ReliabilityandUsefulnessofthePressurePainThresholdMeasurementinPatientswithMyofascialPain

Myofascial pain syndrome (MPS) is a common musculoskeletal condition, particularly among office workers who spend long hours at visual display terminals (VDTs). Diagnosing MPS traditionally relies on physical examination findings such as local pain, taut bands in muscles, trigger points that cause referred pain, and limited joint motion. However, clinicians have sought more objective ways to measure muscle tenderness and quantify pain. Pressure algometers, devices that measure the amount of pressure needed to produce pain (pressure pain threshold, or PPT), have been used since the 1980s to evaluate musculoskeletal conditions.

Fischer's method proposes that a PPT of ≤3 kg/cm², a difference of ≥2 kg/cm² between sides, or a value below normal indicates MPS. Despite widespread use, questions remain about whether PPT measurements are reliable enough and sufficiently accurate to diagnose MPS in clinical practice, particularly in Korean populations where normative data are limited.

The researchers recruited 222 desk workers from a National Health Insurance Corporation office who complained of upper body pain. Five experienced physiatrists (each with at least ten years of experience) examined the participants. The clinicians diagnosed MPS using the standard criteria from Simons et al. (1999), which includes local pain, palpable taut bands, pain on pressure, trigger points with referred pain, and limited range of motion.

They then measured PPT in eight muscles using a digital pressure algometer (FDX®, Wagner Instrument): bilateral upper trapezius, infraspinatus, extensor carpi radialis, and extensor indicis proprius. Each muscle was tested three times with 5-minute rest periods between trials. The investigators pressed vertically at a constant rate of 1 kg/cm² until the subject reported slight pain. They analyzed reliability using Cronbach's alpha, compared PPT values by gender, side, and dominant hand, and evaluated the diagnostic accuracy of Fischer's method against the clinical diagnosis.

Finally, they used receiver operating characteristic (ROC) curve analysis to determine optimal PPT cut-off values for each muscle.

Of the 222 subjects, 156 (70%) were diagnosed with MPS. The group included 113 men and 108 women with a mean age of 43.2 years, who averaged 7.3 hours of computer use daily. The pressure algometer demonstrated excellent intra-rater reliability, with Cronbach's alpha values ranging from 0.934 to 0.980 across all muscles. PPT values varied significantly by gender and side: men had higher thresholds than women, and the left side had higher thresholds than the right side for all muscles (p<0.05).

Notably, there was no significant difference between dominant and non-dominant sides. The highest PPT was in the right extensor carpi radialis (3.6±1.8 kg/cm²) and the lowest in the left extensor carpi radialis (4.9±1.9 kg/cm²). When tested against clinical diagnosis, Fischer's method showed poor sensitivity but relatively high specificity: for the trapezius, specificity was 55% with sensitivity of -42%; for infraspinatus, 70% specificity and 30% sensitivity; and for extensor carpi radialis, 80% specificity but only 5% sensitivity. The ROC-derived cut-off values ranged from 3.35 kg/cm² (right infraspinatus) to 4.69 kg/cm² (right extensor carpi radialis), with sensitivities of 0.52-0.71 and specificities of 0.52-0.65.

This study provides important guidance for clinicians who use pressure algometry in patients with suspected myofascial pain. The excellent reliability of the digital pressure algometer confirms it as a consistent measurement tool, which supports its use for tracking treatment response over time. However, the poor sensitivity of Fischer's standard method means it misses many true cases of MPS, making it unsuitable as a standalone diagnostic or screening test. The finding that PPT varies by gender and side—but not by hand dominance—suggests clinicians should use side-to-side comparisons cautiously and consider gender-specific norms.

The newly proposed ROC-based cut-off values may improve diagnostic accuracy somewhat, but even these show only moderate performance. For patients, this means that while pressure testing with an algometer can help monitor whether treatments are working, a proper diagnosis of myofascial pain still requires a thorough hands-on examination by an experienced clinician who evaluates the full constellation of symptoms and physical findings.