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A Novel Intramedullary PIP Arthrodesis Construct Outperforms Standard Techniques
Scott Hadley, MD1, Paolo Caravaggi, PhD2, Steven Rivero, BS2, Benhoor Shamian, MD2; John Capo, MD1
1NYU-Hospital for Joint Diseases, New York, NY; 2Department of Orthopaedics, University of Medicine and Dentistry of New Jersey- New Jersey Medical School, Newark, NJ

Introduction: Arthrodesis of the proximal interphalangeal (PIP) joint is a proven surgical technique for end-stage arthritis. This study uses a cadaveric model to evaluate the biomechanical rigidity of five different PIP joint arthrodesis constructs. Our hypothesis is that the intramedullary arthrodesis construct will provide increased rigidity as compared to other common techniques.

Methods: The index and ring digits from cadaver hands were disarticulated at the metacarpophalangeal joint and randomly assigned to one of five different implant groups. There were 7 specimens per group. Group 1 was fixed with an interosseous wire plus pinning; group 2 used a tension-band wire; group 3 was fixed with a dorsal plate; group 4 used a novel intramedullary linked screw device (IMS); and group 5 was fixed with a 90-90 wiring technique. The fingers were potted with cement 30mm from the PIP joint and a load application ring was fixed to the shaft of the middle phalanx. The actuator of an MTS machine was used to apply a bending moment to the PIP joint through the ring in each of 4 direction vectors: flexion, extension, radial, and ulnar. The bending moment was applied to the middle phalanx 20mm from the PIP joint at a constant rate of 0.01mm/s. For a maximum bending moment of 0.1N*m. Force/displacement curve obtained was used to estimate the stiffness of each construct. After completion of testing in all vectors the fingers were failed in extension and the ultimate strength was recorded. Kruskal-Wallis nonparametric testing was used to determine the difference in stiffness between groups.

Results: There was a statistically significant increase in the rigidity of the IMS device in all parameters tested when compared to the other fusion techniques. The IMS stiffness exceeded 10N/mm stiffness in the four vectors tested and had an ultimate strength in extension of 21.0± 8.3N. The only non-IMS constructs to demonstrate a statistically significant difference from the other techniques was the dorsal plate technique in the ulnar/radial plane.

Conclusion:

  • The novel IMS device outperformed the other four common method of PIP fusion in all four direction vectors tested.
  • The IM screw fixation had the greatest ultimate strength.
  • The dorsal plate was more rigid than the other non-IMS in radial/ulnar plane, otherwise all non-IMS contructs were equivalent.
  • IMS arthrodesis is the strongest biomechanical construct and may be the superior technique for PIP arthrodesis.
  • Further clinical studies are warranted to evaluate this new technique.


Fig 1. Schematic of finger testing apparatus and gross specimen example.



Table 2: The intramedullary fusion device out performed all other fixation techniques. The dorsal plate construct was significantly stronger than all of the remaining constructs except in the extension testing position.



Table 3: All specimens were failed in extension to determine the ultimate strength. The IM Fusion device was statistically stronger than the rest.
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