The second annular pulley: a histologic examination

Area of Science:

• Anatomy
• Histology
• Biomechanics

Background:

• The annular pulleys are crucial for finger flexion.
• Understanding their structure is key to treating tendon injuries.

Purpose of the Study:

• To investigate the histological structure of the second annular pulley.
• To correlate structure with function in the pulley apparatus.

Main Methods:

• Histological analysis of 15 fresh frozen finger specimens.
• Staining techniques included hematoxylin-eosin, Verhoeff-Van Gieson (Elastin), Masson's trichrome, and hyaluronic acid detection.

Main Results:

• Identified three distinct layers in the second annular pulley.
• Outer layer: vascularized, continuous with membranous sheath.
• Middle layer: radially oriented collagen, significant elastin, resists bowstringing.
• Inner layer: longitudinally oriented collagen, modified fibroblasts secreting hyaluronic acid for gliding.

Conclusions:

• The three layers of the second annular pulley are specialized for distinct functions.
• These layers facilitate vascular supply, structural integrity, and efficient flexor tendon gliding.