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

To the best of our knowledge, no prior biomechanical study has determined how much fracture obliquity can be tolerated with intramedullary screw fixation. The purpose of this study was to compare the stiffness, load to failure, and fracture gapping of intramedullary fixation for oblique metacarpal fractures.

Forty-five metacarpal sawbones were divided into three fracture pattern treatment groups: transverse, short oblique, and long oblique. Fourth-generation sawbones models were used, which have been validated to simulate cortical bone strength and modulus. Osteotomies (0°, 30°, and 60°) were made through the shaft of each metacarpal to simulate fracture patterns, corresponding to each treatment group. Each metacarpal was reduced and fixed with a retrograde 3.5 × 52 mm intramedullary screw. Each construct was cycled under a cantilever bending force at a 45° angle to simulate physiologic loading and then loaded to failure. Stiffness, load to failure, and fracture gapping were measured and compared.

There was no difference in the load to failure or stiffness among the three groups. The mean load to failure for the transverse, short oblique, and long oblique fractures was 222.0, 260.3, and 249.7 N, respectively, while the mean stiffness was 78.2, 78.3, and 72.2 MPa, respectively. Long oblique fractures had less gapping than short oblique and transverse fracture constructs following load removal. There was no difference in gapping between the short oblique and transverse fracture constructs. The mean fracture gapping for the transverse, short oblique, and long oblique fractures was 5.0, 3.3, and 0.6 mm, respectively.

Intramedullary fixation for simulated short oblique and long oblique metacarpal fracture patterns provides similar stability when compared to transverse fracture fixation.

Intramedullary fixation of oblique metacarpal fractures may be able to achieve adequate fixation, regardless of fracture obliquity.