Methodological and statistical approaches for the assessment of foot shape using three-dimensional foot scanning: a scoping review

Abstract

Objective

The objectives of this study were to: (i) review and provide a narrative synthesis of three-dimensional (3D) foot surface scanning methodological and statistical analysis protocols, and (ii) develop a set of recommendations for standardising the reporting of 3D foot scanning approaches.

Methods

A systematic search of the SCOPUS, ProQuest, and Web of Science databases were conducted to identify papers reporting 3D foot scanning protocols and analysis techniques. To be included, studies were required to be published in English, have more than ten participants, and involve the use of static 3D surface scans of the foot. Papers were excluded if they reported two-dimensional footprints only, 3D scans that did not include the medial arch, dynamic scans, or derived foot data from a full body scan.

Results

The search yielded 78 relevant studies from 17 different countries. The available evidence showed a large variation in scanning protocols. The subcategories displaying the most variation included scanner specifications (model, type, accuracy, resolution, capture duration), scanning conditions (markers, weightbearing, number of scans), foot measurements and definitions used, and statistical analysis approaches. A 16-item checklist was developed to improve the consistency of reporting of future 3D scanning studies.

Conclusion

3D foot scanning methodological and statistical analysis protocol consistency and reporting has been lacking in the literature to date. Improved reporting of the included subcategories could assist in data pooling and facilitate collaboration between researchers. As a result, larger sample sizes and diversification of population groups could be obtained to vastly improve the quantification of foot shape and inform the development of orthotic and footwear interventions and products.

Background

Human foot morphology is highly variable and is influenced by a broad array of factors, including age [1], sex [2], ethnicity [3], body mass [4], genetic disorders [5], and musculoskeletal foot conditions such as hallux valgus [6, 7] and osteoarthritis [8]. Foot shape impacts many aspects of an individual's life, including standing balance, movement during walking, sporting performance, predisposition to lower limb injury, and footwear fit [9]. Sub-optimal footwear fit has a significant impact on an individuals comfort, risk of foot pathology development, and falls risk [10].

The impact of variation in foot shape and on footwear fit are significant barriers that consumers, clinicians, and industry face. With the use of three-dimensional (3D) scanning technology, detailed information about the foot can be obtained and analysed to quantify foot shape [11]. This detailed foot shape data can provide researchers with a greater understanding of foot shape across population groups to improve footwear design and fit. Obtaining optimal footwear fit has been increasingly difficult with the continued rise of online purchasing. Currently, there are hundreds of footwear brands on the market, and they do not follow a standardised sizing system [12, 13]. For example, length measurement differences (in the same US size) of 0.5 cm can be observed when comparing a Nike and Adidas running shoe [12]. Difficulties in obtaining correct footwear fit have resulted in higher return rates from online orders due to fit uncertainty, resulting in a negative client experience and increased cost for the company [12, 14]. Additionally, the higher return rates has a significant environmental and economic impact [15].

Although 3D surface scanning has been used to measure foot shape since the mid-1990s [16], only recently has statistical shape modelling using sophisticated morphometric and multivariate statistical analysis techniques been used to identify discrete foot types from 3D shape data [17]. These techniques allow foot shape to be separated from overall object size by using rich 3D data to identify characteristics that are unable to be measured using predetermined 2D measurements [18]. The ability to differentiate foot shape according to sex, age, ethnicity, and pathology has practical applications for footwear design from a structural and functional perspective.

Capturing a 3D model of the foot has been achieved through a variety of methods since its inception. The type of 3D scanning systems have been varied, ranging from the use of stereophotogrammetry (which uses multiple photographs taken from different angles) to structured light (patterns projected on the object) and laser scanning systems (laser/s are repeatedly projected onto a surface while the camera/s and computer system acquires the 3D data) [19]. Early scanning equipment involved using a projector paired with a charged coupled device to capture 3D foot shape [16]. In addition to these methods, smart phone cameras, digitisers, RealSense depth cameras (Microsoft® Kinect; Microsoft, Redmond, WA, USA), and adjustable height pins (Amfit® system, Amfit Inc, Vancouver, WA, USA) have been used to generate 3D foot data [20,21,22]. Recent studies primarily employ laser scanning technology; however, a wide range of laser scanners are currently available. As a result of the large variety of 3D scanning systems, potential differences in scanner specifications, scanning condition protocols, foot measurements, and statistical analysis techniques may exist between studies. To help overcome some of these issues, 3D surface scanning standards have been created by the International Organisation for Standardisation (ISO) [23] and the Institute of Electrical and Electronics Engineers (IEEE) [24], with the first ISO standard being released in 2015. However, currently it is unclear if these standards have been adopted in the literature.

To the best of our knowledge, with the exception of a broad overview of 3D foot scanning published in 2010 [25], and recent reviews specifically focused on smartphone apps [26] and comparing 3D scanning to traditional methods for fabricating orthoses [27], no studies have consolidated and reviewed the literature pertaining to 3D foot scanning methods in detail. Therefore, the objectives of this paper are to: (i) review and provide a detailed narrative synthesis of 3D foot surface scanning methodological and statistical analysis protocols, and (ii) construct a methodological checklist to help homogenise the reporting of 3D scanning and statistical analysis protocols for future studies.

Methods

This scoping review was conducted and reported in accordance with the Joanna Briggs Institute methodology for scoping reviews [28] and the PRISMA extension for scoping reviews [29].

Search strategy

Three electronic databases were searched. An initial limited search of SCOPUS, ProQuest, and Web of Science were undertaken by two independent reviewers (JJA, HBM) to identify key studies for the topic. A reviewer (JJA) and research librarian (NP) identified key text words contained in the titles and abstracts of key studies and these were used to develop a full search strategy for SCOPUS, ProQuest, and Web of Science. Key search terms were grouped into three main concepts and adapted to each database: (i) 3D foot scanning, (ii) shape modelling/analysis/morphology, and (iii) foot/feet. Concept synonyms were searched under ‘topic’ which included title, abstract, and key words. Results from within each concept were combined with ‘OR’ and between concepts were combined with ‘AND’. The search strategy is provided in Supplementary file 1. Manual citation tracking and reference checking of included studies were performed. Grey literature such as conference proceedings were screened for additional studies. Only studies published in the English language were included. Studies published from inception to March 28^th, 2022, were included. Titles and abstracts were screened by two independent reviewers (JJA and HBM) for assessment against the inclusion/exclusion criteria for the review. Any disagreements on eligibility were resolved at a consensus meeting by a third independent reviewer (SEM).

Inclusion / exclusion criteria

To be included, papers needed to report studies that employed static 3D surface scanning of the foot. Studies with participants of any age, sex, geographical location, musculoskeletal pathology, or health setting were included. Papers were excluded if the studies used two-dimensional footprints only, 3D scans that did not include the medial arch, dynamic/sequential scans to infer foot movement, derived foot data from a full body scan, or diagnostic imaging techniques that may be used to create 3D models of the foot (such as x-ray, magnetic resonance imaging or computed tomography). Single case studies, studies involving 10 or fewer participants, non-English full text or conference proceedings/abstracts with less than four text pages were excluded due to a lack of detail provided, as were papers which described a scanning technique but provided no data on foot shape, and thesis dissertations. Foot dimensions measured were included if used in two or more studies.

Study selection and data extraction

Study selection and data extraction were performed independently by two reviewers (JJA and HBM). Any disagreements on study eligibility were discussed between reviewers (JJA and HBM) and resolved at a consensus meeting by a third independent reviewer (SEM). A custom generated data extraction template was created in Covidence (Covidence, Melbourne, Australia). The following individual study data were extracted from included studies: general study information (title, author, database / journal, country, and primary objective), 3D scanner characteristics (name, type, accuracy, and capture duration), study methods (e.g., sample size), 3D scanner methodology (e.g., calibration, data collection, 3D foot measures), scanner reliability (intra- and inter-rater), participant demographics (participant subgroup, age, sex, weight, height, body mass index [BMI], co-morbidities, shoe size, and ethnicity), processing techniques (meshing, smoothing, cropping, scaling, and software used), broad study design, statistical analysis approach, inclusion/exclusion criteria, and main outcomes. All 3D foot measures were cross checked using the IEEE and ISO definitions.

Results

A flowchart of included studies is shown in Fig. 1. The initial search yielded 1,635 articles; from which 224 duplicates were removed. A further 1,180 articles were excluded in the title and abstract screening with an additional 153 excluded after the full text screening. A final 78 studies were deemed to meet the inclusion criteria.

Fig. 1

Flowchart of included studies

Characteristics of included studies

The included studies originated from 17 different countries: China (n = 41) [4, 11, 30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68], Japan (n = 6) [16, 44, 69,70,71,72], Germany (n = 4) [13, 73,74,75], Romania (n = 3) [8, 76, 77], South Korea (n = 3) [78,79,80], Spain (n = 3) [22, 81, 82], United States (n = 3) [83,84,85], Italy (n = 3) [20, 21, 86], India (n = 2) [5, 87], Malaysia (n = 2) [3, 88], New Zealand (n = 2) [35, 62], Australia (n = 2) [89, 90], Belgium (n = 2) [18, 91], United Kingdom (n = 2) [92, 93], Canada (n = 1) [94], Iran (n = 1) [9], Russia (n = 1) [47], Slovenia (n = 1) [95], and Sweden (n = 1) [75]. Several study designs were utilised in the literature, these included: 51 comparisons of mean differences between groups [3, 5, 8, 9, 22, 30,31,32,33,34,35, 38,39,40,41, 43,44,45, 47,48,49,50, 52,53,54,55,56,57,58,59,60,61,62, 66, 68, 70, 72, 75,76,77,78, 80, 83, 85,86,87,88,89, 93,94,95], 20 cluster/principal component analyses [5, 11, 13, 16, 18, 31, 32, 38, 42, 51, 58, 63, 64, 68, 73, 79, 82, 85, 87, 90], 14 reliability studies [20,21,22, 34, 37, 39, 48, 49, 53, 75, 78, 88, 90, 91], 10 validation studies [20, 21, 39, 40, 46, 48, 53, 65, 78, 81], one correlation study [33], one comparison of distributions between groups [92], one regression analysis [87], and 11 repeated measures studies were reported, which were grouped into three subcategories; seven studies reported the effect of different loading conditions [4, 22, 36, 39, 74, 84, 90], three reported changes before/after exercise [62, 69, 71], and one reported different alignment methods [67]. Thirty-one studies reported participant inclusion criteria [4, 5, 9, 11, 13, 16, 32, 34, 36, 40, 43, 47, 50, 52, 56, 58, 61, 69, 71, 73, 74, 78, 79, 81, 83, 84, 87, 89, 91, 92, 94] and 30 studies reported exclusion criteria [4, 5, 9, 22, 32,33,34,35,36, 40,41,42, 46, 47, 52, 61, 67, 69, 71, 73,74,75,76, 78, 84, 89,90,91,92, 94].

Sample size ranged from 11 to 1,200,847, with 57 studies including healthy young adults [3, 4, 8, 11, 13, 16, 18, 20, 21, 30,31,32,33,34,35,36,37,38,39,40, 42,43,44,45,46, 48,49,50, 54,55,56, 59,60,61, 63,64,65,66,67,68,69,70,71, 74, 77, 78, 80,81,82,83,84, 87, 88, 90, 91, 93, 94]. Other groups included: older adults (> 65 years) (n = 18) [8, 9, 34, 38, 45, 56, 61, 70, 72, 74, 77, 82,83,84, 87, 91, 93, 94], children/adolescents (< 18 years) (n = 11) [5, 13, 37, 38, 41, 52, 56, 75, 80, 89, 92], participants with medical conditions (n = 7) (such as Down syndrome [89], diabetes [8, 34, 87], arthritis [8, 94], and cerebral palsy [5]), sports people (n = 8) (such as football (soccer) players [73], American football players [85], road cyclists [22], collegiate runners [69, 71], recreational runners [35, 62], and amateur sprinters [50]), non-habitual exercisers [50], pregnant women [4], and habitually barefoot or shod participants [35, 47]. Additionally, five studies included controls in their sample [8, 73, 87, 89, 93], while other studies did not provide specific participant characteristics [51, 58, 79, 86].

All but six studies [21, 53, 57, 65, 73, 79] reported participant sex. Fifty-three studies reported mean age (ranging from 8 to 75 years) [3, 4, 8, 9, 11, 13, 16, 18, 22, 30,31,32,33,34,35,36, 38, 40, 43,44,45,46, 48, 50, 51, 54,55,56, 58, 59, 61,62,63,64, 67,68,69,70,71,72, 74, 75, 77, 82,83,84, 86,87,88,89,90, 93, 94], and 51 reported age standard deviation [3, 4, 8, 9, 11, 13, 16, 18, 22, 30,31,32,33,34,35,36, 38, 40, 43,44,45,46, 48, 50, 51, 54,55,56, 58, 59, 61,62,63,64, 68,69,70,71,72, 74, 75, 77, 82,83,84, 86,87,88,89,90, 94]. Fifty-four studies reported minimum age (ranging from 2 to 69 years), maximum age (ranging from 7 to 87 years), and age range (2 to 87 years) [3,4,5, 9, 11, 16, 18, 20, 21, 30,31,32,33,34, 36,37,38,39,40,41,42, 46, 48,49,50, 52, 54, 55, 59, 60, 63,64,65,66,67,68, 70, 72, 74, 75, 77, 78, 80,81,82,83,84, 88,89,90,91,92,93,94]. Fifty-three studies reported mean height (ranging from 100.9 to 187.8 cm) and 52 reported height standard deviation [3, 4, 8, 9, 11, 16, 18, 22, 30,31,32, 35, 36, 38, 39, 41,42,43,44,45,46,47,48,49,50,51,52, 54,55,56, 58, 59, 61,62,63,64, 68,69,70,71,72, 74, 75, 84,85,86,87,88,89,90,91, 93, 94]. Fifty-four studies reported mean weight (ranging from 15.7 to 111.8 kg) and 53 reported weight standard deviation [3, 4, 8, 9, 11, 16, 18, 22, 30,31,32,33, 35, 36, 38, 39, 41,42,43,44,45,46,47,48,49,50,51,52, 54,55,56, 58, 59, 61,62,63,64, 68,69,70,71,72, 74, 75, 84,85,86,87,88,89,90,91, 93, 94]. Twenty-four studies reported BMI mean (ranging from 15.2 to 32.9 kg/m²), and 23 reported standard deviation [18, 20, 21, 34, 35, 41, 43,44,45, 47, 50, 52, 54, 55, 61, 68, 70,71,72, 74, 75, 89, 93, 94]. Twenty-three studies reported participant ethnicity/cultural background [3, 4, 11, 13, 31,32,33, 35, 40,41,42, 44, 55, 59,60,61, 63, 64, 68, 76, 77, 80, 88].

Scanning conditions

Sixty-seven of the included studies performed 3D surface scanning of participants in bipedal stance (half bodyweight) [3, 4, 9, 11, 13, 16, 18, 20,21,22, 30,31,32,33,34,35,36,37, 39,40,41,42,43,44,45, 47, 48, 50,51,52,53,54, 56,57,58,59, 61,62,63,64,65,66,67,68,69,70,71,72,73,74,75, 78,79,80,81,82, 84,85,86, 88,89,90,91,92,93,94,95], 11 studies with partial/semi weightbearing (seated/standing) [22, 43, 52, 59, 70,71,72, 83, 84, 86, 90], six studies in unipedal stance (full bodyweight) [18, 57, 59, 75, 84, 90], five studies in non-weightbearing (prone/supine) [4, 30, 34, 46, 57], and two studies with external bodyweight [36, 57]. Nine studies did not report the weightbearing condition [5, 8, 38, 49, 55, 60, 76, 77, 87]. Thirty-nine studies reported performing scans bilaterally [3, 5, 9, 11, 13, 18, 20,21,22, 30, 31, 33, 37, 40, 43, 44, 50, 52, 53, 55, 56, 58, 59, 61, 62, 65, 69, 70, 72, 73, 76, 77, 79, 86,87,88, 91, 92, 95] and 32 reported unilateral scanning [4, 16, 32, 34, 35, 39, 41, 42, 45,46,47,48,49, 51, 63, 64, 66,67,68, 71, 74, 75, 78, 80,81,82,83,84,85, 89, 90, 93]. Seventeen studies provided a justification if unilateral scanning was performed (random, dominant, left, right, most painful) [16, 34, 45, 63, 64, 67, 68, 74, 75, 81, 82, 84, 85, 89, 90, 93, 94]. Thirty studies analysed the right foot only [4, 9, 16, 32, 35, 39, 41,42,43,44,45, 47,48,49, 51, 63, 64, 68,69,70,71, 78, 80,81,82,83,84, 89, 92, 93], 30 analysed both feet [3, 5, 8, 11, 13, 18, 21, 22, 31, 33, 37, 40, 50, 52, 53, 55, 56, 58, 59, 61, 65, 72, 73, 75,76,77, 86,87,88, 91], and three analysed the left foot only [67, 85, 90]. Forty studies reported scanning the foot in a barefoot condition [3, 9, 16, 20,21,22, 30, 32,33,34, 36, 39, 40, 43,44,45, 47, 48, 52,53,54,55, 59, 64,65,66,67,68,69,70,71,72, 74, 81, 83, 84, 86, 92, 94, 95], while one study reported the use of socks/hosiery [46]. Twenty-eight studies reported the number of scans per foot (ranging from two to 15 scans) [4, 16, 18, 21, 22, 33, 34, 36, 39, 50, 52,53,54,55, 63, 64, 66, 68, 69, 71, 72, 75, 78, 86, 88, 90,91,92]. Thirty-three studies reported the use of scanning markers [3, 13, 16, 32,33,34, 39, 40, 42, 44, 48, 50, 51, 54, 55, 59, 61, 63, 64, 67,68,69, 71, 72, 77, 80,81,82,83,84, 86, 88, 91] and 12 used markerless scanning [20, 30, 46, 47, 52, 53, 75, 79, 92,93,94,95]. Thirty studies reported the number of markers used in their scanning process, which included a range of one to 14 markers [3, 16, 32,33,34, 39, 40, 42, 44, 48, 50, 51, 54, 55, 59, 61, 63, 64, 67,68,69, 71, 72, 80,81,82,83,84, 86, 91]. Except for four studies [22, 34, 46, 92], static platform scanners were used. Fifty-nine studies captured at or above malleolar level [3, 8, 11, 16, 18, 22, 30,31,32,33,34, 37,38,39,40,41,42, 44, 46,47,48,49,50, 53,54,55,56,57,58,59, 61, 62, 64, 66,67,68,69, 72,73,74,75,76,77, 79, 81,82,83,84,85,86,87,88,89,90,91,92,93,94,95], six studies captured the plantar surface only [4, 20, 21, 52, 65, 78], and thirteen studies did not report the depth of scan [5, 9, 13, 35, 36, 43, 45, 51, 60, 63, 70, 71, 80].

Scanner specifications

Seventy-two of the included studies reported the 3D scanner model. Twenty-five studies used the INFOOT USB scanning system (IFU-S-01, I-Ware Laboratory Co., Ltd, Japan) [3, 8, 33, 40, 41, 44, 50, 54,55,56, 58, 61, 63, 64, 68, 76, 77, 80,81,82, 85, 87,88,89, 91], seven used the YETI foot scanner (Vorum Research Corporation, Canada) [38, 48, 51, 59, 66, 67, 73], four used the Microsoft® Kinect [11, 20, 21, 53], four used the 3D easy-foot-scan (OrthoBaltic, Kaunas, Lithuania) [35, 36, 47, 62], three used the FSN-2100 (Dream GP Inc., Osaka, Japan) [43, 45, 70], two used the FotoScan 3D scanner (Precision 3D Limited, United Kingdom) [89, 94], two used the FootIn3D (Elinvision, Lithuania) [18, 90], and 25 studies reported using other scanner models not used in any other study included in this review [4, 9, 13, 16, 22, 30, 34, 37, 39, 42, 46, 49, 52, 69, 71, 72, 74, 75, 78, 79, 83, 86, 92, 93, 95]. Sixty-one studies reported the scanner type. Forty-two studies stated the use of a laser scanner [3,4,5, 9, 18, 33, 36, 38, 40, 43,44,45, 47, 48, 50,51,52, 54,55,56,57,58,59, 61, 63,64,65, 67, 68, 70, 72, 73, 79,80,81,82, 84, 85, 87, 89, 91, 93], eight studies stated the use of a structured/projected light scanner [16, 34, 37, 74, 75, 78, 89, 92], 11 studies stated other scanner types (RGB-depth camera, smartphone [LiDAR], and author own custom devices) [11, 20,21,22, 30, 32, 39, 41, 42, 46, 86], and 18 studies did not state a scanner type [8, 13, 31, 35, 49, 53, 60, 62, 66, 69, 71, 76, 77, 83, 88, 90, 94, 95]. Forty-five studies reported scanner accuracy, with a range of < 0.2 to 3.4 mm [3,4,5, 9, 11, 16, 18, 21, 30, 31, 33,34,35, 37, 40, 44, 46, 47, 49,50,51,52,53,54,55, 58, 59, 62,63,64, 68, 69, 71, 73,74,75, 78, 83, 84, 86, 89, 90, 92,93,94]. Thirty-two studies reported scanner resolution [4, 13, 16, 18, 21, 30, 33,34,35,36,37, 40, 43, 46,47,48, 51, 56, 58, 59, 70, 72,73,74,75, 78, 82,83,84,85, 88, 90, 92]. Thirty-four studies reported scanner capture duration (ranging from 0.1 to 30 s) [3, 4, 16, 18, 21, 30, 32, 34, 37, 39, 40, 42,43,44,45,46,47, 49, 50, 52,53,54, 59, 63, 64, 68, 70, 72, 78, 84, 90,91,92, 95]. Eleven studies performed independent testing for scanner accuracy [21, 39, 49, 53, 59, 69, 71, 75, 78, 86, 91].

Scanner reliability and calibration methods

Twenty-seven studies reported 3D scanner intra-rater (test–retest) reliability [20,21,22, 30,31,32,33,34, 37, 39, 40, 46, 49, 53, 59, 69, 71, 73, 75, 78, 82, 86, 88, 90,91,92,93]. Two studies reported scanner inter-rater reliability [90, 93]. Fourteen studies reported scanner calibration methods [22, 30, 33, 37, 39, 49, 57, 59, 78, 83, 84, 86, 89, 93].

Foot dimensions measured

A wide range of foot measures to quantify foot shape were reported within the included studies (see Fig. 2). Sixty-five studies measured foot length [3,4,5, 8, 9, 11, 13, 20,21,22, 30,31,32,33,34,35,36,37,38, 40,41,42,43,44, 46,47,48,49,50, 53, 55,56,57,58,59,60,61,62,63,64, 66,67,68,69,70,71,72,73,74,75,76,77, 79,80,81,82, 84, 85, 87,88,89, 91, 93,94,95], 64 studies measured ball width/breadth [3,4,5, 9, 11, 13, 20,21,22, 30,31,32,33,34,35, 37, 39,40,41,42,43,44, 46,47,48,49,50, 53, 55,56,57,58,59,60,61,62,63,64, 66,67,68,69,70,71,72,73,74,75,76,77, 79, 81,82,83,84,85,86,87,88,89, 91, 93,94,95], 51 studies measured ball girth [3, 5, 11, 22, 30,31,32,33, 37, 38, 40,41,42,43,44, 47,48,49, 53, 55,56,57, 59, 61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77, 79, 82,83,84,85,86,87,88,89, 91, 93], 51 studies measured instep height [4, 8, 13, 20, 21, 30,31,32,33,34, 38, 40,41,42,43,44, 47,48,49,50, 54, 55, 57,58,59, 61,62,63,64, 67,68,69,70,71,72,73,74,75, 78,79,80,81,82,83,84, 89, 91, 93,94,95], 43 studies measured heel width [8, 9, 13, 30,31,32,33, 40,41,42,43,44, 46,47,48, 55, 57,58,59, 61, 63, 64, 66,67,68,69, 71,72,73,74,75,76, 79, 81, 83,84,85,86, 89, 91, 93, 95], 43 studies measured length to first metatarsal head (medial arch length) [13, 21, 30,31,32,33,34, 40,41,42,43,44, 47, 48, 50, 54,55,56,57, 59, 61,62,63,64, 67,68,69,70,71, 73,74,75,76, 79, 80, 83,84,85,86, 88, 89, 91, 93], 38 studies measured instep girth [8, 22, 30,31,32,33,34, 37, 38, 40,41,42,43,44, 47,48,49,50, 55, 56, 61,62,63,64, 66,67,68, 72, 75,76,77, 79, 82, 84, 86, 87, 89, 91], 27 studies measured length to fifth metatarsal head (lateral arch length) [13, 32, 33, 40, 41, 43, 44, 47, 50, 55, 56, 61, 63, 64, 68,69,70,71, 73,74,75, 79, 84, 88, 89, 91, 93], 20 studies measured first toe angle [33, 35, 39,40,41, 43, 44, 47, 50, 61, 63, 64, 69,70,71,72, 74,75,76, 91], 20 studies measured malleolus/sphyrion height [8, 30,31,32, 41, 42, 44, 46, 48, 49, 55, 57, 59, 61, 73, 76, 81, 83, 84, 91], 19 studies measured toe height [8, 13, 32, 33, 41, 42, 57, 61, 63, 64, 68, 72, 73, 76, 81,82,83,84, 89], 17 studies measured fifth toe angle [33, 39, 40, 43, 44, 50, 61, 63, 64, 69,70,71,72, 74,75,76, 91], 13 studies measured instep width [21, 30, 31, 48, 56, 58, 59, 67, 78, 79, 83,84,85], 13 studies measured ball height [33, 37, 39, 40, 42, 50, 55, 61, 73,74,75, 91, 93], 13 studies measured navicular height (sitting/standing) [34, 41, 42, 50, 55, 61, 63, 69, 71, 72, 76, 80, 91], 12 studies measured short heel girth [5, 30, 32, 37, 41, 44, 48, 55, 67, 76, 82, 87], eight studies measured ankle girth [30, 32, 42, 48, 49, 73, 79, 87], six studies measured heel angle (frontal plane) [69, 71, 73, 76, 91, 94], six studies measured ball angle [32, 74, 75, 79, 83, 84], five studies measured long heel girth [30, 34, 48, 67, 86], three studies measured flare angle [11, 58, 85], and two studies measured toe length [50, 84]. Figure 3 shows the most commonly reported foot dimensions.

Fig. 2

Frequency of reported 3D foot scan dimensions from the included papers

Fig. 3

The most frequently reported 3D foot scan dimensions from the included papers. A: foot length (FL), B: ball width, C: ball girth, D: instep height, E: heel width, F: length to first metatarsal head, G: instep girth

IEEE and ISO reporting

Thirteen studies cited the ISO standards [33, 35, 39, 47, 49, 50, 57, 63, 64, 68, 80, 82, 88]. No studies cited the IEEE whitepaper standards.

Processing techniques and software used

Nineteen studies reported the processing techniques used. Sixteen studies used meshing [11, 16, 18, 20, 37, 39, 49, 52, 65, 79, 82, 88, 90, 92, 94, 95], 11 studies used smoothing [20, 35,36,37, 42, 47, 58, 78, 85, 92, 94], six studies used scaling [18, 44, 46, 79, 82, 90], and four studies used cropping [18, 79, 85, 93].

Statistical analysis techniques

Forty-three studies reported analysing mean differences (i.e., t-tests or ANOVAs) [3,4,5, 8, 9, 11, 22, 32,33,34,35,36, 39,40,41, 43,44,45, 47, 48, 50, 52, 54,55,56, 59,60,61,62, 68,69,70,71,72, 75, 76, 80, 83, 86, 87, 89, 91, 93], 24 studies reported analysing associations (i.e., Pearson’s r, Spearman’s rho, or intraclass correlation coefficients) [5, 9, 11, 16, 20, 22, 32,33,34, 40, 41, 43, 45, 49, 51, 52, 55, 58, 75, 78, 80, 84, 87,