Translation and Psychometric Testing of the Norwegian Foot Functional Index Revised, Short Version.

Foot Functional Index, revised short form is a foot specific patient reported outcome measurement (PROM) which covers pain, stiffness, activity limitations, disability as well as psychosocial issues.

The aim of this study is to translate into Norwegian and cross-culturally adapt Foot Functional Index revised, short form (NFFI-RS). Furthermore, the reliability, validity, interpretability and responsiveness will be determined.

The Department of Physical Medicine and Rehabilitation at Oslo University Hospital has an ongoing double blind, randomized sham-controlled trial (RCT) comparing the effect of radial extracorporeal shock wave therapy (rESWT), sham rESWT, standardized exercise program and usual care for patients with longstanding plantar fasciopathy (NCT03472989). The testing of the psychometric properties of the NFFI-RS will include totally hundred patients, both from the mentioned RCT as well as patients with other foot diagnosis recruited from our department.

The translation of the original FFI-RS into Norwegian has been done following the official guidelines.

In the test-retest study fifty patients will complete the NFFI-RS at a one week interval.

Smallest detectable change, measurement error, floor and ceiling effects as well as internal consistency will be calculated by using the baseline data. To decide the construct validity we will test the various hypothesis at baseline.

To calculate the responsiveness and the minimal clinically important change three months data will be assessed. Patient Global Impression of Change Scale will be used to assess the minimal clinically important change and responsiveness of the NFFI-RS with ROC and AUC analyses.

Inclusion criteria

• Patients with pain localized in the foot
• Patients understanding oral and written Norwegian

Exclusion criteria

• Patients without pain in the foot
• Patients not understanding oral and written Norwegian