Table 1.

Studies found using compression elastography (CE) in the assessment of injured or pathologic tendons

Authors year [reference]	Subjects (symptomatic and asymptomatic; structures assessed)	Study design, comparison modality	Major findings	Diagnostic performance and correlations (including comparison with clinical examination, functional scores, conventional US and MRI)
Achilles tendon
De Zordo et al. 2010 [27]	25 volunteers/50 asymptomatic tendons. 25 patients/25 tendons.	Cross-sectional, case–control study. Comparison of USE with conventional US using clinical examination as reference standard.	Symptomatic tendons were softer. The distal and middle third were more frequently involved than the proximal third of Achilles tendon.	USE detected more alterations in contralateral asymptomatic tendons than conventional US. USE has comparable accuracy to conventional US and clinical examination. USE showed good correlation with conventional US (κ = 0.89, p < 0.001), being greater for lesions of the distal third compared to the middle and proximal parts. Ac: 97%, Sp: 99.2%, Sv: 93.7% compared to standard clinical findings. Ac: 99%, Sp: 100%, Sv: 93% compared to conventional US.
Sconfienza et al. 2010 [28]	18 volunteers/36 asymptomatic tendons. 12 patients/12 tendons.	Cross-sectional, case–control study. Comparison of USE with conventional US/MRI using clinical symptoms as reference standard.	Symptomatic tendons were harder. No difference between symptomatic and control tendons at the enthesis and myotendinous junction.	USE showed good correlation with conventional US and MRI.
Tan et al. 2012 [29]	20 volunteers/40 asymptomatic tendons. 16 patients in post-operative period for tendon rupture correction/19 tendons.	Cross-sectional, case–control study.	Healing tendons demonstrated a harder and heterogeneous texture compared to the healthy ones.
Gehmert et al. 2012 [30]	9 rabbits: 12 ruptured tendons, 6 tendons treated with stem cells, 6 ruptured tendons not treated, 6 healthy tendons.	Laboratory study with New Zealand white rabbits.	Treated tendons with stem cells had higher elasticity compared with those not treated. Stem cells restored the elastic properties of Achilles tendon.
Klauser et al. 2013 [31]	10 cadavers/13 tendons.	Laboratory study using cadaveric models. Comparison with conventional US using clinical histology as reference standard.	Injured tendons were softer than asymptomatic tendons.	USE showed perfect agreement with histology results and moderate agreement with conventional US (κ = 0.52, p < 0.001). Sv: 100%, Sp: 100% (histologic findings as the reference standard).
Turan et al. 2013 [32]	41 patients with ankylosing spondylitis (AE)/82 tendons. 32 healthy volunteers/64 tendons.	Cross-sectional, case–control study. Comparison with conventional US using clinical examination as reference standard.	Distal third of Achilles tendon was softer on patients with AE compared with healthy individuals (p = 0.001) and it was associated with enthesopathy findings (p = 0.07). The intensity of achillodynia tended to be higher in patients with abnormal USE examination findings (p = 0.07).	USE had moderate to good correlation with conventional US (κ = 0.80 for proximal third, κ = 0.58 for middle third, κ = 0.39 for distal third).
Evranos et al. 2015 [33]	78 patients with diabetes: 35 patients with foot ulcers, 43 patients without foot ulcers, 33 healthy individuals	Cross-sectional, case–control study.	The Achilles tendon was softer in diabetic patients with foot ulcers than in patients without ulcers (p < 0.001) or in non-diabetics (p = 0.03). A softer medial third of the Achilles tendon was related to longer duration of diabetes, use of insulin, foot ulcers and presence of neuropathy or peripheral arterial disease.
Ooi et al. 2015 [34]	120 patients/120 symptomatic tendons 120 volunteers/120 asymptomatic tendons	Cross-sectional, case–control study. Comparison with conventional US and functional scores using clinical examination as reference standard.	Symptomatic tendons were softer than asymptomatic tendons (SR = 1.70 ± 0.84 vs. 0.76 ± 0.30, p < 0.001).	USE had excellent sensitivity, specificity and diagnostic accuracy (Sv: 97.5%, Sp: 94.5%, Ac: 97.8%). USE had excellent correlation with clinical findings (k = 0.91, p < 0.05). USE showed good to excellent agreement with B-mode US (k = 0.81, p < 0.001). SR had moderate correlation with functional scores (ρ = − 0.62, p < 0.001).
Busilacchi et al. 2016 [17]	30 volunteers/60 asymptomatic tendons. 25 patients in post-operative period of tendon rupture correction/50 tendons.	Prospective cohort study. Comparison of USE with functional score.	After surgery, the tendons were harder and achieved a peak thickness 6 months after, compared to contralateral and control group tendons. Contralateral tendons were stiffer than control group tendons (p < 0.001).	SR had a negative correlation with functional score (ρ = − 0.42, p = 0.03).
Onal et al. 2016 [35]	42 acromegaly patients/84 tendons. 42 healthy volunteers/84 tendons.	Cross-sectional, case–control study. Comparison of USE with biological markers.	Achilles tendons in patients with acromegaly were softer than the healthy ones (p = 0.0001).	No significant correlation between USE and biological markers of the disease.
Yamamoto et al. 2017 [36]	24 New Zealand rabbits with Achilles tendon transection.	Laboratory study. SR calculation and mechanical testing of ultimate load, ultimate stress, elastic modulus and linear stiffness and histological analysis at weeks 2, 4, 8 and 12.	Mean SR at the healing site after Achilles tendon rupture gradually decreased and the Achilles tendon became significantly harder over time (p < 0.001).	SR showed correlation with all mechanical evaluations [ultimate stress (ρ = 0.68, p < 0.001), elastic modulus (ρ = 0.78, p < 0.001) and histologic evaluation of the healing site (ρ = 0.87, p < 0.001)].
Patellar tendon
Rist and Mauch 2012 [37]	75 athletes: 37 asymptomatic tendons, 38 symptomatic tendons.	Cross-sectional, case–control study.	Symptomatic tendons showed higher strain scores than asymptomatic ones in longitudinal and cross-section.
Ooi et al. 2016 [38]	35 volleyball athletes: 40 symptomatic tendons, 30 asymptomatic tendons.	Cross-sectional, case–control study. Comparison with conventional US using clinical examination as reference standard.	Symptomatic tendons were softer than asymptomatic tendons.	USE alone: Ac: 62.9%, Sv: 70%; Sp: 53.3%. USE + B-mode US: Ac: 61.4%, Sv: 82.5%, Sp: 33.3%. USE + power Doppler US: Ac: 60.0%, Sv: 72.5%, Sp: 43.3%. Specificity of USE alone and combined with conventional US were low. USE may increase conventional US sensitivity and accuracy in the diagnosis of patellar tendinopathy. Softening of symptomatic patellar tendons were better related with functional scores (p = 0.004) than conventional US (p = 0.10).
Epicondylar tendons
De Zordo et al. 2009 [39]	28 volunteers/44 asymptomatic tendons. 32 patients with lateral epicondylitis/38 symptomatic tendons.	Cross-sectional, case–control study. Comparison with conventional US using clinical examination as reference standard.	Symptomatic tendons were softer than asymptomatic tendons (p < 0.001).	Sv: 100%, Sp: 89%, Ac: 94%. USE had higher sensitivity and accuracy than conventional US in detecting clinically symptomatic epicondylar tendinopathy. USE had higher sensitivity than conventional US in detecting intratendinous and peritendinous lesions. Good correlation with conventional US findings (ρ ≥ 0.900, p < 0.001).
Ahn et al. 2014 [40]	79 patients and 14 healthy volunteers. 97 symptomatic tendons. 89 asymptomatic tendons.	Cross-sectional, case–control study. Comparison with conventional US and clinical parameters using clinical examination as reference standard.	Symptomatic tendons were softer (mean SR = 1.45 ± 0.45) than asymptomatic tendons (mean SR = 2.07 ± 0.70) (p < 0.001).	Significant correlation with conventional US (p < 0.001).
Park et al. 2014 [41]	28 patients with unilateral lateral epicondylitis: 14 symptomatic tendons, 14 asymptomatic tendons.	Cross-sectional, case–control study. Comparison with conventional US using clinical examination as reference standard.	Symptomatic tendons were softer than asymptomatic tendons.	USE alone: Sv: 96.4%, Sp: 96.4%, Ac: 96.4% (p < 0.01). USE had greater diagnostic accuracy compared to conventional echography (Ac: 96.4% vs. 89.5%, p < 0.01). USE was correlated with severity of tendon pathology estimated by conventional US (p < 0.01). USE was correlated with cortical irregularities around the lateral epicondyle, history of steroid injection and symptom duration (p < 0.05). USE findings had correlation with pain during resistive middle finger extension on physical examination (p < 0.05).
Kocyigit et al. 2016 [42]	17 volunteers with lateral epicondylitis/34 tendons.	Cross-sectional, case–control study. Comparison with conventional US using clinical examination as reference standard.	Symptomatic tendons were softer than asymptomatic tendons (p < 0.001). Mean SR: medial portion = 0.45 ± 0.12, middle portion = 0.44 ± 0.8, lateral portion = 0.47 ± 0.19.	USE was superior to conventional US distinguishing healthy tendons from those with tendinopathy. The SR of medial portion of the extensor tendon correlates with night pain (ρ = − 0.522, p = 0.03) and duration of symptoms (ρ = − 0.61, p = 0.01).
Klauser et al. 2017 [43]	16 cadavers/25 common flexor tendons.	Laboratory study using cadaveric models. Agreement comparison of conventional US and USE with histological evaluation.	Tendons with tendinopathy were softer than normal tendons.	USE combined with conventional US had better correlation (k = 0.84) with histology compared with the use of B-mode US (k = 0.57) or USE alone (k = 0.68) (p < 0.02).
Klauser et al. 2017 [44]	17 cadavers/26 common flexor tendons.	Laboratory study using cadaveric models. Agreement comparison of conventional US and USE with histological evaluation.	Tendons with tendinopathy were softer than normal tendons.	USE alone: Sv: 85%, Sp: 86%, Ac: 86%. USE + B-mode US: Sv: 95%, Sp: 81%, Ac: 92%. USE in combination with conventional US provided improved sensitivity (p < 0.02) without loss of specificity and had correlation with histology evaluation (κ = 0.78, p < 0.02).
Rotator cuff tendons
Seo et al. 2014 [45]	98 patients/101 shoulders with lesions (cuff tears, tendinopathies, adhesive capsulitis, calcific tendinitis, labral lesions).	Cross-sectional. Comparison of USE with conventional US/MRI using MRI findings as reference standard.	USE allowed quantification of the severity of adipose involution on the supraspinatus muscle tendon.	Sv: 95.6%, Sp: 87.5%, Ac: 91.1%. USE had excellent correlation with MRI (ρ = 0.855, p < 0.001) and conventional US (ρ = 0.793, p < 0.001).
Seo et al. 2014 [46]	118 patients/118 shoulders with supraspinatus tendinopathy.	Cross-sectional. Comparison of USE with conventional US/MRI using MRI findings as reference standard.	Tendons with tendinopathy had focal areas of softness.	Positive correlation between grades of MRI and USE (ρ = 0.829, p = < 0.001). Positive correlation between grades of US and USE (ρ = 0.723, p = < 0.001).
Tudisco et al. 2015 [47]	100 shoulders: 50 with supraspinatus tear, 50 healthy contralateral shoulders.	Cross-sectional, case–control study. Comparison of USE (SR) of the tendons between the two groups. Comparison of USE (SR) with demographic data and functional scores.	Mean SR in the affected shoulder (0.75 ± 0.08) was lower than the contralateral healthy shoulder (1.01 ± 0.07) (p < 0.0001).	Negative correlation between SR and VAS (Visual Analogue Scale) score for pain (r = − 0.76). Strong positive correlation between SR and functional scores.
Kocyigit et al. 2016 [48]	50 shoulders: 25 patients diagnosed with unilateral subacromial impingement, 25 healthy shoulders.	Cross-sectional, case–control study. Comparison of USE (including SR) of the tendons between the two groups. Comparison of SR of the tendons with demographic data and functional scores.	Decreased stiffness of the supraspinatus tendon of the affected shoulder compared to healthy shoulder (p < 0.001).	There was no correlation between the findings in USE and functional scores, gender and age.
Lee et al. 2016 [49]	39 patients with chronic supraspinatus tendinopathy.	Cross-sectional. Comparison of the supraspinatus tendon SR with the degree of tendinosis on MRI.		Positive correlation of SR with degree of tendinosis in MRI (p < 0.001).
Long head of biceps tendon (LHBT)
Seo et al. 2014 [50]	34 patients/38 shoulders with tendinopathy of LHBT. 98 patients/114 shoulders without tendinopathy of LHBT.	Cross-sectional, case–control study. Comparison of USE between the two groups. Comparison with conventional US using clinical examination as reference standard.	Focal areas of softening in affected tendons.	Positive correlation between USE and conventional ultrasound (ρ = 0.585, p < 0.001).
Quadriceps tendon
Teber et al. 2015 [51]	53 patients with chronic renal failure undergoing dialysis/106 quadriceps tendons. 25 healthy individuals/50 quadriceps tendons.	Cross-sectional, case–control study. Comparison of USE of the quadriceps tendon between the two groups.	Quadriceps tendons in patients with chronic renal failure were softer (right knee, p = 0.03; left knee, p = 0.02) compared to controls.

Ac accuracy; MRI magnetic resonance imaging; Sp specificity; Sv sensitivity; SR strain ratio; ρ Spearman rank correlation coefficient; r Pearson correlation coefficient; k kappa coefficient