Does muscle guarding play a role in range of motion loss in patients with frozen shoulder?

Key points

1. 01Passive abduction increased after anaesthesia in all 5 patients, by 53 to 111 degrees (60% to 223% above the pre-anaesthetic range).
2. 023 of 5 patients also gained 15 to 41 degrees of passive external rotation under anaesthesia at similar applied force.
3. 03Such large gains under anaesthesia point to active muscle guarding, rather than a fixed tight capsule, as a major driver of stiffness in some patients.
4. 041 patient with the longest symptoms (30 months) barely changed, suggesting genuinely shortened connective tissue in that case.
5. 05The results question whether bedside passive range testing in awake, painful patients truly reflects capsular tightness.

How it was conducted

Design

Observational cross-sectional case series (Level 4 evidence)

Participants

5 patients (3 female, 2 male, ages 51 to 64) scheduled for capsular release surgery for idiopathic frozen shoulder, symptoms 6 to 30 months

Comparison

Passive shoulder range of motion measured awake versus immediately after general anaesthesia, in the same patients

Outcomes

Passive abduction (measured from a digital photo) and passive external rotation (recorded with an instrumented arm frame measuring angle and applied torque) in side-lying

Procedure

External rotation torque under anaesthesia matched the pre-anaesthetic level where pain had not limited movement; otherwise torque was increased gradually until resistance

What they found

• Passive abduction increased after anaesthesia in all 5 participants, by 53 to 111 degrees, representing increases of 60% to 223%.
• Participant 1: abduction 47 to 152 degrees (105 degrees, 223%); external rotation 26.3 to 67.7 degrees (41.4 degrees, 156%).
• Participant 2: abduction 70 to 153 degrees (83 degrees, 119%); external rotation 28.3 to 48.3 degrees (20 degrees, 71%).
• Participant 3: abduction 53 to 164 degrees (111 degrees, 209%); external rotation 17.3 to 32.7 degrees (15.4 degrees, 89%), having been pain-limited while awake.
• Participant 4: abduction 90 to 144 degrees (54 degrees, 60%); external rotation essentially unchanged at 68 to 69 degrees (1 degree, under 1%), already within normal range in side-lying.
• Participant 5 (30 months of symptoms): abduction 63 to 116 degrees (53 degrees, 84%); external rotation essentially unchanged at 17 to 20 degrees (3 degrees, 18%), suggesting shortened connective tissue.
• SPADI scores ranged from 67 to 87, indicating moderate to high pain and disability.

Limitations

• Only 5 surgical patients, so the findings may not generalise to the wider frozen shoulder population.
• Abduction was measured without stabilising the scapula, so some gain could reflect scapular rather than glenohumeral movement.
• The study was not designed to robustly test the validity of passive range assessment, and there was no control group.
• Individual responses varied, with 2 of 5 patients showing little or no external rotation change, so muscle guarding is not the explanation for everyone.

Why it matters

For patients

If you have a frozen shoulder, some of your stiffness may come from muscles tensing in response to pain rather than permanent scar tissue, which may improve as pain and anxiety settle.

For clinicians

Large range gains under anaesthesia suggest awake passive range testing in painful frozen shoulder may overstate capsular contracture, so consider muscle guarding when interpreting findings and planning treatment.

For readers

This small case series challenges the assumption that frozen shoulder stiffness is mainly fixed capsular contracture, but larger studies are needed before changing practice.