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Related Experiment Video

Updated: Apr 7, 2026

Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact
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Internal Rotation Behind-the-Back Angle: A Reliable Angular Measurement for Shoulder Internal Rotation Behind the

Shafic A Sraj1

  • 1Stonewall Jackson Memorial Hospital, Weston, West Virginia.

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PubMed
Summary

The new internal rotation behind-the-back (IRB) angle measurement is reproducible and easy to use. This method provides reliable numeric data for shoulder internal rotation, reducing examiner variability.

Keywords:
hand behind backinternal rotation behind backphysical examinationrange of motionshoulder

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Area of Science:

  • Orthopedics
  • Biomechanics
  • Sports Medicine

Background:

  • The traditional hand-behind-back method for assessing shoulder internal rotation is widely used but prone to inconsistencies.
  • Recent studies have questioned the reliability of the conventional technique.

Purpose of the Study:

  • To introduce and validate a new measurable angle for internal rotation behind the back (IRB).
  • To reduce the influence of other joints and provide objective, numeric data.

Main Methods:

  • Defined the IRB angle as the measurement between the ulna and the line of gravity.
  • Used a goniometer with a pendulum attachment, centered over the pisiform.
  • Assessed 60 volunteers' shoulders twice by two blinded examiners.

Main Results:

  • The IRB angles measured between 50° and 125°.
  • Demonstrated high reproducibility with strong interobserver (kappa=0.88) and intraobserver (kappa=0.77) agreement.
  • Showed high correlation coefficients (0.98 and 0.92) for inter- and intraobserver reliability.

Conclusions:

  • The IRB angle offers a simple, reproducible, and objective method for evaluating shoulder internal rotation.
  • This technique provides valuable numeric data, potentially improving diagnostic accuracy and reducing reliance on subjective spinal level estimation.