Level of pain catastrophising determines if patients with long-standing subacromial impingement benefit from more resistance exercise

Key points

1. 01Pain catastrophising at baseline predicts who benefits: lower catastrophisers improved significantly on shoulder disability with extra exercise, higher catastrophisers did not
2. 02Extra exercise was not better than usual care for improving pain mechanisms (temporal summation, conditioned pain modulation, local pressure pain threshold)
3. 03Both groups improved in pain catastrophising scores over 16 weeks, with no difference between them
4. 04Higher exercise dose was linked to greater disability improvement, but not to stronger shoulders
5. 05Patients with higher pain catastrophising completed less of the add-on exercise (2.0 vs 3.7 hours total time under tension)

How it was conducted

Design

Predefined secondary analyses from a pragmatic, assessor-blinded, participant-blinded, randomised controlled superiority trial (SExSI Trial)

Participants

200 consecutive patients, age 18-65, with persistent subacromial impingement (>3 months), recruited from an orthopaedic outpatient clinic in Copenhagen, Denmark

Groups

Intervention: usual exercise-based care plus progressive high-volume elastic band resistance exercise; Control: usual exercise-based care alone

Primary outcomes (this paper)

Pain mechanisms (temporal summation of pain, conditioned pain modulation, pressure pain threshold at deltoid) and pain catastrophising at 16 weeks; modifying effects on shoulder disability (SPADI) and strength

Follow-up

16 weeks (assessments at baseline, 5, 10, and 16 weeks)

Exercise dose tracking

Bandcizer sensor measured time under tension for elastic band exercises; usual care time tracked weekly via SMS

What they found

• No between-group difference in pain mechanisms at any time point
• Pain catastrophising improved in both groups with no between-group difference: control group -7 points (95% CI -9 to -5), intervention group -6 points (95% CI -8 to -4), mean difference 1 point (95% CI -2 to 4)
• Interaction effect of baseline pain catastrophising on SPADI: effect size 14 points (95% CI 2 to 25)
• Patients with lower pain catastrophising (PCS score <=16): intervention group improved -31 points (95% CI -35 to -26) vs control -23 points (95% CI -28 to -18), between-group difference -8 points (95% CI -14 to -1)
• Patients with higher pain catastrophising (PCS score >16): intervention group improved -14 points (95% CI -22 to -6) vs control -23 points (95% CI -29 to -17), no significant benefit from extra exercise
• Each additional hour of time under tension was associated with -2.6 SPADI points improvement (95% CI -4.1 to -1.1, p=0.001) after adjustment for usual care exercise time
• Each additional 60 minutes per week of usual care exercise was associated with approximately 3 SPADI points improvement
• Higher pain catastrophisers completed 2.0 hours vs 3.7 hours of add-on exercise (difference 1.7 hours, 95% CI 0.5 to 2.7)
• CPM-detection modified external rotation strength improvement: effect size -0.04 Nm/kg (95% CI -0.06 to -0.01)
• PPT-deltoid modified external rotation strength improvement: effect size 0.03 Nm/kg (95% CI 0.00 to 0.06)

Limitations

• Sample size was powered for the primary hypothesis, so these secondary analyses are exploratory and require confirmatory studies
• Pain mechanisms were not assessed at baseline, only from 5 weeks onward, limiting baseline comparisons
• Risk of measurement bias in intention-to-treat estimates due to missing data imputed with multiple imputation
• The study team was exclusively Danish, and participants needed to understand Danish, limiting generalisability

Why it matters

For patients

If you tend to fear or catastrophise about your shoulder pain, simply adding more exercises may not help and a different approach targeting your pain beliefs may be needed first.

For clinicians

Screening for pain catastrophising before prescribing a higher-dose exercise programme for subacromial impingement can identify which patients are likely to benefit; those with high catastrophising may need targeted psychological or pain education strategies before or instead of dose escalation.

For readers

This is one of the first RCT-based studies to provide clinical evidence supporting stratified care for shoulder impingement, showing that a biopsychosocial factor (pain catastrophising) meaningfully moderates exercise response.