The sagittal band: anatomic and biomechanical study

Area of Science:

• Orthopedic surgery
• Hand anatomy
• Biomechanics

Background:

• The sagittal band (SB) is a crucial structure stabilizing the extensor tendons at the metacarpophalangeal (MCP) joint.
• Understanding SB anatomy and biomechanics is vital for diagnosing and treating extensor tendon instability.
• Previous studies have not fully elucidated the mechanism of SB injury and its contribution to tendon instability.

Purpose of the Study:

• To investigate the anatomy and biomechanics of the human sagittal band (SB).
• To determine the mechanism of sagittal band injury and its effect on extensor tendon stability.
• To correlate SB disruption with the degree of extensor tendon instability.

Main Methods:

• Dissection and histological analysis of 48 human cadaveric hand digits.
• Observation of dynamic SB fiber orientation across various MCP and wrist joint positions.
• Measurement of pressures deep to the SB using Swan-Ganz catheters in different joint configurations.
• Serial sectioning of radial and ulnar sagittal bands to assess extensor tendon stability.

Main Results:

• Sagittal band fibers exhibit dynamic orientation changes with MCP and wrist joint movement.
• Pressure generation deep to the SB is highest during full MCP flexion.
• Radial SB sectioning, especially proximally, leads to extensor tendon subluxation or dislocation.
• Ulnar SB sectioning did not result in extensor tendon instability.
• Wrist flexion exacerbates extensor tendon instability following radial SB disruption.

Conclusions:

• Extensor tendon instability is most common in the long finger following SB disruption.
• Radial sagittal band integrity is critical for preventing ulnar extensor tendon instability.
• The degree of instability correlates with the extent and location (proximal) of SB compromise.
• High forces on the SB during MCP joint extension or flexion may cause injury.
• Wrist flexion can worsen extensor tendon instability after SB injury.