Table 1 Detailed description of non-radiographic measurement methods, equipment and technique used in the included studies

Biophotogrammetry

Biophotogrammetric analysis involves measuring, off-lateral posture photographs, the distance from a plumbline to the lordotic and cervical apex [25] or C7, S1 prominences [30].

Digital camera with vertical plumbline reference posterior to the subject within field of view and a known (presized) object within field of view to establish distance scaling. Computer with graphic editing software

Adhesive stickers that can be seen from the lateral margin of the body are placed on the C7 and S1 landmarks. After calibration, the distance from the plumbline to the landmark points are measured using graphic editing software.

[25, 30]

Infra-red motion analysis

Motion analysis computer-interfaced stereovideographic acquisition of infra-red-activated anatomical markers at C7 [21, 26], T1 [28] and S1.

Minimum of three motion analysis cameras linked to a computer via an image processor. Infra-red light reflected on the adhesive markers

Adhesive infra-red markers are affixed to C7/T1 and S1. The markers are activated by infra-red light and the dedicated computer system triangulates the spine data measuring the sagittal arrows.

[21, 26, 28]

Plumbline

A ruler and plumbline to measure the distance to the C7 and L3 [29, 31], or C7 and S1 [21] anatomical points on the body

Ruler and plumbline

The plumbline is held against or very near to the posterior surface of the skin. The distance from the plumbline to C7 and L3 or S1 is measured.

[21, 29, 31]

Spinal mouse

Spinal mouse assessment uses a wireless computer-interfaced rollerball input device to determine the inclination of the spine from C7 to S1 and the vertical.

Spinal Mouse (Idiag, Voletswil, Switzerland) and computer

The spinal mouse is rolled along the contour of the spine from C7 to S1 measuring distance of travel and angulation.

[23, 24]

Surface topography

Surface topography based on Moire stereovideography measures the distortion of a predicted light grid to create a 3D model of the back providing angular or distance offset data from the vertebral prominens (C7 or T1) to the midpoint between the PSIS.

Surface topography machine (Biomod, AXS Ingenierie, Bordeaux, France) [13] formetric (Diers International, Schlangenbad, Germany) [19, 20, 22, 27] and computer interface

Depending on system, optional, infra-red adhesive markers are placed on C7, PSISs and inter-gluteal cleft. Scanning is performed according to the specifications of the manufacturer.

[13, 19, 20, 22, 27]

Freepoint ultrasound

Freepoint ultrasound system emits an ultrasonic signal from the probe to receivers which triangulate the position of T1 and C7 in space.

Freepoint ultrasound system (GTCO Calcomp, Scottsdale, USA) and interfaced computer

The freepoint probe is used to identify the T1 and S1 landmarks, which are triangulated and digitised allowing for computerised 3D reconstruction.

[28]