Effect of knee position on the ultrasound elastography appearance of the patellar tendon

Chinese Ultrasound Doctors Association Guideline on Operational Standards for 2-D Shear Wave Elastography Examination of Musculoskeletal Tissues

The Ultrasound Physician Branch of the Chinese Medical Doctor Association sought to develop evidence-based recommendations on the operational standards for 2-D shear wave elastography examination of musculoskeletal tissues. A consensus panel of 22 Chinese musculoskeletal ultrasound experts reviewed current scientific evidence and proposed a set of 12 recommendations for 13 key issues, including instruments, operating methods, influencing factors and image interpretation. A final consensus was reached through discussion and voting. On the basis of research evidence and expert opinions, the strength of recommendation for each proposition was assessed using a visual analog scale, while further emphasizing the best available evidence during the question-and-answer session. These expert consensus guidelines encourage facilitation of the standardization of clinical practices for collecting and reporting shear wave elastography data.

Quantitative evaluation of the biomechanical and viscoelastic properties of the dog patellar tendon in response to neuromuscular blockade at different stifle angles

The patellar tendon (PT) is crucial for maintaining stability and facilitating movement in the stifle joint. Elastography has been recognized as a prominent method for evaluating PT properties in humans and dogs. The utilization of oscillation methods in canine studies remains limited despite their extensive documentation in human studies. Our study represents the first effort to quantitatively assess and compare the effects of muscle relaxant on the biomechanical and viscoelastic characteristics of the PT at varying stifle angles in living dogs. Five healthy female beagles were used in this study. Biomechanical (tone, stiffness, and decrement) and viscoelastic (relaxation time and creep) properties of the PT were measured using MyotonPRO (Myoton Ltd, Estonia) prior to and following administration of rocuronium (0.5 mg/kg/body weight) at normal, extended, and flexed positions. Rocuronium was selected for its safety, controllability, and widespread clinical use in veterinary anesthesia. Two-way analysis of variance showed that tone, stiffness, and decrement were significantly higher (P < 0.001) in the control group than in the muscle relaxation group. At the same time, relaxation time and creep were significantly lower (P < 0.001) in the control group than in the muscle relaxation group. The findings indicate that stifle angle position and muscle rexalant administration fundamentally alter the biomechanical loading conditions of the PT, leading to changes in its viscoelastic properties. Therefore, this novel quantitative data could benefit clinical settings that necessitate accurate and objective methods for risk identification and monitoring PT biomechanics in dogs.

The Use of Shear-Wave Ultrasound Elastography in the Diagnosis and Monitoring of Musculoskeletal Injuries

Ultrasound elastography is a valuable method employed to evaluate tissue stiffness, with shear-wave elastography (SWE) recently gaining significance in various settings. This literature review aims to explore the potential of SWE as a diagnostic and monitoring tool for musculoskeletal injuries. In total, 15 studies were found and included in the review. The outcomes of these studies demonstrate the effectiveness of SWE in detecting stiffness changes in individuals diagnosed with Achilles tendinopathy, Achilles tendon rupture, rotator cuff rupture, tendinosis of the long head of the biceps tendon, injury of the supraspinatus muscle, medial tibial stress syndrome, and patellar tendinopathy. Moreover, SWE proves its efficacy in distinguishing variations in tissue stiffness before the commencement and after the completion of rehabilitation in cases of Achilles tendon rupture and patellar tendinopathy. In summary, the findings from this review suggest that SWE holds promise as a viable tool for diagnosing and monitoring specific musculoskeletal injuries. However, while the field of ultrasound elastography for assessing musculoskeletal injuries has made considerable progress, further research is imperative to corroborate these findings in the future.

Effect of Physical Parameters and Training Load on Patellar Tendon Stiffness in Professional Athletes

BACKGROUND

Injuries of the patellar tendon commonly occur as a result of mechanical loading of the tendon during physical activity. Shear wave elastography (SWE) is an established technique for assessing tendon stiffness, and has good interindividual reliability. The aim of this study was to investigate the impacts of physical parameters and different sports on patellar tendon stiffness in professional athletes using SWE.

METHODS

Standardized patellar tendon SWE was performed in a relaxed supine position with a small roll under the knee (20° flexion) in 60 healthy professional athletes (30 female, 30 male). Multiple linear regression was performed for patellar tendon stiffness including gender, age, body mass index (BMI), and type of sport.

RESULTS

Patellar tendon stiffness showed no significant difference between female (3.320 m/s) and male (3.416 m/s) professional athletes. Mean age (female: 20.53 years; male: 19.80 years) and BMI (female: 23.24 kg/m2; male: 23.52 kg/m2) were comparable. Female professional athletes with oral contraceptive (OC) intake showed higher patellar tendon stiffness than athletes without OC intake (3.723 versus 3.017; p = 0.053), but not significantly.

CONCLUSION

In professional athletes, there are no significant differences in patellar tendon stiffness according to gender, age, BMI and type of sport (handball, volleyball, soccer, sprint, hammer throw). Oral contraceptives may not have an impact on patellar tendon stiffness in female athletes. Further studies are necessary.

Stiffness of Muscles and Tendons of the Lower Limb of Professional and Semiprofessional Athletes Using Shear Wave Elastography

OBJECTIVE

Shear wave elastography (SWE) allows assessment of muscle and tendon stiffness and can be used to diagnose soft tissue pathologies such as tendinopathies. In sports medicine, SWE may have the potential to uncover structural changes early on before they lead to functional impairment. To systematically analyze possible differences in tendon and muscle stiffness of the lower limb between professional (PG) and semiprofessional female athletes (SG) using SWE and to compile reference values for developing preventive medicine approaches for professional athletes.

METHODS

Standardized SWE of both lower limb tendons and muscles (Achilles tendon [AT], soleus muscle insertion [SM], patellar tendon [PT], quadriceps tendon [QT], vastus medialis muscle [VM]) in the longitudinal plane was performed with the tendons in relaxed position in 24 healthy professional female athletes (PG) in comparison with 24 healthy semiprofessional female athletes (SG).

RESULTS

Median tendon and muscle stiffness was significantly higher in professional athletes (AT:PG, 11.12 m/s vs SG, 7.33 m/s, P < .001; SM: 1.77 m/s vs 1.14 m/s, P < .001; VM: 1.63 m/s vs 0.87 m/s, P < .001; QT: 3.31 m/s vs 2.61 m/s, P < .05). There was no significant difference in patellar tendon stiffness between PG and SG (PT: 2.57 m/s vs 3.21, P = .25).

CONCLUSION

Professional female athletes have higher stiffness values than semiprofessional female athletes in lower limb muscles and tendons, except for the patellar tendon. Knowledge of such differences is necessary for diagnosing tendinopathy and injuries. Musculoskeletal SWE could offer great benefits in sports medicine as well as in rehabilitation and preventive medicine.

Concurrent validity and intrarater reliability of two ultrasound-based methods for assessing patellar tendon stiffness

Introduction

Assessment of tendon stiffness in vivo traditionally involves maximal muscle contractions, which can be challenging in pain populations. Alternative methods are suggested, although the clinimetric properties are sparse. This study investigated the concurrent validity and the intrarater reliability of two ultrasound-based methods for assessing patellar tendon stiffness.

Methods

Patellar tendon stiffness was assessed in 17 healthy adults with (a) the dynamometer and B-mode ultrasonography method (DBUS) and (b) the strain elastography method. Correlations between the two methods were analysed using Kendall’s Tau-b. The relative reliability of both methods was evaluated using intraclass correlation coefficient (ICC). The absolute reliability was presented by Bland–Altman plots, standard error of measurement (SEM) and minimum detectable change (MDC).

Results

No correlation was found between the two methods, irrespective of reference tissue in strain elastography (Kendall’s Tau-b Hoffa = –0.01 (p = 1.00), Kendall’s Tau-b subcutis = 0.04 (p = 0.87)). Tracking of the tendon elongation in the DBUS method had good to excellent relative reliability (ICC = 0.95 (95% confidence interval – CI: 0.85–0.98)) and high absolute reliability (SEM = 0.04 mm (1%), MDC = 0.11 mm (3%)). The strain elastography method had good to excellent relative reliability, regardless of reference tissue (ICC Hoffa = 0.95 (95% CI: 0.86–0.98), ICC subcutis = 0.94 (95% CI: 0.82–0.98)), but low absolute reliability (SEM Hoffa = 0.06 (20%), MDC Hoffa = 0.18 (60%), SEM subcutis = 0.12 (41%), MDC subcutis = 0.32 (110%)).

Conclusions

No concurrent validity existed for DBUS and strain elastography, suggesting that the two methods measure different tendon properties. The overall reliability for the DBUS method was high, but the absolute reliability was low for strain elastography stiffness ratios. Therefore, the strain elastography method may not be recommended for tracking differences in patellar tendon stiffness in healthy adults.

In vivo stiffness assessment of patellar and quadriceps tendons by strain ultrasound elastography

BACKGROUND:

The patellar and quadriceps tendons are responsible for the extension mechanism of the knee joint and frequently become inflamed during sports. Diagnosis and determination of when an athlete can return to sports following these injuries are usually performed by assessing morphological features and functional outcomes. Nevertheless, mechanical properties are not being assessed.

OBJECTIVE:

To describe the stiffness characteristics of these two tendons over the range of knee flexion and to test the feasibility of using strain ultrasound elastography (SE).

METHODS:

SE with an acoustic coupler as the reference was performed for nine healthy males. Relative stiffness measurements were obtained using the strain ratio (SR = target tissue strain/reference strain) by placing the knee in five different flexion angles. Lower SR indicates higher relative stiffness.

RESULTS:

This study showed reliable measurement with good intra- and inter-rater agreement for SR at 30°. SR of the quadriceps tendon decreases as knee flexion increases, indicating increased relative stiffness. In the patellar tendon, no significant difference was observed between 30° and 60°. Beyond 60°, relative stiffness increased constantly.

CONCLUSIONS:

SE is a reproducible and feasible tool to monitor relative stiffness of the patellar and quadriceps tendons in routine clinical settings.

Effect of Knee Angle and Quadriceps Muscle Force on Shear-Wave Elastography Measurements at the Patellar Tendon

Shear-wave elastography (SWE) is a non-invasive imaging technique that provides estimates of tissue stiffness via shear-wave speed measurements. No standardized protocol currently exists for SWE of the patellar tendon, which may be influenced by knee angle and quadriceps muscle force. In this study, the reliability of SWE in cadaveric patellar tendons was examined at three knee angles (0°, 30° and 60°) and three quadriceps muscle forces (0, 50 and 100 N). Shear-wave speed was significantly higher at a knee angle of 60° than at 0° or 30° (increases of 7% and 9%, respectively), and when the quadriceps muscle force was greater than or equal to 50 N (increase of 15%). SWE of the patellar tendon displayed excellent repeatability regardless of knee angle as long as no quadriceps force was generated (intra-class correlation coefficient ≥0.91). This research illustrates the importance of controlling knee angle and quadriceps force for consistency and comparison of SWE results.

Influence of Bias in the Assessment of Patellar Tendon Stiffness: A Systematic Review and Meta-analysis

The aim of the present study was to provide a systematic review and meta-analysis of the main biases in practical applications of the different types of elastography in assessment of the stiffness of healthy patellar tendons. A literature search on four databases (Scopus, Web of Science, Pubmed and SportDiscus) was conducted on March 25, 2020. After analysis of 1,052 resultant articles, studies were included if they met two inclusion criteria: (1) studies were observational or randomized controlled trials; (2) studies included outcomes of patellar tendon stiffness. Twenty-one studies met the inclusion criteria and were included in this meta-analysis. Four meta-analyses were performed with respect to assessment procedure and participant characteristics. This meta-analysis found a low effect of examined portion of patellar tendon (standardized mean difference [SMD] = 0.27, 95% confidence interval [CI]: 0.01-0.54, n = 379, Z = 2.01, p = 0.04) and a high effect of knee flexion angle during assessment (SMD = -2.12; 95% CI: -2.67 to -1.58, n = 97, Z = 7.68, p < 0.01) in stiffness outcomes. The risk of bias was generally low, but the heterogenicity of the results downgraded the level of evidence. There is evidence in the elastography assessment of patellar tendon suggesting that the knee position and patellar tendon portion evaluated influence stiffness outcomes for patellar tendon in healthy volunteers.

Physical Activity and Investigation With Magnetic Resonance Imaging Partly Explain Variability in the Prevalence of Patellar Tendon Abnormalities: A Systematic Review With Meta-analysis of Imaging Studies in Asymptomatic Individuals

OBJECTIVE

To estimate the pooled prevalence of, and factors associated with, the presence of patellar tendon abnormalities observed on imaging in people without symptoms.

DESIGN

Systematic review with stratified meta-analysis and meta-regression.

LITERATURE SEARCH

We searched Embase, Scopus, MEDLINE, CINAHL, SPORTDiscus, and Web of Science from 1980 to August 2020.

STUDY SELECTION CRITERIA

We included studies that reported the prevalence of asymptomatic patellar tendon abnormalities on imaging. We excluded studies of participants with current tendon pain, a history of tendon pain, or other systemic conditions.

DATA SYNTHESIS

Stratification and meta-regression of studies based on study-level descriptive statistics (mean age, body mass index, proportion of female participants, physical activity participation, imaging modality) were performed using a random-effects model to account for between-study heterogeneity. Risk of bias was assessed using the modified Newcastle-Ottawa scale.

RESULTS

Meta-analysis of 64 studies (7125 limbs from 4616 participants) found significant between-study heterogeneity (I²≥90%, P<.01), which precluded a summary prevalence estimate. Heterogeneity was partially explained by studies that included participants who were physically active and studies that assessed tendon abnormalities using magnetic resonance imaging compared to ultrasound (P<.05). Mean age, body mass index, proportion of female participants, and sample size did not explain the remaining heterogeneity.

CONCLUSION

There was substantial variability in the reported prevalence of asymptomatic patellar tendon abnormalities. A clear and valid method is needed to assess and report the presence of patellar tendon abnormalities to increase research capacity and establish the clinical value of imaging the patellar tendon. J Orthop Sports Phys Ther 2021;51(5):216-231. Epub 28 Mar 2021. doi:10.2519/jospt.2021.10054.

Can patient characteristics explain variance in ultrasound strain elastography measures of the quadratus femoris and patellar tendons?

OBJECTIVES

To explore the associations between participant characteristics and magnitudes of difference in paired elastography measures of knee tendon from different ultrasound systems, and to compare strain elastography pattern description.

MATERIALS AND METHODS

Quadriceps and patellar tendons of 20 healthy volunteers (40 tendons) were examined by an experienced operator employing two ultrasound systems (GE S8 and Esaote MyLab 70XVG). Pearson/Spearman correlations explored the influence of participant characteristics (BMI, body fat %, leg circumference, activity level) on the magnitude of differences between measures. Paired-sample t test or Wilcoxon signed rank test were performed to compare repeated measures of individual ultrasound systems.

RESULTS

The quadriceps tendon was characteristically stiffer than the patellar tendon. Participant characteristics were associated with within machine differences of the distal quadriceps tendon (BMI; r = 0.49, p = 0.028-0.03 and body fat %; r = 0.43, p = 0.05-0.056) ER measures.

CONCLUSIONS

Anthropometric and body composition parameters were associated with within machine differences for elasticity measures, where high BMI and body fat % contribute to paired measurement variance at the distal quadriceps tendon. Strain elastography protocols should be standardised, repeated ER measures performed using the same US system and patient characteristics considered for future clinical applications.

Effect of Stifle Flexion Angle on the Repeatability of Real-Time Elastosonography of the Patellar Ligament in Medium- to Large-Breed Dogs

OBJECTIVE

 The aims of this study were to describe the elastosonographic findings of the patellar ligament in healthy dogs >15 kg in different positions and determine the most appropriate stifle angle to perform elastosonography of the patellar ligament.

STUDY DESIGN

 Eighteen clinically healthy dogs, weighing >15 kg, were prospectively recruited. B-mode ultrasound and real-time elastosonography of both patellar ligaments were performed on days 0 and 14. Elastosonography examinations were performed with the stifle in four positions: standing position, lateral recumbency with the stifle positioned at 135 degrees extension and in full passive flexion and extension.

RESULTS

 The percentage hardness of the patellar ligament was significantly lower when the elastosonographic examination was performed with the dog standing, compared with the other positions (p < 0.005). The variability in the elastosonography readings for each stifle position was lowest when the dog was standing (89.32%).

CONCLUSION

 Elastosonography is a feasible technique for evaluating the elasticity of the normal canine patellar ligament in dogs >15 kg and would be a useful technique for investigating the mechanical changes within the patellar ligament following stifle surgery. Elastosonography of the patellar ligament should be performed with the dog standing to provide the most accurate elastosonograms with lowest variability between readings.

Intermachine Variation of Ultrasound Strain Elastographic Measures of the Quadriceps and Patellar Tendons in Healthy Participants: Implications for Clinical Practice

OBJECTIVES

To evaluate intermachine variation and compare intraoperator and interoperator agreement and repeatability characteristics of 2 ultrasound (US) systems for measurements of quadriceps and patellar tendons by strain elastography (SE).

METHODS

Forty tendons from 20 healthy participants were investigated by operators with different experience (operator 1, 12 years of US experience and >50 SE examinations; operator 2, no US experience and 1 day of SE training). Repeated measures were performed on GE Healthcare (Waukesha, WI) and Esaote (Genoa, Italy) US systems. The percentage of agreement, Cohen κ, intraclass correlation coefficient, and correlation tests assessed agreement, repeatability, and associations of SE measures. A paired t test and Wilcoxon signed rank test assessed differences in SE measures.

RESULTS

The study participants included 5 male and 15 female volunteers (mean [range] age, 29.3 [21-39] years). Better agreement and repeatability characteristics were observed for the patellar compared to the quadriceps tendon and the color score (CS) method over the elasticity ratio (ER). Intraoperator agreement was better for the experienced operator. Intraoperator repeatability was achieved in 55% of ER (intraclass correlation coefficient, 0.40-0.91; P < .05) and 77% to 85% (κ = -0.25-1) of CS measures. Interoperator repeatability was achieved in 35% (t/z, -2.93-7.94; P < .001-.048) of all ER measures. No significant differences in proximal (z, -0.13- -0.78) and distal patellar (z, -1.52-2.26; P > .5) patellar ER measures were observed. Seventy-four percent to 75% mean agreement (κ = 0-0.5) for CS measures comparable across both US systems was observed. Intermachine ER associations were poor (r = -0.39-0.13; P > .05), whereas greater than 70% agreement (κ = -0.87-0.53) for the CS was achieved.

CONCLUSIONS

The reproducibility of knee tendon SE measurements is influenced by the operator experience, US system, and tendon site.

The association between patellar tendon stiffness measured with shear-wave elastography and patellar tendinopathy-a case-control study

OBJECTIVES

(1) To determine the association between patellar tendon stiffness and the presence of patellar tendinopathy (PT). (2) To evaluate the reliability of shear-wave elastography (SWE).

METHODS

Participants were consecutively enrolled between January 2017 and June 2019. PT was diagnosed clinically and confirmed by either grayscale US or power Doppler US, or both. Controls had no history of anterior knee pain and no clinical signs of PT. Patellar tendon stiffness (kilopascal, kPa) was assessed using SWE. Logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). Reliability analyses included coefficients-of-variation (CV), coefficients-of-repeatability (CR), intraclass correlation coefficient (ICC) for intraobserver and interobserver reliability, and Bland-Altman analysis.

RESULTS

In total, 76 participants with PT (58 men, mean age 24.4 ± 3.8 years) and 35 asymptomatic controls (16 men, mean age 21.5 ± 3.8 years) were included. Univariate analyses (OR 1.094, 95% CI 1.061-1.128, p < .001) and adjusted multivariate analyses (OR 1.294, 95% CI 1.044-1.605, p = .018) showed that athletes with PT had significantly increased patellar tendon stiffness. ICC for intraobserver reliability was 0.95 (95% CI 0.92-0.97), CR (CV) 12 kPa (10%) and 0.79 (95% CI 0.65-0.88), CR (CV) 18 kPa (21%) for interobserver reliability. Mean differences from Bland-Altman analysis were 5.6 kPa (95% CI 3.1-8.1, p < .001) for intraobserver reliability and 4.6 kPa (95% CI 1.9-7.2, p < .001) for interobserver reliability.

CONCLUSIONS

PT is associated with significantly higher patellar tendon stiffness. SWE measurements demonstrate excellent intraobserver reliability and good interobserver reliability. Therefore, SWE is a promising tool to implement in longitudinal studies and future studies should evaluate its prognostic value and utility as a monitoring tool in athletes with PT.

KEY POINTS

• Patellar tendon stiffness measured with shear-wave elastography (SWE) is higher in athletes with patellar tendinopathy than in healthy controls, also after adjusting for potential confounders. • Excellent intraobserver reliability and good interobserver reliability were found for the quantitative assessment of patellar tendon stiffness using SWE.

Strain Ratio Measurements of Patellar and Achilles Tendons With Different Reference Regions in Healthy Volunteers

Strain ratio measurements of tendons vary because of the reference tissue selection. The main purpose of this study is to highlight, in detail, the numeric variability attributable to the use of various reference materials on strain ratio measurements of patellar and Achilles tendons. Measurements were performed at the proximal, middle and distal thirds of the patellar and Achilles tendons on the dominant site of healthy volunteers. A total of 3 references were used: the Hoffa's fat pad for the patellar tendon, the Kager's fat pad for the Achilles tendon, subcutaneous tissue and Aquaflex gel pads (Parker Laboratories, Fairfield, NJ, USA) for both tendons. Although the same methods were used by the same physician for each tendon site on repeated measurements, strain ratio values had numeric variability with various reference materials in each measurement. Therefore, comparison of numeric strain ratio results of various studies with various reference materials could confuse the clinical interpretations of these numeric data, and, using a reference material with standard stiffness like Aquaflex ultrasound gel pads, should be considered by verifying these results with further studies.

Reliability of ultrasound strain elastography in the assessment of the quadriceps and patellar tendon in healthy adults

Objective

To report the intra- and inter-operator reliability of ultrasound strain elastography measures in the assessment of quadriceps and patellar tendons.

Materials and methods

Forty tendons were investigated of 20 healthy volunteers. Five anatomical sites were examined and analysed by three operators of differing levels of experience. Ultrasound was performed over two measures, employing three sonoelastography measurement techniques using a GE S8 with linear probe (L6-15 MHz). The percentage of exact agreement, Cohen's kappa and ICC_2,1 were performed to assess intra- and inter-operator reliability.

Results

The patellar tendon is more reliably measured across all techniques compared to the quadriceps tendon, particularly the distal region. Colour scoring was the most reliable method of sonoelastography. Colour scoring intra- and inter-operator reliability was better for patella tendon sites across all operators (60-95% agreement range), and greatest for experienced operators. Elasticity index intra-operator reliability was greatest for the most experienced operator compared with the least (ICC range 0.35-0.72 and ICC 0.17-0.60). Elasticity ratio intra-operator reliability of the patella tendon was fair-excellent for the experienced operator (ICC range 0.43-0.91), excluding the mid patellar region (ICC 0.13). Poor-fair inter-operator reliability was observed for elasticity ratio (ICC range 0.0-0.54) and elasticity index (ICC range 0.0-0.57).

Conclusions

Strain elastography of the patellar tendon is more reliable than the quadriceps tendon. Intra- and inter-operator reliability was better when undertaken by more experienced operators. Colour scoring was more reliable than elasticity ratio and index methods. Poor-fair intra- and inter-operator reliability of the elasticity ratio and elasticity index was observed.

Shear wave elastography of the healing human patellar tendon following ACL reconstruction

PURPOSE

Anterior cruciate ligament (ACL) ruptures are common and are frequently reconstructed using a patellar tendon (PT) autograft. Unfortunately, the time course of PT healing after ACL reconstruction is not particularly well understood. Thus, the primary objective of this study was to use shear wave elastography (SWE) to evaluate the extent to which shear wave speed (SWS) is associated with time after ACL reconstruction.

METHODS

Longitudinal SWE images were acquired from lateral, central, and medial regions of the PT from two groups: 30 patients who had undergone ACL reconstruction with a PT autograft within the preceding 40 months, and 30 age-matched asymptomatic control subjects. SWE images were acquired at 20° and 90° of passive flexion from both knees. In each subject group, statistical analyses assessed changes in mean SWS with time post-surgery, as well as differences in mean SWS between PT regions and limbs.

RESULTS

In the ACL reconstruction patients, mean SWS increased with time post-surgery in the lateral region of the involved knee (p = 0.025) and decreased with time post-surgery in the central region of the contralateral knee (p = 0.022).

CONCLUSION

The findings suggest that there is an association between the mechanical properties of the PT and time post-surgery in both the involved and contralateral limbs after ACL reconstruction. These changes are likely due to maturation of the donor site tissue and changes in gait/loading patterns following ACL rupture and reconstruction.

LEVEL OF EVIDENCE

Level II - Prospective Cohort.

Ultrasound elastography of the patellar tendon in young, asymptomatic sedentary and moderately active individuals

BACKGROUND

The recent use of ultrasound elastography to study patellar tendon softness has demonstrated increased tendon softness in high-level athletes. We hypothesized that measurable alterations in patellar tendon softness may be present in young asymptomatic subjects engaging in moderate levels of physical activity.

METHODS

This was a cross-sectional study. Gray-scale ultrasound and ultrasound elastography of the right and left patellar tendons were performed in young asymptomatic sedentary subjects and moderately active subjects who engaged in at least 30 min of physical activity 4-5 times weekly. The distribution of soft, intermediate and stiff tissue within each tendon was analyzed. Tendon softness was correlated with subject age, gender and level of athletic activity.

RESULTS

Sixty patellar tendons in 30 subjects were evaluated (18 males, 12 females, mean age 22.5 years). Seventeen subjects were defined as "active" and 13 as "sedentary." All tendons had a normal gray-scale sonographic appearance. Tendon softness was significantly higher in active subjects (P = 0.01) and decreased with age (P = 0.04). In sedentary individuals there was no significant correlation between age and tendon softness (P = 0.404). Similarly, gender showed no correlation with tendon softness (P > 0.05).

CONCLUSIONS

Patellar tendon softness is higher in young subjects and in those engaging in moderate physical activity. This may reflect an adaptation to increased tendon load. Tendon softness in active subjects decreases with age, while it remains at a constant value in sedentary individuals.

LEVEL OF EVIDENCE

Level 3.

Effect of High-Induction Magnetic Stimulation on Elasticity of the Patellar Tendon

Nowadays, a high-induction magnetic stimulation is starting to be increasingly applied as a biophysical stimulation in the conservative treatment of the degenerative locomotor system diseases. These are mainly in correlation with the changes in soft tissue elasticity, which should be positively influenced by the flow-induced electrical currents of high current density during high-induction magnetic stimulation. This assumption was verified within the interventional and prospective study using the ultrasound elastography. The group consisted of 6 volunteers, whose elasticity of the patellar tendons was measured using the 2D shear-wave ultrasound elastography. The volunteers were then exposed to a 20-minute high-induction magnetic stimulation session with a frequency of 20 Hz, in 2 s package intervals, with a 5 s pause, and a induced electric current density of 100 Am⁻² in the tendons area. A tendon tension was measured five times for all volunteers, where mean tension at the marked area of the tendon, as well as the highest point tension indicated by the Q-Box, was monitored. The measurement results show that high-induction magnetic stimulation has an influence on the patellar tendon tension change, which occurred in the case of all involved volunteers when the patellar tension was decreased.

Ultrasound elastography: compression elastography and shear-wave elastography in the assessment of tendon injury

Ultrasound elastography (USE) is a recent technology that has experienced major developments in the past two decades. The assessment of the main mechanical properties of tissues can be made with this technology by characterisation of their response to stress. This article reviews the two major techniques used in musculoskeletal elastography, compression elastography (CE) and shear-wave elastography (SWE), and evaluates the studies published on major electronic databases that use both techniques in the context of tendon pathology. CE accounts for more studies than SWE. The mechanical properties of tendons, particularly their stiffness, may be altered in the presence of tendon injury. CE and SWE have already been used for the assessment of Achilles tendons, patellar tendon, quadriceps tendon, epicondylar tendons and rotator cuff tendons and muscles. Achilles tendinopathy is the most studied tendon injury with USE, including the postoperative period after surgical repair of Achilles rupture tendon. In relation to conventional ultrasound (US), USE potentially increases the sensitivity and diagnostic accuracy in tendinopathy, and can detect pathological changes before they are visible in conventional US imaging. Several technical limitations are recognised, and standardisation is necessary to ensure repeatability and comparability of the results when using these techniques. Still, USE is a promising technique under development and may be used not only to promote an early diagnosis, but also to identify the risk of injury and to support the evaluation of rehabilitation interventions. KEY POINTS: • USE is used for the assessment of the mechanical properties of tissues, including the tendons. • USE increases diagnostic performance when coupled to conventional US imaging modalities. • USE will be useful in early diagnosis, tracking outcomes and monitoring treatments of tendon injury. • Technical issues and lack of standardisation limits USE use in the assessment of tendon injury.

Ultrasound elastography and ultrasound tissue characterisation for tendon evaluation

Ultrasound elastography (UE) and ultrasound tissue characterisation (UTC) are two newer modes of ultrasound (US) which have begun to attract scientific interests as ways to improve tendon characterisation. These modes of US show early promise in improved diagnostic accuracy, prediction of at-risk tendons and prognostication capability beyond conventional grey-scale US. Here, we provide a review of the literature on UE and UTC for Achilles, patellar and rotator cuff tendons.

The translational potential of this article: The present literature indicates that UE and UTC could potentially increase the clinician's ability to accurately diagnose the extent of tendon pathology, including preclinical injury.

Ultrasound elastography in tendon pathology: state of the art

Elastography assesses the biomechanical and structural properties of tissues by measuring their stiffness. Despite promising results, elastography has not yet earned its place in the daily practice of musculoskeletal radiologists. The purpose of this article is to present and examine the data available to date on ultrasound elastography of the tendons through a review of the literature to provide musculoskeletal radiologists with an overview that may help them better understand and use elastography routinely. The most common techniques in ultrasound elastography are described. Then, the aspects of the physiologic and pathologic tendon are presented and discussed. One must make this technique one's own to better apprehend its contribution to the musculoskeletal imaging field, while bearing in mind that further research will be required before admitting elastography as a reliable and validated tool able to optimize our daily clinical practice.