3D computational anatomy of the scaphoid and its waist for use in fracture treatment

Abstract

Background: A detailed understanding of scaphoid anatomy helps anatomic fracture reduction, and optimal screw position. Therefore, we analysed (1) the size and shape variations of the cartilage and osseous surface, (2) the distribution of volumetric bone mineral density (vBMD) and (3) if the vBMD values differ between a peripheral and a central screw pathway?

Methods: Forty-three fresh frozen hand specimens (17 females, 26 males) were analysed with high-resolution peripheral quantitative computed tomography (HR-pQCT) and dissected to compute a 3D-statistical osseous and cartilage surface model and a 3D-averaged vBMD model of the scaphoid. 3D patterns were analysed using principal component analysis (PCA). vBMD was analysed via averaging HR-pQCT grey values and virtual bone probing along a central and peripheral pathway.

Results: (1) PCA displayed most notable variation in length ranging from 1.7 cm (- 2SD) to 2.6 cm (mean) and 3.7 cm (+ 2SD) associated with differences of the width and configuration of the dorsal surface (curved and narrow (4 mm) to a wider width (9 mm)). (2) High vBMD was located in the peripheral zone. Lowest vBMD was observed in the centre and waist. (3) Virtual probing along a peripheral pathway near to the cartilage surfaces for the capitate and lunate allowed the center region to be bypassed, resulting in increased vBMD compared to a central pathway.

Conclusion: High anatomical variations regarding the osseous and cartilage surfaces were associated with three distinct concentrically arranged zones with notable different vBMD. The complex scaphoid anatomy with its waist might alter the strategy of fracture fixation, education and research.

Keywords: Anatomy of the scaphoid; Bone models; Bone shape and density.

Fig. 1

a–c Scaphoid model with manually set landmarks with ulnar view on the articular surface for capitate (a), volar view (b) and view on the articular surface for radius (c). d Scaphoid with anatomical and equidistant segment landmarks computed with view on the articular surface for capitate

Fig. 2

HR-pQCT-based 3D statistical surface model of the right scaphoid demonstrating 3D shape and size variation pattern of osseous and articular surfaces. Columns display 1^st and 2^nd PC with 3D views revealing most relevant variation patterns: 1^st PC with ± 2 SD models (top and bottom row) and mean model (middle row) mainly exhibited size variation, i.e. length. 2^nd PC with ± 2 SD models (top and bottom row) and mean model (middle row) with predominately a 3D shape variation of the osseous and articular surfaces (osseous surface (purple) and cartilage surfaces (yellow: cartilage surface for capitate, red: for lunate, green: for trapezium and trapezoid, blue: for radius))

Fig. 3

Orthogonal slice of the 3D averaged bone density model of the scaphoid including its waist. Zones with different vBMD values: outer zone (not coloured) with dense cortical and subchondral bone, intermediate zone with four subregions (light blue: lateral subregion, dark blue: medial subregion, red: proximal pole, yellow: distal pole, green: centre zone with lowest bone mass

Fig. 4

3D averaged density model of the scaphoid to characterize its inner configuration. The left figure displays the mean model of the scaphoid with osseous and cartilage surfaces. Middle and right figures exhibit orthogonal sections with the three concentrically arranged zones displaying high, intermediate and low vBMD values: 1. peripheral zone (blue) with high vBMD values; 2. intermediate zone with intermediate vBMD values and four subregions: subregion located medially (dark blue), near to the proximal pole (red); near to the distal pole (yellow) and laterally (light blue): 3. centre zone with lowest vBMD values (green)

Fig. 5

Virtual probing (3.0 mm diameter) for a central and peripheral pathway