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 UK 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.