RENEW OR SUBSCRIBE TO PPM
Subscription is FREE for qualified healthcare professionals in the US.
6 Articles in Volume 1, Issue #6
Accurate Diagnosis
Getting Off the Pain Roller Coaster
Getting to the Point
Opioid Rotation: Mechanisms, Concepts, and Benefits
The Neural Plasticity Model of Fibromyalgia Theory, Assessment, and Treatment: Part 4
The Pain and Sleep Relationship

Accurate Diagnosis

Sonograms are useful tools in the detection of stenosing tenosynovitis and other conditions.

Sonography, or ultrasound imaging, is a dynamic study permitting physiologic real time observation of an anatomic region. It is a perfect tool for detecting stenosing tenosynovitis and has distinct advantages over magnetic resonance imaging (MRI) and computerized tomography (CT). Used in conjunction with power Doppler, sonography can be used to direct joint aspirations and the installation of medicines.

Scanning Principles

Musculoskeletal ultrasound imaging can accurately diagnose a large variety of tendon and joint pathologies by using frequencies at least 7.5 MHz and specially designed and focused linear array transducers.1 Ankle and foot structures are small and superficial in location and are best examined with probes more than 10 MHz in frequency. The higher the scanning frequency, the lower the sound penetration. For example, in measuring axial resolution, the discrimination between two points in the y axis, is 0.3 mm at 5 MHz, 0.15 mm at 10 MHz, and 0.12 mm at 13 MHz. This results in improved resolution, but the loss of distal information may occur when scanning deeper structures such as the bursae subtendinea and the flexor hallucis longus 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 that 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 body surface appears highly echogenic as do the bony structures. Bone, air, foreign bodies, and calcification stop the transmission of sound waves producing a sonic shadow — 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.

Comparison with CT and MRI

Transverse and longitudinal scans or any set of orthogonal planes are acquired to produce a three dimensional representation of abnormalities. Subluxations of tendons may be diagnosed dynamically with sonography. Unlike CT and MRI, metal prostheses and postsurgical metallic clips are not a major hindrance since alternative scan planes may be used to look around these devices. In addition, the magic angle effect noted in curving tendons is not present. Poor images due to increased signal and 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 joint may make imaging of the adjacent tendons and synovium 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.2 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.3 Intra-articular loose bodies have various MRI signals, where as 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.4

Chondrocalcinosis may appear a focal bright signal mimicking tears of menisci and similar structures.5 Ultrasound distinguishes easily between calcific 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 with sonography. For example, a low lying belly of the muscular peroneus brevis so that it lies within the fibular groove is said to 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.6 The dynamic nature of sonograms 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 that are difficult to visualize in total course by standard MRI sequences and planes. Fibrosis and scar tissue in the plane of a ruptured tendon may simulate a partial tear of the tendon when in fact the tendon may be retracted to the proximal region of the increased signal. Also, MRI resolution is best with smaller fields of view and therefore focused field may miss tendon pathology out of the plane of scan.7

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 microfractures may similarly be discovered.

The examiner should look for normal variants and other pathologic processes associated with any abnormal finding.

Patient comfort is another important consideration that makes sonograms preferable as a diagnostic procedure. Infants or uncooperative patients may be accurately scanned with real time units providing instantaneous data on foreign bodies, cellulitis, bursitis, and other entities simulating arthritis. Indeed, children may be held in their parents 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.

Sonography of Tendons 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 bandlike 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.

Tenosynovitis

Tenosynovitis of tendons presents with hypoechoic features and enlargement. The hypoechoic rim of the peritendon fluid is larger than the contralateral side. This appears as a target sign in cross section with the echogenic centrally located tendon surrounded by the echo poor or echo free fluid. Irregularity of the tendon contour may be noted indicative of tenosynovitis due to the eroding synovial tissue. This diagnosis may suggest more aggressive medical treatment or early surgical intervention before complete rupture occurs.

Sonography of Synovial Diseases

Dynamic study of the joint for diagnosis of synovial pathology of the fluid or proliferative variety includes searching for bursal fluid and abnormalities of the adjacent tendons, articular cartilage, and juxta-articular bone. The use of power Doppler aids in differentiating solid synovial hypertrophy from simple fluid collections. Conventional pulsed and continuous wave Doppler exams are used to demonstrate blood flow. However, these are time consuming and relatively insensitive. Color Doppler uses computer coding to demonstrate directional blood flows in a clinically useful manner. Power Doppler is a new feature of blood flow analysis that is proportional to the total number of moving scatterers. This allows low flow states and minute vascular structures to be imaged.

Chronic untreated bursitis may appear solid on MRI. In tenosynovitis, the complete disappearance of peritendon echo poor areas during compression signifies that fluid was present as opposed to pannus or thickened synovial membrane. Careful search for intratendinous rheumatoid nodules as well as areas of rupture of the peroneal and posterior tibial tendons must be performed. Synovial cysts may be simply diagnosed by ultrasound. Ganglia and their possible communication with a joint or tendon sheath may be evaluated. Rheumatoid nodules are a vasculitis that destroys by contact with adjacent structures. Power Doppler shows increased flow in active synovitis and active nodules and has proven valuable in separating synovial fluid from active pannus and nodules.

The joint is best evaluated in the longitudinal scan plane. Posttraumatic fluid collections are echo free and usually resolve within a month following injury. Since the presence of joint fluid is a natural ultrasonic window for evaluation of intraarticular lesions, small loose bodies may be readily identified as the examiner presses alternately on the lateral and medial joint recesses. Ultrasound is considered the most appropriate modality for diagnosing loose bodies in the joint. Unlike MRI, debris within fluid may be classified as to calcific or soft tissue. Calcific foci produce bright echoes on perpendicular scanning that cast sonic shadows in appropriate planes. Soft tissue debris parallels the specific pathology as to echo poor or echogenic entities, without the bright specular reflectors and sonic shadow signs. Free air or gaseous media within a fluid filled joint will also cast a sonic shadow with bright echoes, however, this may be diagnosed by plain film radiographs and ultrasonic compression techniques. Tenosynovitis with increased tendon echogenicity is an anomaly found with inflamed tendons within large fluid collections. The usual inflamed tendon is echo poor and enlarged. However, the pathologic tendon that is surrounded by a water type medium will show higher echogenicity than expected due to the greatly increased sound penetration in fluid. If possible, scanning the tendon in a path that avoids the fluid region will produce more useful information, thus avoiding the false impression of normal tendon echogenicity. Compression maneuvers that disperse the fluid away from the site under investigation may also be useful in deciding the true echogenicity of a tendon. Transient synovitis shows increased soft tissue in the joint while color flow Doppler signals are absent. Patients with seropositive rheumatoid factor arthritis tend to develop nodules and cartilage destruction that is ongoing throughout life. While early findings are at the second proximal interphalangeal joint and the metatarsophalangeal joints, any joint undergoing major stress will be affected.

Spinal arthritis may continue as disease in the small joints stabilizes. Nodule formation is a major cause of tendon rupture. Power Doppler flow in arthritis is correlated with activity. The color Doppler may be used to show increased inflammatory neovascularity as well as map the location of the adjacent artery and adjacent nerve. An increase in size of the bursa compared to the contralateral side and increase in the echogenicity of the fluid occur in pathologic states. Color power Doppler flows correlate better with pain from associated inflammation and the loss of color signal accompanies resolution of the inflammatory process. This evaluation is better made with the new ultrasonic contrast agents. Increased use of very high frequency transducers is showing debris within effusion that fails to move and may be mistaken for intrasynovial mass lesions such as pigmented villonodular synovitis (PVNS). This benign entity will not have color flow on Doppler and biopsy of these areas may be avoided since PVNS typically has significant vascularity.

Ultrasound guided procedures are real time and accurate because the advancing needle tip is monitored in relation to the area to be injected or aspirated.

Treatment

Ultrasound guided procedures are real time and accurate because the advancing needle tip is monitored in relation to the area to be injected or aspirated. Indeed, painful fluid collections in and around the synovial recesses of joints may be successfully aspirated.8 Steroid or other medications may be accurately instilled into tendon sheaths or bursae without damaging adjacent arteries, veins, and nerves.9 Surgical problems mimicking arthritis such as full thickness rotator cuff tears may be more quickly diagnosed and appropriately managed by operative modalities.10

Conclusion

Pain may be due to many factors. Sonography is both accurate in diagnosis and directed to the relevant site by the patient. The ability to easily image fluid collections and simultaneously removing them in a cost-effective manner makes this modality superior to X-ray, MRI, and CT scans.

Last updated on: December 22, 2011
close X
SHOW MAIN MENU
SHOW SUB MENU