Foot Posture Index is an observational assessment tool that enables clinicians to easily and quickly identify the level of pronation in the patient’s standing feet. It uses set criteria and a simple scale to classify the foot as neutral, pronated, or supinated.
Previous research has established the reliability of FPI scores in asymptomatic populations. This study aimed to establish FPI normative values in children, taking age and gender into consideration.
Normative Values
Foot posture plays an important role in the alignment and mechanics of the lower extremity. Abnormal foot posture can lead to common conditions such as plantar fasciitis, patellofemoral pain syndrome, and low back pain. Accurately assessing foot posture is essential for the clinician to determine the best treatment approach. However, relying solely on subjective opinions can lead to inconsistent outcomes. This is where the Foot Posture Index (FPI) comes in.
The FPI assesses standing foot posture across multiple foot segments through palpation and observation. It includes six independently evaluated criteria: talar head palpation; supralateral and infralateral malleolar curvature; inversion/eversion of the calcaneus; bulking of the talonavicular joint; and congruence of the medial longitudinal arch. Each criterion is rated on a scale of -2, -1, 0 (neutral), or +1, where more pronated features are rated as higher and more supinated features are rated as lower.
Previous studies have shown the FPI to be a reliable tool for assessing foot posture. This study aimed to establish normative values for the paediatric population, using a cross-sectional sample of 1,762 children (863 boys and 899 girls) aged 6-11 years from Malaga, Granada and Plasencia (Spain). The results confirm that the FPI is a valid and reliable method of determining foot posture in childhood, as well as its normal variation with age. As a guideline, the 50th percentile of the FPI score is 4 points in both genders at age 6, which progressively falls to 3 points in children aged 11 years.
Reliability
Foot posture is a critical component of overall musculoskeletal health, and abnormal foot position contributes to common conditions like plantar fasciitis and patellofemoral pain syndrome. Therefore, it is important for clinicians to accurately and reliably evaluate foot posture, as this can inform treatment plans to optimise outcomes.
Most measures of foot posture have been extensively scrutinised for reliability in the adult population, however not so much attention has been directed towards establishing their validity and reliability in paediatric patients. This is despite the fact that many of these measurements are used in the context of treating children with foot and ankle pathologies.
To address this, Cornwall et al sought to determine FPI reference values in the paediatric population. They did so by investigating test-retest and inter-rater reliability of the FPI-6 total score and individual criteria for both the left and right feet of each participant.
They found that the overall score of the FPI-6 was a reliable measure of foot posture, with excellent test-retest and inter-rater agreement. This was in part due to the FPI-6 assessing the alignment of five image-based criteria. The raw score, however, was less reliable and should be interpreted with caution. This is because of the varying foot structures seen in the paediatric population, such as oedema or severe deformities that may obscure the visualisation of the bony structure.
Correlation with Radiographic Measurements
There is a belief that foot morphology influences lower extremity function, and consequently may predispose to injury [1]. Although radiographic evaluation is considered the gold standard for assessing foot posture, its time-consuming nature and high costs often limit its use in clinical practice. Therefore, it is imperative to be able to quickly and reliably evaluate the shape of the foot.
The Foot Posture Index is a practical clinical tool that utilizes six separately evaluated criteria to assess standing foot posture. It is performed while the patient stands in a relaxed, natural stance. The clinician palpates the medial and lateral sides of the talar head and rates the posture according to the table below. Inter-rater reliability was good and significant.
In the asymptomatic group, the mean total FPI-6 score for each rater ranged from 0.73 to 1.15, indicating a slightly pronated foot posture. As expected, the patient group exhibited a wider range of scores due to the presence of various foot conditions and pathologies.
The results showed that the FPI-6 had a close, but constrained correlation with radiographic measurements of the valgus and arch indexes in both bipedal and single-leg stance. Furthermore, the navicular drop and drift was also found to correlate with both the valgus and arch indexes. This indicates that the FPI-6 could be a useful tool to identify patients with subclinical pathology in whom a full musculoskeletal evaluation is not warranted.
Patient Education
Accurately assessing foot posture is an important component of patient care. Having tools like the Foot Posture Index can help you determine whether a patient’s foot posture is normal or abnormal, as well as helping to identify risk factors for common foot and ankle conditions like plantar fasciitis and patellofemoral pain syndrome. Using the Foot Posture Index requires careful palpation, paying attention to anatomical landmarks and keeping a consistent pressure while measuring. It also helps to be familiar with the scoring system, as some of the items are subjective and could be affected by patient tenseness or positioning.
Normative data collated included centres, age, gender, foot pathology (where relevant), individual item scores for the left and right foot, total Foot Posture Index six score, and BMI values where available. Ordinal data that fit the Rasch model can be transformed to interval measurement levels using logit, and a table of transformed Foot Posture Index scores for both feet has been provided.
The most common foot posture observed was neutral, with the next most frequent being pronated. The least common foot posture was supinated, which is considered an abnormal presentation. The data also shows that foot posture tends to decline with age, although the reduction is not linear and the mean varies across different years of childhood. The Foot Posture Index score was shown to be related to BMI, however this was a weak relationship and did not demonstrate a clear association with any of the specific Foot Posture Index measures.