Frozen Shoulder Is More Than Local Pain: Widespread Sensory Hyperalgesia or Hypoesthesia?

BACKGROUND

Frozen shoulder (FS) has long been considered a localised musculoskeletal disorder, yet FS often involves widespread pain, suggesting central sensory dysregulation. While pressure pain threshold (PPT) assesses mechanical sensitivity, electrical measures such as current perception threshold (CPT) and electrical pain threshold (EPT) may capture various sensory alterations but are rarely applied in FS.

OBJECTIVE

To map somatosensory alterations in unilateral FS by comparing PPT, CPT, and EPT across multiple regions with matched healthy controls (HC).

METHODS

37 unilateral FS participants and 35 matched HCs underwent PPT, CPT, and EPT measurements at lateral deltoid (LD), medial forearm (MF), cervical spine (CS), and lumbar spine (LS). Bilateral LD and MF were tested in FS participants. Between-group and regional differences were analysed using linear mixed models, and correlations with pain intensity were examined.

RESULTS

FS participants exhibited significantly reduced PPT across all sites (d = 1.27-4.55) and increased CPT and EPT at affected LD and CS regions (d = 2.89-4.92). Electrical thresholds were higher over CS than LS in the FS group, whereas the opposite pattern appeared in the HC group. EPT correlated with PPT (ρ = 0.54), and both were negatively associated with pain intensity (ρ = -0.72 and -0.69, p < 0.001).

CONCLUSIONS

FS demonstrates mechanical hyperalgesia and electrical hypoesthesia, indicating central neuroplastic changes beyond the affected shoulder.

SIGNIFICANCE STATEMENT: This study integrates electrical and mechanical sensory testing, revealing multimodal evidence of central sensitization in FS and offering novel quantitative markers to guide individualised pain assessment and rehabilitation.

TRAIL REGISTRATION: ClinicalTrials.gov identifier: ChiCTR2400086393.