Abstract
Introduction:
External rotation (ER) of the shoulder is a commonly used clinical measurement to assess the glenohumeral joint; however, the position in which these measurements are obtained varies between clinicians. The purpose of this study was to compare the following: ER in the upright & supine positions, motion capture & goniometric values of ER, active & passive ER, ER in the right & left shoulders, and ER in male & female subjects.
Methods:
Eighteen subjects (mean age 25.4 yrs) with ‘normal’ shoulders (by screening questionnaire) were enrolled in the study and subject to triplicate measurements of active and passive ER of both shoulders with a goniometer and a 12 camera, high speed optical motion analysis system in both the upright and supine positions. ANOVA was used to compare variables and linear regression used to correlate the goniometer & optical motion capture measurements.
Results:
On average, shoulder ER in the supine position was 10.0° greater than in the upright position (p < 0.001) using the motion capture data and 5.8° greater using the goniometer (p = 0.025). There was a strong correlation between the goniometer and optical motion capture measurements with an R2 value of 0.6573 (p = 2.39E-13); on average, the goniometer readings were 11.0° greater than the corresponding optical measurements. External rotation of the right shoulder was 7.2° greater than the left using the optical measurements (p = 0.02) and 4.4° greater with the goniometer (p = 0.039). In addition, females did have significantly greater external rotation than males using the optical measurements (p < 0.001), averaging 16.7° more external rotation; findings were similar for the goniometric measurements with 18.5° greater average external rotation seen in female subjects (p < 0.001). There was no significant difference between measured active and passive external rotation (p = 0.589).
Conclusion:
Significant differences do exist between measured values of external rotation depending on the position of measurement (upright vs supine), hand dominance, and gender. It does not appear that there is a difference between active and passive external rotation. Our recommendations are for the musculoskeletal clinician to be meticulous when documenting the position of measured external rotation, as values vary depending on the position of measurement. One should also be cautious of comparing external rotation of one shoulder to the contralateral side, as well as comparing values between genders, as these measurements appear to be different as well.
