MR Imaging of Disorders of the Posterior Tibialis Tendon

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1 MR Imaging of Disorders of the Posterior Tibialis Tendon Fig. 1. Drawing shows relationship of posterior tibialis tendon to remainder of tarsal tunnel. Note relative sites and distal extent of tendon sheaths in black. lso note that flexor hallucis and flexor digitorum tendons cross distally at knot of Henry (straight arrow). Last, note tibial artery and nerve (curved arrow) between flexor digitorum longus tendon and flexor halluceus longus tendon in tarsal tunnel. PTT = posterior tibialis tendon, FR = flexor retinaculum, FDL = flexor digitorum longus tendon, FHL = flexor halluceus longus tendon, TT = anterior tibialis tendon. lthough posterior tibial tenosynovitis was first described in 1930 [1], it was not until the 1980s that posterior tendon dysfunction became recognized as a clinical entity [2, 3]. It is best to think of posterior tibialis tendon abnormalities as a continuum of disorders that causes dysfunction because the predominant manifestations of pathoanatomy are functional rather than symptomatic [4]. ecause most of these disorders are not clinically painful, patients seek medical attention relatively late [5]. Therefore, on imaging, we usually see the later stages of the disorder [6]. More recently, many patients, particularly those with inflammatory processes such as rheumatoid arthritis, are presenting earlier, and the imaging spectrum of the disease is becoming better understood [7, 8]. Fig. 2. Drawing shows complex insertions of posterior tibialis tendon beneath undersurface of foot with muscle dissected away. Note main slip inserting onto tubercle of navicular (arrow). lso note close anatomic relationship of distal tendon, spring ligament, and distal deltoid ligament. PTT = posterior tibialis tendon, C = calcaneus, N = navicular. Review Mark E. Schweitzer 1 and David Karasick natomy The tibialis posterior muscle originates from the interosseous membrane and adjacent tibial posterior surface in the proximal third of the leg. The tendon forms in the distal third of the leg and lies closely apposed to the tibia posteromedially. Distally, the posterior tibialis tendon sits in a medial or posterior concavity on the medial edge of the posterior tibia. Just lateral to the posterior tibialis tendon lies the flexor digitorum tendon. The posterior tibialis tendon curves distally around the medial malleolus. It is at this level that the tendon lies beneath the flexor retinaculum, which prevents the flexor tendons from bowstringing as they curve around the malleolus [9]. Fig year-old man at risk for posterior tibialis dysfunction. xial T2-weighted fatsuppressed MR image (TR/TE, 6000/70) shows hypertrophy of navicular tubercle (arrow), consistent with cornuate navicular. Received July 12, 1999; accepted after revision February 22, oth authors: Department of Radiology, Thomas Jefferson University Hospital, 111 S. 11th St., 3390 Gibbon, Philadelphia, P ddress correspondence to M. E. Schweitzer. JR 2000;175: X/00/ merican Roentgen Ray Society JR:175, September

2 Schweitzer and Karasick The flexor retinaculum is the roof of the tarsal tunnel. The tarsal tunnel contains the three ankle flexor tendons, the adjacent posterior tibial artery and vein, and the tibial nerve [10] (Fig. 1). Past the tarsal tunnel, the posterior tibialis tendon has a complex insertion. Several slips of the posterior tibialis tendon extend to the cuneiforms and the bases of the second, third, and fourth metatarsals. However, the bulk of the tendon inserts on a prominence on the medial aspect of the navicular (Fig. 2). This prominence is called the navicular tubercle. This tubercle prevents the navicular from being perfectly symmetric on axial images. Excessive prominence of this tubercle is likely the result of a fused accessory navicular and is called a cornuate navicular (Fig. 3). true accessory navicular is present in approximately 4% of the population [11]; however, accessory naviculars are present in a much higher percentage of patients with posterior tibialis tendon disorders [12] (Fig. 4). The accessory navicular acts as if it were a native navicular with the bulk of the posterior tibialis tendon inserting onto the accessory navicular. The presence of either an accessory navicular or a cornuate navicular is a risk factor for posterior tibialis tendon tears. However, most people with an accessory or cornuate navicular will not have a disorder of the posterior tibialis tendon [12]. lood Supply The proximal aspect of the posterior tibialis tendon is fed by branches of the posterior tibial artery. The distal aspect of the tendon, at the enthesis, is supplied by the posterior tibial and dorsalis pedis arteries [13]. The mid tendon, similar to the chilles tendon, is poorly supplied with blood. In addition, the mesotenon is absent distally because the synovial sheath ends at the mid portion of the talus. ecause of the absence of a mesotenon [14] and the zone of hypovascularity, the level of the medial malleolus in relation to the tubercle is the most common location for posterior tibialis tendon dysfunction [3]. Posterior tibialis tendon disorders are predominantly ischemic and, similar to strokes and myocardial infarction, are senescent diseases. Impingement also plays a role in posterior tibialis tendon dysfunction because the posterior tibialis tendon has a focal point of stress as it curves around the medial malleolus [5]. This point of stress can be analogous to the pressure on the rotator cuff in the subacromial space [15]. This combination of ischemia and mechanical compression causes most posterior tibialis tendon disorders. Functional natomy The posterior tibialis muscles act to plantarflex the ankle and invert the foot. During normal gait, this unit locks the calcaneus to the cuboid and the talus to the navicular, creating a rigid midfoot lever for forward propulsion [16]. If posterior tibialis dysfunction is present, the lack of a rigid midfoot causes gastrocnemius and soleus flexion to occur at the midfoot instead of at the metatarsal heads [17]. This problem will eventually lead to midfoot collapse, forefoot abduction, and heel valgus. These deformities are exacerbated by the action of the peroneus brevis, the antagonist muscle to the posterior tibialis. ecause the cross-sectional area of the peroneus brevis is half that of the posterior tibialis tendon, a significant degree and length of time of posterior tibialis dysfunction must be present before these abnormalities appear [17]. Epidemiology Posterior tibialis tendon dysfunction is a disorder primarily occurring in women who are middle-aged or elderly [2]. Systemic risk factors are noted more frequently in dysfunction of the posterior tibialis tendon than in disorders of the chilles tendon. The most important of these risk factors are hypertension, obesity, lupus, gout, rheumatoid arthritis, and, somewhat less commonly, Reiter s syndrome [18 20]. Patients with rheumatoid arthritis more frequently develop synovitis than tears [20]. This synovitis causes fibrosis from recurrent inflammatory episodes and then posterior tibialis tendon dysfunction. subtype of seronegative arthropathies with a positive Cw6 human leukocyte antigen is associated with tears of the posterior tibialis tendon [21]. Prior trauma and surgery are not strong predictors of posterior tibialis tendon disorder nor is systemic steroid exposure [18]. However, direct injection of steroids into the tendon can cause posterior tibialis tendon tears [22]. MR Imaging The technical aspects of performing MR imaging of the posterior tibialis tendon are controversial. The axial plane is optimal; however, some institutions prefer oblique axial imaging perpendicular to the long axis of the posterior tibialis tendon. Sagittal imaging is the secondary plane, with coronal used only as a supplement. Two sets of axial images are ideal. One set of images should be morphology weighted to optimize the signal-to-noise ratio (fast spin echo; TR/TE, 4000/38; echo Fig year-old man at risk for posterior tibialis dysfunction., Sagittal T2-weighted MR image (TR/TE, 6000/70) reveals accessory navicula (a). Note normal low signal intensity between accessory navicular and native navicular (curved arrow). lso note straight line (instead of normal smooth curve) that posterior tibialis tendon makes as it extends from medial malleolus. This abnormality causes focal point of friction at medial malleolus (straight arrow)., xial intermediate-weighted MR image (6000/40) shows accessory navicular with low-signal-intensity synchondrosis (arrow). 628 JR:175, September 2000

3 MR Imaging of Posterior Tibialis Tendon Fig year-old healthy man. Sagittal short tau inversion recovery MR image (TR/TE, 4000/48; inversion time, 150) reveals normal smooth malleolar curve of posterior tibialis tendon (arrows). Fig year-old woman with posterior tibial tendon tear. Sagittal T1-weighted MR image (TR/TE, 500/15) reveals straightening of normal malleolar curve in patient with markedly thickened posterior tibialis tendon (black arrows) with large segment of internal signal intensity (white arrows). train length, four; field of view, 14; matrix, ), and one set of images should be T2-weighted using fat suppression and fast spin-echo (6000/~70) protocols. Sagittal images should be T1-weighted and either T2- weighted with fat suppression or short tau inversion recovery. The sagittal images depict the distal posterior tibialis tendon and its malleolar curve (Figs. 5 and 6), and the axial images depict perimalleolar abnormalities. dedicated extremity coil is necessary, and some institutions slightly plantarflex the foot to minimize the magic angle artifact. Contrast material is useful only in some patients. We use contrast material when unenhanced MR imaging shows subtle or no findings suggestive of abnormality but the clinician suspects an abnormality of the posterior tibialis tendon. We also use contrast material for suspected synovitis, infection, or inflammatory arthritis. Last, contrast material is helpful for insertional tendonitis. On MR imaging, the posterior tibialis tendon is normally black without any internal signal intensity [23]. The exception to this lack of signal intensity is the result of the magic angle artifact 5 because the posterior tibialis tendon curves around the medial malleolus (Fig. 7). In comparison with the chilles tendon, the distal posterior tibialis tendon has no normal internal signal intensity. However, there is variability of signal intensity distally related to volume averaging of the spring ligament (extremely distally), tibial navicular, and tibiotalar components of the deltoid ligament (slightly more proximally) [24] (Figs. 2 and 8). On sagittal images, the posterior tibialis tendon should have a smooth curve around the medial malleolus to limit focal compression and 6 Fig year-old healthy man., xial T1-weighted MR image (TR/TE, 500/12) shows diffuse internal signal in posterior tibialis tendon (arrow)., xial T2-weighted fat-suppressed MR image (6000/78) reveals internal signal intensity in posterior tibialis tendon that fades on long TE images, consistent with magic angle artifact (arrow). Fig year-old man with normal posterior tibialis tendon. MR image (TR/TE, 3000/38) shows close proximity of posterior tibialis tendon (straight solid arrow), spring ligament (curved arrow), and tibial navicular ligament (open arrow), giving appearance of thickened distal posterior tibialis tendon. JR:175, September

4 Schweitzer and Karasick Fig year-old man with tenonitis synovitis., xial proton density weighted MR image (TR/TE, 4000/42) shows thickened tendon and synovitis (arrow)., xial T2-weighted fat-suppressed MR image (6000/82) reveals posterior tibialis tendon with multifocal speckled internal signal intensity surrounded by excessive synovial fluid (arrow). impingement (Fig. 5). small amount of fluid in the synovial sheath of the posterior tibialis tendon is normal, measuring no more than 1 2 mm and almost never circumferential [25]. ecause, anatomically, there is no normal sheath around the distal posterior tibialis tendon (Figs. 1 and 9), fluid observed at the distal 1 2 cm is abnormal and related to the metaplastic synovium [25]. bnormal natomy similar continuum of posterior tibialis tendon disorders exists in the chilles tendon, and a similar concept of cumulative injury is useful in understanding posterior tibialis tendon disorders [26]. However, in contradistinction to the chilles tendon, complete tears with a gap that show no evidence of fibrosis are a fairly unusual manifestation of posterior tibialis tendon dysfunction, and ischemia appears to be a more important causal factor [5]. Clinically, the first presenting stage of posterior tibialis tendon dysfunction is paratendonitis or synovitis. The MR imaging appearance of this paratendonitis is similar to that seen in the chilles tendon, with partially circumferential high signal intensity located Fig year-old woman with posterior tibialis tenosynovitis., xial intermediate-weighted MR image (TR/TE, 4000/28) reveals speckled internal signal intensity of posterior tibialis tendon (arrow)., Signal intensity is more intense on T2-weighted MR image (6000/76) and is associated with synovitis (arrow). distally around the posterior tibialis tendon. This signal intensity is usually slightly hypointense to fluid. ecause normally no fluid is present distally around the posterior tibialis tendon on MR imaging, the term synovitis should be used to describe this disorder only when it occurs more proximally [23] (Fig. 10). If apparent synovitis is seen distally, it is anatomically a paratendonitis and often reveals fluid slightly lower in signal intensity than is typical for bland fluid (Fig. 9). t this stage of the disorder, the tendon itself is normal and should not show intratendon signal. Posterior Fig year-old woman with insertional tendonitis. Sagittal fast short tau inversion recovery MR image (TR/TE, 6000/50; flip angle, 50 ) reveals fluid and diffuse flocculent signal intensity in distal posterior tibialis tendon consistent with insertional tendonitis (arrow). Note adjacent soft-tissue edema. lso note longitudinal areas of high signal intensity in tendon consistent with interstitial tear. 630 JR:175, September 2000

5 MR Imaging of Posterior Tibialis Tendon Fig year-old man with synovitis and interstitial tear. xial contrast-enhanced fat-suppressed MR image (TR/TE, 600/8) reveals excessive contrast enhancement around posterior tibialis tendon (arrow) in region of medial malleolus, consistent with synovitis. Enhancement is also seen in posterior tibialis tendon and is consistent with component of interstitial tear. tibialis tendon disorders manifested by synovitis are often acutely symptomatic. The next stage of posterior tibialis tendon dysfunction is tendonitis, which is correctly termed tendonosis. Tendonitis is a less preferred nomenclature because the pathophysiology is degenerative dysfunction without a true inflammatory component [26]. True tendonitis of the posterior tibialis tendon is unusual (Fig. 11). Many cases that are clinically believed to be tendonitis are in fact synovitis. In tendonosis, patients have degeneration in the posterior tibialis tendon. Histologically, there is no inflammation, but evidence of intratendinous collagen degeneration, local necrosis, calcification, and hypocellularity, similar to that seen in chilles tendon degeneration, is present [27]. lthough degeneration is histologically common, in our experience, signal abnormalities caused by degeneration on MR images are seen infrequently. In most patients, degeneration presents with an apparently normal posterior tibialis tendon on MR imaging. There is a transition stage of posterior tibialis tendon disorder in which there are microscopic and eventually macroscopic tendon fiber tears. Few partial tears are seen on MR imaging, although most are seen on sonography [28] (Fig. 12). On MR imaging, if visible, subtle focal high signal intensity is visible in the tendon. t surgery, the disruption is often more extensive than it appears on MR imaging. Therefore, Fig year-old woman with atrophic tear. xial T2-weighted MR image (TR/TE, 6000/80) reveals attenuated threadlike posterior tibialis tendon (arrow) consistent with atrophic-type tear. what may appear on imaging as synovitis or tendonitis may in fact be a partial tear. Partial tears can scar over and lead to tendon thickening, retract and lead to tendon thinning, or severely weaken the tendon and result in a gap [23]. Thin tendons are atrophic (Fig. 13) and thick tendons are hypertrophic (Fig. 14). Most patients have mixed regions of hypertrophic and atrophic tendons. This mixture occurs because there are interstitial tendon tears Fig year-old man with mixed hypertrophic and atrophic tendon tear. Sagittal short tau inversion recovery MR image (TR/TE, 4800/48; flip angle, 15º) reveals focal tear of submalleolar (thick arrow) with tendon thinning. Retracted fibers cause spurious tendon thickening (thin arrow). Fig year-old man with hypertrophic tear. xial T2-weighted MR image (TR/TE, 6500/65) reveals enlarged tendon (black arrow) adjacent to deltoid ligament (white arrow). This posterior tibialis tendon is roughly three to four times the size of adjacent flexor hallucus and flexor digitorum tendons, consistent with hypertrophic dysfunction. with bulbous hypertrophic proximal tendon fibers and because of retraction, atrophic fibers distally (Fig. 15). ecause abnormal size may be the only indicator of tendon dysfunction, the relative sizes of the posterior tibialis tendon, flexor digitorum tendon, and flexor hallucis tendon should be examined. In a healthy person, the posterior tibialis tendon is roughly twice the size of the two adjacent tendons [26] (Fig. 16). dditionally, the pos- Fig year-old healthy man. T1-weighted fatsuppressed MR image (TR/TE, 500/18) shows size ratio of posterior tibialis tendon (open arrow) to flexor digitorum tendon (solid straight arrow). lso note how normal posterior tibialis tendon is slightly smaller than summated peroneal tendons (curved arrow). JR:175, September

6 Schweitzer and Karasick terior tibialis tendon should be slightly smaller than the anterior tibialis tendon, and the posterior tibialis tendon should be slightly smaller than the summated measurements of the peroneus brevis and peroneus longus tendons (Fig. 17). Normally, there may be a small amount of fluid around the tendon. If too much fluid is present, the patient may have pain and dysfunction. dditionally, fibrotic synovium contributes to the pathophysiology, causing a thickened tendon. lso, fibrosing tenosynovitis, related to paratendonitis and synovitis, causes thickening of the tendon [29]. In fibrosing tenosynovitis, the synovium may appear black on MR images [30]. The dark adherent synovium makes the tendon appear hypertrophic. posterior tibialis tendon tear with a gap is unusual. Usually, what is seen is severe thinning Fig year-old woman with hypertrophic tendon dysfunction. and, xial T1-weighted MR image (TR/TE, 500/12) () and T2-weighted MR image (6500/90) () reveal posterior tibialis tendon tear with thickening synovitis and internal signal intensity (white arrow). Note enlarged posterior tibialis tendon relative to flexor digitorum and flexor hallucis (black arrows) tendons. lso note how abnormal posterior tibialis tendon is larger than tibialis anterior (open arrow) of the posterior tibialis tendon with thin residual threads clinically presenting as a dysfunctional tendon. The presence of an interstitial tear with a longitudinal split of the posterior tibialis tendon is also common (Figs. 18). This is the only type of posterior tibialis tendon disorder that appears with high signal intensity on T2-weighted MR imaging, and it is almost invariably associated with synovitis. dditionally, involvement Fig year-old man with interstitial tendon tear. xial intermediate-weighted MR image (TR/TE, 4000/48) reveals enlarged posterior tibialis tendon with several linear regions of signal splitting posterior tibialis tendon into fasicles (arrow). Fig year-old woman with talonavicular fault. Sagittal T2-weighted MR image (TR/TE, 500/10) reveals that line drawn along long axis of navicular extends inferiorly rather than bisecting navicular. Fig year-old man with talonavicular unroofing. MR image (TR/ TE, 7000/78) shows unroofing of upper aspect of talus with navicula subluxed laterally (solid arrow), exposing medial talonavicular head, a secondary sign of posterior tibialis tendon insufficiency. Patient also had interstitial tear of posterior tibial tendon (open arrow). 632 JR:175, September 2000

7 MR Imaging of Posterior Tibialis Tendon of the spring ligament may be seen with severe posterior tibialis tendon tears and some of the foot deformities discussed next. The typical location of posterior tibialis tendon disorders is perimalleolar, although they are epicentered somewhat distal to the malleolus [31]. second location at which disorders occur is distal [12]. Distal is a typical location for injury in young athletic individuals and in patients with inflammatory arthropathies. Secondary Signs of Posterior Tibialis Tendon Dysfunction The abnormal mechanics of the posterior tibialis tendon can result in anatomic changes Fig year-old woman with atrophic tendon and tibial spur. xial T2-weighted MR image (TR/TE, 6000/ 80) reveals thinned posterior tibialis tendon (straight arrow) adjacent to spur (curved arrow) characteristic of posterior tibialis tendon dysfunction. TLE 1 Secondary Signs of Posterior Tibialis Tendon Tears that appear on MR imaging. lthough most MR imaging is not performed while the tendons are bearing weight, MR imaging is a tomographic technique, and subtle mechanical disturbances may be apparent. These secondary signs can increase diagnostic confidence in describing subtle posterior tibialis tendon disorders. Most of these signs are not pathognomonic of posterior tibialis tendon dysfunction because they can be seen with other causes of pes planus and foot faults. In addition, separation is made between reducible and nonreducible deformities clinically. On MR imaging, the only distinction is that nonreducible deformities tend to be more severe with secondary osteoarthritic changes. Fig year-old woman with tendon dysfunction and heel valgus. Coronal fast short tau inversion recovery MR image (TR/TE, 4000/35; inversion time, 150) reveals heel valgus. Lines of reference go through long axes of tibia and calcaneus. One mechanical disturbance is termed talonavicular fault [12]. This is the result of excessive plantar flexion of the talus. To evaluate this finding, use sagittal MR imaging. On the sagittal image in which the base of the first metatarsal is visible, a long axis is drawn on the talus and is extended into the navicular. Failure of this line to divide a navicular into equal superoinferior parts, with the line positioned inferiorly, is a manifestation of the talonavicular fault and a dysfunctional posterior tibialis tendon (Fig. 19). The second morphologic abnormality results from the unopposed pull of the peroneus brevis shifting the entire mid- and forefoot laterally. This will result in a navicular subluxing in rela- Fig year-old woman with tendon dysfunction and subtendonous edema. Coronal short tau inversion recovery MR image (TR/TE, 6000/40; inversion time, 150) reveals edema in medial malleolus related to posterior tibialis tendon dysfunction (arrow). Sign Imaging Plane/Image Imaging ppearance Unroofing of the talus Upper axial of the talonavicular joint Less than 85% of articular surface of the talus navicular is covered by the navicular Talonavicular fault Sagittal in which the base of the first metatarsal is visible Longitudinal axis of the talus does not bisect the navicular Tibial spur xial through the tibial metaphysis Focal sharpening of the medial aspect of the posterior tibialis tendon groove Cornuate navicular xial through the mid navicular Inability to symmetrically fold the navicular because of the hypertrophied tubercle ccessory navicular a Sagittal Medial image inferior and proximal to the navicular with intervening low signal intensity Heel valgus Coronal through the subtalar joint Medial angulation of the tibia with respect to the talus Subtendinous edema xial fat-suppressed T2-weighted Subcortical edema under the course of the posterior tibialis tendon Straightening of curve Sagittal medial n abrupt point of friction of the posterior tibialis tendon at the medial malleolus a Not a true secondary sign. JR:175, September

8 Schweitzer and Karasick Fig year-old man with subtendonous edema. xial T2-weighted fat-suppressed MR image (TR/TE, 6000/80) reveals edema (arrow) under posterior tibialis tendon groove caused by posterior tibialis tendon dysfunction. Image shows reactive marrow edema. tionship 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 [11, 32] (Fig. 20). nother secondary finding of a posterior tibialis tendon disorder is a focal spur in the distal tibia [31]. ecause the posterior tibialis 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 (Fig. 21). The last secondary sign of a posterior tibialis tendon tear is a heel valgus revealed on coronal images (Fig. 22) comparing lines along the long axes of the calcaneus and the tibia (Table 1). The normal range is from 0 to 6 of valgus. Marrow bnormalities one marrow findings related to posterior tibialis tendon disorders include the accessory navicular, the cornuate navicular, and marrow edema. The former two entities lead to a more proximal insertion of the posterior tibialis tendon reducing the curve around the malleolus. This straightening of the curve leads to focal attritional wear and tears of the posterior tibialis tendon [11] (Figs. 4 and 6). Fig year-old man with accessory navicular pseudoarthrosis. xial T2-weighted MR image (TR/TE, 6000/78) reveals fluid between navicular and accessory navicular consistent with pseudoarthritis. lso note edema in both bones (arrows) representing altered mechanics. Posterior tibialis tendon disorders can also cause focal areas of marrow edema. This marrow edema is typically seen underneath the course of the posterior tibialis tendon, typically in the tibia and less commonly in the talus and navicular. Usually, patients with marrow edema under the course of the posterior tibialis tendon are symptomatic (Figs. 23 and 24). The presence of marrow edema is somewhat more frequent in people with seronegative and seropositive arthropathies. However, most marrow edema is seen in patients with routine degenerative posterior tibialis tendon disorders. Interestingly, marrow edema is frequently seen around the tibial spur and 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 posterior tibialis tendon. Chronic posterior tibialis tendon pull can lead to fracture of the normal synchondrosis. On MR imaging, fluid will be visible between the two bones, with kissing marrow edema on either side of the pseudoarthrosis (Fig. 25). Fig year-old man with dislocated posterior tibialis tendon. xial T2-weighted MR image (TR/TE, 6000/90) reveals posterior tibialis tendon to be dislocated anteriorly out of its groove (solid arrow). Note how normal flexor digitorum tendon (open arrow) remains posterior to tibia while posterior tibialis tendon is subluxed medially and anteriorly. Dislocations of the Posterior Tibialis Tendon Dislocation of the posterior tibialis tendon is a rare injury that is often diagnosed late. Radiographically, a dislocated posterior tibialis tendon can be diagnosed by noting the presence of a small avulsion fracture by the insertion of the flexor retinaculum on the medial malleolus. On MR imaging, the posterior tibialis tendon is seen subluxed anteriorly and medially, visible as the most medial aspect of the tibia rather than behind it (Fig. 26). lthough posterior tibialis tendon dislocation is uncommon, this is the second most common dislocation of ankle tendons, after peroneal dislocation. It also may be true Fig year-old woman with subluxed tendon. xial proton density weighted MR image (4000/48) reveals posterior tibialis tendon (straight arrow) to be slightly subluxed medially out of its groove (curved arrow). 634 JR:175, September 2000

9 MR Imaging of Posterior Tibialis Tendon that repetitive transient subluxation is part of the pathophysiology of more typical posterior tibialis tendon tears. The retromalleolar groove is usually shallow in patients who dislocate their posterior tibialis tendon, and the retinaculum may be visibly stripped off or torn. Infrequently, a related tear in the tendon is discovered [33]. The posterior tibialis tendon can also sublux, often subtly, outside its groove (Fig. 27). Conclusion The posterior tibialis tendon is one of the most commonly disordered tendons in the body. Most patients present with dysfunction. This dysfunction is relative to failure of the posterior tibialis tendon to perform its normal function and to the unopposed force of the peroneus brevis. Patients can also present with symptoms related to marrow edema or synovitis. References 1. Kulowski J. Tenovaginitis (tenosynovitis): general discussion and report of one case involving the posterior tibial tendon. J Miss State Med ssoc 1936;33: Funk D, Cass JR, Johnson K. cquired adult flat foot secondary to posterior tibial-tendon pathology. J one Joint Surg m 1986;68-: Mann R, Thompson FM. Rupture of the posterior tibial tendon causing flat foot. J one Joint Surg m 1985;67-: Michelson J, Easley M, Wigley FM. Posterior tibial tendon dysfunction in rheumatoid arthritis. Foot nkle Int 1995;16: Johnson K, Strom DE. Tibialis posterior tendon dysfunction. Clin Orthop 1989;239: Johnson K. Tibialis posterior tendon rupture. Clin Orthop 1983;177: Rubens DJ, lebea JS, Totterman SMS, Hooper MM. Rheumatoid arthritis: evaluation of wrist extensor tendons with clinical examination versus MR imaging a preliminary report. Radiology 1993;187: Michelson JD, Easley M, Wigley F. Foot and ankle problems in rheumatoid arthritis. Foot nkle Int 1994;15: Netter FH. Muscles arteries, and nerves of leg: superficial and partial dissections. In: The Ciba collection of medical illustrations: musculoskeletal system. 1. natomy, physiology, and metabolic disorders. Summit, NJ: Ciba-Geigy 1991: aille DS, Kelikian S. Tarsal tunnel syndrome: diagnosis, surgical technique, and functional outcome. Foot nkle Int 1998;19: Lim PS, Schweitzer ME, Deely D, et al. Posterior tibial tendon dysfunction: secondary MR signs. Foot nkle Int 1997;18: Schweitzer ME, Caccese R, Karasick D. Posterior tibial tendon tears: utility of secondary signs for MR imaging diagnosis. Radiology 1993;188: Jahss MH. Spontaneous rupture of the tibialis posterior tendon: clinical findings, tenographic studies, and a new technique of repair. Foot nkle Int 1982;3: Lovell GH, Tanner HH. Synovial membranes, with special reference to those related to the tendons of the foot and ankle. J nat 1988;42: Rothman RH, Parke WW. The vascular anatomy of the rotator cuff. Clin Orthop 1965;41: erquist TH. Radiology of the foot and ankle. In: erquist TH, ed. Diagnostic techniques. Philadelphia: Lippincott, Williams & Wilkins, 2000: Sutherland DH. n electromyographic study of the plantar flexors of the ankle in normal walking on the level. J one Joint Surg m 1966;48-: Holmes J Jr, Mann R. Possible epidemilogical factors associated with rupture of the posterior tibial tendon. Foot nkle Int 1992;13: Cruckshank. Lesions of joints and tendon sheaths in systemic lupus erythematosus. nn Rheum Dis 1959;18: Downey DJ, Simpkin P, Mack L. Tibialis posterior tendon rupture: a cause of rheumatoid flat foot. rthritis Rheum 1988;31: Myerson M, Solomon G, Shereff M. Posterior tibial tendon dysfunction: its association with seronegative inflammatory disease. Foot nkle Int 1989;9: alasubramian P, Prathap K. The effect of injection of hydrocortisone into rabbit calcaneal tendons. J one Joint Surg r 1972;54-: Khoury NJ, El-Khoury G, Saltzman C, randser E. Magnetic resonance imaging of posterior tibial tendon dysfunction. JR 1996;167: Rule J, Yao L, Seeger LL. Spring ligament of the ankle: normal MR anatomy. JR 1993;161: Nazarian LN, Rawool NM, Martin CE, Schweitzer ME. Synovial fluid in the hindfoot and ankle: detection of amount and distribution with US. Radiology 1995;197: Schweitzer ME. Magnetic resonance imaging of the foot and ankle. Magn Reson Q 1993;9: Clancy WG. Tendon trauma and overuse injuries. In: Leadbetter W, uckwalter J, Gordon SL, eds. Sports-induced inflammation: clinical and basic science concepts. Park Ridge, IL: merican cademy of Orthopedic Surgery, 1990: Kainberger F, Mittermaier F, Seidl G. Imaging of tendon adaptation degeneration and rupture. Eur J Radiol 1997;25: Trevino S, Gould N, Korson R. Surgical treatment of stenosing tenosynovitis at the ankle. Foot nkle Int 1982;2: Glajchen N, Schweitzer ME. Magnetic resonance imaging features of dequevain s teno-synovitis of the wrist. Skeletal Radiol 1996;25: Rosenberg ZS, Cheung Y, Jahss MH. Rupture of the posterior tibial tendon: CT and MR imaging with surgical correlation. Radiology 1988;169: Karasick D, Schweitzer ME. Tear of the posterior tibial tendon causing asymmetric flatfoot: radiologic findings. JR 1993;161: encardino J, Rosenberg ZS, eltran J, et al. Magnetic resonance imaging of dislocation of the posterior tibial tendon. JR 1997;169: JR:175, September