November 2021

THE VIABILITY OF IN-SHOE INSOLES TO MEASURE PRESSURE AND SHEAR IN PATIENTS WITH CHARCOT ARTHROPATHY

By Jessi Martin, Brian Davis, Grant McMillan, and Larry Goss

Peripheral neuropathy is a condition that occurs as a complication of diabetes mellitus and disrupts the sensory, autonomic, and motor systems. Clinical symptoms of peripheral neuropathy can include muscle weakness, numbness, lack of coordination, and pain.

Charcot arthropathy can develop when an injury occurs in a patient with peripheral neuropathy. Repeated loading on this injury creates an inflammatory response and eventual bone resorption. If left untreated, this disease can progress to the collapse of the medial arch. Once the longitudinal arch has collapsed, high-pressure concentrations can occur due to abnormal loading . If left untreated, these pressure concentrations can result in ulceration, infection, and subsequent limb loss. At this stage, the only treatment option is surgical intervention.

To date, about 60% of surgical implants used in the correction surgery for Charcot Arthropathy fail. The failure can be attributed to the unnatural loading of the implants. Ergo, the best treatment for Charcot arthropathy is prevention and early detection before the foot collapses.

Davis et al [doi:10.1016/j.jbiomech.2016.12.024] showed that in neuropathic patients, the difference in shear between the 1st metatarsal and the heel increases when the arch is collapsing. The limitations in their approach is that patients must walk across a stationary platform. To be able to truly detect early signs of arch collapse in patients with Charcot arthropathy, an in-shoe insole would be a preferred solution. This abstract assesses the viability of the use of in-shoe insoles to measure pressure and shear as compared to the over-ground shear-measuring platform.

METHODS

Ten healthy participants were recruited for this IRB-approved study [age range, 20-42 years; average weight for women, 148.6 ± 20 lbs, for men, 170.0 ± 11 lbs; no gait-altering medical history].

The 2 instrument systems used in this study were the shear platform utilized in Davis et al created by ISSI in Dayton, Ohio, and in-shoe insoles, also created by ISSI. Both  measure shear and pressure.

The shear platform measures shear and pressure across the entire foot whereas the insoles measured pressure and shear from sensors placed under the heel, first metatarsal, and fifth metatarsal.

Each participant took 1 step barefoot over the shear platform with 1 foot. The participant repeated this 5 times. Then, the participant placed the insoles in both shoes, barefoot, and took approximately 5-7 steps while the website was recording. These sets of steps were repeated twice.

Pressure and shear data from each sensor were analyzed using custom software. Shear values from the platform were extracted to match data from corresponding sensor locations in the insoles.

Time intervals corresponding to when both the heel and metatarsal were registered on the plate/insoles were selected [corresponding to when the arch could be ‘collapsing’]. To assess the shear ratio and accurately compare the platform to the insoles, the difference in anterior/posterior (a/p) shear for the first metatarsal and the heel were calculated and compared. The peak difference was then recorded.

RESULTS AND DISCUSSION

There was no significant difference in shear differences (1st MTH – heel) when comparing insole and overground data (Figure 1).

The peak shear difference for the insoles was approximately 4.09 kPa with standard deviation of approximately 0.8 kPa, whereas the peak shear difference for the shear platform was about 5.41 kPa with a standard deviation of approximately 0.8 kPa. There were roughly equal amounts of variation in the difference measurements for the insoles and the shear platform. The variation in differences can be attributed to the fact that the participants had varying shoe sizes, but only one insole size was used.

Additionally, the a/p shear difference results obtained in Davis et al were approximately 9 times larger than the peak a/p shear difference from the insoles and approximately 6 times larger than the peak a/p shear differences from the platform. These differences can be attributed to the a/p shear calculation for the heel and 1st metatarsal. Davis et al calculated using the first 50% of stance, including heel strike until midstance. This study calculated a/p values using the period where both the heel and 1st metatarsal are on the ground, excluding heel strike and toe-off.

CONCLUSION

The results indicate that in-shoe insoles are a viable option for measuring shear and pressure forces under the foot. Further studies should be conducted with diabetic neuropathic patients to assess the same viability at detection in disease state and to assess the interference of socks inside the insoles.

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