Researchers at Glasgow Caledonian University in Scotland are investigating how 
computer-aided design and additive manufacturing technologies can improve fabrication of custom orthoses to optimize outcomes for various foot conditions.

“One of the major research themes of our group is looking at how foot orthoses can be personalized to the individual patient,” Scott Telfer, PhD, a research fellow at the School of Health and Life Sciences at Glasgow Caledonian University, told O&P Business News. “Part of this involves looking at whether we can use objective, instrumented gait analysis data taken from the individual to better inform the design of the orthoses, rather than the static and visual observation methods that are normally used.

“However, to be able to do this, we first need to better quantify the effects of changing the orthoses design on gait, and if there is a dose-response effect that we can induce on biomechanical variables,” Telfer said.

Dose response testing

In their study, researchers specifically looked at how the rearfoot post in an orthosis, which is intended to help control the movement of the rearfoot during the stance phase of gait, affects lower limb muscle activity and plantar pressures. To examine this, Telfer and colleagues recruited 12 participants with a pronated foot type. Each participant received a pair of 3/4 semi-rigid orthoses that were custom fabricated based on a 3-D scan of the participant’s feet. Once the original orthoses were fitted, nine variations of the original design were fabricated using a 3-D printer.

The participants walked in a motion analysis lab, and the researchers measured electromyography signals for the biceps femoris, lateral gastrocnemius, medial gastrocnemius, peroneus longus, tibialis anterior, vastus lateralis and vastus medialis as they walked. EMG data was then compared with recorded measurements of 12 age- and gender-matched controls with normal foot type.

The researchers found posting level had no significant effect on muscle activity. However, they did find a significant reduction in activity in the muscles above the knee — vastus medialis, vastus lateralis and biceps femoris — for the test subjects as they walked.

“Although changing the level of posting in the orthoses did not cause any significant changes in any of muscles tested, when participants with pronated foot type used an orthoses of any posting level, it significantly reduced activity in muscles above the knee compared to walking in a shoe without an orthosis,” Telfer said. “The effect was not seen in the group with normal foot type, and indeed was not seen in any muscles below the knee.”

Clinical considerations

The researchers are not sure what caused this reduction in muscle activity, but Telfer said it may be related to improved stability when the pronated foot type is corrected.

“We are running a follow-up study to look further into this,” Telfer said. “There have been some suggestions that pronated foot type may be associated with knee osteoarthritis, so this is potentially highly clinically relevant.”

Telfer also noted these study results can provide insight about quantifying the mechanical effects of foot orthoses.

“Clinicians should be aware that by prescribing a medial post, they will progressively increase the loading on the lateral forefoot,” Telfer said. “They should also be aware that prescribing the type of foot orthoses used in this study to a patient with pronated foot type may decrease above knee muscle activity during walking compared with wearing shoes only.”

Additionally, the study is important for validating the use of 3-D technologies as a research tool. This study was conducted as part of A-FOOTPRINT, an initiative led by Glasgow Caledonian University that is investigating how prescription and manufacturing technologies can be combined to improve ankle and foot orthoses.

“Primarily, the aim of A-FOOTPRINT is to exploit additive manufacturing technologies and use the design freedom provided to develop new devices,” Telfer said. “The dose response study was made possible by our use of a low-cost 3-D printing system, which meant that we could manufacture many variations on a customized orthosis design for each participant at a relatively low cost.” — by Megan Gilbride

Disclosure: This study was conducted as part of A-FOOTPRINT, which is coordinated by Glasgow Caledonian University.