Low-field magnetic resonance imaging (0.2 T) of tendons with sonographic and histologic correlation. Cadaveric study

Focal experimental injury leads to widespread gene expression and histologic changes in equine flexor tendons

It is not known how extensively a localised flexor tendon injury affects the entire tendon. This study examined the extent of and relationship between histopathologic and gene expression changes in equine superficial digital flexor tendon after a surgical injury. One forelimb tendon was hemi-transected in six horses, and in three other horses, one tendon underwent a sham operation. After euthanasia at six weeks, transected and control (sham and non-operated contralateral) tendons were regionally sampled (medial and lateral halves each divided into six 3 cm regions) for histologic (scoring and immunohistochemistry) and gene expression (real time PCR) analysis of extracellular matrix changes. The histopathology score was significantly higher in transected tendons compared to control tendons in all regions except for the most distal (P ≤ 0.03) with no differences between overstressed (medial) and stress-deprived (lateral) tendon halves. Proteoglycan scores were increased by transection in all but the most proximal region (P < 0.02), with increased immunostaining for aggrecan, biglycan and versican. After correcting for location within the tendon, gene expression for aggrecan, versican, biglycan, lumican, collagen types I, II and III, MMP14 and TIMP1 was increased in transected tendons compared with control tendons (P < 0.02) and decreased for ADAMTS4, MMP3 and TIMP3 (P < 0.001). Aggrecan, biglycan, fibromodulin, and collagen types I and III expression positively correlated with all histopathology scores (P < 0.001), whereas lumican, ADAMTS4 and MMP14 expression positively correlated only with collagen fiber malalignment (P < 0.001). In summary, histologic and associated gene expression changes were significant and widespread six weeks after injury to the equine SDFT, suggesting rapid and active development of tendinopathy throughout the entire length of the tendon. These extensive changes distant to the focal injury may contribute to poor functional outcomes and re-injury in clinical cases. Our data suggest that successful treatments of focal injuries will need to address pathology in the entire tendon, and that better methods to monitor the development and resolution of tendinopathy are required.

Do low field magnetic resonance imaging abnormalities correlate with macroscopical and histological changes within the equine deep digital flexor tendon?

Correlating magnetic resonance (MR) imaging and histopathological findings is essential to validate low field MR imaging in lame horses. This study aimed to compare signal changes in the deep digital flexor tendon (DDFT) of the distal limb on low field MR imaging with macroscopical and histological findings. Cadaver limbs from lame horses with DDFT lesions were selected. The DDFT MR imaging findings and histopathological results were graded, and macroscopical abnormalities were recorded. There was a strong correlation between MR imaging and histopathology grades (rs = 0.76, p < 0.001) in the foot. There was moderate agreement (Kappa statistic 0.52) between the MR and histopathology grades; agreement was superior further proximal in the foot. The presence and severity of pathology in the DDFT are well represented by the presence and severity of MR imaging signal changes. The study supports the use of low field MR imaging for diagnosis of equine distal limb DDFT lesions.

Alterations of tendons in patients with diabetes mellitus: a systematic review

AIMS

To perform a systematic review of observational studies which analyse tendon alterations in patients with diabetes mellitus compared with healthy individuals.

METHODS

Data collection was performed, with no language restriction, using the databases of PubMed/Medline, BIREME, CINAHL, LILACS and Cochrane, as well as the references found in these studies. Three reviewers performed independent extractions of articles. Subsequently, these reviewers analysed the articles, focusing on their methodological quality, using the appropriate scale to evaluate observational studies from the Agency for Healthcare Research and Quality.

RESULTS

Six articles were included in the analysis. Of these, four had used ultrasonographic diagnostics, one computed tomography and one magnetic resonance imaging. The patient pool comprised 396 individuals. All the articles evaluated tendon thickness and presented heterogeneous results. Two articles stated thickening or increased volume of the tendons in diabetic people, one article did not report any alteration, the fourth failed to determine any alterations and the fifth showed thinning of the tendons. The arrangement of collagen fibrils and the presence of calcification were analysed in only one article (n = 80), showing that 88.10% (n = 68) of individuals with diabetes presented disorientation of collagen fibril arrangement, while only 10% (n = 1) of healthy individuals presented this condition. Regarding tendon calcification, the article showed diabetic individuals with higher values than healthy individuals.

CONCLUSIONS

All the articles indicated some relation between diabetes mellitus and tendon alterations in human beings, but due to methodological drawbacks, this association could not be sustained.

Ultrasound assessment of tendons in asymptomatic volunteers: a study of reproducibility

The purpose was to evaluate the inter-visit, inter-observer and intra-observer variation of quantitative and qualitative tendon examinations in vivo for a cohort of asymptomatic volunteers. Eleven healthy male subjects were recruited. The following tendons were assessed by ultrasonography: Achilles tendon, patellar tendon, triceps tendon, extensor pollicis longus, flexor carpi radialis and supraspinatus. For each tendon a quantitative measurement of tendon size was made at a predefined anatomical location. Two experienced sonologists, blind to one another's findings, evaluated each of the tendons independently. Each tendon was evaluated on two occasions 1 week apart. No difference was found to be attributed to variation in tendon size between visits. Inter-observer variation was a source of error with intra-subject, inter-visit measurements proving more reproducible. There was some significant variation between observers. This variation was more marked with some tendon measures than others. Inter-observer variation for triceps, flexor carpi radialis and supraspinatus was most marked. Minimum detectable change in tendons varied from 13 to 57% depending on the plane of scanning and the tendon being examined. Good reproducibility of quantitative tendon measurements can be achieved within a study using two observers by following a defined scanning protocol. However, it is recommended that the same observer perform serial assessments. The data allow minimal detectable changes in tendon size to be calculated.

Computerized ultrasonographic tissue characterization of equine superficial digital flexor tendons by means of stability quantification of echo patterns in contiguous transverse ultrasonographic images

OBJECTIVE

To describe a method of computerized ultrasonographic tissue characterization that includes structures below the size limits of resolution in equine superficial digital flexor tendons.

SAMPLE POPULATION

2 damaged and 2 structurally normal superficial digital flexor tendons.

PROCEDURE

Transverse ultrasonographic images were collected along the tendon long axis. Stability of echo pattern was quantified by means of variation in gray levels of each pixel in contiguous images and expressed as correlation, entropy, and waviness ratios.

RESULTS

Normal young and normal old tissues were characterized by high correlation and low entropy and waviness ratios. In necrotic tissue, collapsed intratendinous septa resulted in high correlation, moderate entropy, and high waviness ratios. In early granulation tissue, complete lack of bundle formation resulted in values of zero for correlation and waviness ratios; loose connective tissue matrix resulted in a high entropy ratio. In late granulation tissue, formation of new bundles resulted in a high correlation ratio; swollen intratendinous septa and incomplete organization of connective tissue matrix were reflected in high entropy and waviness ratios. In early fibrotic tissue, rearrangement of tendon bundles resulted in a correlation ratio within reference range and a slight increase in the waviness ratio; an increase in cellularity and lack of fibrillar arrangement led to an increase in the entropy ratio. In late fibrotic and scar tissues, inferior quality of repair with almost complete lack of organization was reflected in low to moderate correlation, low waviness, and high entropy ratios.

CONCLUSIONS AND CLINICAL RELEVANCE

Stability of echo patterns accurately reflects homogeneity of tendons in horses.

Current concepts in imaging of tendinopathy

With the rising popularity of recreational sports, radiologists are being asked to image tendons with increasing frequency. Recognition of the critical link tendons provide between muscle and bone has also led to a better understanding of the processes leading to tendon damage. While plain radiography and CT have only a limited role to play in the diagnosis of tendon abnormality, the improvements in ultrasound and MRI technology mean that tendons can now be demonstrated in exquisite detail and previously undetectable abnormalities are readily demonstrated. This article reviews the structure and pathological processes affecting tendons and discusses the role of imaging in their assessment with an emphasis on ultrasound and MRI.