Supplementary information- Multi-segment model development including marker location, anatomical reference frames and joint rotation definitions.

S1. Marker locations

Table S1.Summary of segment marker name, type and anatomical locations.

Segment / Marker / Type / Description
Shank / HFIB / Anatomical (SM) / Proximal apex of the head of fibula
TTUB / Anatomical (SM) / Anterior prominence of the tibial tuberosity
MMAL / Anatomical (SM) / Distal apex of the medial malleolus
LMAL / Anatomical (SM) / Distal apex of the lateral malleolus
SHN1 / Tracking (PM) / Array of 4 plate-mounted markers located on the lateral lower third of the shank
SHN2 / Tracking (PM)
SHN3 / Tracking (PM)
SHN4 / Tracking (PM)
Rearfoot / SCAL / Anatomical and Tracking (SM) / Array of 2 plate-mounted markers located superiorly (SCAL) and inferiorly (ICAL) on the posterior aspect of the calcaneus
ICAL / Anatomical and Tracking (SM)
LCAL / Anatomical and Tracking (SM) / Prominence of the peroneal tubercle
MCAL / Anatomical (SM) / Prominence of the sustentaculum tali
Midfoot / NAV / Anatomical and Tracking (SM) / Medial apex of the tuberosity of the navicular
ICUN / Anatomical and Tracking (SM) / Distal and dorsal aspect of the intermediate cuneiform
CUB / Anatomical and Tracking (SM) / Lateral apex of the tuberosity of the cuboid
1st Metatarsal / P1MT / Anatomical and Tracking (SM) / Dorso-medial aspect of the base of the 1st metatarsal
M1MH / Anatomical and Tracking (SM) / Dorso-medial aspect of the head of the 1st metatarsal
L1MH / Anatomical (SM) / Dorso-lateral aspect of the head of the 1st metatarsal
C1MT / Tracking (PM) / Single marker on a skin-mounted wand projected dorso-medially from the mid-shaft of the 1st metatarsal
Lateral forefoot / P5MT / Anatomical (SM) / Dorso-lateral aspect of the base of the 5th metatarsal
D5MT / Anatomical (SM) / Dorso-lateral aspect of the head of the 5th metatarsal
FFT1 / Anatomical and Tracking (PM) / Array of 3 plate-mounted markers located on the dorsal aspect of metatarsals 2-5 with FFT1 overlying the 2nd metatarsal head
FFT2 / Tracking (PM)
FFT3 / Tracking (PM)
Hallux / HLX1 / Anatomical and Tracking (SM) / Dorsum of the base of the proximal phalanx of the hallux
HLX2 / Tracking(PM) / Single marker on a skin-mounted wand projected dorsally from the superior aspect of the proximal phalanx of the hallux
HLX3 / Anatomical and Tracking (SM) / Dorsum of the distal phalanx of the hallux over the nail-plate

(SM- Skin mounted; PM- plate mounted)

The skin- and plate mounted markers for the construction and tracking of this model are summarised in Table S1. Nineteen anatomical markers were used during the static calibration trial to build the model (see Table S1). The anatomy only markers were removed during walking trials (TTUB, HFIB, MMAL, LMAL, MCAL, L1MH, P5MT, and D5MT). A further 8 markers were used to track the segments during walking trials (SHN1-4, C1MT, FFT2, FFT3, and HLX2), see Table S1.

S2. Anatomical reference frames

The landmarks outlined in S1, along with projected or virtual markers created within the Visual3D software system were used to define the segment anatomical reference frames (see Table S2). Orientation of the axes was standardised such that the X-axis was medial/lateral with X+ pointing to the right; the Y-axis was anterior/posterior with Y+pointing forward; and the Z-axis as vertical with Z+ pointing upwards (See Figure S1).

Table S2. Anatomical reference frame definitions for the model segments.

Segment / Description
Shank
Origin / A virtual TTUB marker is projected onto the frontal plane of the shank created by HFIB, LMAL and MMAL. The shank origin is located here.
x-axis / The x-axis is the projection of the line joining the origin and HFIB on the frontal plane of the shank.
y-axis / The y-axis is the projection of the line joining the origin and TTUB on the sagittal plane passing through the origin, TTUB and a virtual marker located at the midpoint between the medial and lateral malleoli.
z-axis / The z-axis is the projection of the line joining the midpoint of the medial malleoli and the origin and lies in the frontal plane.
Rearfoot
Origin / A virtual SCAL marker is projected onto the frontal plane of the rearfoot created by ICAL and 2 virtual markers projected from ICAL in the xz plane. The rearfoot origin is located here.
x-axis / The x-axis is orthogonal to the yz plane.
y-axis / The y-axis is the projection of a line joining the rearfoot origin and the midpoint between the LCAL and MCAL markers.
z-axis / The z-axis is the projection of the line joining ICAL and a virtual marker projected from SCAL onto the frontal plane of the rearfoot.
Midfoot
Origin / The origin is located at the midpoint between NAV and a virtual marker projected from CUB to lie in the transverse plane of NAV and virtual markers projected from NAV in X+ and Y+.
x-axis / The x-axis is the projection of the line joining the origin and the virtual marker projected from CUB as described for the origin and lies in the frontal plane of the midfoot created by NAV, CUB and CUB projected.
y-axis / The y-axis is a projection of the line joining the origin and a virtual marker defining 40% of the distance between markers projected from P1MT and P5MT. These projected markers lie in the same transverse plane as described for the origin, such that the xy plane of the midfoot lies parallel to the floor.
z-axis / The z-axis is orthogonal to the xy plane.
1st Metatarsal
Origin / The origin is located at the midpoint between P1MT and a virtual marker projected from P1MT onto the sagittal plane formed by L1MH and virtual markers projected from L1MH in Z+ and Y-.
x-axis / The x-axis is the projection of the line joining the origin and the virtual marker projected from P1MT.
y-axis / The y-axis is the projection of the line joining the origin and a virtual marker at 50% of the distance between M1MH and a virtual marker projected from L1MH to sit on a plane created by M1MH and virtual markers projected in X+ and Y+.
z-axis / The z-axis is orthogonal to the xy plane.
Lateral forefoot
Origin / Taking the virtual marker located on the lateral base of the 1st metatarsal a further virtual marker is projected onto a sagittal plane created from P5MT and virtual markers projected from P5MT in Y+ and Z+. The origin is located at the midpoint between these two virtual markers.
x-axis / The x-axis is the projection of the line joining the origin and the virtual marker projected from lateral base of the 1st metatarsal onto a sagittal plane created from P5MT and virtual markers projected from P5MT in Y+ and Z+.
y-axis / The y-axis is the projection of the line joining the origin and a virtual marker located at 25% distance from FFT1 and D5MT.
z-axis / The z-axis is orthogonal to the xy plane.
Hallux
Origin / The origin is located at HLX1
x-axis / The x-axis is orthogonal to y.
y-axis / The y-axis is a projection of the line joining the origin and a virtual marker projected from HLX3 onto a plane formed by HLX1 and virtual markers projected from HLX1 in X+ and Y+.
z-axis / The z-axis is orthogonal to the xy plane.
Foot
Origin / The origin is located at 50% distance between MMAL and a virtual marker projected from LMAL onto a plane created by MMAL and virtual markers projected from MMAL in X+ ,Y+and Z+.
x-axis / The x-axis is a projection of the line joining the origin and the virtual marker projected from LMAL as described for the origin.
y-axis / Virtual markers are created from projections in Y+ from M1MH and D5MT to the longest toe. These distances are derived from calliper measurements for each subject. The y-axis is a projection of the line joining the origin and the 50% distance between these two projected virtual markers.
z-axis / The z-axis is orthogonal to the xy plane.

S3. Joint rotation definitions

The cardan sequence order of rotation was x-y-z. Intersegment rotations were defined using clinical meaningful terms. Rearfoot motion was expressed in the local coordinate system of the shank. Therefore dorsiflexion (+) / plantarflexion (-) was occurred about the x-axis, inversion (+) / eversion (-) about the y-axis, and internal (+) / external (-) rotation about the z-axis. Midfoot motion was expressed in the local coordinate system of the rearfoot. Therefore dorsiflexion (+) / plantarflexion (-) was occurred about the x-axis, inversion (+) / eversion (-) about the y-axis, and adduction (+) / abduction (-) rotation about the z-axis. The vertical height of the navicular was derived from the z-coordinate of the navicular marker. 1st Metatarsal motion was expressed in the local coordinate system of the midfoot. Therefore dorsiflexion (+) / plantarflexion (-) was occurred about the x-axis, inversion (+) / eversion (-) about the y-axis, and adduction (+) / abduction (-) rotation about the z-axis. Lateral forefoot motion was expressed in the local coordinate system of the midfoot. Therefore dorsiflexion (+) / plantarflexion (-) was occurred about the x-axis, inversion (+) / eversion (-) about the y-axis, and adduction (+) / abduction (-) rotation about the z-axis. Hallux motion was expressed in the local coordinate system of the 1st metatarsal. Therefore dorsiflexion (+) / plantarflexion (-) was occurred about the x-axis, inversion (+) / eversion (-) about the y-axis, and adduction (+) / abduction (-) rotation about the z-axis. Foot segment motion was expressed in the local coordinate system of the shank. Therefore dorsiflexion (+) / plantarflexion (-) was occurred about the x-axis, inversion (+) / eversion (-) about the y-axis, and internal (+) / external (-) rotation about the z-axis.

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