Foot Shapes Captured by Plaster Casts vs. Resin-Impregnated Slipper Socks: A Qualitative Comparison Kathleen M. Halat, DPM San Francisco Bay Area Foot & Ankle Residency Program Kaiser Permanente - Oakland, CA

Description of the Slipper Sock One-time use slipper sock impregnated with an extra-fast setting water- curable polyurethane resin New alternative to plaster casting Manufactured by STS of Mill Valley, CA Comes in 4 sizes (S,M,L,XL)

Why use the Slipper Sock? Clean Easy to use Quick drying Light Less likely to be damaged during shipping

Application of the Sock Apply clear plastic bag to foot Wet the sock Apply the sock over the foot Apply the plastic velcro strip across the dorsum of foot at the level of the arch Hold foot in desired position for casting After cast dry, detach strip, slip off sock

Purpose of this Study Will a resin-impregnated slipper sock capture the same qualitative foot shape as plaster casting What is the time difference in casting between the two methods?

Patient Population 13 subjects, 26 feet Subjects recruited from student volunteers in the podiatry program at Samuel Merritt College in Oakland, CA

Study Protocol - Casting Each foot was casted with both techniques and by the same person All patients were casted supine with the subtalar joint held in neutral position Prior to casting, heel bisection drawn on patient’s posterior heel/leg After cast dried, the heel bisection from the posterior leg was reflected back onto the cast before removal from the foot

Time to dry: Time measured from when cast placed on subject’s foot to when cast considered dry enough to be removed without deforming the cast Time measured from when cast placed on subject’s foot to when cast considered dry enough to be removed without deforming the cast Average time to dry compared between plaster and resin-impregnated socks Average time to dry compared between plaster and resin-impregnated socks Study Protocol - Timing

Each cast was balanced to perpendicular using the reflected heel bisection and then cut to a standard 2cm height Each cast was balanced to perpendicular using the reflected heel bisection and then cut to a standard 2cm height The cast was then balanced and scanned using a 3D CamCad system at Prolab-USA The cast was then balanced and scanned using a 3D CamCad system at Prolab-USA From the scan, the following information was collected and compared between the 2 techniques: From the scan, the following information was collected and compared between the 2 techniques: Forefoot width Heel width Arch height Location of maximum arch height Study Protocol - Scanning

Cast Evaluation From the AP scan: -Forefoot width -Heel width From the Lateral scan: -Arch height -Location maximum arch height

Results – Time for Casting Average time for resin-impregnated sock: 1 minute, 50 seconds (range seconds) Average time for plaster cast: 2 minutes, 55 seconds (range seconds), difference statistically significant (p<0.01) STS cast 37% faster, difference statistically significant (p<0.01)

Results – Cast shapes Mean forefoot width: Sock: 3.38 cm, Plaster: 3.53 cm Sock: 3.38 cm, Plaster: 3.53 cm Difference between Plaster – Sock for each foot: Range (-0.04 to 0.39 cm), mean difference = 0.14cm Difference between Plaster – Sock for each foot: Range (-0.04 to 0.39 cm), mean difference = 0.14cm Statistically significant difference in average value? NO (p=0.06) Statistically significant difference in average value? NO (p=0.06) Mean heel width Sock: 2.56 cm, Plaster: 2.49 cm Sock: 2.56 cm, Plaster: 2.49 cm Difference between Plaster – Sock for each foot: Range (-0.2 to 0.13 cm), mean difference = cm Difference between Plaster – Sock for each foot: Range (-0.2 to 0.13 cm), mean difference = cm Statistically significant difference in average value? NO (p=0.08) Statistically significant difference in average value? NO (p=0.08)

Arch height Sock: 0.87 cm, Plaster: 0.98 cm Sock: 0.87 cm, Plaster: 0.98 cm Difference between Plaster - Sock for each foot: Difference between Plaster - Sock for each foot: Range (-0.20 to 0.39 cm), mean difference = 0.08cm Range (-0.20 to 0.39 cm), mean difference = 0.08cm Statistically significant difference in average value? YES (p=0.03) Statistically significant difference in average value? YES (p=0.03) Location of maximum arch height STS: 3.74 cm, Plaster: 3.78 cm STS: 3.74 cm, Plaster: 3.78 cm Difference between Plaster - Sock for each foot: Difference between Plaster - Sock for each foot: Range (-0.50 to 0.70 cm), mean difference = 0.02cm Range (-0.50 to 0.70 cm), mean difference = 0.02cm Statistically significant difference in average value? NO (p=0.71) Statistically significant difference in average value? NO (p=0.71) Results – Cast shapes

Summary Forefoot width, heel width and location of maximum height are similar between the two methods Arch height is slightly lower when using the sock, being on average 1mm less. Casting with the resin-impregnated sock is 37% faster than plaster

Troubleshooting the Resin- Impregnated Socks To get the best possible cast: Use the proper size sock Use the proper size sock Apply the velcro strip correctly Apply the velcro strip correctly Wet the sock completely and smooth the resin over the entire sock before it dries Wet the sock completely and smooth the resin over the entire sock before it dries After applying sock, pull on posterior heel to capture the heel contour After applying sock, pull on posterior heel to capture the heel contour Use cold water the first few times you are using the sock, allowing you to become familiar with the technique/product Use cold water the first few times you are using the sock, allowing you to become familiar with the technique/product

Do these differences really matter? Average differences between the two techniques for each measurement ranged from 1-1.5mm Is this going to make a difference in an orthosis? Additional research comparing orthoses made from the two different techniques is needed

Conclusions Qualitative foot shapes captured by the two methods are very similar While arch height was lower with the resin- impregnated sock on average, it is not known whether or not this difference is clinically significant In terms of time, resin-impregnated socks offer a substantial benefit

Thank You! To : ProLab-USA, in particular Ray Dixon ProLab-USA, in particular Ray Dixon student volunteers at the San Francisco Veterans Administration Health Center student volunteers at the San Francisco Veterans Administration Health Center STS of Mill Valley, CA STS of Mill Valley, CA