Posterior Tibial (Tibialis Posterior) Tendon Dysfunction Imaging

Tibialis posterior tendon (posterior tibial 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. The condition is recognized as a disabling cause of progressive flatfoot deformity. Posterior tibial tendon dysfunction insufficiency is the most common cause of acquired flatfoot in adults. ^{[1, 2, 3, 4]} Surrounding ligamentous structures are affected, eventually leading to bony involvement and deformity. 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. ^{[5, 6, 7, 8, 9]}

Imaging is critical in determining severity of disease and treatment. Both anteroposterior (AP) and lateral radiographs are essential. The AP radiograph will display increased talonavicular uncoverage and increased talo-first metatarsal angle. Talo-first metatarsal angle over 16° indicates flatfoot deformity. On weight-bearing lateral radiographs, talo-first metatarsal angle typically measures over 20° in cases of flatfoot deformity. ^{[1, 10, 11, 12]}

MRI is frequently used in the evaluation and treatment of tibialis posterior tendon dysfunction and has been reported to have a sensitivity of up to 95%, with 100% specificity in tdetecting rupture of the tibialis posterior tendon. ^[13]  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. ^{[9, 14, 15]}

Thickening of the tibialis posterior tendon and peritendinous fluid are ultrasonographic characteristics of  tibialis posterior tendon tenosynovitis. ^[16]  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. It has been reported that a tendon width of more than 6 mm is suggestive of tenosynovitis, especially if it is associated with a target sign, which is a hypoechoic rim of fluid surrounding the hyperechoic tendon substance. ^{[14, 15, 16, 17, 18, 18]}  CT is best used for excluding bony flatfeet etiologies such as tarsal coalition. ^[18]

Preferred examination

Imaging is critical in determining severity of disease and treatment. Both anteroposterior (AP) and lateral radiographs are essential. The AP radiograph will display increased talonavicular uncoverage and increased talo-first metatarsal angle. Talo-first metatarsal angle over 16° indicates flatfoot deformity. On weight-bearing lateral radiographs, talo-first metatarsal angle typically measures over 20° in cases of flatfoot deformity. ^{[1, 10, 11, 12]}

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. ^{[19, 20]}

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.

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. ^[21]

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. ^{[19, 22]}

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

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

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.

Plain radiography and bone scintigraphy lack sensitivity.

Staging

Staging of posterior tibial tendon deficiency is as follows ^{[1, 23]} :

Stage 1: Normal radiographs, able to perform single-heel raise, and mild tenosynovitis.

Stage 2A: Arch collapse on a radiograph, unable to perform single-heel raise, and a flexible flatfoot deformity.

Stage 2B: Arch collapse and talonavicular uncoverage (over 40%) on a radiograph, unable to perform single heel raise, flexible flatfoot deformity, and characteristic forefoot abduction or “too many toes” sign.

Stage 3: Subtalar arthritis on a radiograph, unable to perform single heel raise, flatfoot deformity with rigid forefoot abduction, and hindfoot valgus.

Stage 4: Valgus deformity of talus in the ankle mortise visualized on AP radiograph of the ankle — talar tilt due to deltoid ligament compromise, subtalar arthritis on radiographs, unable to perform single heel raise, flatfoot deformity with rigid forefoot abduction, and hindfoot valgus.

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

Both anteroposterior (AP) and lateral radiographs are essential. The AP radiograph will display increased talonavicular uncoverage and increased talo-first metatarsal angle. Talo-first metatarsal angle over 16° indicates flatfoot deformity. On weight-bearing lateral radiographs, talo-first metatarsal angle typically measures over 20° in cases of flatfoot deformity. ^{[1, 10, 11, 12]}

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 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.

(See the images below.)

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).

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).

CT scanning can be used effectively to study the tendons of the foot and ankle. ^{[24, 25]}  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).

In a study of 410 patients who underwent ankle CT, tendon injuries were commonly found in CT examinations performed for fractures. Pilon fractures carried 2.2 times the increased risk of tibialis posterior tendon injury (P=0.0094), and talus fractures carried 3.43 times the increased risk of tibialis posterior tendon injury (P< 0.0001). ^[26]   

Degree of confidence

Diagnostic difficulties are encountered with CT scanning because of beam-hardening artifacts that cause inaccurate assessment of the attenuation values and because of 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.

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. ^[27] 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.

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. ^[10]

MRI is frequently used in the evaluation and treatment of tibialis posterior tendon dysfunction and has been reported to have a sensitivity of up to 95%, with 100% specificity in tdetecting rupture of the tibialis posterior tendon. ^[13]  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. ^{[9, 14, 15]}

While applying their classification, Rosenberg et al found MRI for diagnosing tendon ruptures to be sensitive in 95% of cases and specific in 100%. ^[27]  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.

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. ^{[20, 28, 29, 30, 31, 32, 33, 34, 35]}

(Examples of MRI scans of injuries of the tibialis posterior tendon are shown in the images below.)

Technical aspects

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.

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.

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).

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).

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).

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).

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).

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.

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, because of 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).

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.)

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 ^[36] 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).

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.

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).

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.

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).

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).

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.

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.

 

Thickening of the tibialis posterior tendon and peritendinous fluid are ultrasonographic characteristics of  tibialis posterior tendon tenosynovitis.  ^[16]   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. It has been reported that a tendon width of more than 6 mm is suggestive of tenosynovitis, especially if it is associated with a target sign, which is a hypoechoic rim of fluid surrounding the hyperechoic tendon substance. ^{[14, 15, 16, 17, 18]}   CT is best used for excluding bony flatfeet etiologies such as tarsal coalition.  ^[18]

High-resolution ultrasonography has gained acceptance for musculoskeletal abnormalities. It has the advantages of ready availability, noninvasiveness, and low cost. 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. 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. In the diagnosis of peritendinosis, the combined criteria of flow and increased soft tissue in the area around the tendon yield the best positive predictive value (89%) and the best negative predictive value (75%) for ultrasonography. ^{[32, 33, 37, 38, 39, 40, 41, 42, 43]}

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.)

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.

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).

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.

Tibialis posterior tendon enthesis has been reported in rheumatoid arthritis (RA) patients and spondyloarthropathy (SpA) patients. In a study of 78 subjects(37 healthy control, 21 RA, and 20 SpA), novel angled view of the tibialis posterior tendon and its distal enthesis allowed for improved visualization of the enthesis complex. By orienting the transducer base at a 45‐degree cephalad angle, the anisotropy and hypoechogenicity typically encountered in standard imaging were overcome, and the superficial fibers became more apparent. Distal tibialis posterior tendon enthesopathy was identified in a significant number of patients with either rheumatoid arthritis or spondyloarthropathy. ^[17]

 

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. ^{[44, 45]}

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.