Menz HB, Munteanu SE. Validity of 3 Clinical Techniques for the Measurement of Static Foot Posture in Older People. J Orthop Sports Phys Ther. 2005;35(8):479-486.

Study Design: Concurrent validity study.
Objectives: To determine the validity of 3 clinical methods for assessing static foot posture in older people.
Background: Variations in the structure of the medial longitudinal arch are thought to influence lower extremity function; however, the validity of clinical measurements has not been fully established.
Methods and Measures: Clinical measurements of arch index (AI), navicular height (NH), and Foot Posture Index (FPI) were performed on 95 subjects (31 men and 64 women), aged 62 to 94 years (mean ± SD, 78.6 ± 6.5 years). These clinical measurements were then correlated with 3 arch-related measurements from radiographs: navicular height (NHr), calcaneal inclination angle (CIA), and calcaneal first metatarsal angle (C1MA).
Results: All 3 clinical measures demonstrated significant associations with each of the radiographic parameters (P<.01). NH was highly correlated with NHr (Pearson r = 0.79), followed by C1MA (r = –0.53), and CIA (r = 0.44). The AI was highly correlated with the C1MA (r = 0.71) and CIA (r = –0.68), but only moderately correlated with NHr (r = 0.52). The FPI demonstrated weaker correlations with the radiographic parameters (NHr, r = 0.59; CIA, r = 0.36; C1MA, r = 0.42).
Conclusion: Clinical measurements of AI, NH, and FPI provide valid information regarding the structure of the medial longitudinal arch; however, each test may reflect different aspects of arch structure. NH would appear to be the most useful clinical measure, as it is simple to perform and provides an accurate representation of the skeletal alignment of the medial longitudinal arch. Further refinement of the clinical measurement of NH is now required to improve its moderate intratester and intertester reliability.