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Published online before print April 28, 2005, 10.1148/radiol.2353040617
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(Radiology 2005;235:977-984.)
© RSNA, 2005

Musculoskeletal Imaging

Anterior Tibial Tendon Abnormalities: MR Imaging Findings1

Bernard Mengiardi, MD, Christian W. A. Pfirrmann, MD, Patrick Vienne, MD, Hans-Peter Kundert, MD, Pascal F. Rippstein, MD, Hans Zollinger, MD, Jürg Hodler, MD, MBA and Marco Zanetti, MD

1 From the Departments of Radiology (B.M., C.W.A.P., J.H., M.Z.) and Orthopedic Surgery (P.V.), Orthopedic University Hospital Balgrist, Forchstrasse 340, CH-8008 Zurich, Switzerland; Foot and Ankle Center at Hirslanden Clinic, Zurich, Switzerland (H.P.K., H.Z.); and Department of Foot and Ankle Surgery, Schulthess Clinic, Zurich, Switzerland (P.F.R.). Received April 4, 2004; revision requested June 16; revision received July 21; accepted August 18. Address correspondence to B.M. (e-mail: mengiardi@yahoo.de).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
PURPOSE: To retrospectively evaluate the magnetic resonance (MR) imaging findings of anterior tibial tendon (ATT) abnormalities.

MATERIALS AND METHODS: Institutional review board approval was not necessary for review of patient images and was granted for examination of the volunteers; informed consent was obtained. MR imaging findings in 28 consecutive patients (20 women, eight men; mean age, 63.2 years) clinically suspected of having an ATT abnormality were compared with those in an age- and sex-matched control group of 28 asymptomatic volunteers (20 women, eight men; mean age, 62.9 years). Surgical correlation was available for 11 patients. The short-axis diameter of the ATT and the longitudinal extent of signal intensity abnormalities were measured (Mann-Whitney U test). Signal intensity abnormalities of the ATT and irregularities of the underlying tarsal bones were analyzed in consensus by two blinded radiologists ({chi}2 test).

RESULTS: In the symptomatic group, three cases of tendinosis and 13 partial and 12 complete ATT tears were diagnosed. In 11 cases (one case of tendinosis and two cases of partial and eight cases of complete ATT tear), surgical correlation was available and the MR imaging diagnosis was confirmed. In the asymptomatic group, four cases of tendinosis of the ATT were seen. The ATT diameter was significantly thicker in symptomatic patients at 1 cm (5.1 vs 3.1 mm in control group, P < .001), 3 cm (5.8 vs 3.4 mm, P < .001), and 6 cm (5.4 vs 4.3 mm, P = .006) proximal to the distal point of insertion. Most ATT abnormalities (in 23 [82%] of 28 patients) were located within the first 3 cm proximal to the insertion. Signal intensity abnormalities were seen in the anterior portion of the ATT in two (7%) of the 28 symptomatic patients and in the posterior portion in 11 (39%); diffuse involvement was seen in 15 (54%). Bone spurs on the navicular surface (nine [32%] patients vs no [0%] control subjects, P = .001), a ridged shape of the medial surface of the medial cuneiform bone (13 [46%] vs one [4%], P < .001), and osteophyte formation at the first tarsometasarsal joint (eight [29%] vs two [7%], P = .036) were significantly more common in the symptomatic patient group.

CONCLUSION: Characteristic findings of ATT abnormalities include tendon thickening (≥5 mm) and diffuse or posterior signal intensity abnormalities of the tendon within 3 cm from the distal point of insertion.

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The anterior tibial tendon (ATT) is usually only exposed to minor mechanical stress owing to its straight course (1). Consequently, abnormalities are less common in this tendon than in other tendons. Nevertheless, hypoxic degenerative tendinosis or mucoid degeneration occurs and may lead to a partial or complete tear of the ATT (2). Most tears occur without a trauma. Patients often present with slight foot drop preceded by a long history of swelling and pain at the dorsomedial aspect of the midfoot. Discontinuity of the ATT and, occasionally, a mass at the anterior part of the ankle are palpable (3). Whereas a complete tear usually can be easily recognized, the clinical diagnosis of tendinosis or partial tear can be challenging.

In the orthopedic literature, only about 50 cases of complete ATT tears have beendescribed (4,5). In the radiology literature, approximately 10 cases have been reported (6–10). In their reports of the largest series, Gallo et al (7) and Khoury et al (8) each described the magnetic resonance (MR) imaging findings in three ATT tears. To our knowledge, no report that describes the spectrum of MR imaging findings of ATT abnormalities in a large series has been published. Thus, the purpose of our study was to retrospectively evaluate the MR imaging findings of ATT abnormalities.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
The institutional review board of Orthopedic University Hospital Balgrist does not require its approval for retrospective review of patient records or images. Before examination, all patients are informed about the possibility that their charts and radiographs may be reviewed for scientific purposes. They may refuse this possible further use of their data. This patient right is protected by law. The institutional review board approved the examination of the control group volunteers in our study, and informed consent was obtained.

Patient Group
Between January 1998 and December 2003, MR imaging of the ankle was performed in 1474 patients at Orthopedic University Hospital Balgrist. In this retrospective study we included 28 consecutive patients (20 women, eight men) for whom all of the following criteria were present: (a) clinical suspicion of an ATT lesion on the basis of pain, tenderness, or swelling in the dorsomedial part of the midfoot or a palpable defect of the ATT; (b) a report of ATT abnormalities at MR imaging; (c) availability of clinical information, including treatment performed (according to a medical chart [n = 12] or a questionnaire filled out by the referring clinician [n = 16]); and (d) no surgery before MR imaging. A total of 34 patients fulfilled the first two criteria, but three patients were excluded owing to missing clinical information. Three additional patients were excluded because they had previously undergone ATT surgery; hence, the symptomatic patient group comprised 28 patients.

Twenty-four patients had been referred by orthopedic foot surgeons (P.V., H.P.K., P.F.R., H.Z.), three had been referred by general orthopedic surgeons, and one had been referred by a rheumatologist. The patients ranged in age from 30 to 82 years (mean age, 63.2 years). The female patients ranged in age from 41 to 82 years (mean age, 64.8 years), and the male patients ranged in age from 30 to 82 years (mean age, 59.3 years). One patient had diabetes mellitus. No patient had systemic inflammatory disease. Only one patient had a history of trauma. The onset of symptoms was acute in four patients. Twenty-four patients had a slow onset of symptoms with a chronic course (mean course, 65 weeks; range, 10–300 weeks). Six patients with a chronic course reported acute pain exacerbation.

Physical examination revealed a palpable ATT defect (n = 9), swelling along the ATT (n = 17), and/or reduced dorsiflexion (n = 15). Indications for MR imaging were as follows: (a) probable complete ATT tear (n = 8), (b) probable other ATT abnormality (n = 12), and (c) possible ATT abnormality (n = 8). For 11 patients who underwent open reconstruction of the ATT, surgical confirmation of MR imaging findings was available. Seventeen patients were treated conservatively. After conservative treatment, 14 patients reported a reduction in their symptoms, and two patients were free of symptoms. In one patient, a complete tear occurred 5 months after the initial presentation, and surgery was performed.

Control Group
The control group consisted of 28 age- and sex-matched asymptomatic volunteers. Criteria for inclusion were as follows: (a) no foot pain, (b) no trauma to the ankle or foot in the previous 2 years, (c) no previous visit to a physician because of foot complaints, (d) no prior foot surgery, and (e) no systemic inflammatory disease. The volunteers ranged in age from 33 to 83 years (mean age, 62.9 years). The 20 female volunteers ranged in age from 45 to 83 years (mean age, 64.3 years), and the eight male volunteers ranged in age from 33 to 83 years (mean age, 59.3 years).

MR Imaging Protocol
MR imaging was performed with a 1.0- or 1.5-T system (Expert or Symphony; Siemens Medical Solutions, Erlangen, Germany). Patients and volunteers were examined in the supine position, with one ankle placed in a neutral position in the extremity coil. T1-weighted spin-echo MR images were obtained in the coronal plane (repetition time msec/echo time msec, 450–722/14–20; section thickness, 3–4 mm; field of view, 16 cm) and in the oblique transverse plane (45° between the coronal and transverse planes) (435–722/14–20; section thickness, 3–4 mm; field of view, 16 cm). T2-weighted fast spin-echo MR images were obtained in the coronal plane (4000/91–96; section thickness, 3–4 mm; field of view, 16 cm) and in the transverse plane (4000/86–96; section thickness, 4 mm; field of view, 15–16 cm). A fast spin-echo short inversion time inversion-recovery sequence (repetition time msec/echo time msec/inversion time msec, 4000–4800/30/150; section thickness, 3–4 mm; field of view, 17–18 cm) was performed in the sagittal plane.

MR Image Analysis
Qualitative evaluation.—MR imaging results were analyzed in consensus by two experienced musculoskeletal radiologists (two staff radiologists with 12 [M.Z.] and 7 years [C.W.A.P.] of experience in musculoskeletal radiology) who were blinded to the diagnosis. The review of the MR imaging examination results for the patients and the volunteers was performed in a randomized fashion. The following qualitative criteria were evaluated: signal intensity abnormalities of the ATT substance (defined as elevated signal intensity compared with the low signal intensity of normal tendon) on T1- and T2-weighted images and the location of signal intensity abnormalities within the cross section of the ATT. In terms of their locations, the signal intensity abnormalities were recorded as being in the anterior or posterior portion of the ATT or as being diffuse. In addition, the presence of a longitudinal split of the ATT prior to its point of insertion was recorded.

The readers were then asked to render one of the following diagnoses for each ATT: (a) a normal ATT, (b) a normal ATT that had signal intensity changes within its substance owing to a magic-angle effect (which was defined as a signal intensity abnormality in the ATT where the tendon was oriented 50°–60° to the main magnetic field that was seen only on T1-weighted images in the absence of circumscribed thinning or thickening of the tendon [11,12]), (c) tendinosis (which was diagnosed when there was a signal intensity change that was predominantly visible on T1-weighted images—a change that was not limited to the magic-angle region and/or was associated with changes in the tendon diameter), (d) a partial tear (which was diagnosed when there were signal intensity abnormalities on both T1- and T2-weighted images, with or without changes in the tendon diameter), or (e) a complete tear (discontinuity of the ATT). As part of evaluating the magic-angle effect, the angle between the main magnetic field B0 and the tendon at the location of the signal intensity changes was measured on sagittal images.

The images were also evaluated for the following associated findings: fluid within the ATT sheath (whether present or absent); edema-like bone marrow abnormalities at the distal point of insertion; dorsal osteophytes at the talonavicular, cuneonavicular, and medial tarsometatarsal joints; and bone spurs on the surface of the navicular bone adjacent to the ATT. In addition, the shape of the medial surface of the medial cuneiform bone was characterized as convex, smooth concave, or ridged.

Measurements.—Measurements were performed by a fellow in musculoskeletal radiology (B.M., with 2 years of experience in musculoskeletal radiology) who used a picture archiving and communication system workstation (Image Devices, Idstein, Germany) and were obtained to the nearest tenth of a millimeter and then rounded to the nearest millimeter (Fig 1).



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  		Figure 1. Diagrams show anatomy of ATT and method of measurement. A, Schematic display of course and insertion of the ATT, as well as the retaining retinacula. Cm = medial cuneiform bone, imIER = inferomedial band of inferior extensor retinaculum, Mt I = first metatarsal bone, SER = superior extensor retinaculum, smIER = superomedial band of inferior extensor retinaculum, trb = transverse retinaculum band, and TS = tendon sheath of ATT. B, In cases of tendinosis or partial tear, (1) the distance between the beginning of the signal intensity abnormalities and the distal point of insertion, (2) the longitudinal extent of the signal intensity abnormalities, (3) the maximal short-axis diameter of the portion of the ATT with signal intensity abnormalities, and (4) the distance between the point of this maximal short-axis diameter and the point of insertion were measured. The joint space of the medial tarsometatarsal joint was defined as the distal point of insertion. C, In cases of complete tear, (5) the distance between the tear and the distal point of insertion and (6) the gap between the tendon stumps were measured. For the measurements in B and C, transverse oblique and sagittal images were used. D, For all ATTs that were not completely torn, (7) the short-axis diameter of the ATT at 1, 3, and 6 cm from the point of insertion was measured on transverse oblique images.

 
The short-axis diameter of the normal, the tendinopathic, and the partially torn ATTs was measured at 1, 3, and 6 cm proximal to the point of insertion on oblique transverse T1-weighted MR images. These measurements were performed without knowledge of the diagnosis. In the tendinopathic, the partially torn, and the completely torn ATTs, the signal intensity abnormalities were measured in terms of their longitudinal extent and distance from the distal point of insertion. In addition, the maximal short-axis diameter of the portion of the tendon with signal intensity abnormalities (Fig 1), the distance between the point of this maximal short-axis diameter and the point of insertion, and the relationship of this point to the underlying tarsal bones were determined. In cases of complete tear, the distance between the point of insertion and the location of the tear, as well as the size of the gap between the tendon stumps, was measured. The ATT has multiple attachment sites; it attaches to the first metatarsal as well as to the medial cuneiform bone. For simplification, the joint space of the medial tarsometatarsal joint was chosen as the site of the distal attachment so that we could perform reproducible measurements.

Statistical Analysis
Surgical reports (available for 11 patients) or results of clinical follow-up examinations at which a diagnosis was confirmed by the clinician were the standard of reference for the diagnosis of an ATT abnormality. These reports and results were reviewed in consensus by an experienced musculoskeletal radiologist (M.Z.) and a fellow in musculoskeletal radiology (B.M.). In cases for which no surgical correlation was available, the criteria used by the clinician for the diagnosis of ATT abnormality were swelling and pain at the insertion point of the ATT, with or without reduced dorsiflexion force, and reduction in the severity of symptoms with conservative treatment. Qualitative criteria were compared by using the {chi}2 test. Continuous data were analyzed with the two-tailed Mann-Whitney U test. Using results for the 16 symptomatic patients with tendinosis or partial tears and the 28 asymptomatic volunteers, we calculated the sensitivity and specificity of MR imaging in the diagnosis of abnormal ATTs for different cutoff values for the short-axis diameter of the tendon as measured within the first 3 cm from the distal point of insertion. Completely torn ATTs were not included in this calculation because in such situations the tendon diameter can no longer be measured. A P value of less than .05 was considered to indicate a statistically significant difference.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Qualitative Evaluation
In the symptomatic patient group (n = 28), three (11%) patients had tendinosis (Fig 2, B), 13 (46%) had partial tears (Fig 2, C), and 12 (43%) had complete tears (Fig 3) of the ATT (Table 1). In 11 cases (39%) (one case of tendinosis and two cases of partial and eight cases of complete ATT tears), surgical correlation was available and the MR imaging diagnosis was confirmed. In one patient in whom a partial tear was seen on MR images (Fig 4a, 4b), acute pain exacerbation associated with increased foot drop occurred abruptly 5 months later. Surgery was then performed, and a complete tear was found (Fig 4c). In the control group (n = 28), MR images of three (11%) ATTs showed a magic-angle effect (the angles between the ATT and the main magnetic field were 52°, 53°, and 58°). In four (14%) volunteers in the control group, tendinosis was diagnosed. A longitudinal split close to the point of insertion was present in five ATTs in the control group and in one ATT in the symptomatic patient group (Fig 5). Signal intensity abnormalities were seen in the anterior portion of the ATT in two (7%) of the symptomatic patients and in the posterior (adjacent to bone) portion of the ATT in 11 (39%) such patients; diffuse involvement was seen in 15 (54%) patients.



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  		Figure 2. Spectrum of appearances of ATT (arrowheads) on MR images. Left: T1-weighted transverse oblique images (435-722/14-20). Middle: T1-weighted coronal images (450-722/14-20). Right: T2-weighted fast spin-echo coronal images (4000/91-96). A, Normal ATT in asymptomatic 53-year-old woman in control group has low signal intensity on T1- and T2-weighted images. B, Images in symptomatic 61-year-old man with tendinosis. Note the signal intensity abnormalities in the posterior portion of the tendon on the T1-weighted images, whereas on the T2-weighted image, normal low signal intensity is present. C, Images in symptomatic 79-year-old woman with partial tear. The predominantly posteriorly located signal intensity abnormalities are seen on the T1- and the T2-weighted images. The ATT is also slightly thickened.

 


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  		Figure 3. Sagittal fast spin-echo short inversion time inversion-recovery MR image (4800/30/150) in symptomatic 76-year-old man with complete ATT tear. The distally torn ATT is retracted and has a thickened stump (arrowheads) at the level of the ankle joint. Fluid (arrow) in the tendon sheath is visible inferiorly.

 

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  		TABLE 1. Results of Qualitative Evaluation of MR Images of ATT in Two Groups

 


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  		Figure 4a. Images in symptomatic 56-year-old woman with an initially partial tear of the ATT that spontaneously became a complete tear 5 months later. On (a) coronal T1-weighted image (450/14) and (b) coronal T2-weighted fast spin-echo image (4000/91) obtained at initial presentation, the ATT is thickened and there are signal intensity abnormalities (arrowheads) located predominantly in the posterior portion of the tendon. (c) Intraoperative photograph obtained 5 months after a and b shows the ATT (white arrows) with a complete tear distally. A gap between the proximal (white arrowheads) and thickened distal (black arrows) stumps is visible.

 


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  		Figure 4b. Images in symptomatic 56-year-old woman with an initially partial tear of the ATT that spontaneously became a complete tear 5 months later. On (a) coronal T1-weighted image (450/14) and (b) coronal T2-weighted fast spin-echo image (4000/91) obtained at initial presentation, the ATT is thickened and there are signal intensity abnormalities (arrowheads) located predominantly in the posterior portion of the tendon. (c) Intraoperative photograph obtained 5 months after a and b shows the ATT (white arrows) with a complete tear distally. A gap between the proximal (white arrowheads) and thickened distal (black arrows) stumps is visible.

 


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  		Figure 4c. Images in symptomatic 56-year-old woman with an initially partial tear of the ATT that spontaneously became a complete tear 5 months later. On (a) coronal T1-weighted image (450/14) and (b) coronal T2-weighted fast spin-echo image (4000/91) obtained at initial presentation, the ATT is thickened and there are signal intensity abnormalities (arrowheads) located predominantly in the posterior portion of the tendon. (c) Intraoperative photograph obtained 5 months after a and b shows the ATT (white arrows) with a complete tear distally. A gap between the proximal (white arrowheads) and thickened distal (black arrows) stumps is visible.

 


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  		Figure 5. Distal split of ATT. Left: Line drawing. Right: Corresponding T1-weighted transverse oblique image (435/14) obtained in asymptomatic 55-year-old man. Drawing and image show a longitudinal split (arrowheads) of the distal portion of the ATT just prior to insertion; this may represent a normal variant in this individual.

 
Associated Findings
Fluid in the ATT sheath was a common finding in the symptomatic group, manifesting in 82% of patients but in only 7% of volunteers (P < .001); 12 of 12 ATTs with a complete tear (Fig 3), nine of 13 ATTs with a partial tear, and two of three ATTs with tendinosis had fluid within the tendon sheath. Edema-like bone marrow abnormalities at the distal point of insertion of the ATT were seen in nine (32%) of the 28 patients in the symptomatic group but in no subjects in the asymptomatic control group (P = .001). None of the three ATTs with tendinosis in the patient group had bone marrow abnormalities at the point of insertion.

Bone spurs with ATT contact on the surface of the navicular bone (32% of patients vs 0% of volunteers, P = .001) (Fig 6) and osteophytes at the medial tarsometatarsal joint (29% of patients vs 7% of volunteers, P = .036) were significantly more frequent in the symptomatic patients than in the control group. There was a significant difference between patients and volunteers in the shape of the medial surface of the medial cuneiform bone (Fig 7): More symptomatic patients had a medial cuneiform bone with a ridged shape (46% of patients vs 4% of volunteers, P < .001) than one with a convex shape, which was more common in asymptomatic subjects (21% of patients vs 61% of volunteers, P = .003). Dorsal osteophytes of the cuneonavicular joint (Fig 6) were more frequent in the symptomatic patients, occurring in 29% of patients and 14% of volunteers, but this difference was not significant (P = .19).



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  		Figure 6a. T1-weighted transverse oblique MR images (435/14) show bone spurs associated with ATT disorders. (a) Image in symptomatic 61-year-old man with severe osteoarthritis of the cuneonavicular joint shows dorsal osteophytes (arrowheads). Just above these osteophytes, the ATT is completely torn (curved arrow) but has an intact distal portion (straight arrows). (b) Image in symptomatic 70-year-old woman with a partial ATT tear, indicated by thickening of and a signal intensity abnormality in the ATT (arrows), shows a large underlying spur (arrowheads) of the navicular bone. The location of pain was marked with a nitroglycerin pellet. Note the posterolateral location of the ATT signal intensity abnormality, which is in close proximity to the spur.

 


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  		Figure 6b. T1-weighted transverse oblique MR images (435/14) show bone spurs associated with ATT disorders. (a) Image in symptomatic 61-year-old man with severe osteoarthritis of the cuneonavicular joint shows dorsal osteophytes (arrowheads). Just above these osteophytes, the ATT is completely torn (curved arrow) but has an intact distal portion (straight arrows). (b) Image in symptomatic 70-year-old woman with a partial ATT tear, indicated by thickening of and a signal intensity abnormality in the ATT (arrows), shows a large underlying spur (arrowheads) of the navicular bone. The location of pain was marked with a nitroglycerin pellet. Note the posterolateral location of the ATT signal intensity abnormality, which is in close proximity to the spur.

 


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  		Figure 7. Line drawings (left) and corresponding T1-weighted transverse oblique MR images (435-722/14-20) (right) show various appearances of medial surface (arrowheads) of medial cuneiform bone (mC): A, a convex shape (in an asymptomatic 52-year-old woman); B, a smooth concave shape (in an asymptomatic 46-year-old man); and, C, a ridged shape (in a symptomatic 64-year-old woman). A partial tear of the ATT (arrows), with thickening and a signal intensity abnormality, is also shown in C.

 
Measurements
The short-axis diameter of the ATT was significantly larger in the symptomatic group than in the control group at 1 cm (5.1 vs 3.1 mm, P < .001), 3 cm (5.8 vs 3.4 mm, P < .001), and 6 cm (5.4 vs 4.3 mm, P = .006) proximal to the point of insertion (Table 2). A short-axis diameter of 5 mm or greater within the first 3 cm proximal to the point of insertion had a sensitivity of 94% and a specificity of 98% for the diagnosis of tendinosis or partial tear of the ATT. Signal intensity abnormalities of the ATT substance began 0–51 mm from the distal point of insertion (mean distance, 8.8 mm) and had a mean longitudinal extent of 42 mm (range, 6–102 mm) (Table 3). In cases of tendinosis (n = 3) or partial tear (n = 13), the maximal short tendon diameter was 4–11 mm (mean, 7.1 mm), and this point of maximal diameter was located 3–76 mm (mean, 23.8 mm) proximal to the point of insertion (Table 3). Complete tears (n = 12) were found within the distal 0–35 mm (mean, 8.8 mm) from the point of insertion, with a gap of 12–77 mm (mean, 48.8 mm) (Table 3).


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  		TABLE 2. Results of Measurement of Short-Axis Diameter of ATTs

 

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  		TABLE 3. Measurements in 28 Symptomatic Patients with ATT Lesions

 
ATT abnormalities were most commonly found within the distal 3 cm of the ATT (in 23 [82%] of the 28 symptomatic patients). Nine (32%) of the 28 ATT lesions in the symptomatic group were located at the level of the cuneonavicular joint, and 14 (50%) were located at the level of the medial cuneiform bone.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
REFERENCES
 
There are two different clinical manifestations of ATT tears. The more common manifestation is that when a patient between the ages of 60 and 70 years reports the development of chronic symptoms (3) that accompany a swelling at the dorsomedial aspect of the midfoot, possibly in combination with an acute exacerbation of pain (13). Acute ATT tears are uncommon, occur at any age, and are the result of massive trauma associated with fractures or soft-tissue lacerations. According to the literature, ATT tears in general are more commonly seen in men than in women (7,14). Although the age distribution of our study population was in accordance with that in other studies, we observed a female predominance of 71%. A spontaneous tear of the ATT occurs mainly in the presence of hypoxic or mucoid degeneration (2). In cases of tendinosis or partial tear, the patient experiences pain and swelling along the distal part of the ATT that become worse during dorsiflexion of the foot. Although a complete tear of the ATT is usually diagnosed clinically, compensation by the extensor hallucis longus and extensor digitorum longus muscles for the loss of function may confuse the issue, and the diagnosis of an ATT tear may be missed (15). Late diagnosis may hamper primary surgical repair (13).

The anterior tibial muscle originates from the lateral tibial condyle and from the proximal half to proximal two-thirds of the tibia. The musculotendinous junction is located at the middle third of the tibia. The superior extensor retinaculum above the ankle retains the ATT. The tendon crosses the anteromedial aspect of the ankle and runs toward the medial border of the foot. It inserts at a tubercle on the anteromedial aspect of the medial cuneiform bone and on the inferomedial aspect of the base of the first metatarsal bone. The tendon is retained close to the talar head by the superomedial band and close to the medial cuneiform bone by the inferomedial band of the inferior extensor retinaculum, as well as by the transverse retinaculum band (16). In 84%–96% of individuals, the tendon inserts on both the medial cuneiform bone and first metatarsal bone, with a division just prior to insertion (16–18). In our series, a longitudinal split of the distal part of the ATT was visible in five asymptomatic volunteers in the control group and in one patient who had a partial tear. Although Khoury et al (8) reported a case of longitudinal tear in the midportion of the ATT with surgical correlation, a longitudinal split of the distal portion of the ATT may represent a normal variant.

At the ankle joint, the cross section of the ATT is round or oval and becomes flat distally. Our study results revealed that, within 3 cm of the distal point of insertion, an ATT thickness of 5 mm or less should be considered normal. This threshold value had a sensitivity of 94% and a specificity of 98% for the differentiation of normal ATTs from those with tendinosis or partial tears. In cases in which there is a normal diameter and signal intensity abnormalities are seen only on T1-weighted images, diagnosis of a clinically relevant ATT lesion should be made with caution. Signal intensity abnormalities may be caused by a magic-angle effect, as seen in three ATTs in the control group. Also, four volunteers in the control group had MR imaging signs of tendinosis but no clinical symptoms.

According to the orthopedic literature, ATT tears are typically located within 5–30 mm from the point of insertion (19–22). This is consistent with the data in our population, in which all ATT tears occurred within 35 mm of the distal point of insertion. In addition, signal intensity abnormalities associated with tendinosis and partial tears began a mean of 8.8 mm from the insertion point, and maximal tendon thickening was observed a mean of 23.8 mm from the insertion point. In terms of their relationship to the tarsal bones, 82% of all ATT abnormalities were found at the level of the cuneonavicular joint and the medial cuneiform bone. At this location, the ATT is slightly bent over the tarsal bones and retained by the supero- and inferomedial bands of the inferior extensor retinaculum and the transverse retinaculum band.

The etiology of ATT tears is still being debated. Although some investigators have reported homogeneous vascularity throughout the ATT (21), others consider an anterior area of hypovascularity in the ATT in the region of the retinacula to be a possible cause of ATT disorders. Petersen et al (23) have reported the presence of an avascular zone in the anterior half of the ATT that begins 5–16 mm from the insertion point and extends 45–67 mm. Our data do not support this theory: The signal intensity abnormalities in our study were most commonly found either in the posterior portion (39%) of the tendon—close to the bone—or in a diffuse distribution (54%); they were found in the anterior portion of the ATT in only 7% of cases. The significant association of bone morphologic features (P = .001 for a bone spur on the navicular surface, P < .001 for a ridged shape of the medial cuneiform bone, and P = .036 for osteophytes at the medial tarsometatarsal joint) with ATT abnormalities indicates that a mechanical irritation of the ATT by bone structures may be pathogenetically relevant.

Markarian et al (13) recommend surgical reconstruction of ATT tears in younger active patients, whereas nonsurgical forms of management like bracing or ankle-foot orthosis are appropriate treatments in less active elderly patients. In cases of partial tear, surgical management must also be considered.

The fact that surgical correlation was available for only 11 of our 28 patients represents an important study limitation. However, this ratio between surgically and conservatively treated patients corresponds to clinical experiences with ATT tears. Our use of reported MR imaging abnormalities of the ATT as an inclusion criterion introduced a selection bias because subtle ATT abnormalities may therefore have been underrepresented in our investigation. Owing to the retrospective design of this study, there may have been an influence of the MR imaging interpretations on the clinical diagnosis; this can be another source of bias. However, initial clinical findings and follow-up examination results that revealed a reduction in symptoms after conservative treatment represented an independent source of information for the final diagnosis.

In conclusion, characteristic findings of ATT abnormalities include tendon thickening (≥5 mm) and diffuse or posterior signal intensity abnormalities of the tendon within 3 cm from the distal point of insertion. The significant association between irregularities of the underlying tarsal bones and ATT lesions may indicate that mechanical irritation is a pathogenetic factor in ATT lesions.


   FOOTNOTES
 
Abbreviation: ATT = anterior tibial tendon

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, B.M., M.Z.; study concepts and design, B.M., M.Z., J.H., C.W.A.P.; literature research, B.M.; clinical studies, P.F.R., H.P.K., H.Z., P.V.; data acquisition, B.M., M.Z., C.W.A.P., P.F.R., H.P.K., H.Z., P.V.; data analysis/interpretation, B.M., M.Z., C.W.A.P.; statistical analysis, B.M., C.W.A.P.; manuscript preparation, B.M., M.Z., C.W.A.P., J.H., P.V.; manuscript definition of intellectual content, B.M., M.Z., C.W.A.P., P.F.R.; manuscript editing, B.M.; manuscript revision/review, M.Z., C.W.A.P., J.H., P.F.R., H.P.K., H.Z., P.V.; manuscript final version approval, B.M., M.Z., J.H.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
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