Related Experiment Video
Updated: Apr 7, 2026
10:07
Measurement of Dynamic Scapular Kinematics Using an Acromion Marker Cluster to Minimize Skin Movement Artifact
Published on: February 10, 2015
20.2K
Internal Rotation Behind-the-Back Angle: A Reliable Angular Measurement for Shoulder Internal Rotation Behind the
1Stonewall Jackson Memorial Hospital, Weston, West Virginia.
Sports Health
|July 3, 2015
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.
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.
Related Concept Videos
01:13Angle of Twist - Elastic Range
919
Consider a cylindrical shaft with a length denoted by L and a consistent cross-sectional radius referred to as r. This shaft undergoes a torque at the free end. The highest shearing strain within the shaft is directly proportional to the twist angle and the radial distance from the shaft axis. When the shaft behaves elastically, this shearing strain can be articulated using variables such as the applied torque, radial distance, the polar moment of inertia, and the modulus of rigidity. By...
919
01:15Unsymmetric Bending - Angle of Neutral Axis
1.0K
Unsymmetrical bending occurs when a structural member is subjected to bending moments in a plane that does not align with the member's principal axes. This scenario typically arises in beams and other structural components when loads are applied at non-ideal angles, introducing complexities in stress analysis.
When a bending moment is applied at an angle θ concerning the vertical axis of a symmetrical member, it can be resolved into components along the member's principal...
When a bending moment is applied at an angle θ concerning the vertical axis of a symmetrical member, it can be resolved into components along the member's principal...
1.0K
01:26Rotational Motion about a Fixed Axis
1.9K
A rigid body's rotation around a fixed axis makes every point within it trace a circular path around a specific line or point. The term given to this type of spinning is defined by the angular position, symbolized by the angle θ. This angle is gauged from a static reference line to the revolving object. From this angular position, any variation is referred to as angular displacement, denoted by dθ. The extent of this displacement can be calculated in degrees, radians, or...
1.9K
01:23Muscles of the Shoulder
11.3K
The muscles surrounding the shoulder girdle, including the clavicle and scapula, primarily stabilize the scapula. This stable base allows other muscles to move the humerus effectively. Scapular movements often mirror those of the humerus and extend its range of motion. For instance, raising the arm above the head would not be feasible without simultaneous upward rotation of the scapula.
Anterior Thoracic Muscles
The anterior thoracic muscles include the serratus anterior, subclavius, and...
Anterior Thoracic Muscles
The anterior thoracic muscles include the serratus anterior, subclavius, and...
11.3K
01:13Angle of Twist: Problem Solving
874
An electric motor applies a torque of 700 N·m to an aluminum shaft, triggering a stable rotation. Two pulleys, B and C, are subjected to torques of 300 N·m and 400 N·m, respectively. The modulus of rigidity is provided as 25 GPa. With the knowledge of the length and diameter of each segment, the twist angle between the two pulleys can be computed. First, a section cut is made between pulleys B and C, and the cut cross-section is analyzed using a free-body diagram. Given that the torque...
874
01:12Adjusting a Traverse
442
In the site survey of a four-sided traverse, internal angles are essential to ensure geometric accuracy. The survey revealed that the sum of the measured internal angles was 359 degrees and 48 minutes, which is 12 minutes less than the expected 360 degrees. This discrepancy signals an error likely arising from measurement inaccuracies during the fieldwork.To rectify this error, the adjustment process involved distributing the 12-minute shortfall equally across the four internal angles. By...
442