Subacromial anaesthetics increase asymmetry of scapular kinematics in patients with subacromial pain syndrome

Highlights

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Alternative diagnoses were found in 32% of patients clinically identified with SAPS.

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The affected shoulder in our SAPS group revealed more scapular internal rotation.

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Subacromial infiltration of lidocaine did not lead to symmetrical kinematics.

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More pain was associated with less scapular upward rotation.

Abstract

Background

Subacromial pain syndrome (SAPS) and scapular dyskinesis are closely associated, but the role of pain is unknown. We hypothesized that pain results in asymmetrical scapular kinematics, and we expected more symmetrical kinematics after infiltration of subacromial anaesthetics.

Objective

To investigate the effect of subacromial anaesthetics on scapular kinematics in patients with SAPS.

Design

Observational cohort study.

Methods

We evaluated shoulder kinematics in 34 patients clinically and radiologically (magnetic resonance arthrography) identified with unilateral SAPS using three-dimensional electromagnetic motion analysis (Flock of Birds). Scapular internal rotation, upward rotation and posterior tilt of the affected shoulder were compared with the kinematics of the unaffected shoulder and following subacromial anaesthetics. Additionally, the association of pain (Visual Analogue Scale, VAS) and scapular rotation was analysed.

Results

Compared with the contralateral healthy shoulder, 5° more (95% CI 0.4–9.7, p = 0.034) scapular internal rotation was observed in the affected shoulder at 110–120° of abduction. Following subacromial anaesthetics in the affected shoulder, internal rotation increased (2°, 95% CI 0.5–3.9, p = 0.045) and posterior tilt decreased (3°, 95% CI 1.5–5.0, p = 0.001) at 110–120° of abduction. Less scapular upward rotation was significantly associated with higher pain scores before infiltration (R = 0.45, p = 0.013).

Conclusions

More scapular internal rotation was observed in affected shoulders of patients with SAPS compared with unaffected shoulders. Subacromial infiltration did not restore kinematics toward symmetrical scapular motion. These findings suggest that subacromial anaesthesia is not an effective means to instantly restore symmetry of shoulder motion.