Dr. Robert L. Bard, Leader in Clinical Imaging and Radiology. From online telemedicine to imaging diagnosis through ultrasound for famous NFL football teams, doctor Bard is the expert the experts turn to.

l Why Ultrasound l When Is It Effective l Scanning Principles l Comparison With CT & MRI l Sonography of Tendons l Sonograpy of Muscle l Evaluation of Foreign Bodies l References l

Image2: Ultrasound of the tendon

Ultrasound imaging, often referred to as sonography, uses waves and their reflected echoes to characterize and/or study internal structures and tissues. Because of its safety and accuracy, it has proven its usefulness in diagnosing a multitude of injuries and areas including bone, soft tissues, muscle, tendons, and ligaments. Most of us will think of fetal ultrasound because of its commonality, but this method of imaging is particularly useful in the area of sports medicine as well. Ultrasound allows doctors to see motion. Not only can a diagnosis be made, but those movements causing or leading up to a particular injury can also be diagnosed. Ultrasound imaging can also distinguish between degrees of injury, giving doctors more finite diagnosis which ultimately leads to safer, less invasive treatments, healthier patients, and better athletes.

Ultrasound Uses in Sports Medicine and Trauma

Tendons: Ultrasound is considered more effective in tendon disease diagnosis than MRI, especially in the ankle, wrist and rotator cuff shoulder areas. Tears, inflammation and dislocations are visible.

Ligaments: Tears of ligaments are shown that heal more slowly than bony fractures and may produce longstanding pain.

Joints: Arthritic processes and potentially treatable adjacent tendon damage may be serially followed with this modality. Fluid collections increasing pain may be diagnosed.

Muscles: Muscle strains may be separated from more serious muscle ruptures. Hematomas and contusions may be followed.

Bones: Occult fractures of the spine, shoulder and ankle are routinely detected that are missed by conventional x-rays.

Soft Tissues: Foreign bodies and abscesses found and removed. Ultrasound guidance may be used to dreain fluid collections. Post traumatic neuromas in the forefoot may be diagnosed. Heel pain syndromes including plantar fasciitis quickly imaged.

Nerves: Nerves, centrally and peripherally, are imaged. This allows us to document neck and lower back pain, and possibly, to focus on the specific region producing diffuse symptoms. This is important since MRI of the spine has many false positive results. Carpal tunnel syndrome in the wrist is best imaged with this modality. This is significant since the EMG exam for this condition has many false negative results. Hematomas or masses adjacent to nerves causing neurological findings may be disclosed.

Personal Injury: Because ultrasound is able to diagnose injuries with such accuracy, it is often called upon to document accidents where legal action has been taken.

"Ultrasound effective in diagnosing sports injuries."
-American College of Radiology Bulletin

Bard, R: Ultrasound of Hand Injuries -Mayo Clinic, 1994
Bard, R: Muskuloskeletal Sonography -St. Vincent's Hospital, 1997
Bard, R: Ultrasonography of Arthritis -Mt. Sinai Hospital, 1997
Bard, R: Ultrasonography of the Rear Foot in "Disorders of the Ankle and Rear Foot" Ranawat, C etal -Churchill Livingstone New York, 1997

It must be recognized that routine x-rays see only bones and miss the soft tissues which consist of tendons, ligaments and muscles. State of the art musculoskeletal ultrasound imaging requires frequencies at least 5 MHz and specially designed and focused linear array transducers. The small anatomic ankle and foot structures and superficial locations are best examined with probes over 10 MHz in frequency. The higher the scanning frequency, the poorer the sound penetration. This results in improved resolution, but the loss of distal information may occur when scanning deeper structures such as the bursae subtendinea and the tricipitis surae muscle when examining the Achilles tendon in the standard ultrasound scanning planes. Linear probes, as contrasted with sector scanners, better outline the course of tendons which are most often aligned in straight paths. Also, sector scanners produce bright echoes at the center of the image and fewer echoes at the periphery. A standoff pad may sometimes be used to insonate the subcutaneous structures. Comparison with the opposite side is possible and usually helpful in diagnosis. Cysts or fluid filled areas are without internal echoes and are called echo free. Solid regions have internal echoes and are classified as echo poor or hypoechoic if there are few internal echoes. The term echogenic or hyperechoic is used if there are many internal echoes. The skin of the foot appears highly echogenic as do the bony structures. Bone, air, foreign bodies and calcification stop the transmission of sound waves producing a "sonic shadow" which is a dark region distal to the echogenic obstructing region. The term acoustical shadowing is also used to describe the low or absent echoes associated with these lesions. Acoustic window refers to an optimal placing of the transducers so that the areas of interest are clearly imaged.

As with any imaging modality, transverse and longitudinal scans or any set of orthogonal planes is acquired to produce a three dimensional representation of abnormalities. Sonography is a dynamic study permitting physiologic real time observation of an anatomic region. Subluxations of peroneal tendons may be diagnosed dynamically. Unlike, CT and MRI, metal prostheses and postsurgical metallic clips do not prove a major hindrance since alternative scan planes may be used to look around these devices. The magic angle effect noted in curving tendons is not present. Haziness from vaguely increased signal due to the specific MRI partial volume effect of the surrounding fat is common in the peroneal tendons. In particular, the partial volume effect of the cortical bone of the malleolus may make imaging of the more anteriorly located peroneus brevis more difficult. Likewise, the dark bands of MRI signal-less retinaculae may be inseparable from tendon with MRI, although the retinaculum is an echogenic structure with ultrasound and readily separable during scanning. Similarly, peritendineum of the Achilles tendon that appears as an echo poor or echo free space on Sonography, cannot be distinguished on the MRI scan as a distinct structure. Intra-articular loose bodies have various MRI signals. Mature marrow fat will have high signal. Heavily calcified bodies are often dark on all imaging sequences. Chondral and soft tissue areas often have intermediate signals. Ultrasound distinguished easily between calficic and non calcific regions due to the bright signals produced by the highly reflective calcium and bony entity. Errors due to MRI and CT positioning may also be avoided by Sonography. For example, a low lying belly of the muscular peroneus brevis so that it lies within the fibular groove is said increase the risk of peroneus brevis tendon rupture or dislocation. A recent report shows that this anatomic occurrence may occur in dorsiflexion of the foot during examination. The dynamic nature of monograms often prevents misinterpretation due to anatomic positioning. Additionally, Sonography by its real time dynamic nature permits full length imaging of the posterior tibial tendon, peroneal tendons and fibulocalcaneal ligament which are difficult to visualize in total course by standard MRI sequences and planes.

MRI, the so called "Gold Standard" apparently underestimates the degree of tendon damage and nerve root inflammation when compared to high resolution ultrasound with power doppler.

However, use of ultra high frequency probes limits penetration of the sound beam. Examination of a pathologically enlarged Achilles tendon with a 12-15 MHz probe may result in poor penetration of the sound waves to the deeper pre-Achilles fat pad, the bursae subtendinea and the tricipitis surae muscle. Likewise, a lower extremity that is edematous due to lymphedema, heart failure and similar etiologies of limb swelling could limit tendon imaging. In these cases, MRI examination would provide better anatomic detail. MRI also affords a panoramic view which is easier to the surgeon to utilize. The deeper structures, or, superficial regions that lie deep to the skin surface due to overlying edema, tumor or hematoma, may be imaged with lower frequency transducers offering greater penetration of the sound beams. Imaging from the side that is closer to the structure of interest is also possible to avoid degradation of the high frequency images due to excessive distance parameters.

The examiner should look for normal variants and other pathologic processes associated with any abnormal finding. For example, in tears of the peroneus brevis tendon, ruptures of the lateral collateral ligaments, stripping of the superior peroneal retinaculum, peroneal longus subluxations and low lying muscle bellies of the peroneus brevis and peroneus quartus may be concomitantly identified. Bony pathologies such as abnormally curved surfaces or osteophytes and avulsion type micro fractures may similarly be discovered. Patient comfort is another important consideration that makes monograms preferable as a diagnostic procedure. Infants or uncooperative patients may be accurately scanned with real time units providing instantaneous data. Indeed, children may be held in their mother's arms. If necessary, portable equipment may be brought to the bedside or nursing home. Since scan times with low strength MRI units may exceed half an hour, the rapidity of ultrasound examination for the elderly provides a significant positive patient compliance factor. Claustrophobia does not occur as a problem either. Other imaging methods are cited here for completeness. Tenography technique is highly examiner dependent and is so specialized that it does not fall within the scope of this chapter. Light scanning, also known as fiberoptic transillumination or diaphanography is discussed later.

Normal Anatomy

The imaged anatomy of normal tendons depends on the frequency and angulation of the transducer applied to the structure. The probes from 5-10 MHz usually show internal linear echogenic bands regularly alternating with echo poor areas within the tendon while higher frequency probes (11-20 MHz) will demonstrate many more and thinner echogenic band like regions. These correspond to the parallel alignment of the regularly arranged collagen fiber bundles. Angulation of the probe to a oblique incidence of the sound beam will cause the tendon to lose the internal echogenic stepladder architecture and appear echo free in certain cases and is due to the normal anisotropic nature of sound in tendon. This seeming artifact is used to diagnostic advantage when looking at pathology that may simulate a tendon. The absence of disappearance of internal echoes during angulation maneuvers suggests that the structure is other than tendinous in nature.

Achilles Tendon

The Achilles tendon is a confluence of the individual tendons of the gastrocnemius and the soleus muscles. In the ankle, the tendon lies immediately beneath the skin and subcutaneous tissues. The most common variety of formation is two thirds from the gastrocnemius and one third from the soleus. The fibers twist about 6 cm proximal to the calcaneal insertion which is also a hypovascular region, accounting for the majority of ruptures at this anatomic site. The anteroposterior diameter of the tendon in normal males is less than 6.9 mm and less than 5.2 mm in normal females. The distal surface is flat to slightly concave anteriorly, although the distal tendon near its calcaneal insertion assumes a more ovoid and anteriorly flattened shape assuming a width that is twice the size of the anteroposterior diameter. The edges are rounded and the tendon is 10-15 cm in length. The muscle fibers at the musculotendinous junction appear linear and hypoechoic and must be distinguished from a tear. Dorsal to the tendon is the hypoechoic Kager's fat. Deeper yet is the flexor hallucis longus muscle. Pathology in both these structures may be elicited at the time of examination of the Achilles tendon. The patient is scanned prone with the feet hanging over the table edge. Dynamic dorsal and plantar flexion positioning are performed. The diagnosis of tendon rupture is easily made by ultrasound, usually with the tear located at the level of the posterior malleolus and the defect in the echogenic tendon filled with anechoic blood or f luid. Retraction of the proximal and distal edges may be better observed during dorsiflexion and plantar flexion maneuvers. Longitudinal partial tears may be imaged similarly and the presence of peritendon fluid or Achille's bursal fluid documented. Chronic tears may lose the tendon fluid interface and even the disrupted tendons may be quite difficult to image. Tendinitis is diagnosed when the distance between the tendon bundles increased and there is a 2 mm increase in anteroposterior diameter of the entire tendon as compared to the normal contralateral side. Xanthomas of the Achilles tendon is the most characteristic location for heterozygous familial hypercholesterolemia. This appears as a speckled or reticulated pattern within the tendon although focal nodules are also found. Due to the exquisite sensitivity of ultrasonic findings, it has been suggested that sonography be part of the work up of suspected patients. Although there is no tendon sheath, fluid may be found in the adjacent bursae. A finding associated with both tendonitis and tears is increased echogenicity of the subjacent fat pad. This is due to decreased tissue or increased fluid in the region of the normal tendon allowing better sonic penetration. Healing of the tendon may be followed by serial ultrasound scans. The differential diagnosis of accessory soleus muscle may be easily made due to the characteristic appearance of the muscle fibers in the supracalcaneal region.

Normal muscle bundles are hypoechoic and separated by well ordered symmetric hyperechoic bands of fibroadipose septae. Hypertrophy, atrophy and variations from normal are imaged. Muscle anomalies, such as the accessory soleus muscle, appear as normal muscular striations within the echopoor background. Trauma is the most common muscular traumatic condition in the lower extremity. Muscles are best examined during rest and during contraction. Comparison with the contralateral side is often helpful. Direct trauma usually crushes muscle adjacent to underlying bone whereas indirect trauma stretches the muscle beyond its normal limit. The most commonly injured muscle is the medial gastrocnemius due to jumping during athletic sports. Strains produce no visible alteration of the normal oblique parallel echogenic straie. contusions have a variety of appearances depending on the degree of focal fluid collection and the time course. Indeed, the only finding may be enlargement in the anteroposterior diameter of the muscle. Partial rupture shows disruption of the homogeneous striations and the presence of extracellular fluid. The gastrocnemius frequently demonstrates a detachment of the lower end of the medialis muscle fibers from the common aponeurosis of the triceps surae. Partial ruptures are shown to better advantage during the contraction phase. Complete rupture appears as a hypoechoic hematoma with the retracted ends of the muscle noted as echogenic fragments at the border of the fluid collection, occasionally appearing as a bell clapper configuration. Early healing shows an infusion of echogenic vessels at the periphery, which is later serially followed to complete resolution. This influx of neovascularity produces a blizzard like picture which may mimic the snow storm appearance of ruptured silicone prostheses and may be differentiated by power Doppler exam which literally shows the neovascularity in the healing region. Cystic lesions, fibrous scars, myositis ossificans and hernias (especially of the tibialis anterior muscle) are sequellae of incomplete healing. Fibrous scars are initially echo poor and later become echogenic. Dynamic Sonography may be used to document the functional damage caused by adhesions and permanent scarring.

Only 15% of wooden fragments are seen on plain film x-rays. Sutures, plastic and small glass pieces are similarly difficult to identify radiographically. Ultrasound quickly images these echogenic structures either by their bright reflections or by the associated acoustic shadowing that occurs when sound transmission is blocked. Indeed, intraoperative transducers are commercially available to localized and remove foreign bodies such as thorns and cactus needles that may hide along fascial planes. The often associated inflammatory response may be distinguished as an echo free region of fluid or echopoor abscess focus that typically forms a halo around the foreign body. Metal objects have a specific comet tail artifact that is recognizable as a series of bright echoes trailing the initial bright echo. Skin lesions, free subcutaneous air, sesamoid bones, post inflammatory, post traumatic and bursal calcifications all cast acoustic shadows.

Robert L. Bard, MD
121 E. 60th Street
New York, New York 10022
phone:(212) 355-7017, fax:(212) 752-6192