Reliability and responsiveness of a tissue hardness meter and algometer for measuring tissue hardness and pressure pain threshold in upper trapezius myofascial trigger points.

Background: Tissue hardness meter and algometer (THA) are used to assess tissue hardness (TH) and pressure pain threshold (PPT), particularly in the evaluation of myofascial trigger points (MTrPs). This study introduces a side-lying protocol designed to comprehensively measure all portions of the upper trapezius (UT) muscle.

Purpose: The objective was to determine the reliability and responsiveness of THA to measure TH and PPT in patients with MTrPs in the UT muscle.

Methods: Reliability of TH and PPT measurements was assessed in a sample of 24 participants. Intra-rater and inter-rater reliability were evaluated using the intra-class correlation coefficient (ICC), while absolute reliability was established Bland-Altman analysis, including the calculation of 95% limits of agreement (95% LoA). To assess responsiveness, 36 additional participants were recruited. Both distribution-based methods (mean difference, effect size (ES), standardized response mean (SRM), standard error of measurement (SEM), and minimal detectable change at 95% confidence (MDC)) and anchor-based methods (minimal clinically important difference (MCID) and area under the curve (AUC)) were utilized in the analysis.

Results: Intra-rater reliability was excellent for both TH and PPT (ICC: 0.95-0.97), while inter-rater reliability was moderate (ICC: 0.60). Evidence of both fixed and proportional bias was identified for both TH and PPT. For TH, the SEM and MDC were 2.66% and 7.37%, respectively, while for PPT, they were 0.12 kg/cm and 0.34 kg/cm, respectively. Following six physical therapy sessions, significant reductions in TH (mean: -7.86%; MCID: -7.43%; AUC: 0.97) and significant increases in PPT (mean: 0.20 kg/cm; MCID: 0.21 kg/cm; AUC: 0.86) were observed. Additionally, changes in PPT showed a negative correlation with improvements in the Neck Disability Index (NDI) (r = -0.35, < 0.05).

Conclusion: The side-lying protocol demonstrated reliable and clinically relevant TH and PPT measurements, supporting its use for monitoring treatment outcomes in patients with MTrPs in the UT muscle.