A hip test battery for clinical practice: reliability, reference values, and the pitfalls of the Limb Symmetry Index

Reliable and clinically interpretable assessments are essential to guide evaluation, monitoring, and return-to-sport decision-making after hip injury or surgery. However, no comprehensive test battery currently integrates intra- and inter-rater reliability, reference values in healthy individuals, and the reliability of the Limb Symmetry Index (LSI). We propose an integrated clinical assessment framework linking measurement reliability (ICC), interpretability (SEM, MDC, reference values), and clinical decision-making.

This cross-sectional reliability study included 94 healthy recreational adults (mean age 28.4 ± 8.5 years; 39% women). A subsample (n = 20) underwent a retest after 7 ± 2 days to assess intra-rater reliability. Outcome measures included hip range of motion (flexion, internal and external rotation), isometric hip strength (flexors, abductors, adductors), and functional performance tests (medial hop, single-leg squat, modified Star Excursion Balance Test [SEBTm], and endurance squat). The LSI was calculated for relevant outcomes. Reliability was assessed using intraclass correlation coefficients (ICC [2,1]), along with standard error of measurement (SEM) and minimal detectable change at the 95% confidence level (MDC95%).

Most hip strength and range-of-motion measures demonstrated good reliability (ICC > 0.70), with MDC values of 55-79 N for strength and 12-18° for hip flexion. Medial hop performance showed excellent reliability (ICC = 0.89-0.95; MDC = 18-26 cm), and SEBTm demonstrated low measurement error (MDC = 9-14 cm). In contrast, single-leg squat and endurance squat tests showed lower reliability. Medial hop performance was strongly correlated with hip abductor (r = 0.52) and adductor strength (r = 0.51). All LSIs demonstrated poor reliability (ICC < 0.50; MDC range: 11.9-47.9%, mean ≈ 27%).

Range-of-motion measures, particularly active and passive hip flexion, demonstrated the highest reliability, with MDC values ranging from 12° to 18°. Strength tests showed good reliability but substantial measurement error, limiting their ability to detect meaningful individual changes. Among functional assessments, the medial hop demonstrated excellent reliability. In contrast, adductor-to-abductor strength ratios and the Limb Symmetry Index (LSI) exhibited poor reliability and large MDC values (≈ 27%), questioning their usefulness as standalone criteria for clinical decision-making and return-to-sport assessment. These findings support prioritizing absolute measures interpreted against their MDC and reference values within a multidimensional assessment framework.