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A New Adjustable Dynamic External Fixator for Fracture-Dislocations of the Proximal Interphalangeal Joint: a Cadaver Study
Kun Liu, MD1, Jean-Yves Beaulieu, MD2, Pierre Hoffmeyer, MD2, Guanglei Tian, MD1; Jan van Aaken, MD2
1Hand Surgery Department, Beijing Jishuitan Hospital, Beijing, China; 2Orthopaedic Department, Geneva University Hospital, Geneva, Switzerland

Introduction: Unstable fracture-dislocations of the proximal interphalangeal joint (PIPJ) frequently lead to pain, stiffness, instability and degenerative arthritis. One treatment option is a dynamic external fixator. However, common shortcomings of current fixators include obscuring the fracture site on true lateral radiograms, time consuming assembly, and lack of adjustability. For these reasons we designed a new adjustable dynamic external fixator (Adynex). This study reflects its use in a cadaver model.

Materials and Methods: We created an unstable PIPJ fracture-dislocation model in eight cadaveric fingers. We applied the Adynex, which consists of a pair of rods and nuts (radiolucent spacers) made of Polyetheretherketone (PEEK) and a pair of stainless steel springs. The Adynex was fixed to two parallel K-wires which were put through the center of the head of the proximal and middle phalanges. The distraction force was generated by turning the springs in clockwise direction. Fracture reduction and congruency of the PIPJ were documented throughout its whole range of motion under dynamic lateral fluoroscopic. The distances between the center of the proximal phalangeal head and the palmar margin (a) and/or dorsal margin (b) of the residual articular surface of the middle phalangeal base were measured at PIPJ extension, flexion 45°, 90° and maximal flexion positions to evaluate reduction of the PIPJ. The range of motion of the PIPJ maintained in reduction position by distraction of Adynex was measured.

Results: The fracture site and joint surface were not obscured on a true lateral view. The distraction force could be easily changed seperately by turning the springs on either side during distraction period. Adynex established satisfactory reduction of the fracture and congruency of the PIP joint surfaces. There was no significant difference (P>0.05) between distance a and distance b when the PIPJ was at any of the the four postions, which means subluxation of the PIPJ was completely corrected. The PIPJ could be maintained in reduction position by Adynex in a range of motion of 0°~106° .

Conclusion: The Adynex fulfilled its objectives in a cadaver model. It is adjustable, not bulky, quick to assemble and easy to use, did not block visualization of the joint surface on a true lateral view, and could maintain reduction of an unstable PIPJ throughout its full range of motion.

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