Both ultrasonography and magnetic resonance imaging (MRI) are valuable for assessing tendon injuries throughout the body. This lecture focuses on the role of MRI in clinical practice.

Normal tendons are composed of collagen bundles arranged in a well-ordered structural pattern, appearing hypointense on all conventional MRI sequences. However, when the tendon is oriented at 55 degrees to the static magnetic field, i.e. the “magic angle”, an area of spurious hyperintensity is produced, depending on the type of sequence and echo time. The magic angle effects are unlikely to be significant above a certain critical echo time.

MRI at stronger magnetic fields is more sensitive than at lower fields for detection of tendon injury, due to higher signal-to-noise ratios and improved imaging resolution. Use of local surface or dedicated coils help achieve a higher resolution. T2-weighted imaging helps identify fluid signal changes in tendon tears and for showing changes in surrounding tissues. Proton density and T1-weighted images should be done with sufficiently long echo time to avoid the magic angle effect.

Tendon pathology related to injury commonly results in tendinosis or tendinopathy, reflecting its degenerative nature. There are various predisposing risk factors associated with tendinosis, including age and metabolic conditions. Abnormal and excessive loading of the tendon due to instability or impingement predisposes to injury. Tendon degeneration results in collagen structure disorientation, accumulation of mucoid material, increased water and proteoglycan content, with tendon thickening. Collagen fibril rupture leads to intrasubstance tears which may extend to the tendon surface (partial tears) and then progress to full thickness tears.

On MRI, tendon abnormality usually manifests initially as hyperintense signal on gradient echo and then T1-weighted images; with associated tendon thickening. Tendon tears show fluid signal on T2-weighted or STIR images. Structural changes include tendon thinning, irregularity, splitting and dislocation. Associated bony changes include marrow oedema and spurs. Common regions where tendon injuries occur include the foot and ankle, shoulder, hip, knee, elbow and wrist.