Use the 'SHEAR_ALL' plugin to perform an afine shear transformation a surface in one of the three orthogonal planes.

Click the menu icon to enable this plugin.

After the plugin is enabled, select the required orthogonal projection view tab. Then click and hold on a control point of the surface to be sheared.

Drag the mouse to shear the control points. The shear factor is displayed in the mode text box above the 3D view.

Release the mouse to complete the shear transformation.

Click the menu item to disable the plugin mode.

This plugin is undo-able.

For the dedicated staff at Hammersmith Hospital.