Related Experiment Video
Updated: Mar 21, 2026

In Vivo Quantification of Hip Arthrokinematics during Dynamic Weight-bearing Activities using Dual Fluoroscopy
Published on: July 2, 2021
Functional shape of the proximal radioulnar joint: anatomical characterization through Alpha and Beta Angles
Aurelien Traverso1, Valeria Vismara2, Simone Cassin2
1Department of Orthopaedics and Traumatology, Centre Hopitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland.
Background:
The proximal radioulnar joint (PRUJ) plays a critical role in forearm rotation through the articulation between the radial head (RH) and the ulnar notch. While previous studies have emphasized the importance of congruency for joint stability, limited data exist on anatomical variations in healthy individuals and their potential biomechanical implications. This study aimed to describe novel anatomical parameters of the PRUJ.
Methods:
A retrospective analysis of 104 elbow computed tomography scans from patients without elbow instability or deformities was performed. Measurements were taken on standardized axial computed tomography slices using two novel angular metrics: the Alpha and Beta Angle. Linear regression was used to assess the association between these angles.
Results:
The mean Alpha Angle was 139.82° (standard deviation 10.08°), while the mean Beta Angle was 81.25° (standard deviation 11.04°), both showing high interindividual variability. A statistically significant negative correlation was found between Alpha and Beta Angles (β = -0.53, 95% confidence interval: -0.72 to -0.34, P < .0001).
Discussion:
A larger Alpha Angle implies a less concave notch and reduced bony constraint of the RH, increasing the reliance on ligamentous structures, particularly the annular ligament, for joint stability. Conversely, a higher Beta Angle, indicating increased RH coverage, may confer greater intrinsic stability.
Conclusion:
The study identifies a significant inverse relationship between the Alpha and Beta Angles of the PRUJ, supporting the concept that ulnar notch morphology affects RH coverage and forearm stability. These reference values in healthy elbows may serve as a baseline for future comparisons in pathological conditions and inform the diagnosis and management of joint instability and degeneration.
Related Concept Videos
Bones of the Upper Limb: Ulna
Bones of the Upper Limb: Radius
The radius has a nail-shaped head, and a...
Bones of the Upper Limb: Humerus
Muscles that Move the Forearm
Forearm Flexors
The biceps brachii, brachialis, and brachioradialis are forearm flexors. The biceps brachii is made up of two heads. Its long head originates at the supraglenoid tubercle of the scapula, whereas that of the short head is...
Functional Classification of Joints
The functional classification of joints is determined by the amount of mobility between the adjacent bones. Joints are functionally classified as a synarthrosis or immobile joint, an amphiarthrosis or slightly moveable joint, or as a diarthrosis, a freely moveable joint. Fibrous and cartilaginous joints can be functionally classified as either synarthroses or amphiarthroses, whereas all synovial joints are classified as diarthroses.
Synarthrosis
An...
Classification of Bones
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The...
