MRI Web Clinic — September 2005

Posterior Tibial Tendinopathy
Pamela H. Burdett, M.D.

Clinical History: A 55 year old woman presents with a history of chronic progressive arch pain. Sagittal T1-weighted (1a), axial T2-weighted (1b), and fat suppressed coronal proton density-weighted (1c) images are shown below. What are the findings and what is your diagnosis?

1a
1b
1c
Figure 1:

Sagittal T1-weighted (1a), axial T2-weighted (1b), and fat suppressed coronal proton density-weighted (1c) images

Findings

2a
2b
2c
Figure 2:

(2a) A sagittal T1-weighted image demonstrates abnormal high signal intensity within the posterior tibial tendon (PTT), (arrow) just below the medial malleolus. (2b) An axial T2-weighted image just below the medial malleolus demonstrates increased diameter of the PTT and linear increased signal intensity within the tendon (arrow). (2c) A coronal fat-suppressed proton density-weighted image demonstrates a thickened PTT with increased signal intensity within its substance (black arrow).

Diagnosis

Tear of the Posterior Tibial Tendon (PTT).

Discussion

Posterior tibial tendon tears typically occur in middle-aged women, presenting with chronic pain and progressive flat foot deformity. Type I tears (as in the test case above) demonstrate interstitial tearing of the tendon as well as increased size, with the diameter of the PTT increased as much as five to ten times the diameter of the adjacent flexor digitorum longus tendon. (The normal diameter is approximately twice that of the flexor digitorum longus tendon.)1 Type II tears demonstrate decreased diameter, equal to or less than that of the flexor digitorum longus tendon (3a), whereas Type III tears demonstrate complete rupture of the tendon (4a).

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Figure 3:

(3a) On this fat-suppressed T2-weighted axial image, an abnormally small PTT (white arrow) is noted, consistent with a type II tear.

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Figure 4:

(4a) A T2-weighted axial view of a Type III PTT tear demonstrates a nearly fluid-filled posterior tibial tendon sheath (arrow), with only a few edematous irregular tendon fibers visible.

The tibialis posterior muscle originates in two heads at the interosseous membrane and the posterior surface of the fibula. It runs within the retromalleolar groove at the ankle and inserts onto the medial aspect of the navicular, with smaller tendon slips inserting onto the cuneiforms and the bases of the second, third and fourth metatarsal bases. It inverts and plantar flexes the foot, and supports the medial arch of the foot. This is why chronic tears demonstrate associated flatfoot deformity, with plantar flexion of the talus often seen on sagittal MR images. The site of chronic tears is most commonly at the level of the medial malleolus, where a zone of relative hypovascularity exists. In addition, the tendon is also susceptible to greater mechanical stress and potential impingement as is turns about the medial malleolus. Other etiologic factors for PTT tears include inflammatory arthropathy, obesity, hypertension, an accessory navicular, a cornuate navicular, and congenital flat foot deformity.1,2

Posterior tibial tendon dysfunction may also occur in the younger athletic population where it usually presents as an acutely symptomatic tenosynovitis.3 Acute ruptures are rare in these patients, and are usually near the navicular insertion.1,3 MRI can also localize tears in unusual locations, such as the rare tear of the distal fibers at the level of the cuneiforms and metatarsal bases (5a).

5
Figure 5:

(5a) An empty, fluid-filled tendon sheath is noted (arrow) in this case of a full-thickness tear of the distal posterior tibial tendon at the level of the cuneiforms.

Dislocation of the posterior tibial tendon is rare, and thought to be traumatic. It is usually associated with a torn flexor retinaculum, which allows the tendon to slip out of the retromalleolar groove. (6a) An avulsion fracture at the medial malleolar attachment of the flexor retinaculum may be seen in such cases.4

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Figure 6:

(6a) Anterior and medial subluxation of the posterior tibial tendon (arrow) is apparent on this T1-weighted axial image.

With chronic rupture of the posterior tibial tendon and failure of the medial longitudinal arch of the foot, increased force is transmitted to other static stabilizers of the arch such as the spring ligament, the ligaments of the sinus tarsi, and the plantar fascia. Abnormalities of all of these structures can be readily seen on MRI and have been demonstrated to occur in association with advanced posterior tibial tendon dysfunction.5,6

Sinus tarsi syndrome is strongly associated with posterior tibial tendon dysfunction and can be an important secondary sign of tendon disease.7 It can also be seen in inflammatory arthropathy, which may or may not co-exist with posterior tibial tendon pathology. Sinus tarsi syndrome is readily detectable on sagittal T1-weighted images when fluid or edema within the sinus tarsi obliterates the normal fat signal intensity surrounding the interosseous and cervical ligaments. (7a)

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Figure 7:

(7a) A sagittal T1-weighted image demonstrates fluid signal intensity filling the sinus tarsi (arrow) in this patient who also had a type I PTT tear at the medial malleolus (not shown).

Abnormalities of the spring ligament have been reported to occur in high association (92%) with advanced posterior tibial tendon injury.5 The spring ligament can be seen on MRI running deep to the posterior tibial tendon, and contiguous with the deltoid ligament superiorly (8a). Preoperative MRI evaluation of the spring ligament is important in surgical planning for patients with PTT tears.

The differential diagnosis of chronic midfoot pain also includes Charcot arthropathy, inflammatory arthropathy, osteochondral lesions/avascular necrosis and stress fracture. MRI readily demonstrates findings to distinguish between these entities.

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Figure 8:

(8a) Thickening and abnormal increased fluid signal intensity within the spring ligament (arrows) consistent with tear is noted in this patient with a proximal PTT tear (not shown).

Conclusion

MRI is useful in evaluating the full range of posterior tibial tendon dysfunction, including tenosynovitis, tendon tears, and pes planus deformity. The ability of MR to judge the extent of disease and associated abnormalities such as spring ligament tears is important in surgical planning.

References

1 Bencardino JT., Rosenberg ZS, Serrnao LF. MR Imaging of Tendon Abnormalities of the Foot and Ankle. MRI Clinics Aug 2001, vol. 9 no. 3 pp 482-486

2 Pomeroy GC, Pike RH, Beals TC, Manoli A. Acquired flatfoot in adults due to dysfunction of the posterior tibial tendon. J Bone Joint Surg Am 1999;81-A:1173 -1182

3 Teitz CC, Garret WE, Miniaci A, Lee MH, Mann RA. Tendon problems in athletic individuals. J Bone Joint Surg Am 1997; 79:138-152.

4 Schweitzer ME, Karasick D MR Imaging of Disorders of the Posterior Tibialis Tendon Am. J. Roentgenol., Sep 2000; 175: 627 – 635.

5 Balen P, Helms C. Association of posterior tibial tendon injury with spring ligament injury, sinus tarsi abnormality, and plantar fasciitis on MRI Imaging. AJR2001; 176:1137 “1143

6 L. R. Toye, C. A. Helms, B. D. Hoffman, M. Easley, and J. A. Nunley MRI of Spring Ligament Tears Am. J. Roentgenol., May 1, 2005; 184(5): 1475 – 1480.

7 Anderson MW, Kaplan PA, Dussault RG, Hurwitz S Association of Posterior Tibial Tendon Abnormalities with Abnormal Signal Intensity in the Sinus Tarsi on MR Imaging Skeletal Radiology, vol 29 no. 9, Sept 2000 pp. 514-519

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