Intramedullary Fixation for Short and Long Oblique Metacarpal Fractures: A Biomechanical Analysis

Area of Science:

• Orthopedic biomechanics
• Surgical fixation techniques
• Fracture healing research

Background:

• Metacarpal fractures are common hand injuries.
• Intramedullary screw fixation is a potential treatment method.
• The biomechanical tolerance of oblique fractures to this fixation is not well-established.

Purpose of the Study:

• To compare the biomechanical performance of intramedullary screw fixation for different metacarpal fracture obliquities.
• To evaluate stiffness, load to failure, and fracture gapping.
• To determine the limits of fracture obliquity for effective intramedullary fixation.

Main Methods:

• Forty-five metacarpal sawbones were used, simulating transverse, short oblique (30°), and long oblique (60°) fractures.
• Sawbones were fixed with retrograde 3.5 × 52 mm intramedullary screws.
• Constructs underwent cyclic loading and load-to-failure testing under cantilever bending.

Main Results:

• No significant differences in load to failure or stiffness were observed among the three fracture obliquity groups.
• Long oblique fractures exhibited significantly less fracture gapping (0.6 mm) compared to short oblique (3.3 mm) and transverse (5.0 mm) fractures.
• Mean load to failure ranged from 222.0 N (transverse) to 260.3 N (short oblique).

Conclusions:

• Intramedullary fixation offers similar stability for transverse, short oblique, and long oblique metacarpal fractures.
• Fracture obliquity does not appear to compromise the stability of intramedullary screw fixation in simulated metacarpal fractures.
• This fixation method may be suitable for a range of metacarpal fracture obliquities.