American Association for Hand Surgery

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Biomechanical Testing of a Novel Locking Pin Cap to Create a Fixed Angle K-wire Plate Construct
David M Brogan, MD, MSc1, Simon Tang, Ph.D.2, Kaitlyn Broz, BS2 and Christopher Dy, MD MPH FACS1, (1)Washington University School of Medicine, St. Louis, MO, (2)Washington University in St. Louis, St. Louis, MO

Purpose: Fixation of small peri-articular fracture fragments can prove challenging. Current methods of securing K-wires to plates do not provide a fixed angle construct and can be technically difficult. We therefore developed a novel locking pin cap to rigidly attach a K-wire to a volar locking plate in a fixed angle construct (Figure 1). Biomechanical testing of prototypes was performed and compared to commercially available alternatives.


Methods: Two different methods of fracture fixation were tested on a total of 12 sawbone volar shear distal radius fracture models with a coronal split between the scaphoid and lunate facets (6 per group). The fragments were fixed to the intact metaphysis with either two commercially available pin plates with two K-wires in each fragment (industry standard), or a volar plate with two locking screws fixing the scaphoid facet and two pins with our novel locking pin can in the lunate facet (Figure 2). All plates were fixed proximally in the standard fashion according to the manufacturer's instructions. Each sawbone was rigidly fixed proximally and fatigue conditioning was performed on an Instron ElectroPuls with five loads to 250 N. Each specimen was then subjected to 1000 cycles of sinusoidal loading to 250 N. An OptiTrack optical tracking system was used to assess motion at both of the fracture fragments relative to the intact shaft (Figure 3). Load to clinical failure was defined as the force required to cause gap formation or shifting more than 2 mm. Ultimate load to failure was then assessed on an Instron 5866 MTS, samples were loaded to failure at 50 mm/s.


Results: One industry standard pin plate demonstrated dissociation of the pin from the plate after fatigue conditioning, this did not occur in the locking pin cap group. The locking pin cap construct reached clinical failure at a mean of 491 N, (SD 262.9) (Figure 4), while the industry standard failed clinically at 64 N (SD 73 N). Ultimate load to failure was significantly higher in the locking pin cap group as well (mean= 632.4 N) compared to the industry standard (mean =309.8 N) (Figure 5).


Conclusion: Our novel locking pin cap creates a fixed angle attachment of a K-wire to an existing locking screw hole in a plate. A fixed angle K-wire is significantly stronger in preventing clinically relevant failure and in resisting ultimate failure loads than commercially available plates that use K-wires bent over plates.








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