Reliability and validity of combined imaging and pressures assessment methods for diabetic feet

Objectives: To determine the reliability of using 3-dimensional (3D) spiral x-ray computed tomography (SXCT) imaging methods to measure anatomic foot structure and to test the validity of using a loading device to simulate walking pressures on the plantar foot during SXCT examination. Design: Nonrandomized control trial of consecutive patients with complete data compared with age-matched controls. Setting: A clinical SXCT scanner and physical therapy laboratory in a local hospital. Participants: Eight subjects with diabetes and a history of forefoot ulcers and 8 control subjects. Interventions: SXCT imaging and plantar pressure analysis were used to acquire 3D volumetric structure and pressure data of the foot during 4 foot positions, 2 weight bearing and 2 non-weight bearing. Main Outcome Measures: Differences between repeated SXCT measures of foot structure. Comparisons of plantar foot pressure. Foot structure measurements. Methods for measuring the bony angles and soft-tissue thickness were developed and reliability tests were performed. Results: There was essentially no bias (<+/-0.5mm or +/-0.5degrees) and a high degree of reliability (81% of the measures had a reliability <2.0mm or 2degrees) when measuring foot structures. Correlations of pressure measures collected on the loading device compared with those collected during walking were (mean standard deviation) r = .66 +/- .06. The percentage agreement between the pressures collected on the loading device and during walking was 91.1% +/- 4.7%. Conclusion: Reliability of anatomic foot structure measurements and validity of plantar loading during visualization were good. These methods may be used to determine structural differences between diabetic and healthy feet and to evaluate how these differences relate to plantar pressures.