Quantitative 3-dimensional CT analyses of fractures of the middle phalanx base.

Background: Quantitative 3-dimensional computed tomography (3DCT) analyses can provide a more detailed understanding of fracture morphology. For fracture-dislocation of the proximal interphalangeal joint, the extent of fragmentation of the volar lip of the middle phalanx-a factor that might influence treatment-is not always apparent from radiographs. We hypothesized that there is no correlation between number of fracture fragments and the percentage of articular surface area involved in intra-articular fractures of the base of the middle phalanx using quantitative 3DCT analyses.

Methods: We used 13 computed tomography scans with a slice thickness of 1.25 mm or less to create 3-dimensional models of 15 intra-articular fractures of the base of the middle phalanx in 13 patients. We resized 3-dimensional models of a non-fractured middle phalanx of the same hand to fit the fractured middle phalanx in order to approximate the size and shape of the fractured middle phalanx in its pre-injury state. We created a heatmap to demonstrate the location of the fractured articular surface.

Results: With the number of scans available, we did not find a significant correlation between the percentage of articular surface area involved and the number of fracture fragments. The median percentage of articular surface area involved was 46 % (range, 21-90 %). The heatmap demonstrated that the radio-volar side of the articular surface seems to be more involved than the ulnar-volar side in intra-articular fractures of the base of the middle phalanx.

Conclusion: Quantitative 3DCT analysis of fracture fragments provides useful information that could facilitate surgery and analysis of complex fractures of the base of the middle phalanx.

Level Of Evidence: IV, Basic Science Study, Anatomic Study, Imaging.