Mechanical Properties and Microstructural Collagen Alignment of the Ulnar Collateral Ligament During Dynamic Loading

Area of Science:

• Biomechanics
• Biomaterials Science
• Orthopedic Surgery

Background:

• The microstructural organization of the ulnar collateral ligament (UCL) and its collagen fiber behavior under load remain unclear.
• Understanding these properties is crucial for diagnosing and treating UCL injuries.

Purpose of the Study:

• To investigate real-time microstructural collagen changes in the anterior bundle (AB) and posterior bundle (PB) of the UCL under tensile load.
• To test the hypothesis that the UCL AB is stronger, stiffer, and has more aligned collagen fibers than the PB during loading.

Main Methods:

• Quantitative polarized light imaging was used on 34 fresh cadaveric UCL specimens (AB and PB).
• Specimens underwent cyclic preconditioning, stress-relaxation, and quasi-static tensile testing.
• Real-time microstructural data on collagen fiber alignment and organization were captured during testing.

Main Results:

• The AB exhibited significantly larger elastic moduli (toe and linear regions) and stress values compared to the PB.
• The AB demonstrated stronger collagen alignment and more uniform organization during stress-relaxation and across the stress-strain curve.
• PB collagen fibers were consistently more disorganized than those in the AB.

Conclusions:

• The anterior bundle of the UCL is stiffer, stronger, and possesses more aligned and uniformly oriented collagen fibers than the posterior bundle.
• The UCL's response to load is primarily attributed to its inherent collagen organization rather than dynamic alignment changes.
• This specific collagen organization may predispose the UCL to injury from repetitive valgus loads.