American Association for Hand Surgery
Theme: Beyond Innovation

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Volar Plate Positioning on the Distal Radius and Contact Pressure on the FPL and Plate Edge
Matthew J Gluck, BS1; Kristen M. Meier, MD MS2; Joshua McGough, BS3; Amy Ahn, BS3; Todd A Rubin, MD1; Michael R Hausman, MD1
1Mount Sinai Hospital, New York, NY, 2Mount Sinai School of Medicine, New York, NY, 3Icahn School of Medicine- Mount Sinai, New York, NY

Hypothesis: The purpose of this study was to assess the effect of restoring volar tilt in distal radius fractures on flexor pollicis longus (FPL) tendon rupture. We hypothesize that restoring the anatomic volar tilt (10.8 degrees) of the distal radial fragment, will result in less contact force between the volar plate and FPL than in fragments fixed without volar tilt restoration.

Methods: We used six (n=6) cadaveric upper extremities with no history of hand, wrist, or forearm trauma. The radius and ulna were fixed in a custom jig. Using Kirschner wires, the wrist was fixed at 30 degrees of extension, and the interphalangeal and metacarpophalangeal joints were each fixed at 15 degrees of flexion while the Carpometacarpal joint was fixed in opposition simulating a "pinch configuration". Loads of 1kg and 3 kg were fastened to the FPL tendon to simulate anatomic forces across the tendon during use. Contact force between the FPL and volar lip of the radius/plate was measured using a small force transducer. Contact force was assessed at 4 surgical conditions: Control (intact control wrist with no plate), Anatomic plate (after creating a distal radius fracture, a volar locking plate was utilized to achieve fixation with 10.8 degrees of volar tilt), Neutral Plate (distal fragment was fixed neutral), Dorsal Plate (distal fragment was fixed with an additional 5 degrees of dorsal angulation).

Results: A two-way ANOVA was used to assess for statistical significance (p<0.05). No significant difference in contact force was observed between Control and Anatomic Plate conditions at both 1kg and 3kg with mean differences of 0.26N (p=0.7179) and1.36N (p=0.0608) respectively. A significant increase was observed between the Control and Neutral plate conditions at both 1kg and 3kg with mean differences of 1.41N(p<0.0001) and 4.6N (p<0.0001) respectively. Similar trends were seen between Control and Dorsal Plate with mean differences of 1.62N(p<0.0001) and 4.85N(p<0.0001) for 1kg and 3kg respectively.
Summary Points:
- Restoration of volar tilt using a volar locking plate shows no increase in FPL contact force compared to an intact Control wrist.
- FPL contact force increases without adequate restoration of volar tilt (as demonstrated by a neutral and exaggerated dorsal angulation)
- Failure to recreate anatomic volar tilt in distal radius fracture fixation puts patients at risk for FPL tendon rupture

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