An exploration of normative values in New Zealand to inform the Targeted Interventions for Patellofemoral Pain approach

Abstract

Background: The Targeted Interventions for Patellofemoral Pain studies (TIPPs) have identified three subgroups exist in United Kingdom and Turkish patellofemoral pain (PFP) populations: Strong; Weak and Tight; and Weak and Pronated, based on six clinical assessments. The thresholds used to develop the subgrouping algorithms were based on normative values sourced from various populations and countries.

Objectives: Explore normative scores from the clinical assessments in a singular non-PFP population whilst considering potential differences between ethnicities and sex (primary aim). Revisit inter-rater reliability of each assessment (secondary aim).

Design: Cross-sectional and test-retest.

Method: The six assessments; rectus femoris length, gastrocnemius length, patellar mobility, hip abductor strength, quadriceps strength, and Foot Posture index (FPI) were measured in 89 New Zealanders (34% Māori, 45% female). Two raters independently assessed 17 participants to examine inter-rater reliability.

Results: Significant interactions between ethnic group and sex were noted for rectus femoris length and patella mobility. Māori versus European males exhibited greater rectus femoris tightness (p = 0.001). Māori versus European females demonstrated greater patellar mobility (p = 0.002). Females were significantly weaker than males in normalised strength measures (p < 0.001), and had lower FPIs. Mean differences between testers for all measures were small and not significant, except for FPI which had a 2.0 point median difference (p = 0.021).

Conclusions: Our results indicate that sex is an important factor worth considering within the TIPPs subgrouping approach, more than ethnicity, especially for the normalised strength measures. The sub-optimal reliability of FPI warrant reconsideration of its inclusion within TIPPs.

Keywords: Ethnicity; Knee; Normative data; Physiotherapy.