Tibialis Posterior Tendon Injury Imaging

Updated: Aug 06, 2015
  • Author: Sherif Wassef, MD, MS, FRCS; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Overview

Overview

Tibialis posterior tendon dysfunction presents one of the most challenging problems that a foot and ankle specialist faces (see the images below). This dysfunction often results in the progressive loss of function and in significant disability for the patient. The condition is recognized as a disabling cause of progressive flatfoot deformity. [1, 2] Many cases of posterior tibial tendon dysfunction may go undiagnosed. The tibialis posterior is, by far, the most frequently ruptured tendon in the rear foot, but injuries to this structure are often overlooked. [3, 4, 5, 6, 7]

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted fat-suppressed MRI in an adult man with peritendinous edema. Image reveals reactive marrow edema (open arrow) under the tibialis posterior tendon groove; this is caused by tibialis posterior tendon dysfunction.
Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T1-weighted MRI in an adult woman with tibialis posterior tenosynovitis. Image reveals the speckled internal signal intensity of the tibialis posterior tendon (open arrow).
Ankle, tibialis posterior tendon injuries. Lateral Ankle, tibialis posterior tendon injuries. Lateral plain radiograph of a flat foot resulting from long-standing tibialis posterior tendon rupture.
Ankle, tibialis posterior tendon injuries. Drawing Ankle, tibialis posterior tendon injuries. Drawing shows the relationship of the tibialis posterior tendon to the remainder of the tarsal tunnel. Note the relative sites and the distal extent of tendon sheaths in black. Also note that the flexor hallucis and flexor digitorum tendons cross distally at the knot of Henry (straight arrow). Last, note the tibial artery and nerve (curved arrow) between the flexor digitorum longus tendon and the flexor hallucis longus tendon in the tarsal tunnel. ATT, anterior tibialis tendon; FDL, flexor digitorum longus tendon; FHL, flexor hallucis longus tendon; FR, flexor retinaculum; and PTT, tibialis posterior tendon.
Ankle, tibialis posterior tendon injuries. Drawing Ankle, tibialis posterior tendon injuries. Drawing shows the complex insertions of the tibialis posterior tendon beneath the undersurface of the foot with the muscle dissected away. Note the main slip inserting onto the tubercle of the navicular. Also note the close anatomic relationship of the distal tendon, spring ligament, and distal deltoid ligament. C, calcaneus; N, navicular; PTT, tibialis posterior tendon.

Preferred examination

Different imaging techniques can be used to assess tendon and tendon sheath abnormalities. [8, 9, 10, 11]

Tendon abnormalities can be evaluated with tenography. This is accomplished with a needle puncture of the tendon sheath. [12]

Ultrasonography is becoming an increasingly important imaging modality for evaluating musculoskeletal disorders because of its availability, noninvasiveness, lack of ionizing radiation, multiplanar and real-time capabilities, and low cost. Higher-resolution transducers and the dynamic real-time capability of ultrasonography make it attractive for evaluating muscles and tendons. Because of its superficial location, the posterior tibial tendon is particularly amenable to evaluation with ultrasonography. [13]

In the delineation of tendon calcification and retinacular avulsions of bone, computed tomography (CT) scanning is superior to magnetic resonance imaging (MRI). However, in analysis of tendon dislocation, CT scanning and MRI are of nearly equal value. [14, 15]

With its superior soft-tissue contrast resolution and multiplanar capabilities, MRI is the imaging procedure of choice for evaluating the musculoskeletal system, particularly in detecting tenosynovitis and in assessing partial and complete ruptures of the tendons. MRI and ultrasonography can be used to distinguish tendinosis from peritendinosis. This distinction is important because a more rigorous treatment is needed if the tendon is involved, because it might lead to partial and complete tear.

Enhancement of the tendon and the area around it on MRI scans and increased flow on color-flow Doppler ultrasonograms are the most useful features for diagnosing tendinosis and peritendinosis. Other useful, but less specific and less sensitive, criteria are as follows: for tendinosis, a change in signal intensity of the tendon on MRI scans and inhomogeneity of the tendon on ultrasonograms; for peritendinosis, increased soft tissue and fluid in the area around the tendon.

Imaging also provides insight into the pathophysiology of the disease process. Tendinosis and peritendinosis are often seen together (45% of cases); this observation is readily explained by a common causal mechanism of injury to the 2 sites. The finding of peritendinosis by itself, without tendinosis, is more common (20% of cases) than tendinosis alone without peritendinosis (7%), possibly because the tendon is stronger than the peritendinous tissue and therefore more resistant to injury.

Limitations of techniques

Plain radiography and bone scintigraphy lack sensitivity.

An inherent drawback of MRI and ultrasonographic modalities is an inability to further categorize tendon abnormalities. Inhomogeneity of the tendon on MRI could be due to tendinitis, partial tears, degeneration, or other tendinopathies. All of these entities fall into a spectrum of pathologic disorders, and determining when one ends and the second begins is difficult. One can speculate that inhomogeneity alone without enhancement is indicative of partial tear or chronic tendinopathy, but those disorders cannot be diagnosed on MRI scans, and ultrasonography does not help in resolving this problem.

CT scanning is valuable only when an associated bony abnormality is present; however, tendinous or peritendinous abnormalities are least confidently detected by using imaging.

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Radiography

Routine radiographic findings associated with abnormalities of the tendons and tendon sheaths of the foot and ankle include the following: soft tissue swelling; a change in the contour, calcification, or ossification of a tendon; bone proliferation; fracture fragments; and sesamoid displacement.

Soft-tissue swelling and fullness may accompany synovitis, but the finding is not specific.

Osseous proliferation or erosion is a recognized manifestation of inflammation of tendons and tendon sheaths that are close or directly on the surface of a bone. In the foot and ankle, this finding is most commonly observed in the posteromedial portion of the tibia in patients with rheumatoid arthritis or seronegative spondyloarthropathy who have involvement of the tibialis posterior tendon and sheath. Infections of tendons and tendon sheaths also can lead to infective or reactive periosteitis in the subjacent bone.

Radiographically, a dislocated tibialis posterior tendon can be diagnosed by noting the presence of a small avulsion fracture near the insertion of the flexor retinaculum on the medial malleolus.

Tenography

Tenography is a procedure in which the tendon sheath is directly opacified with contrast medium. The peroneal tendon sheath is the first to be studied with tenography.

The frequency with which tenography is performed throughout the United States and worldwide is not known. However, about half of the tenographic imaging procedures are performed to evaluate the tibialis posterior tendon.

Although MRI and CT scanning may have replaced tenography in many institutions, tenography still has a role in the management of chronic foot and ankle pain. It is used in verifying that a patient's pain is coming from the tendon sheath, in surgical decision making, and in the injection of therapeutic steroids.

Technique

After the administration of a local anesthetic, a 25-gauge needle is inserted into the tendon. A 10-mL syringe filled with a mixture of contrast material diluted 2:1 with a local anesthetic is attached via flexible tubing. During the gentle injection, the needle is withdrawn until free filling of the tendon sheath is observed under fluoroscopy. The injection continues until the tendon sheath fails to fill at its distal end, until contrast material flows proximally into the fascial sheath around the muscle, or until the patient feels discomfort. Betamethasone has the lowest risk of a flare response after the injection.

Normally, the tendon sheath demonstrates a smooth contour. At the level of the tibial plafond, there is normally extrinsic compression on the tibialis posterior tendon sheath produced by the flexor retinaculum. This should not be confused with pathologic adhesion or stenosis (see the image below).

Ankle, tibialis posterior tendon injuries. Lateral Ankle, tibialis posterior tendon injuries. Lateral tenogram shows extrinsic compression on tibialis posterior tenograms at the level of the tibial plafond produced by the flexor retinaculum (between arrowheads). This should not to be mistaken for pathologic adhesion or stenosis. Note the injecting needle (arrow).

Radiographically, mild tenosynovitis is correlated with the presence of 1-5 sacculations; moderate tenosynovitis, with 6-10 sacculations (see the first image below); and severe tenosynovitis, with more than 10 sacculations or an area of adhesion larger than 3 cm (see the second image below).

Ankle, tibialis posterior tendon injuries. Tenogra Ankle, tibialis posterior tendon injuries. Tenogram shows 6-10 sacculations (arrowheads) suggesting moderate tenosynovitis of the tibialis posterior tendon sheath. Note normal narrowing of the tendon sheath (between arrows) overlies the tibial plafond.
Ankle, tibialis posterior tendon injuries. Tenogra Ankle, tibialis posterior tendon injuries. Tenogram shows more than 10 sacculations along the margins of the tibialis posterior tendon sheath suggestive of severe tenosynovitis. Note the defect in the distal tibialis posterior tendon sheath allowing contrast material to pass into the talonavicular joint and the distal subtalar facet (arrows).

However, this tenographic classification does not correlate well with the clinical classification of peritendinitis and chronic tenosynovitis. Moreover, a long segment of stenosis (longer than 3 cm) is considered as severe, representing stenosing tenosynovitis. Stenosis or nonfilling of segments of the sheath could occur from sheath fibrosis or from enlargement of the tendon occluding the sheath. Tibialis posterior tendon rupture can be seen as a filling defect suggestive of a mass effect (see the images below).

Ankle, tibialis posterior tendon injuries. Lateral Ankle, tibialis posterior tendon injuries. Lateral tenogram depicts a filling defect/mass effect (arrowheads) of the tibialis posterior tendon representing a tear, which was confirmed at surgery.
Ankle, tibialis posterior tendon injuries. Lateral Ankle, tibialis posterior tendon injuries. Lateral tenogram depicts a mass/filling defect (arrows), which represents a torn tibialis posterior tendon. Note contrast material, which fills the sheaths of both the tibialis posterior tendon and the flexor digitorum longus (arrowheads) tendon.
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Computed Tomography

CT scanning can be used effectively to study the tendons of the foot and ankle. [16, 17]

Transaxial CT images are the easiest to acquire, and they provide the most useful information, although reformatted transaxial images in the coronal and sagittal planes are occasionally required.

The CT scan features of a normal tendon include a smooth contour, a size similar to that on the opposite side, a well-defined margin, and attenuation values 75-115 HU (Hounsfield unit) higher than those of the respective muscles.

Tenosynovitis is manifest as an enlarged tendon with an inhomogeneous appearance. The surrounding swollen, fluid-containing tendon sheath has a lower attenuation value than that of the tendon itself. Tendon displacement, tethering, or rupture may be evident, and the relationship of the tendon to the adjacent bone is identified readily. Tendon ruptures are associated with partial or complete discontinuity of the fibers and a decrease in the attenuation values (30-50 HU).

Degree of confidence

Diagnostic difficulties are encountered with CT scanning, owing to beam-hardening artifacts that cause inaccurate assessment of the attenuation values and to the presence of surrounding inflammation that obscures the contour of the tendon and the tendon sheath.

MRI is superior to CT scanning in delineating small amounts of fluid around the tendon and in allowing differentiation of scar tissue from edema and fluid. CT scanning is superior to MRI in demonstrating regions of tendon calcification and avulsion fractures related to the retinacula.

False positives/negatives

Rosenberg et al found that CT scanning is sensitive in 90% of cases of tibialis posterior rupture and is specific in 100% of these cases. [18] They defined 3 categories of injury: type 1 is a partially torn bullous or hypertrophied tendon with vertical splits and defects; type 2, partially torn and attenuated; and type 3, complete tendinous disruption with an intratendinous gap. CT scanning has an accuracy of 91% in detecting tendon ruptures.

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Magnetic Resonance Imaging

MRI has been applied to the assessment of the tendons and other structures in the ankle and foot. The tibialis posterior tendon and the Achilles tendon have received the greatest attention. [19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36] Examples of MRI scans of injuries of the tibialis posterior tendon are shown in the images below.

Ankle, tibialis posterior tendon injuries. Axial u Ankle, tibialis posterior tendon injuries. Axial unenhanced T1-weighted MRI in a healthy adult male shows normal low-signal intensity tibialis posterior (long arrow) and flexor digitorum longus (short arrow) tendons; note the relative sizes.
Ankle, tibialis posterior tendon injuries. Axial u Ankle, tibialis posterior tendon injuries. Axial unenhanced STIR weighted MRI in a healthy adult male shows normal low-signal intensity tibialis posterior (long arrow) and flexor digitorum longus (short arrow) tendons; note the relative sizes.
Ankle, tibialis posterior tendon injuries. T1-weig Ankle, tibialis posterior tendon injuries. T1-weighted fat-suppressed MRI in a young healthy man shows the ratio of the sizes of the tibialis posterior tendon (open arrow) and the flexor digitorum tendon (solid arrow). Also note how the normal tibialis posterior tendon is slightly smaller than the summated peroneal tendons (arrowhead).

Technical aspects

The technical aspects of performing MRI of the tibialis posterior tendon are controversial. MRI scans can be obtained in the sagittal, coronal, or transaxial (plantar) plane or in a combination of these. The specific plane selected depends on the particular anatomic regions and structures to be evaluated and on the clinical questions involved.

The axial plane is optimal; however, some institutions prefer oblique axial imaging perpendicular to the long axis of the tibialis posterior tendon. Sagittal imaging is the secondary plane, with the coronal plane used only as a supplement.

Two sets of axial images are ideal (see the images below). One set of images should be morphology weighted to optimize the signal-to-noise ratio. Parameters for this imaging may include the following: sequence, fast spin echo; repetition time/echo time, 4000/35; echo train length, 4; field of view, 14; and matrix, 256 x 256. Another set of images should be T2-weighted by using fat-suppression and fast spin-echo protocols with a repetition time/echo time of 6000/75.

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T1-weighted image at the level of the dome of the talus showing thickening of the tibialis posterior tendon with adjacent soft tissue edema replacing the surrounding subcutaneous fat.
Ankle, tibialis posterior tendon injuries. This im Ankle, tibialis posterior tendon injuries. This image of the same patient as in the previous image was taken at a slightly distal axial plane showing the progression of tibialis posterior tendon damage.

Sagittal images should be T1-weighted (see the images below) and acquired with either T2-weighting with fat suppression or a short-tau inversion recovery (STIR) sequence.

Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal T1-weighted image showing thickening of the tibialis posterior tendon with adjacent soft tissue edema replacing the surrounding subcutaneous fat at and below the medial malleolus.
Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal T1-weighted image showing thickening of the tibialis posterior tendon with adjacent soft tissue edema replacing the surrounding subcutaneous fat at and below the medial malleolus. Note straightening with loss of normal curvature of the tibialis posterior tendon at and below the medial malleolus.

The sagittal images depict the distal tibialis posterior tendon and its malleolar curve (see the first 3 images below), and the axial images depict perimalleolar abnormalities (see the fourth image below).

Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal T1-weighted MRI in a middle-aged woman with tibialis posterior tendon tear reveals straightening of normal malleolar curve. The patient has a markedly thickened tibialis posterior tendon (open arrow) with a large segment of internal signal intensity (white arrows).
Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal T1-weighted MRI in an adult healthy man shows a low-signal-intensity tibialis posterior tendon (open arrow). Note the normal smooth curve that the tibialis posterior tendon makes as it extends from the medial malleolus.
Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal proton density MRI in a healthy adult man reveals the normal smooth malleolar curve of the tibialis posterior tendon (open arrows).
Ankle, tibialis posterior tendon injuries. Axial S Ankle, tibialis posterior tendon injuries. Axial STIR (short-tau inversion recovery) MRI in a woman with tendon dysfunction and subtendinous edema. Image reveals edema in the medial malleolus related to tibialis posterior tendon dysfunction (open arrow).

A dedicated extremity coil is necessary, and some institutions slightly plantarflex the foot to minimize the magic-angle artifact. T1- and STIR-weighted coronal imaging might be helpful (see the images below).

Ankle, tibialis posterior tendon injuries. Coronal Ankle, tibialis posterior tendon injuries. Coronal T2-weighted image showing absence of the tibialis posterior tendon due to complete tear with fluid signal filling the tendon sheath and soft tissue edema replacing the surrounding subcutaneous fat.
Ankle, tibialis posterior tendon injuries. Coronal Ankle, tibialis posterior tendon injuries. Coronal T2-weighted image (same patient as in the previous image; slightly posterior planes) showing absence of the tibialis posterior tendon due to complete tear with fluid signal filling the tendon sheath and soft tissue edema replacing the surrounding subcutaneous fat.

Contrast material is useful only in some patients. Contrast material can be used when nonenhanced MRI scans show subtle or no findings suggestive of abnormality but when the clinician suspects an abnormality of the tibialis posterior tendon. Moreover, contrast material can be used for the evaluation of suspected synovitis, infection, and inflammatory arthritis. Lastly, contrast material is helpful in the assessment of insertional tendinitis (see the image below).

Ankle, tibialis posterior tendon injuries. Axial c Ankle, tibialis posterior tendon injuries. Axial contrast-enhanced fat-suppressed MRI in a middle-aged man with synovitis and interstitial tear reveals excessive contrast enhancement around the tibialis posterior tendon (open arrow) in the region of the medial malleolus; this finding is consistent with synovitis. Enhancement is also seen in the tibialis posterior tendon; this is suggestive of an interstitial tear.

General findings

On MRI scans, the tibialis posterior tendon is normally black without any internal signal intensity. The exception to this lack of signal intensity is the result of the magic-angle artifact (see the first image below), because the tibialis posterior tendon curves around the medial malleolus. In comparison with the Achilles tendon, the distal tibialis posterior tendon has no normal internal signal intensity. However, the signal intensity varies distally; the variations are related to volume averaging of the spring ligament (extremely distal), the tibial navicular, and the tibiotalar components of the deltoid ligament (slightly more proximal) (see the second image below).

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted fat-suppressed MRI in a young adult man. Note that internal signal intensity in tibialis posterior tendon fades on long-TE images. This finding is consistent with magic-angle artifact (open arrow).
Ankle, tibialis posterior tendon injuries. MRI T1- Ankle, tibialis posterior tendon injuries. MRI T1-weighted in an adult man with a normal tibialis posterior tendon. Image shows the close proximity of the tibialis posterior tendon (arrowhead); spring ligament (curved arrow); and tibial navicular ligament (open arrow), which gives the appearance of a thickened distal tibialis posterior tendon.

On sagittal images, the tibialis posterior tendon should have a smooth curve around the medial malleolus to limit focal compression and impingement. A small amount of fluid in the synovial sheath of the tibialis posterior tendon is normal; this measures no more than 1-2 mm and is almost never circumferential. Because no normal sheath is present around the distal tibialis posterior tendon, fluid observed at the distal 1-2 cm is abnormal and related to the metaplastic synovium.

In common with the findings derived from ultrasonography and CT scanning, the major MRI finding of tenosynovitis is abnormal accumulation of fluid within the tendon sheath. This fluid has low signal intensity on T1-weighted, spin-echo images and high signal intensity on T2- and STIR-weighted images. Pannus and scar formation around a tendon are characterized by intermediate signal intensity on T1-weighted, spin-echo images and intermediate to high signal intensity on T2-weighted, spin-echo images. (See the images below).

Ankle, tibialis posterior tendon injuries. Axial S Ankle, tibialis posterior tendon injuries. Axial STIR MRI in an adult woman with peritendinosis. This is the same patient as in the following 2 images a few months after conservative management. Image shows enhancement of the peritendinous area (open arrow) with slight increase in fluid signal.
Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T1-weighted MRI of the ankle in a young adult woman (same patient as in previous image) with peritendinosis shows increased soft tissue with mixed signal intensity in the peritendinous area (open arrow) in addition to tendon thickening.
Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted MRI in a young woman (same patient as in previous 2 images) with peritendinosis reveals mixed signal intensity and increased peritendinous soft tissue (open arrow).

Tendinitis is accompanied by focal areas of high signal intensity within the substance of the tendon on proton density– and T2-weighted, spin-echo images. With chronic tendinitis, the tendon is enlarged and of low signal intensity in T1-weighted and T2-weigted, spin-echo images.

The MRI appearance of paratendinitis is similar to that seen in the Achilles tendon, with partially circumferential areas of high signal intensity located distally around the tibialis posterior tendon. This signal intensity is usually slightly less than that of fluid. Because normally no fluid is present distally around the tibialis posterior tendon on MRI scans, the term synovitis should be used to describe this disorder only when it occurs more proximally. If apparent synovitis is seen distally, it is anatomically a paratendinitis, and images often reveal fluid with signal intensity that is slightly lower than the typical signal intensity for bland fluid. At this stage of the disorder, the tendon itself is normal and should not show intratendinous hypersensitivity. Tibialis posterior tendon disorders manifested by synovitis are often acutely symptomatic.

Although degeneration is histologically common, signal abnormalities caused by degeneration are infrequently seen on MRI scans. In most patients, degeneration occurs with an apparently normal tibialis posterior tendon, as shown on MRI scans.

In a transitional stage of tibialis posterior tendon disorder, microscopic and, eventually, macroscopic tears of the tendon fiber occur. Few partial tears are seen on MRI scans, although most are seen on ultrasonograms. On MRI scans, subtle focal areas of high signal intensity may be visible in the tendon. At surgery, the disruption is often more extensive than it appears on MRI scans. Therefore, what may appear as synovitis or tendinitis on images may in fact be a partial tear.

Tendon ruptures may be acute or chronic and partial or complete. Recent tendon tears frequently reveal regions of increased signal intensity on T2-weighted, spin-echo images and on certain gradient-echo images, owing to the presence of edema and hemorrhage. Remote tendon tears generally do not have these high-signal-intensity characteristics, owing to the presence of scar tissue.

Patterns of tendon tears

With regard to the extent of tendon tears, 3 MRI patterns have been described: type 1, type 2, and type 3.

Type 1 tears are partial tendon ruptures with tendon hypertrophy. The involved tendon appears hypertrophied or bulbous, and it reveals heterogeneous signal intensity. Focal areas of increased signal intensity are noted within its substance. The MRI pattern corresponds to a surgically evident, partially torn tendon with vertical splits and defects. The presence of an interstitial tear with a longitudinal split of the tibialis posterior tendon is also common (see the image below). This is the only type of tibialis posterior tendon disorder that appears with high signal intensity on T2-weighted MRIs, and it is almost invariably associated with synovitis.

Ankle, tibialis posterior tendon injuries. Axial i Ankle, tibialis posterior tendon injuries. Axial intermediate-weighted MRI in a middle aged man with an interstitial tendon tear. Image reveals an enlarged tibialis posterior tendon with several linear regions of signal intensity that split tibialis posterior tendon into fascicles (open arrow).

Type 2 tears are partial tendon ruptures with tendon attenuation. The involved tendon is stretched and attenuated in size; the MRI findings correspond to those found at surgery.

Type 3 tears are complete tendon ruptures with tendon retraction. The involved tendon is discontinuous; in some cases, a gap filled with fluid, fat, or scar tissue, depending on the age of the tear, is evident. The size of the gap is variable on MRI and at surgery, and this gap reflects the degree of tendon retraction. A tibialis posterior tendon tear with a gap is unusual. Usually, what is seen is severe thinning of the tibialis posterior tendon with thin residual threads that appear as a dysfunctional tendon during clinical examination.

Additionally, involvement of the spring ligament may be seen with severe tibialis posterior tendon tears.

Tendon subluxation or dislocation is easily detected with MRI, as with CT scanning, owing to an abnormal relationship of the tendon to the adjacent tissues. The tendon itself may be enlarged or partially torn, and associated soft-tissue and bony injury may be evident (see the images below).

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted MRI in an adult man with a dislocated tibialis posterior tendon. Image reveals that the tibialis posterior tendon is dislocated anteriorly, out of its groove (arrow). Note how the normal flexor digitorum tendon (open arrow) remains posterior to tibia, while the tibialis posterior tendon is subluxed medially and anteriorly.
Ankle, tibialis posterior tendon injuries. Axial p Ankle, tibialis posterior tendon injuries. Axial proton density–weighted MRI in a middle-aged woman with a subluxed tendon. Image reveals that the tibialis posterior tendon (open arrow) is slightly subluxed medially, out of its groove (arrowhead).

Exceptions to general findings

With minor exceptions, the normal tendons in the ankle and foot are homogeneous and of low signal intensity with all MRI sequences. They generally are equal in size on the 2 sides of the body, and they have a smooth contour. However, some exceptions to these general rules include the following: magic-angle effect, tenosynovial fluid, bulbous tendon insertion sites, and tendon striations.

Magic-angle effect

Increased signal intensity may be seen in normal tendons oriented obliquely with respect to the main magnetic field; this effect is greatest when this orientation is at 55° to that of the magnetic field. This effect is greater when the MRI involves a spin-echo technique with short echo times or a gradient-echo technique. (See the image below.)

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted fat-suppressed MRI in a young adult man. Note that internal signal intensity in tibialis posterior tendon fades on long-TE images. This finding is consistent with magic-angle artifact (open arrow).

The tibialis posterior tendon approximates this orientation at its site of attachment to the navicular bone, resulting in a normal appearance of increased signal intensity or heterogeneous signal intensity in this area. This alteration in signal intensity may be accentuated by volume averaging of different signal intensities derived from the joint capsule and fat in this region. Furthermore, repeating the MRI examination with a foot in plantar flexion diminishes or eliminates this magic-angle phenomenon.

Tenosynovial fluid

The differentiation of thickened tendons from one surrounded by a fluid-filled synovial sheath is difficult on T1-weighted, spin-echo MRI scans. Moreover, the presence of small, or even moderate, amounts of fluid within a tendon sheath, by itself, is not diagnostic of an abnormality, because such fluid is seen in asymptomatic persons. Tenosynovial fluid is more common in flexor tendons than in extensor tendons, and this may be particularly prominent around the flexor hallucis longus tendon.

Bulbous tendon insertion sites

Insertion sites of tendons may appear bulbous. This appearance is perhaps related to volume averaging of their signal intensity with that of adjacent cortical bone. This appearance can simulate that of a tendon disruption, particularly one of the tibialis posterior tendons.

Tendon striations

When 3-dimensional, gradient-recalled-echo MRI scans are obtained, longitudinal lines of intermediate signal intensity may be noted in the distal portion of the tibialis posterior tendon. These lines probably represent branches of the tendon, although their appearance may simulate that of a tendon tear.

Secondary signs of tibialis posterior tendon dysfunction

The abnormal mechanics of the tibialis posterior tendon can result in anatomic changes that appear on MRI scans. Although most MRI examinations are not performed while the tendons are bearing weight, MRI is a tomographic technique, and subtle mechanical disturbances may be apparent. These secondary signs can increase the diagnostic confidence in describing subtle tibialis posterior tendon disorders. Most of these signs are not pathognomonic of tibialis posterior tendon dysfunction, because they can be seen with other causes of pes planus [37] and foot disorders. In addition, reducible and nonreducible deformities are distinguished clinically.

On MRI, the only distinction is that nonreducible deformities tend to be more severe, with secondary osteoarthritic changes. Excessive plantar flexion of the talus results in a mechanical disturbance called talonavicular fault. On the sagittal MRI on which the base of the first metatarsal is visible, a long axis is drawn on the talus and extended into the navicular. The failure of this line to divide the navicular into equal superoinferior parts, with the line positioned inferiorly, is a manifestation of the talonavicular fault and hence a dysfunctional tibialis posterior tendon (see the image below).

Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal T2-weighted MRI in a middle-aged woman with a talonavicular fault. Image reveals that a line drawn along the long axis of talus extends inferiorly rather than bisecting the navicular.

Another morphologic abnormality, talonavicular unroofing (see the image below), results from the unchecked pull of the peroneus brevis shifting the entire midfoot and forefoot laterally. This causes a navicular subluxing in relationship to the talus. Normally, the articular aspect of the talus, when evaluated on proximal axial images, is 85% covered by the navicular. Unopposed peroneal brevis pull causes the uncovering of the talus. In the uncovered talus, less than 85% of the articular surface is covered by the navicular.

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted MRI in a middle-aged man with talonavicular unroofing. Image shows unroofing of the upper aspect of the talus with the navicular subluxed laterally (arrowhead), exposing the medial talonavicular head; this is a secondary sign of tibialis posterior tendon insufficiency. There is also an interstitial tear of the tibialis posterior tendon (open arrow).

A focal spur in the distal tibia is another secondary finding of a tibialis posterior tendon disorder. Because the tibialis posterior tendon normally sits in a slight concavity along the posterior medial aspect of the tibia, this spur is a sharpening of the medial or uppermost aspect of this concavity (see the image below).

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted MRI in a middle-aged woman with an atrophic tendon and a tibial spur. Image reveals a thinned tibialis posterior tendon (open arrow) that is adjacent to a spur (arrowhead); this finding is characteristic of tibialis posterior tendon dysfunction.

Additionally, a heel valgus as revealed on coronal images is an indirect sign of a tibialis posterior tendon tear (see the image below). The long axes of the calcaneus and the tibia normally subtend an angle with 0-6° of valgus.

Ankle, tibialis posterior tendon injuries. Coronal Ankle, tibialis posterior tendon injuries. Coronal T1-weighted MRI in an adult man with tendon dysfunction and heel valgus. Image reveals heel valgus. Lines of reference go through the long axes of the tibia and calcaneus.

Marrow abnormalities

Bone marrow findings related to tibialis posterior tendon disorders include the accessory navicular, the cornuate navicular (see the first image below), and marrow edema. The first 2 entities lead to a more proximal insertion of the tibialis posterior tendon, reducing the curve around the malleolus. This straightening of the curve leads to focal attritional wear and tear of the tibialis posterior tendon (see the second and third images below).

Ankle, tibialis posterior tendon injuries. Axial p Ankle, tibialis posterior tendon injuries. Axial proton density weighted MRI in an adult man at risk for tibialis posterior dysfunction. Image shows hypertrophy of navicular tubercle (open arrow), consistent with a cornuate navicular.
Ankle, tibialis posterior tendon injuries. Sagitta Ankle, tibialis posterior tendon injuries. Sagittal T2-weighted MRI in a man at risk for posterior tibialis dysfunction reveals accessory navicular (a). Note the straight line (instead of the normal smooth curve) that the tibialis posterior tendon makes as it extends from the medial malleolus. This abnormality causes a focal point of friction at the medial malleolus (open arrow).
Ankle, tibialis posterior tendon injuries. Axial i Ankle, tibialis posterior tendon injuries. Axial intermediate-weighted MRI in a young adult at risk for tibialis posterior tendon dysfunction shows the accessory navicular with low-signal-intensity synchondrosis (open arrow).

Tibialis posterior tendon disorders can also cause focal areas of marrow edema. This marrow edema is typically seen underneath the course of the tibialis posterior tendon, typically in the tibia and less commonly in the talus and navicular. Usually, patients with marrow edema under the course of the tibialis posterior tendon are symptomatic (see the images below).

Ankle, tibialis posterior tendon injuries. T2-weig Ankle, tibialis posterior tendon injuries. T2-weighted fat-suppressed MRI of the ankle in an adult woman with several months' history of medial ankle pain and tibialis posterior tendinopathy that is associated with subtendinous bone marrow edema of the medial malleolus. Axial image shows thickening of the tibialis posterior tendon (arrow). Note the marrow edema immediately subjacent to the medial malleolus (open arrow).
Ankle, tibialis posterior tendon injuries. T2-weig Ankle, tibialis posterior tendon injuries. T2-weighted fat-suppressed fast MRI of the ankle. Sagittal image shows thickening of the tibialis posterior tendon with increased internal signal intensity (arrow). Note the marrow edema immediately subjacent to the medial malleolus (open arrow).

The presence of marrow edema is somewhat more frequent in people with seronegative or seropositive arthropathies. However, most findings of marrow edema are seen in patients with routine degenerative tibialis posterior tendon disorders. Interestingly, marrow edema is frequently seen around the tibial spur, and it may be part of the evolution of this spur.

The development of a pseudoarthrosis between the accessory navicular and the native navicular is related to the tibialis posterior tendon (see the image below). A chronic tibialis posterior tendon pull can lead to fracture of the normal synchondrosis. On MRI scans, fluid is visible between the 2 bones, with kissing marrow edema on either side of the pseudoarthrosis.

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted MRI in an adult man with accessory navicular pseudoarthrosis. Image reveals fluid between the navicular and accessory navicular; this is consistent with pseudoarthritis. Also note the edema in both bones (open arrows); this reflects altered mechanics.

On MRI scans, the tibialis posterior tendon is seen subluxed anteriorly and medially, and it is seen as the most medial aspect of the tibia rather than behind it. Although a tibialis posterior tendon dislocation is uncommon, this is the second most common dislocation of the ankle tendons, after peroneal dislocations (see the image below). Repetitive transient subluxation may also be part of the pathophysiology of more typical tibialis posterior tendon tears. The retromalleolar groove is usually shallow in patients with a tibialis posterior tendon dislocation, and the retinaculum may be visibly stripped off or torn. Infrequently, a related tear in the tendon is discovered.

Ankle, tibialis posterior tendon injuries. Axial T Ankle, tibialis posterior tendon injuries. Axial T2-weighted MRI in an adult man with a dislocated tibialis posterior tendon. Image reveals that the tibialis posterior tendon is dislocated anteriorly, out of its groove (arrow). Note how the normal flexor digitorum tendon (open arrow) remains posterior to tibia, while the tibialis posterior tendon is subluxed medially and anteriorly.

Degree of confidence

MRI is the current standard imaging technique for the diagnosis of foot and ankle problems. When inhomogeneity of the tendon is seen on MRI scans, it could be due to tendinitis, a partial tear, degeneration, or another tendinopathy. All these entities fall into a spectrum of disorders, and determining when one ends and another begins is difficult. Hence, all of these entities should be considered in the differential diagnosis.

While applying their classification, Rosenberg et al found MRI for diagnosing tendon ruptures to be sensitive in 95% of cases and specific in 100%. [18] MRI has a 96% accuracy in detecting tendon rupture. The overall accuracy, which reflects a percentage of cases correctly diagnosed, as well as those correctly classified, was 59% for CT scanning and 73% for MRI.

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Ultrasonography

High-resolution ultrasonography has gained acceptance for musculoskeletal abnormalities. It has the advantages of ready availability, noninvasiveness, and low cost. [27, 28, 38, 39, 40, 41, 42, 43, 44]

On ultrasonograms, the posterior tibial tendon normally shows homogeneous, echogenic, longitudinal fibers. No flow is seen in or around the tendon on color-flow Doppler ultrasonograms. Minimal fluid is often seen adjacent to the tendon. (See the images below.)

Ankle, tibialis posterior tendon injuries. Longitu Ankle, tibialis posterior tendon injuries. Longitudinal sonogram in a young healthy woman shows minimal fluid (open arrow) seen adjacent to distal tibialis posterior tendon.
Ankle, tibialis posterior tendon injuries. Longitu Ankle, tibialis posterior tendon injuries. Longitudinal sonogram in a young healthy woman shows a normal tibialis posterior tendon (between calipers). Arrow points to the medial malleolus.
Ankle, tibialis posterior tendon injuries. Transve Ankle, tibialis posterior tendon injuries. Transverse sonogram in a young healthy woman shows a normal tibialis posterior tendon (between calipers). Open arrow points to the flexor digitorum longus tendon adjacent to tibialis posterior tendon.

The findings in tendinosis are flow within the tendon on power Doppler ultrasonography and inhomogeneity of the tendon. Flow in the tendon is seen in about 36% of the tendons (see the image below). Inhomogeneity with mixed echogenicity and disruption of echogenic fibers is seen in 48% of the tendons.

Ankle, tibialis posterior tendon injuries. Transve Ankle, tibialis posterior tendon injuries. Transverse color Doppler sonogram of tibialis posterior tendon in a young adult with tendinosis and peritendinosis. Image shows peritendinous (open arrow) and intratendinous (arrowheads) flow.

The tendon is also enlarged more prominently in the anteroposterior dimension than in the transverse dimension (see the first image below). The findings in peritendinosis are increased flow in the peritendinous area on power Doppler ultrasonograms in 45% of cases, and hypoechoic tissue is seen around the tendon in 36% of patients (see the second image below).

Ankle, tibialis posterior tendon injuries. Transve Ankle, tibialis posterior tendon injuries. Transverse sonogram in a middle-aged woman with tendinosis shows an enlarged inhomogeneous tibialis posterior tendon (between calipers).
Ankle, tibialis posterior tendon injuries. Transve Ankle, tibialis posterior tendon injuries. Transverse sonogram in a young adult woman with peritendinosis (open arrow points to low echogenicity in peritendinous area).

Correlation of MRI and ultrasonographic findings of structural abnormalities

Other than size, the 2 MRI criteria used for the diagnosis of tendinosis are contrast enhancement and the abnormal signal intensity of the tendon. These criteria are compared with color Doppler findings of flow in the tendon and with the ultrasonographic inhomogeneity of the tendon.

For the diagnosis of peritendinosis, the criteria used for MRI are contrast enhancement of the peritendinous tissues and an increase in the amount of soft tissue and fluid in the peritendinous area. The corresponding criteria used for ultrasonography are flow in the peritendinous area on color Doppler images and an increase in the amount of soft tissue and fluid in the peritendinous area.

Technique

Ultrasonography is performed by using a small-parts 10-MHz transducer. The patient is placed in a prone oblique position with his or her ankle slightly elevated on a rolled towel so that the posterior tibial tendon and flexor digitorum longus tendon can be optimally evaluated.

The posterior tibial tendon is first identified just posterior to the medial malleolus. The tendon is followed along its entire length to the insertion into the navicular tuberosity. The anteroposterior diameter is measured on the longitudinal view of the posterior tibial tendon at approximately 1 cm distal to the tip of the medial malleolus. The transducer is then turned 90°, and transverse scans and measurements of the transverse diameter of the posterior tibial tendon are obtained.

The flexor digitorum longus tendon (which lies slightly posterior to the posterior tibial tendon) is then evaluated in a similar manner. Anteroposterior and transverse diameters of the posterior tibial tendon and the flexor digitorum longus tendon are measured 1 cm distal to the medial malleolus. Color and power Doppler ultrasonography are then used to evaluate both tendons and the area around the tendon. The Doppler gain is set so that no flow is present in the cortical bone.

Degree of confidence

Enhancement of the tendon and peritendinous area on MRI scans and increased flow on color-flow Doppler ultrasonograms are the most useful features for diagnosing tendinosis and peritendinosis.

Other useful, but less specific and sensitive, criteria are as follows: for tendinosis, a change in signal intensity of the tendon on MRI and inhomogeneity of the tendon on sonography; for peritendinosis, increased soft tissue and fluid in the peritendinous area.

In the diagnosis of tendinosis, use of the combined criteria of flow and inhomogeneity of the tendon yield the best positive predictive value (90%) and the best negative predictive value (83%) for sonography compared with MRI. The addition of the abnormal size of the tendon as a criterion does not improve the sensitivity, specificity, or predictive values in the diagnosis of tendinosis.

Similarly, in the diagnosis of peritendinosis, the combined criteria of flow and increased soft tissue in the area around the tendon yields the best positive predictive value (89%) and the best negative predictive value (75%) for ultrasonography.

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Nuclear Imaging

Nuclear medicine provides a number of sensitive techniques for the evaluation of foot pain. However, the techniques are not always specific. In subacute or chronic injuries in which prolonged pain is unexplained, the 3-phase bone scan may play a significant role. [45, 46]

Bone scanning may be useful in differentiating soft-tissue pathology from bone pathology, and being a sensitive test, it may indicate the region that needs further specific radiologic examination. It may also indicate the clinical significance of a radiologic finding.

Careful attention to the technique enhances the efficiency of bone scintigraphy, and single-photon emission CT (SPECT) scanning allows better investigation of the hindfoot. With improved technique and instrumentation, the finding of a focal abnormality in the ankle or foot on bone scintigraphy is no longer sufficient. More precise information about perfusion, the blood pool, and the specific location of a lesion can be obtained with high-resolution and tomographic images.

Nuclear medicine studies must be interpreted with knowledge of the patient's history and symptoms and with close correlation with the plain radiographic findings.

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