Three-Dimensional Measurement of Proximal Humerus Fractures Displacement: A Computerized Analysis

Abstract

Neer's classification for proximal humerus fractures (PHFs) uses 10 mm and 45° thresholds to distinguish displaced fragments. While this system was originally developed referencing 2D X-rays, fracture displacements occur in three dimensions. Our work aimed to develop a standardized and reliable computerized method for measuring PHF 3D spatial displacements. CT scans of 77 PHFs were analyzed. A statistical shape model (SSM) was used to generate the pre-fracture humerus. This predicted proximal humerus was then used as a "layer" to manually reduce fragments to their native positions and quantify translation and rotation in three dimensions. 3D computerized measurements could be calculated for 96% of fractures and revealed that 47% of PHFs were displaced according to Neer's criteria. Valgus and varus head rotations in the coronal plane were present in 39% and 45% of cases; these were greater than 45° in 8% of cases and were always associated with axial and sagittal rotations. When compared to 3D measurements, 2D methods underestimated the displacement of tuberosity fragments and did not accurately assess rotational displacements. The use of 3D measurements of fracture displacement is feasible with a computerized method and may help further refine PHF analysis and surgical planning.

Keywords: 3D planning; CT-scan study; Neer classification; proximal humerus fractures; proximal shaft; tuberosity displacement.

Figure 1

Flowchart.

Figure 2

Segmentation of fractured fragments using AMIRA^® software. (A) 3D mesh posterior view; (B) 3D mesh anterior view; (C) Fragment boundaries were contoured by hand on every other axial CT section. Here, the humeral head is in purple, the greater tuberosity in green (unfractured) and blue (posterior fractured portion), and the lesser tuberosity in yellow.

Figure 2

Segmentation of fractured fragments using AMIRA^® software. (A) 3D mesh posterior view; (B) 3D mesh anterior view; (C) Fragment boundaries were contoured by hand on every other axial CT section. Here, the humeral head is in purple, the greater tuberosity in green (unfractured) and blue (posterior fractured portion), and the lesser tuberosity in yellow.

Figure 3

Pre-fractured humerus prediction. (A) A statistical shape model was used to reconstruct the pre-fracture proximal humerus from the most proximal 6 cm of unfractured shaft; (B) Predicted pre-fracture proximal humerus displayed in yellow. The original unfractured shaft is displayed in beige.

Figure 4

Positioning of the pre-fracture humerus relative to the glenoid. The pre-fracture humerus was translated vertically and axially rotated to restore the glenohumeral joint space and the scapulohumeral arch [34].

Figure 5

Computerized reduction of fractured bone fragments. (A) The 3D mesh of the fracture fragments (purple, yellow, green, and blue) is superimposed onto the predicted pre-fracture proximal humerus (grey). The fragments are not reduced at this stage. (B) Each fragment is reduced manually. Here the fractured head (in violet) is reduced based on the pre-fractured humerus (grey). The maneuver is repeated fragment by fragment to obtain an anatomical reduction. (C). At the end of this step, the fracture is reduced. The greater tuberosity is green at its anterior part and blue in its posterior part, the lesser tuberosity is yellow. The anatomy of the proximal pre-fracture humerus is restored.

Figure 5

Computerized reduction of fractured bone fragments. (A) The 3D mesh of the fracture fragments (purple, yellow, green, and blue) is superimposed onto the predicted pre-fracture proximal humerus (grey). The fragments are not reduced at this stage. (B) Each fragment is reduced manually. Here the fractured head (in violet) is reduced based on the pre-fractured humerus (grey). The maneuver is repeated fragment by fragment to obtain an anatomical reduction. (C). At the end of this step, the fracture is reduced. The greater tuberosity is green at its anterior part and blue in its posterior part, the lesser tuberosity is yellow. The anatomy of the proximal pre-fracture humerus is restored.

Figure 6

Three anatomical reference planes with the center $\mathrm{O}$.

Figure 7

Example of rotation in the coronal plane (varus). (A) Surgical neck fracture (3D scanner); (B) In white, the proximal pre-fracture humerus is positioned in a neutral anatomic position at the glenoid. In beige, the fractured humerus with the diaphysis displaced in adduction and the head displaced in varus. (C) The fractured humerus is reduced onto the pre-fracture humerus. The computerized measurement indicates a 33° varus displacement.

Figure 7

Example of rotation in the coronal plane (varus). (A) Surgical neck fracture (3D scanner); (B) In white, the proximal pre-fracture humerus is positioned in a neutral anatomic position at the glenoid. In beige, the fractured humerus with the diaphysis displaced in adduction and the head displaced in varus. (C) The fractured humerus is reduced onto the pre-fracture humerus. The computerized measurement indicates a 33° varus displacement.

Figure 8

Measurement of rotations and translations by the software. (A) Coronal rotation of the head in the varus and valgus measured by our tool; 8% of fractures met Neer’s criteria. (B) Three-dimensional translation of greater tuberosity measured by our tool. 39% of the fractures met Neer’s criteria. (C) Three-dimensional translation of the lesser tuberosity measured by our tool. 53% of the fractures met Neer’s criteria. (B,C) The red line indicates Neer’s criteria threshold. Tuberosity translations are classified as <5 mm (light blue), 5−9 mm (green), 10−15 mm (orange), and >15 mm (red).

Figure 8

Measurement of rotations and translations by the software. (A) Coronal rotation of the head in the varus and valgus measured by our tool; 8% of fractures met Neer’s criteria. (B) Three-dimensional translation of greater tuberosity measured by our tool. 39% of the fractures met Neer’s criteria. (C) Three-dimensional translation of the lesser tuberosity measured by our tool. 53% of the fractures met Neer’s criteria. (B,C) The red line indicates Neer’s criteria threshold. Tuberosity translations are classified as <5 mm (light blue), 5−9 mm (green), 10−15 mm (orange), and >15 mm (red).

Figure 9

Example of a varus displacement with associated humeral head rotation from different perspectives. (A) AP view; (B) oblique anterior view; (C) oblique posterior view; (D) posterior view.

Figure 9

Example of a varus displacement with associated humeral head rotation from different perspectives. (A) AP view; (B) oblique anterior view; (C) oblique posterior view; (D) posterior view.