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Tendon and Ligament Ultrasound

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Authors

Ben Asriel, MD MFA
Ben Oshlag, MD

Summary

Anatomy

  • Tendons connect muscle to bone.
    • They function to transmit tensile force generated by muscle onto bony fulcrums, resulting in movement. They must be both strong and elastic to accomplish this.
    • Type I collagen fibers provide tensile strength and make up the bulk of tendon tissue. They emerge from connective tissue layers of muscle (endo-, peri-, and epimysium), organize into a cable-within-cable structure, and insert into bone at osteo-tendinous
    • junctions.[1]Bordoni B, Varacallo M. Anatomy, Tendons. Statpearls. Published online 2022. Accessed March 20, 2022. https://pubmed.ncbi.nlm.nih.gov/30020609/
    • Collagen bundles are wrapped in successive layers of connective tissue sheaths, allowing sliding motion. These bundles are crimped to provide elasticity to the tendon. Separate elastic fibers also provide elasticity. Tendons also include nerve, blood vessel, and
    • lymphatic components.[2]Jacobson JA. Fundamentals of Musculoskeletal Ultrasound. Elsevier; 2018
    • Structures are organized along the long axis of the tendon. When cut lengthwise into two long semi cylinders, the interior resembles fibrous layers sandwiched on top of each other. When cut in short axis, the tendon appears as a circle composed of other smaller circles.
    • On ultrasound, this structure is reflected in the fibrillar appearance seen in long axis
Normal tendon in long axis.
Normal tendon in short axis.
  • Ligaments connect bone to bone
    • Ligament anatomy is similar and appears similarly on ultrasound.
Normal ligament in long axis.
Normal ligament in short axis.

Ultrasound Evaluation

  • Transducer
    • A high-frequency linear transducer is ideal for imaging most tendons and ligaments, as the higher resolution for superficial structures is key in evaluating pathology.
    • Deeper structures such as hamstring tendons may require a curvilinear transducer, depending on the patient’s body habitus.
  • Anisotropy
    • Tendons and ligaments are anisotropic; their echogenicity changes when the transducer signal strikes the target from different angles.
    • When the transducer is perpendicular to a reflective plane, sound echoes back to the transducer strongly and produces a brighter image than if the waves are reflected at an angle.
    • As a result, a small change in the angle of your transducer or the underlying structure can create a large change in the echogenicity of the tissue ; it is hyperechoic when viewed perpendicular to the long axis of the tissue, but can appear
    • hypoechoic when viewed at a slight angle, creating the false appearance of pathology in a normal structure.
    • Tendon is more anisotropic than ligament; ligament is more anisotropic than nerve. This can sometimes help differentiate these tissues. 
Example of anisotropy
Example of Anisotropy (yellow arrow) seen at different probe positions (blue box) relative to structure of interest.[3]Image courtesy of sonoskills.com, “Anisotropy as most important pitfall in ultrasound imaging”
Video demonstration of anisotropy. The transducer is over the Achilles Tendon and slowly moving from perpendicular to an angle relative to the tendon.
  • Sonographic Appearance of Tendons
    • Tendon is hyperechoic and fibrillar in appearance.
    • Non-compressible, non-vascular, does not branch
    • In long axis (longitudinal view):
      • Fibrillar
      • Parallel borders
      • Rope-like
    • In short axis (transverse view):
      • Appears as “broom” or “brush” end
    • Movement can help identify tendon in a dynamic exam, helping locate the tendon of interest and trace it to its muscular attachment to confirm anatomy.
Dynamic tendon evaluation helps confirm anatomy and identify pathology.
Normal tendon in long axis.
Normal tendon in short axis.
  • Sonographic Appearance of Ligaments
    • Fibrillar, but less so than tendon
    • Hyper- OR Hypoechoic
    • Non-vascular
    • Ligament is subtly denser than tendon on ultrasound, but it is easier to distinguish the two anatomically
      • The examiner can trace a ligament between two bones and trace a tendon to its muscular attachment.
    • Both tendon and ligament exhibit anisotropy, though tendon is more anisotropic than ligament.
Normal ligament in long axis.
Normal ligament in short axis.

Tendon Pathology

  • Trauma
    • Lacerations, penetrating injuries, and crush injuries can all damage or tear tendons.
    • With significant trauma, air may be introduced, which will be hyperechoic, with heterogeneous deep shadowing. Fracture lines and/or fragments of bone may also be visible.
Hand US Dorsal wrist tendon laceration
Laceration of dorsal hand extensor tendon by floor tile. The arrows indicate the two ends of the tendon, the dotted white line represents the ~26 mm gap. [4]Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 59880
Laceration of flexor tendon of the hand following a knife injury. The two ends of the tendon are marked with yellow arrows and a large gap is noted.[5]Image courtesy of ultrasoundcases.info, “Flexor tendon trauma”
  • Tears
    • Tears appear as a hypoechoic break in the continuity of the tendon which is filled with fluid (blood).
      • This is best assessed when the tendon is under tension
      • Tendon is often thin at the location of the tear.
    • Partial tears have a partial fiber disruption.
    • This can appear as a subtle hypoechoic region with indistinct borders that fade into the healthy hyperechoic tendon, or as a distinct hypoechoic region that only extends partially through the tendon.
    • Full tears have a total fiber disruption, with an abrupt full-thickness hypoechoic lesion within the hyperechoic tendon.
    • Dynamic imaging can help distinguish partial tears from full tears; partial tears will have movement throughout the tendon while full tears will have an immobile stump on one side of the tear.
    • Note: physical exam should also be used to help confirm partial vs complete tear
Leg US Achilles Tendon Rupture Long Axis
Ultrasound of achilles tendon tear (arrow pointing to hypoechoic area) seen in long axis. Note the foot is dorsiflexed while the image was obtained, exaggerating the gap sonographically.[6]Image courtesy of jetem.org, “Ultrasonographic Findings of Acute Achilles Tendon Rupture”
Knee US Quadriceps tendon rupture with tendon retraction
Quadriceps tendon rupture seen in long axis. Note the quad tendon is retracted about 5 cm from the patella, which is seen in the top right corner of the screen. A small amount of hypoechoic fluid is seen.[7]Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 12805
Complete Achilles Tendon Rupture in long axis.
Complete Achilles Tendon Rupture in short axis.
  • Tenosynovitis / Acute Tendonitis
    • Thickened tendon
    • Hypoechoic tendon
    • Tendon is hyperemic on doppler
    • Peritendinous fluid is often present
Arm US Biceps Tendonitis and Tenosynovitis
Short axis ultrasound shows biceps tenosynovitis after strenuous swimming. Note the hypoechoic fluid (yellow arrow) surrounding the abnormally echogenic biceps tendon in the bicipital groove and biceps tendinopathy (blue arrow).
Knee US Patellar tendonitis with hyperemia on doppler
Ultrasound of a patellar tendon showing tendonitis in long axis. The color Doppler image shows hypoechogenicity, with a heterogeneous structure (arrows) (a) and diffuse hyperemia of the deep insertional part of the patellar tendon (arrows) (b)[8]Robotti G, Draghi F, Bortolotto C, Canepa MG. Ultrasound of sports injuries of the musculoskeletal system: gender differences. J Ultrasound. 2020;23(3):279-285. doi:10.1007/s40477-020-00438-x
Patellar tendonitis seen in long axis. Note the heterogenous appearance of the tendon with inte-rtendinous fluid proximally greater than distally. The patient was very tendon on sonopalpation.
Patellar tendonitis seen in short axis. Note the heterogenous appearance of the tendon with inte-rtendinous fluid proximally greater than distally. The patient was very tendon on sonopalpation.
  • Chronic Tendinosis/ Tendinopathy
    • Defined by a process of eosinophilic, fibrillar, and mucoid degeneration and the absence of acute inflammatory cells
    • Hypoechoic and heterogeneous due to fluid infiltration
    • May be have visible Doppler flow due to neovascularization
    • May have calcifications
    • Distinguished from tears by:
      • No tendon disruption
      • Thickened tendon
    • May also progress to include tears
Leg US bilateral achilles tendinosis
Right and left achilles tendon in short axis. Both tendons are enlarged, right more than left. Both exhibit disruption of the normal echo pattern. The right tendon is more heterogeneous and exhibits extensive calcification (hyperechoic lesions with posterior acoustic shadowing.[9]Image courtesy of 123sonography.com, “Bilateral Achilles Tendinosis”
Knee US patellar tendinopathy with neovascularization
Patellar tendinopathy seen in long and short axis. There is a high degree of neovascularization (A, B) which improves following treatment (C, D).[10]Abat F, Gelber PE, Polidori F, Monllau JC, Sanchez-Ibañez JM. Clinical results after ultrasound-guided intratissue percutaneous electrolysis (EPI®) and eccentric exercise in the treatment of … Continue reading
  • Neovascularization
    • Defined as increased doppler flow within tendon from the pathologic development of new blood vessels in an attempt to heal damaged tissue
    • Associated with tendinopathy
    • Not found in healthy tendon
    • Pearl: tendon should be relaxed and transducer pressure should be light when assessing for neovascularization; pressure from the transducer or from tendon tension can compress vascular structures and mask neovascular changes
Leg US neovascularization of achilles tendon
Long axis view of Achilles tendinopathy. The sonogram reveals the hypoechoic, darken area of the Achilles tendon, tendon thickening and neovascularization.[11]Sànchez-Ibàñez, J. M., et al. “Ultrasound-Guided EPI® technique and eccentric exercise, new treatment for Achilles and Patellar tendinopathy focused on the region-specific of the … Continue reading
Video of neovascularization in a patient with patellar tendonitis.
  • Calcific Tendinopathy
    • Type 1 calcifications (calcium hydroxyapatite crystal deposition)
      • Formative and resting phases of deposition
      • Well-defined hyperechoic structures with clear acoustic shadowing
    • Type 2 calcifications
      • Beginning of resorptive stage
      • Larger that resting stage and more poorly defined
      • Hyperechoic focus with faint/minimal acoustic shadow
    • Type 3 calcifications
      • End of resorptive stage
      • Isoechoic to hyperechoic
      • Replace normal fibrillar pattern
      • No acoustic shadow
    • Related pathologies:
      • Calcific enthesopathy —calcium deposits at the attachment of a tendon (enthesis)—are linear, thin, and parallel to the long axis of the tendon
      • Avulsion fractures will show bone fragments and tendon retraction
Shoulder US Type 1 Calcific Tendinopathy
Calcific deposit in the supraspinatus and infraspinatus muscle with significant posterior acoustic shadowing (type 1).[12]Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 7501
Calcific deposit infraspinatus muscle with minimal posterior acoustic shadowing (type 2).[13]Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID: 39547
Calcific tendinopathy of Teres Minor

Ligament Pathology

  • General
    • Similar to tendon partial tears
  • Partial tears appear
    • Thickened
    • Heterogenous
    • Hypoechoic
    • May be hyperemic
  • Full thickness tears
    • Discontinuous fibers with well defined hypoechoic fluid-filled tear between two ligament stumps
    • Stumps may widen when joint is stressed if joint is not stable
  • Stressing the joint under ultrasound exam may show joint widening/instability
Ankle US ATFL Sprain and Thickening
Ankle ultrasound of a patient with recurrent ankle pain. Ultrasound reveals thickening of the anterior talofibular ligament consistent with chronic or recurrent sprains.[14]Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 38360
Ankle US ATFL Ligament Tear
Ultrasound of an ankle following an inversion injury reveals a complete tear of the anterior talofibular ligament (arrow) and significant hypoechoic fluid extending from the anterolateral joint recess into subcutaneous plane.[15]Case courtesy of Dr Maulik S Patel, Radiopaedia.org, rID: 46877
Dynamic ultrasound of an MCL tear which reveals widening of joint space and ligamentous instability with valgus stress.
Dynamic ultrasound comparing an intact elbow UCL compared to a torn elbow UCL with subsequent joint instability.

Pearls & Pitfalls

References

References[+]