Table 1 A non-systematic summary of methods across studies that describe intrinsic foot muscle (IFM) morphology using magnetic resonance imaging (MRI)

Andersen et al., 2004 [7]

Not reported

1T; T1-weighted spin echo; 4 mm slice thickness; slice interval 10 mm

All slices, the first section being randomly placed within the first interslice 10-mm

interval

All, as a single group

Semi-automated user set pixel intensity threshold, stereological point-counting method

N/A

Muscle volume (expressed as a percentage of the value of the matched control participant)

Andreassen et al., 2009 [8]

Not reported

1.5T; T1-weighted fast spin echo; 4 mm slice thickness

All slices

All, as a single group

Semi-automated user set pixel intensity threshold, stereological point-counting method

N/A

Muscle volume (cm³)

Brash et al., 1999 [9]

Not reported

0.5T; T1-weighted gradient-echo and T2-weighted spin echo

Sagittal section through first metatarsal head

Muscle tissue under the first metatarsal head

Not described

N/A

Percentage of CSA that was magnetization transfer active

Bus et al., 2002 [12]

Not reported

3T; T2-weighted fast spin echo; 3 mm slice thickness; 0.15 mm interslice gap; acquisition time 30 min

2 datasets collected in frontal plane; 1st dataset 40–46 slices from mid-tarsal joint proximally & distal IP of 2nd toe distally; 2nd dataset 6 slices from distal metatarsal region; one slice through head 5th metatarsal selected for quantitative analysis

All, as a single group

Semi-automated signal intensity levels using CCHIPS software, verified by visual inspection

N/A

Muscle CSA (expressed as a percentage of total foot CSA)

Bus et al., 2006 [10]

Intra-rater reliability; 4 weeks between measures; weighted kappa = 0.94

1.5T; T1-weighted spin echo; slice thickness 3 mm; 0.9 mm interslice gap

Sagittal plane images oriented parallel to long axis 2nd metatarsal and perpendicular to sole of the foot − 19 slices acquired between 1st and 5th metatarsal heads; coronal plane images oriented perpendicular to sagittal plane images − 20 slices between proximal phalanx and cuneiforms; one slice through head 5th metatarsal selected for analysis

All, as a single group

Visual inspection

Semi-quantitative 5-point scale

Fatty atrophy: 0 = healthy muscle or no atrophy; 1 = mild atrophy; 2 = moderate atrophy; 3 = severe atrophy; 4 = almost no or no muscle tissue visible

Bus et al., 2009 [11]

Cited Bus et al., 2006

(Intra-rater reliability;

weighted kappa = 0.94)

1.5T; T1-weighted spin echo; slice thickness 3 mm; 0.9 mm interslice gap

Sagittal plane images − 19 slices acquired between 1st and 5th metatarsal heads; coronal plane images − 20 slices between proximal phalanx and cuneiforms; one slice through head 5th metatarsal selected for analysis

All, as a single group

Visual inspection

Semi-quantitative 5-point scale

Fatty atrophy: 0 = healthy muscle tissue or no atrophy; 1 = mild atrophy;

2 = moderate atrophy; 3

= severe atrophy; 4 =

almost complete or complete loss

of muscle tissue

Chang et al., 2012 [18]

Intra-rater reliability; one image processed 5 times; coefficient of variation of muscle CSA = 1.3%

1.5T; T1-weighted spin echo; slice thickness 4 mm; contiguous slices; acquisition time 25 min

Frontal plane images acquired perpendicular to plantar aspect of foot; every image from calcaneus through to image containing maximum diameter of sesamoid bones

All, as a single group (but excluding EDB)

Interactive custom software programmed in Matlab; Semi-automated user set pixel intensity threshold

N/A

Muscle volume (cm³)

Chen et al., 2016 [26]

Cited Cheung et al., 2016 (who cited Chang 2012)

1.5T; T1-weighted spin echo; slice thickness 4 mm; contiguous slices

Sagittal and frontal plane acquisition; entire length of foot

All, as a single group

Segmented by excluding all non-contractile tissues in Mimics software

N/A

Muscle volume (mm³/kg)

Cheung et al., 2016 [19]

Cited Chang et al., 2012

1.5T; T1-weighted; Slice thickness 4 mm; contiguous slices

Images acquired perpendicularly to the plantar aspect of the foot; entire length of foot

All, as a single group

Segmented by excluding all non-contractile tissues in Mimics software

N/A

Muscle volume (mm³/kg)

Cheuy et al., 2013a [13]

Inter- and intra-rater reliability; 2 raters processed 46 slices with at least 14 days between measures; all ICCs > 0.9

3T; optimised to fat; spin echo pulse; slice thickness 3.5 mm; acquisition time 9–12 min;

Coronal plane images acquired; 35–65 slices; the forefoot (mid-metatarsal), the

midfoot (tarsometatarsal joint of the second metatarsal), the hindfoot (talonavicular joint)

Plantar side muscles, as a single group

Signal intensity threshold automatically identified with optional manual editing of borders and thresholds as required, Matlab software

Quantitative

Volume (cm³):

Subcutaneous fat; Lean muscle; Intermuscular adipose tissue

Cheuy et al., 2013b [14]

Not reported

3T; spin echo pulse; slice thickness 3.5 mm; acquisition time 12 min

Coronal plane images acquired; 35 slices; talonavicular joint to tarsometatarsal joint

Intrinsic foot muscles between the talonavicular and tarsometatarsal joints

Signal intensity threshold automatically identified with optional manual editing of borders and thresholds as required, Matlab software

Quantitative

Volume (cm³):

Subcutaneous fat; Lean muscle; Intermuscular adipose tissue; Intrinsic foot muscle ratio (ratio of intermuscular volume to lean muscle volume

Feger et al., 2016 [25]

Not reported

3T; spiral gradient echo; slice thickness 5 mm; acquisition time 15 min

Axial slices; entire foot

ABH; ADDH-O; ADDH-T; FHB; ABDM; FDM; EDB; FDB; QP, Interosseous

Manual segmentation of each muscle perimeter on each slice using custom software written in MatLab

N/A

Muscle volume (cm³/m.kg)

Feger et al., 2019 [24]

Cited Handsfield et al., 2014 (study of leg muscle segmentation; inter-user variability reported as acceptable at < 0.6%)

3T; spiral gradient echo; slice thickness 5 mm; acquisition time 15 min

Axial slices were obtained in sets of 20 contiguous images from just posterior to the calcaneus anteriorly through the entire foot.

ABH; ADDH-O; ADDH-T; FHB; ABDM; FDM; EDB; FDB; QP, Interosseous

Manual segmentation of each muscle perimeter on each slice using custom software written in MatLab

N/A

Muscle volume (cm³/m.kg)

Gallardo et al., 2006 [23]

Not reported

1.5T; T1-weighted fast spin-echo and fat-supressed proton density-T2 weighted fast spin-echo in both planes;

Transverse plane slice thickness 10 mm with 0.5-1.0 mm slice gap; coronal plane slice thickness 4–5 mm with 0.5-1.0 mm slice gap

Coronal and axial planes

All

Visual inspection

Qualitative

Presence of signal intensity alterations including muscle oedema, fatty infiltration and abnormal enhancement

Gooding et al., 2016 [29]

Not reported

3T; turbo spin echo; slice thickness 10 mm; 0 mm interslice gap; acquisition time 7 min

From most posterior aspect calcaneus to the toes; for each muscle the series of 3 contiguous slices that provided the largest CSA used for analysis

ABH, FDB, ABDM, QP, FDM, ADDH-O, FHB, Interosseous & lumbricals (together)

Each muscle manually outlined; pixel-by-pixel count based on active range (any pixel that exceeded the lower threshold)

N/A

Percentage increase in muscle activation (pre to post exercise)

Green & Briggs, 2013 [32]

Not reported

Magnet strength not specified; T1- & proton density weighted; slice thickness not specified; interslice gap 5 mm;

Coronal plane images acquired with the plane tilted antero-superiorly to lie perpendicular to the long axis of the second metatarsal

5 groups:

(1) Medial - ABH, FHB; (2) ADDH; (3) Central - FDB, QP, lumbricals; (4) Interosseous; (5) Lateral - ABDM, FDM

Measured using a freehand cursor to trace around the muscle groups

N/A

Maximum muscle CSA (cm²)

Greenman et al., 2005 [15]

Not reported

3T; T2-weighted H spin echo: thickness 2.5 mm; acquisition time 6 min 24 s;

RARE pulse: slice thickness 25 mm; acquisition time 4 min

Axial plane slices; 10 contiguous locations

All, as a single group

Interactive data language software; an outline of the muscle tissue and reference standard was created using a contour mapping function set to a single level that was equal to the noise threshold value; count of pixels that represented signal from foot tissues

N/A

Muscle area- to -total area ratio

Kurihara et al., 2014 [33]

Not reported

1.5T; T1-weighted fast spin echo; slice thickness 4 mm; acquisition time ~ 9 min

Whole foot (sesamoids to calcaneal tuberosity); contiguous slices; acquired perpendicular to plantar aspect of foot; image at the MTP joint that was near 20% longitudinal foot length was selected for analysis

3 muscle groups: 1) Medial – FHB, FDB, QP, ABH and lumbricals;

2) ADDH; 3) Lateral – ABDM, FDB, interosseus

Manual; SliceOmatic software; excluded non-contractile tissues where possible

N/A

Muscle CSA (cm²⁾

Lin et al., 2016 [16]

Not reported

3T; T1-weighted ¹H spin: slice thickness 2.5 mm; acquisition time 6 min 24 s; ³¹P-RARE: slice thickness 25 mm; scan time 4 min

Acquired in a plane perpendicular to longitudinal direction of foot through the metatarsal head region; 10 contiguous; Selected for analysis: level of the 5th metatarsal head from T1-weighted images

3 muscle regions:

(1) FHB medial head; (2) ADDH, FHB lateral head, lumbricals; (3) Interosseous, FDM, ABDM

Manually outlined using tracing tool in OsiriX software; pixel threshold technique

Semi-quantitative 5-point scale

Ratio (³¹P/¹H) of the area of viable muscle tissue to total area outlined; Fatty atrophy: 0 = healthy muscle with no atrophy; 1 = mild atrophy; 2 = moderate atrophy; 3 =

severe atrophy; 4 = almost no or no muscle tissue visible.

Miller et al., 2014 [27]

Intra-rater reliability; five measurements on each muscle over multiple days; mean measurement relative error 0.2–4.3%

1.5T; T2 turbo spin echo fat saturation; slice thickness 5 mm

Coronal, sagittal, axial scans; entire foot; muscle measurement from axial scan

ABH; FDB; ABDM

Manually traced in ImageJ

N/A

Muscle CSA (mm²)

Muscle volume (mm³)

log normalised to foot length

Pelayo-Negro et al., 2014 [22]

Not reported

1.5T; T1-weighted fast spin-echo; fat suppressed proton density-T2-weighted fast spin-echo

Slice thickness not specified; axial and coronal planes

All, as a single group

Visual inspection

Semi-quantitative; 5-point scale

Fatty infiltration: 0 = no evidence of fatty infiltration; 1 = some fatty streaks; 2 = fat evident but

less extensive than muscle; 3 = fat equal to muscle;

and stage 4 = fat more extensive than muscle.

Recht et al., 2007 [21]

Not reported

0.2 to 1.5T; T1- and T2-weighted

(with or without fat suppression) in coronal; STIR or T2-weighted in sagittal

All images

ABDM

Visual inspection

Semi-quantitative; 4-point scale

Fatty atrophy: grade 0 =

no fat or minimal fatty streaks; 1 = increased

fat within the muscle but greater amount of muscle; 2 = equal amounts of fat and muscle; 3 = greater amount of fat than

muscle

Savnik et al., 2000 [31]

Not reported

1.5T; T1-weighted spin echo;

T2-weighted spin echo and STIR; slice thickness 3–4 mm; interslice gap 0.3–0.4 mm

Sagittal images acquired; coronal reformatted images used for measurement

QP; FDB; EH

Measured using region-of-interest area function

N/A

Muscle largest diameter and transverse area

Schmid et al., 2009 [20]

Intra-rater reliability CSA measures; 20% of measures repeated; ICCs > 0.9

Inter-rater reliability fatty atrophy score; kappa 0.33 to 0.68

1.5T; T1- and T2-weighted; Slice thickness 3-3.5 mm

Coronal images; CSA measures at the level where the bony insertion of the tibiocalcaneal ligament at the calcaneus was best visualised

ABDM; FDB; ABH; QP

Visual inspection and measurements using OsiriX software

Semi-quantitative 3-point scale

Muscle CSA (cm²)

Fatty muscle atrophy: 0 = normal muscle; 1 = mild fatty atrophy with more muscle than fat; 2 = substantial fatty atrophy

with more fat than muscle or equal parts fat and muscle

Severinsen et al., 2007 [17]

Not reported

1.5T; T1 spin echo; slice thickness 1.5 mm; inter-slice interval 10 mm

The first section being randomly

placed within the first interslice interval

All, as a single group

Semi-automated user set signal intensity threshold, stereological point-counting technique

N/A

Muscle volume (mm³)

Taddei et al., 2018 [28]

Not reported

1.5T; T1-weighted spin-echo; slice thickness 4 mm; contiguous

Images acquired perpendicular to the plantar aspect of the foot; between the most proximal and most distal images in which every intrinsic foot muscle is visible

ABH; ABDM; FHB; FDB

Measured by ImageJ planimeter software for each muscle at each slice

N/A

Muscle CSA (mm²)

Taddei et al., 2020 [30]

Not reported

1.5T; T1-weighted spin-echo; slice thickness 4 mm; contiguous

Images acquired perpendicular to the plantar aspect of the foot; between the most proximal and most distal images in which every intrinsic foot muscle is visible

ABH; ABDM; FHB; FDB

Measured by ImageJ planimeter software for each muscle at each slice

N/A

Muscle CSA (mm²)

Muscle volume (cm²)