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Stability of dorsal PIP joint fracture dislocations: a biomechanical study
Andrew Robert Tyser, MD; Kenneth Means; Curtis National Hand Center
Curtis National Hand Center, Baltimore, UT, USA

Introduction

Dorsal fracture dislocations of the proximal phalangeal (PIP) joints of the fingers are relatively common injuries. Multiple authors have noted that a key factor in avoiding a poor outcome is the maintenance of a concentrically reduced articular surface, i.e., the absence of dorsal subluxation of the middle phalanx at the PIP joint. Furthermore, the main determinant of dorsal subluxation of the middle phalanx has been suggested to be the degree to which the articular base of the middle phalanx is involved in the fracture.

Methods

This biomechanical study investigated the stability of proximal interphalangeal joint fracture dislocations in a cadaveric model. A Brunner incision was used to approach the volar PIP joint in 18 digits on 6 hands. After measuring the anterior-posterior dimension at the base of the middle phalanx, fluoroscopic guidance and an oscillating saw was used to create defects in the volar base of the middle phalanx of 20%, 40%, 60% and 80%. The hands were mounted to a stationary jig, and the extensor tendons were fixed to a force transducer. A force of 16N was placed on each extensor tendon to obtain full extension of the digits at the PIP joint. Using mini-fluoroscopy in cine record mode, DICOM video centered on the PIP joint in a true lateral projection was recorded as each digit was brought from full flexion into full extension. Dorsal subluxation of P2 in relation to P1 at full PIP joint extension was measured from the cine data in each testing scenario.

Results

Compared to the intact state, defects of 20% demonstrated non-statistically significant dorsal subluxation of 0.24mm (p > 0.05). Defects of 40%, 60%, and 80% demonstrated statistically significant dorsal subluxation of 0.77mm, 3.24mm, and 3.06mm, respectively, when compared to the intact state (p < 0.05).

Conclusion

The biomechanical data presented in this report suggest that bony defects that involve more than 40% of the volar articular surface of the middle phalanx may lead to significant PIP joint instability in extension, leading to greater than 1 mm of dorsal subluxation of the middle phalanx. In addition, a 40% defect in our model also resulted in dorsal subluxation of the middle phalanx of 0.77 mm, which, although less than 1 mm, is of potential clinical significance.


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