2012 Annual Conference

Sander, Todd

U.S. Army-Baylor University Doctoral Program in Physical Therapy

Digital scanning techniques have been developed to improve custom orthotic fabrication. The purpose of this study was to determine relationships and agreement of foot shape measurements by the INFOOT digital scanner (INFOOT) and manual measurements in three weight-bearing conditions. We hypothesized that there would be no difference between the two measurement techniques.

Twenty-seven males and 33 females (n = 60) were recruited for this study. All were healthy, active duty service members and Department of Defense beneficiaries (age: 30.1 ± 7.0 years; height: 170.4 ± 8.1 cm; weight: 71.4 ± 13.8 kg). Twenty subjects were recruited into low, normal and high arch categories.

Subjects were categorized according to foot type (High Arch, Normal Arch, Low Arch) based on their scores assessed using the Foot Posture Index. Seven measures of foot shape (foot length (FL), instep length (IL), arch height (AH), ball width (BW), oblique ball width (BW), midfoot width (MFW) and heel width (HW)) from one foot was measured manually and digitally by the INFOOT scanner in three weight bearing conditions; full weight bearing (FWB) (bipedal standing), semi-weight bearing (SWB) (seated) and non-weight bearing (NWB).

The relationship between each individual manual measurement and its corresponding INFOOT scanner measurement by weight bearing condition was performed using Pearson’s r and agreement was determined by evaluating bias and limits of agreement for each measurement technique.

Pearson’s r between the manual and digital measurements ranged from 0.86 to 0.96 in FWB, 0.66 to 0.99 SWB, and 0.34 to 0.48 NWB conditions.  Bias and 95% limits of agreement between the manual and digital measures in the FWB, SWB and NWB conditions respectively for FL was 0.19 cm (-0.84 – 1.22), 0.19 cm (-0.09 – 0.48) and 1.32 cm (-3.53 – 6.17), for AH was -5.6 cm (-1.21 – 0.09), -0.68 cm (-1.66 – 0.29), and -1.22 cm (-2.93 – 0.48) and for HW was 0.08 cm (-0.26 – 0.42), 0.06 cm (-0.22 – 0.35) and -0.14 cm (-1.15 – 0.86).  In the FWB and SWB conditions respectively bias and 95% limits of agreement for IL was 0.75 cm (-0.60 – 2.10) and 0.55 cm (-0.41 – 1.52).  In the FWB condition bias and 95% limits of agreement for BW and OBW were -0.42 cm (-0.99 – 1.45) and 0.33 cm (-0.16 – 0.81).

Strong relationships were found between the INFOOT digital scanning technique and manual measurements in FWB and SWB and bias and limits of agreement were acceptable from a clinical perspective. In NWB, FL, AH and HW demonstrated weak to moderate relationships. Further, agreement between the two measurement techniques in NWB demonstrated larger bias and limits of agreement that may have limited utility in aiding orthotic device construction.

Our findings suggest that in comparison to manual measurements, the INFOOT digital scanner acceptably measures foot shape in full and semi weight bearing conditions. However, caution should be utilized when attempting to use the digital technique in non-weight bearing measurements.