, the lateral shift in the COP also increases the ankle version moment (AEM) [13]. This might have implications for patients with knee OA who have acute ankle sprains or chronic ankle instability [14]. Moreover, the use of lateral wedges has been indicated to increase version of ankle joint [10] and stride width [15] during walking. An increased stride width increases mediolateral ground reaction force (GRF), that might influence the reduction of KAM. To minimize the risk of ankle symptoms in patients with medial knee OA, lateral wedges with custom arch support are suggested [16]. A previous study showed that when patients with medial knee OA wore lateral wedges, individual biomechanical responses, such as the frontal plane moment arm of the GRF at the knee and the peak KAM, ranged from decreases of approximately 25% to increases of over 20% [17]. A possible explanation for this variability in the responses is the foot posture. The prescription of orthotic devices should be patient-specific. This is because various levels of malalignments likely require different FO designs. However, the manufacturing process of a custom foot orthosis (FO) is complicated, labor-intensive, and time-consuming.  
In the conventional subtractive manufacturing process, materials are removed from a larger piece to form the FO. In contrast to subtractive manufacturing, additive manufacturing or three-dimensional (3D) printing processes fabricate objects by adding material layer by layer, and this may be a useful alternative to subtractive manufacturing methodologies. The technology of 3D printing is an ideal method for mass customization, because it has the potential for fabricating customized FOs at relatively low prices and eliminates much of the labor [18]. Moreover, custom FOs fabricated by combining 3D printing with 3D surface scanning and computer-aided design can produce positive biomechanical effects [19].  
Therefore, the purpose of this study was to develop custom FOs using 3D printing techniques and to evaluate the changes of COP path, and knee and ankle joint moments in patients wearing the 3D-printed FOs during level walking. This study hypothesized that the 3D-printed FOs would decrease the peak KAM, KFM, AEM, and ankle inversion moment (AIM), and shift the COP path laterally.