Biomechanical Properties of the Extensor Mechanism Following Retrograde Intramedullary Nailing for Metacarpal...

Area of Science:

• Orthopedic surgery
• Biomechanics
• Hand surgery

Background:

• Metacarpal fracture fixation often uses retrograde intramedullary nails.
• Percutaneous placement risks extensor mechanism injury.
• Minimally invasive, tendon-sparing approaches are alternatives.

Purpose of the Study:

• To evaluate the biomechanical properties of the extensor mechanism after retrograde threaded intramedullary nail insertion using different techniques.
• Compare transtendinous, longitudinal tendon split with repair, and trans-sagittal band insertion methods.

Main Methods:

• Sixty-four cadaveric fingers were used.
• Groups included control, transtendinous, longitudinal tendon split with repair, and trans-sagittal band insertion.
• Extensor mechanisms underwent tensile testing to determine load to failure (LTF) and stiffness.
• Statistical analysis included mixed-effects linear regression and Fisher exact tests.

Main Results:

• No significant differences in mean LTF or stiffness were found between any test group and the control.
• Extensor tendons of the index and long fingers had higher LTF than the fifth.
• Tensile failure occurred at the implant insertion site in 44% (transtendinous), 25% (longitudinal split repair), and 13% (trans-sagittal band) of specimens.

Conclusions:

• Retrograde intramedullary nail placement via extensor tendon, longitudinal split, or sagittal band does not significantly reduce extensor mechanism LTF or stiffness.
• Implant insertion creates a potential failure site, but only under excessive tension.
• All retrograde insertion methods likely have minimal clinical impact on extensor mechanism integrity during early motion.