Synopsis

In this lecture, the pathophysiology of tendon overuse injuries will be discussed from a clinical and radiological perspective. The role of imaging in tendinopathy and limitations of conventional MRI will be cornerstones in this presentation. Implementations of quantitative ultra-short echo time (UTE) MRI will be presented in the context of a trial investigating patellar tendinopathy in jumping athletes.

Target audience

MR physicists and scientists with an interest in imaging of tendons and tendinopathy from a clinical perspective.

Learning objectives

- To learn about tendon anatomy and to understand the important role tendons play in the function of transmitting muscular forces;
- To learn about clinical sequelae and implications of tendinopathy;
- To understand the role of imaging of tendon injuries in clinical practice; ·
- To learn about the limitations of conventional MRI for imaging tendons and the role of ultra-short echo time MRI.

Outline of lecture

Tendinopathies are common injuries of tendons, characterized by load-related pain. These injuries not only affect athletes, but also elderly. Tendons can be found around most joints of the human body, including the knee, shoulder, the hips, hands and feet. Tendons are key to transmitting forces generated by muscles to bone and play an important role in storing energy caused by muscle contraction as so-called ‘elastic recoil’. In order to resist these high tensile forces, tendons consist mainly of regularly arranged collagen fibers. The largest tendon of the human body is the Achilles tendon, which connects the calf muscle to the calcaneus (heel bone). Within the tendon fibers, highly negatively charged large macromolecules called proteoglycans are present that attract water, reduce friction between adjacent collagen fibers and provide resistance to compression. Water is also an intrinsic component of collagen and accounts for about 60% of the substance by weight. Water molecules bind tightly to collagen and are crucial in providing a tendon its biomechanical properties. In tendinopathy, there is an increase in the volume of the water-rich ground substance that is present between the collagen fibers. This occurs as a healing response in reaction to cumulative micro-trauma to the collagen fibers that occur in tendons sustaining high loads. Because this condition is regarded as a degenerative process and inflammatory cells are largely absent, the term ‘tendinitis’ has been changed to ‘tendinopathy’.

The diagnosis of tendinopathy is made primarily clinically, but clinical tests such as palpation tenderness have poor specificity. Imaging of tendons is often performed to confirm the clinical diagnosis and/or to rule out other diagnosis, such as bursitis or cartilage damage (chondropathy). The initial step in imaging often consists of ultrasound, which has the highest spatial resolution for imaging tendons, and therefore has a high sensitivity to detect changes associated with tendinopathy. It is also more easily available than MRI in most clinical settings.

A typical clinical MR protocol is composed of proton-density or intermediate weighted and T2 fat-saturated or water excitation sequences. Typical findings of tendinopathy on MRI are increased water signal and tendon thickening. However, for imaging of tendons, conventional MRI sequences are intrinsically limited because of the fast free induction decay of collagen. This is due to the fact that water in tendons is primarily in a bound state, thereby restricting the motion of water molecules by strong spin-spin interactions and thus resulting in (ultra)short T2* relaxation times. Only loosely bound water or free water pools become visible on conventional imaging sequences because of the longer T2*.

Ultrashort echo time (UTE) MRI enables to capture signal from tissues with a very short relaxation time, such as collagen in tendons. These acquisitions are able to acquire echo times as short as 0.032 milliseconds. The signal that is captured from tendons using UTE MRI also allows for quantification of these tissues. T2* quantification has been implemented in Achilles tendinopathy, rotator cuff tendinopathy and patellar tendinopathy. Research is ongoing to assess if T2* relaxation times can be used as prognostic biomarkers or and imaging biomarker to monitor treatment response.

Acknowledgements

No acknowledgement found.