Load transmission through the wrist in the extended position

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Human Anatomy

Background:

• The wrist experiences high compressive loads during extension, yet the underlying pathoanatomy of injuries remains poorly understood.
• Analyzing force transmission in extreme wrist positions is crucial for understanding injury mechanisms.

Purpose of the Study:

• To investigate force transmission patterns in the maximum wrist extension position.
• To elucidate the pathomechanics of wrist injuries, particularly those associated with extension.

Main Methods:

• Utilized computed tomography (CT) scans from 7 subjects in neutral and maximum extended wrist positions.
• Developed a 3D rigid body spring model to analyze stress distribution within the wrist joint.
• Applied external forces to simulate real-world loading conditions in both positions.

Main Results:

• Force transmission significantly increased on the scaphoid fossa (52% to 62%) and in the midcarpal joint (60% to 69%) during extension.
• Force distribution shifted radially, concentrating on the scaphoid, with new contact areas on the radial articular surface.
• Tension increased significantly in palmar intrinsic ligaments and the flexor retinaculum during wrist extension.

Conclusions:

• Wrist extension concentrates force on the scaphoid, potentially explaining scaphoid fractures due to bending forces.
• Force concentration on the radius may lead to intra-articular fractures, aligning with known fracture patterns.
• Palmar intrinsic ligaments are vital for maintaining carpal stability during extension, as seen in push-up positions.