The Reliability of Foot Torsional Stiffness Measurements in Asymptomatic Recreational Runners

Abstract

Excessive foot mobility has been identified as a risk factor for overuse injuries in runners. Existing tools used to assess foot mobility either lack reliability, correlation with dynamic foot function, or require a significant amount of experience to use reliably. PURPOSE: To develop a clinical tool that can be used by novice clinicians to assess foot flexibility by measuring the torsional stiffness of the foot and evaluate its reliability. METHODS: A novice clinician (less than one year of experience) performed a structural foot assessment on 10 asymptomatic recreational runners. The assessment consisted of dorsal arch height index (DAHI) and foot torsional stiffness (FTS) measurements using a Forefoot Torsion Measurement Device (FTMD). The same clinician repeated the measurements of DAHI and FTS at a second day approximately one week later. The FTMD provides measurements of angular displacement and torque at a sampling rate of 50 Hz and consists of a split platform controlled by a stepper motor with a torque sensor located in series with the motor that allows for forefoot on rearfoot motion. Data analysis consisted of creating torque - angle curves using the FTS data and fitting the curves using a 2-degree polynomial of the form c1X^2+c2X+b. For each subject, a mean c1 and c2 coefficient and DAHI were obtained for the day 1 and day 2 measurement sessions. Intraclass correlations were used to assess the reliability of the coefficients across the three trials on the same day and Pearson correlations were used to assess test-retest reliability of the mean c1 and c2, and DAHI across days. RESULTS: The correlation between the day 1 and 2 DAHI measurements for the right and left feet were r = .842 (p = 0.002) and r = -0.101 (p = 0.8). The intraclass correlation coefficients for the c1 and c2 coefficients for the right and left feet were 0.887 and 0.927 and .813 and .738, respectively. The correlation between the day 1 and day 2 mean c1 and c2 coefficients were r = .493 (p=0.027) and r=.695 (p=.001), respectively. CONCLUSIONS: The FTMD appears to be a more reliable method of assessing foot flexibility than DAHI regardless of extremity that can be used by novice clinicians.