Clinical pressure pain threshold testing in neck pain: comparing protocols, responsiveness, and association with psychological variables.

BACKGROUND

Quantitative sensory testing, including pressure pain threshold (PPT), is seeing increased use in clinical practice. In order to facilitate clinical utility, knowledge of the properties of the tool and interpretation of results are required.

OBJECTIVES

This observational study used a clinical sample of people with mechanical neck pain to determine: (1) the influence of number of testing repetitions on measurement properties, (2) reliability and minimum clinically important difference, and (3) associations between PPT and key psychological constructs.

DESIGN

This study was observational with both cross-sectional and prospective elements.

METHODS

Experienced clinicians measured PPT in patients with mechanical neck pain following a standardized protocol. Subcohorts also provided repeated measures and completed scales of key psychological constructs.

RESULTS

The total sample was 206 participants, but not all participants provided data for all analyses. Interrater and 1-week test-retest reliability were excellent (intraclass correlation coefficients [2,1]=.75-.95). Potentially important differences in reliability and PPT scores were found when using only 1 or 2 repeated measures compared with all 3. The PPT over a distal location (tibialis anterior muscle) was not adequately responsive in this sample, but the local site (upper trapezius muscle) was responsive and may be useful as part of a protocol to evaluate clinical change. Sensitivity values (range=0.08-0.50) and specificity values (range=0.82-0.97) for a range of change scores are presented. Depression, catastrophizing, and kinesiophobia were able to explain small but statistically significant variance in local PPT (3.9%-5.9%), but only catastrophizing and kinesiophobia explained significant variance in the distal PPT (3.6% and 2.9%, respectively).

LIMITATIONS

Limitations of the study include multiple raters, unknown recruitment rates, and unknown measurement properties at sites other than those tested here.

CONCLUSIONS

The results suggest that PPT is adequately reliable and that 3 measurements should be taken to maximize measurement properties. The variance explained by the psychological variables was small but significant for 3 constructs related to catastrophizing, depression, and fear of movement. Clinical implications for application and interpretation of PPT are discussed.