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Table 1 Overview of studies

From: Plantar soft tissues and Achilles tendon thickness and stiffness in people with diabetes: a systematic review

No. Author (year) Study Design Aim Setting; Recruitment timeframe; Sample size and comparison groups Parameters assessed and assessment tools utilised Anatomical sites examined
Plantar soft tissues
 1 Kwak (2020) [34] To compare the mechanical properties and stress-strain behaviours of plantar heel soft tissues between people with Type 2 diabetes, young and old control participants. Foot and ankle tertiary referral clinic at the Seoul National University Bundang Hospital, Seoul, South Korea;
Recruitment time-frame: –
■ 10 young ctrls
■ 10 older ctrls
■ 10 T2DM
PTS: Subject-specific finite element model Heel
 2 Lechner (2019) [36] Descriptive, exploratory study To compare the structure, function and molecular markers of dry and cracked foot skin between people with and without diabetes. Department of Dermatology and allergy; Charité-Universitätsmedizin Berlin, Germany;
September 2016 – April 2017;
■ 20 ctrls
■ 40 T2DM
PTT: Optical coherence tomography
PTS: Cutometer
MTH 1, Heel
 3 Oh (2018) [37] Retrospective To investigate the severity of pedal soft tissue atrophy caused by diabetes and aging. Hospital, Daegu, South Korea;
February 2009 – February 2016;
■ 47 ctrls
■ 52 T2DM
PTT: MRI MTH 1, 2, 3, 4, 5
 4 Kumar (2015) [39] Observational To evaluate the thickness of intrinsic foot muscles, plantar skin, plantar fascia and plantar fat pad in people with Type 2 diabetes (with and without DPN). Tertiary hospital, Manipal, India;
July 2013 – January 2014;
■ 30 ctrls
■ 12 T2DM
■ 18 T2-DPN
PTT: US MTH 1, 2, 3, 4, 5
 5 Chatzistergos (2014) [40] To investigate the correlation between the mechanical properties of the heel pad of people with Type 2 diabetes and the clinical parameters used to monitor their health and ulceration risk (e.g. ABI, duration of diabetes, FBS, HbA1c, triglycerides and VPT) Diabetic referral centre, Chennai, India;
Recruitment time-frame: –
■ 17 ctrls
■ 35 T2DM
PTT and PTS: US probe connected with a dynamometer Heel
 6 Jan (2013) [42] To investigate the effect of diabetes on the biomechanical properties and plantar pressure distribution in the pathogenesis of DFU. Recruitment setting: –
Recruitment timeframe: –
■ 6 ctrls
■ 7 T2-DPN
PTT and PTS: TUPS MTH 1
 7 Chao (2012) [43] To evaluate the association between skin blood flow and oedema and epidermal thickness in the feet of people with and without diabetes. Diabetic clinic of a local hospital, Hong Kong;
January 2009 – November 2010;
■ 33 ctrls
■ 35 T2DM
■ 19 T2-DPN with DFU (active or a history of DFU)
PTT: US Hallux
 8 Periyasamy (2012) [44] Pilot study To investigate the feasibility of measuring PTS variation in people with diabetes. Outpatient clinics of Biomedical and Endocrinology Lab, All India Institute of Medical Sciences, New Delhi, India;
January – March 2011;
■ 10 ctrls
■ 10 T2DM
■ 10 T2-DPN
PTS: Durometer Hallux, MTH 1, 2, 3–5, midfoot, heel
 9 Chao (2011) [45] To examine the changes in epidermal thickness and biomechanical properties of plantar soft tissue in people with Type 2 diabetes (with and without either DPN or DFU). Diabetic clinic of a local hospital, Hong Kong;
Recruitment time-frame: –
■ 40 ctrls
■ 34 T2DM
■ 32 T2-DPN
■ 16 T2-DFU (active or a history of)
PTT: US (epidermis only); TUPS (total plantar soft tissue thickness)
PTS: TUPS (total plantar soft tissue stiffness)
Hallux, MTH 1, 3, 5, heel
10 Sun (2011) [55] Cross-sectional study To compare the thickness and stiffness of plantar soft tissues between people with DPN and healthy participants. University research laboratory, Hong Kong; Participants recruited from a local outpatient diabetes clinic;
Recruitment time-frame: –
■ 54 ctrls
■ 70 DPN (early-stage)
PTT and PTS: TUPS Hallux, MTH 1, 2, heel
11 Hsu (2009) [46] To compare micro- and macrochambers mechanical properties between people with Type 2 diabetes and age-matched healthy participants. Tertiary care hospital, Taiwan;
Recruitment time-frame: –
■ 16 ctrls
■ 18 T2DM (2 with DPN; all nil history of DFUs)
PTT and PTS: US with a load cell Heel
12 Hsu (2007) [49] Pilot study To compare the energy dissipation ratio in the plantar soft tissue under the metatarsal heads between people with Type 2 diabetes and age-matched healthy participants. Recruitment setting: –
Recruitment timeframe: –
■ 8 ctrls
■ 13 T2DM (nil with DPN)
PTT: US with a load cell MTH 1, 2, 3, 4, 5
13 Cheung (2006) [62] Preliminary / pilot study To test the feasibility of applying magnetic resonance elastography to map the elastic modulus of the plantar fat pads, in participants with and without diabetes. Department of Radiology, Dartmouth Medical Centre, Lebanon;
Recruitment timeframe: –
■ 12 ctrls†
■ 4 DPN
PTS: Magnetic resonance elastography Heel
14 Hashmi (2006) [50] Investigative report To quantify specific glycation products generated in plantar epidermal proteins in individuals with Type 2 diabetes and age-matched controls, and to compare these data with the viscoelastic properties of the epidermis. Diabetes Unit and the Diabetes Eye Screening Unit at Whittington hospital, London, UK;
Recruitment timeframe: –
■ 87 ctrls
■ 103 T2DM
PTT: US
PTS: Cutometer
MTH 3
15 Puri (2005) [51] To examine changes in tissue echogenicity due to the altered material properties of the plantar foot in diabetes. Recruitment setting: –
Recruitment timeframe: –
■ 8 ctrls
■ 16 T2DM (3 with neuropathic DFUs)
PTS: Durometer Hallux, MTH 1, 3–5, medial and lateral heel
16 Mueller (2003) [56] To determine the primary forefoot structural factors which predict regional PPP during walking in groups of people with and without DPN. Multidisciplinary tertiary-care diabetic foot clinic and the database from the Institution Diabetes Research Training Centre, Washington University School of Medicine, St. Louis, USA;
Recruitment timeframe: –
■ 20 ctrls
■ 20 DPN with a history of DFUs
PTT and PTS: SXCT PTT: MTH 1, 2, 3, 4, 5
PTS: MTH 1, 3, 5
17 Thomas (2003) [52] Preliminary study To identify relationships between foot pressure, tissue stiffness and thickness at different severities of DPN. Recruitment setting: –
Recruitment timeframe: –
■ 9 ctrls
■ 18 T2-DPN (5 with active DFU).
PTT: US
PTS: Durometer
Hallux, MTH 2, 3–5, heel
18 Klaesner (2002) [63] Case-control study To determine if a difference exists in the plantar soft tissues of people with DPN compared with age-matched controls. Data collection performed in an academic physical therapy laboratory; Participants recruited from multiple sources including those who had participated in previous studies in the laboratory, Washington University’s volunteers for Health subject database, the Diabetic Foot Centre at Barnes-Jewish Hospital, and physician referral, St. Louis, USA;
Recruitment timeframe: –
■ 20 ctrls
■ 20 DPN with a history of DFU
PTS: Indentor system; MTH 1, 3, 5, heel
19 Robertson (2002) [57] To investigate relationships between structural changes of the forefoot in people with diabetes with a prior plantar DFU and in matched controls. Multi-disciplinary tertiary-care diabetes clinic, Washington University School of Medicine, St. Louis, USA;
Recruitment timeframe: –
■ 16 ctrls
■ 16 DPN with a history of DFU
PTT: Computed tomography MTH 1–5
20 Hsu (2000) [53] To compare the heel-pad mechanical properties in people with Type 2 diabetes (with and without forefoot DFU)and age-matched healthy participants using a specially designed loading-unloading device. Recruitment setting: –
Recruitment timeframe: –
■ 20 ctrls
■ 21 T2DM (38% with DPN)
■ 12 T2-DFU (all active, Wagner grade 2 or 3; 75% with DPN)
PTT and PTS: US with a loading/unloading device Heel
21 Zheng (2000) [58] To investigate the biomechanical properties of plantar tissues between older participants with DPN and healthy younger participants. Recruitment setting: –
Recruitment timeframe: –
■ 4 young ctrls
■ 4 elderly DPN
PTT and PTS: US indentation system Hallux, MTH 1, 2, heel
22 Piaggesi (1999) [64] To investigate if neuropathy-associated modification of skin elasticity is found before the occurrence of DFU. Outpatient diabetic clinic, Pisa, Italy;
June – December 1996;
■ 36 ctrls
■ 36 DM
■ 36 DPN
PTS: Durometer Midfoot (median and lateral), heel, posterior mid-calf (as a control site)
23 Brink (1995) [59] To investigate potential differences in periarticular soft tissues at the plantar pedis between people without diabetes and people with a history of neuropathic DFUs. Recruitment setting: –
Recruitment timeframe: –
■ 15 young ctrls
■ 10 older ctrls
■ 10 DPN with a history of recurrent DFUs
PTT: US
PTS: Durometer
MTH 1, 2, 3, 4, 5, heel
24 Gooding (1986) [60] To quantify the loss of foot pad thickness and investigate its relationship to ulceration of the foot. Recruitment setting: –
Recruitment timeframe: –
■ 24 ctrls
■ 38 DM
■ 11 DFUs (active or a history of)
PTT: US MTH 1, 2, 3, 4, 5, heel
25 Gooding (1985) [61] To investigate whether it is feasible for US to evaluate heel pad thickness without the use of radiation. Recruitment setting: –
Recruitment timeframe: –
■ 10 ctrls
■ 38 DM
PTT: US Heel
Plantar soft tissues and Achilles tendon
26 Cheing (2013) [41] To compare the biomechanical properties of the ankle–foot complex of people with diabetes (with and without DPN) with healthy individuals, and to examine its correlation with postural control. Two local outpatient diabetes clinics, Hong Kong;
Recruitment timeframe: –
■ 32 ctrls
■ 23 T2DM
■ 9 T2-DPN
PTT, PTS, ATT and ATS: TUPS Hallux, MTH 1, 3, 5, heel;
AT: Distal portion
Achilles tendon
27 Harish (2020) [33] To evaluate sonographic changes in the AT of people with Type 2 diabetes including thickening, hypoechogenicity, loss of fibrillary pattern and alterations in the elasticity of the AT. Recruitment setting: –
Recruitment timeframe: –
■ 61 ctrls
■ 81 T2DM (30 with symptoms suggestive of DPN, 7 with active DFUs, 8 with leg amputations)
ATT: US
ATS: Elastography (Shear wave elasticity imaging)
ATT: Proximal, mid- and distal portions
ATS: Distal portion only
28 İyidir (2019) [35] Cross-sectional study To evaluate the elastographic features of AT with Acoustic Radiation Force Impulse in people with and without DPN. Endocrinology and radiology departments of Başkent University, Ankara, Turkey;
March 2016 – July 2017;
■ 30 ctrls
■ 23 T2DM
■ 22 T2-DPN
ATT: US
ATS: Elastography (Acoustic Radiation Force Impulse)
Mid-portion
29 Couppé (2016) [68] Cross-sectional study To compare the effect of glycaemic control (based on 2-yr average HbA1c) in two groups of men with diabetes (Type 1 and Type 2) and either well or poorly controlled diabetes. Recruitment setting: –
Recruitment timeframe: –
■ 11 ctrls
■ 44 DM (22 well-controlled DM, 22 poorly-controlled DM)
ATS: US
Collagen tendon fibril density: Electron microscopy
Collagen cross-links: Biopsy specimens
Distal
30 Evranos (2015) [38] Cross-sectional study To evaluate ATT and ATS in people with Type 2 diabetes (with and without foot disease) and to investigate the factors that influence these. Study conducted at endocrinology and radiology departments of a university hospital; Subjects recruited from diabetes clinics, Ankara, Turkey;
July 2012 – December 2014;
■ 33 ctrls
■ 43 T2DM
■ 35 T2-DFU
ATT: US
ATS: Elastography (strain)
Proximal, mid- and distal portions
31 Papanas (2009) [47] To study AT morphology on MRI in people with Type 2 diabetes (with and without DPN). Outpatient clinic of the diabetic foot, tertiary care setting, Greece;
Recruitment timeframe: –
■ 16 ctrls
■ 19 T2DM
■ 19 T2-DPN
ATT and AT volume: MRI
32 Batista (2008) [65] To identify any inherent structural pathology in a consecutive group of asymptomatic individuals with diabetes that might be associated with increased stiffness and the development of forefoot DFUs. Department of Orthopaedic Surgery at the Federal University of São Paulo, Brazil, and Orthopaedic Surgery Clinic at Carmino Caricchio Hospital, Brazil;
Recruitment timeframe: –
■ 10 ctrls
■ 60 DM
ATT: US
Morphology: US
33 Akturk (2007) [48] To investigate the effect of diabetes on the AT that may contribute to the long-term complications in the foot-ankle complex and to investigate the factors relating to its thickening. Endocrinology clinic;
Recruitment timeframe: –
■ 34 ctrls
■ 55 T2DM
ATT: US Mid-portion
34 D’Ambrogi (2005) [66] To examine foot function in the presence of diabetes-induced alterations of the anatomical and biomechanical unit formed by the AT, plantar fascia and MTPJs. Outpatient clinics of the Metabolic Diseases Department at the University of Rome “Tor Vergata”, Italy;
Recruitment timeframe: –
■ 21 ctrls
■ 27 DM
■ 19 DPN
■ 15 DPN with a history of DFU (up to 3 months)
ATT: US Proximal, mid- and distal portions
35 Giacomozzi (2005) [67] To examine the effects that diabetes-induced alterations of AT, plantar fascia and 1st MTPJ — both anatomical and functional — may have on foot loading. Outpatient clinics of the Metabolic Diseases Department at the University of Rome “Tor Vergata”, Italy;
Recruitment timeframe: –
■ 21 ctrls
■ 27 DM
■ 19 DPN
■ 15 DPN with a history of DFU (up to 3 months)
ATT: US Proximal, mid- and distal portions
  1. Symbols: – Not stated, † Discrepancy identified in-text
  2. Abbreviations: ABI ankle brachial index, AT achilles tendon, ATT achilles tendon thickness, ATS achilles tendon stiffness, Ctrls control group, DFU diabetes-related foot ulcer, DM diabetes mellitus, DPN diabetes-related peripheral neuropathy, FBS fasting blood sugar, MRI magnetic resonance imaging, MTH metatarsal head (plantar), MTPJ metatarsophalangeal joint, SXCT spiral X-ray computed tomography, T2 type 2 diabetes only, TUPS tissue ultrasound palpation system, PTT plantar tissue thickness, PTS plantar tissue stiffness, US ultrasonography, VPT vibration perception threshold