DOI: 10.1148/rg.226025034
(Radiographics. 2002;22:1457-1469.)
© RSNA, 2002
Soft-Tissue and Osseous Impingement Syndromes of the Ankle: Role of Imaging in Diagnosis and Management1
Philip Robinson, FRCR and
Lawrence M. White, MD
1 From the Department of Radiology, St James University Hospital, Beckett St, Leeds LS9 7TF, England (P.R.); and the Department of Medical Imaging, Mount Sinai Hospital and the University Health Network, University of Toronto, Ontario, Canada (L.M.W.). Recipient of a Certificate of Merit award for an education exhibit at the 2001 RSNA scientific assembly. Received February 22, 2002; revision requested March 18 and received April 15; accepted April 18. Address correspondence to P.R. (e-mail: philrob66@hotmail.com).
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Abstract
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Soft-tissue and osseous impingement syndromes of the ankle can be an important cause of chronic pain, particularly in the professional athlete. The main impingement syndromes are anterolateral, anterior, anteromedial, and posterior impingement. These conditions arise from initial ankle injuries, which, in the subacute or chronic situation, lead to development of abnormal osseous and soft-tissue thickening within the ankle joint. The relative contributions of the osseous and soft-tissue abnormalities are variable, but whatever component is dominant there is physical impingement and painful limitation of ankle movement. Conventional radiography is usually the first imaging technique performed and allows assessment of any potential bone abnormality, particularly in anterior and posterior impingement. Computed tomography (CT) and isotope bone scanning have been largely superseded by magnetic resonance (MR) imaging, but the accuracy and role of MR imaging in assessment of possible ankle impingement have not been clearly established. MR imaging can demonstrate osseous and soft-tissue edema in anterior or posterior impingement. Studies of conventional MR imaging have produced conflicting sensitivities and specificities in assessment of anterolateral impingement. CT and MR arthrographic techniques allow the most accurate assessment of the capsular recesses, albeit with important limitations in diagnosis of clinical impingement syndromes.
© RSNA, 2002
Index Terms: Ankle, abnormalities, 463.486 • Ankle, injuries, 463.486 • Ankle, MR, 463.12141 • Athletic injuries, 463.486
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Describe the pathologic process and mechanism of impingement for each syndrome.
- List the potential imaging techniques and subsequent findings when identifying soft-tissue or osseous abnormalities for each syndrome.
- Discuss the clinical relevance of imaging in each impingement syndrome.
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Introduction
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Chronic ankle pain is a common clinical problem with a wide differential diagnosis. Soft-tissue and osseous impingement syndromes are now increasingly recognized as a significant cause of chronic ankle pain (1–5). Although comparatively rare, these conditions are important to recognize because they can result in chronic ankle pain and significant morbidity, especially in the professional athlete and younger population (1–5).
Impingement syndromes have been well described in the anterolateral, anterior, and posterior ankle (1–4), with more recent orthopedic and radiologic studies describing the less well-recognized entities of anteromedial and posteromedial impingement (5,6). Symptoms for all of these conditions relate to physical impingement of osseous or soft tissue, resulting in painful limitation of the full range of ankle movement.
In this article, we describe the clinical and potential imaging features, as well as the clinical management strategies, for the four main impingement syndromes of the ankle: anterolateral, anterior, anteromedial, and posterior impingement.
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Anterolateral Impingement
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Anterolateral impingement has been the subject of a significant number of surgical and radiologic studies (1,2,7–13).
Anatomy and Causes
The anterolateral recess of the ankle is bounded posteromedially and laterally by the tibia and fibula, respectively. Anteriorly and laterally, it is limited by the capsule of the tibiotalar joint as well as the anterior tibiofibular, anterior talofibular, and calcaneofibular ligaments (Figs 1, 2) (1). Anterolateral impingement of the ankle is thought to occur subsequent to relatively minor trauma involving forced ankle plantar flexion and supination. Such an injury may result in tearing of the anterolateral capsular tissues and ligaments without significant clinical mechanical instability (1,14). Repeated microtrauma and soft-tissue hemorrhage can result in synovial scarring, inflammation, and hypertrophy in the anterolateral recess of the tibiotalar joint with subsequent soft-tissue impingement (1,2,7,8,14). Other contributing factors are thought to include hypertrophy of the inferior portion of the anterior tibiofibular ligament and occasionally osseous spurs (1,2,7,8). However, these latter two factors are rarely the predominant features (9).
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Figure 1. Drawing of the anterolateral ligaments of the ankle. Note the interval between the anterior tibiofibular ligament (small arrow) and anterior talofibular ligament (large arrows).
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Figure 2a. Normal anterolateral recess. Axial proton-density-weighted (a) and coronal T1-weighted fat-suppressed (b) magnetic resonance (MR) arthrograms show a smooth contour of the anterolateral capsular tissues (white arrows) and a normal anterior talofibular ligament (black arrow).
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Figure 2b. Normal anterolateral recess. Axial proton-density-weighted (a) and coronal T1-weighted fat-suppressed (b) magnetic resonance (MR) arthrograms show a smooth contour of the anterolateral capsular tissues (white arrows) and a normal anterior talofibular ligament (black arrow).
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Clinical Features
Anterolateral impingement of the ankle largely remains a clinical diagnosis of exclusion, with the pathologic condition confirmed at arthroscopy (8). Symptoms consist of focal anterolateral pain aggravated by supinating or pronating the foot. Retrospective surgical series have identified anterolateral tenderness, swelling, pain on single-leg squatting, and pain on ankle dorsiflexion and eversion as the clinical findings most strongly associated with abnormality at arthroscopy (7,8). These features together with the absence of mechanical instability and tendon subluxation suggest the diagnosis (7).
Imaging Features
Conventional radiography is performed in the setting of subacute or chronic anterolateral ankle pain to assess for evidence of a possible previous fracture and subsequent complication (eg, joint degeneration) (1). The role of cross-sectional imaging (especially MR imaging) in diagnosis and management of anterolateral impingement is more controversial (1,2,7–13).
Studies (surgical and radiologic) that investigated the value of conventional (nonarthrographic) MR imaging have reported conflicting results in the assessment of patients with anterolateral impingement preoperatively (8,10–12). Sensitivity (39%–100%) and specificity (50%–100%) for detection of anterolateral soft-tissue abnormality varied widely (8,11,12). One study found MR imaging assessment of the anterolateral recess to be accurate only in the setting of a significant joint effusion (10). A study of computed tomographic (CT) arthrography found a strong association between the appearances of the anterolateral recess at coronal imaging and surgical findings (13).
A major limitation of many imaging and surgical studies of anterolateral impingement has been the retrospective nature of the investigations with resultant study selection bias (8,10–12). A recent prospective study of MR arthrography in assessment of the anterolateral recess of the ankle showed that the findings of an irregular or nodular contour of the anterolateral soft tissues correlated with anterolateral scarring or synovitis of the ankle joint recess at arthroscopy (sensitivity of 100%, specificity of 100%) (Fig 3) (9). Soft-tissue thickening had intermediate to low signal intensity on all sequences and was most easily assessed on axial images between the anterior tibiofibular and talofibular ligaments (Figs 3, 4) (9). A smooth contour to the recess with or without associated thickening of the inferior anterior tibiofibular ligament correlated with negative arthroscopic findings for anterolateral recess scarring (Fig 2). This study also showed that a substantial number of patients without clinical symptoms or signs of anterolateral ankle impingement (11 of 19) had anterolateral recess abnormalities at MR arthrography, which were confirmed at surgery (9). Therefore, identification of abnormal soft tissue in the anterolateral recess of the ankle does not by itself imply the presence of anterolateral impingement clinically. Other abnormalities detected in the clinical impingement group included chondral defects, osseous spurs, and laxity or rupture of the anterior talofibular ligament. These concomitant findings are not surprising considering that the mechanism of injury implicated in the development of anterolateral impingement of the ankle may also result in cartilage and ligament damage.
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Figure 3. Clinical anterolateral impingement. Axial T1-weighted fat-suppressed MR arthrogram shows a diffuse nodular contour (white arrows) of the anterolateral capsule with synechiae (black arrow).
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Figure 4a. (a) Axial T1-weighted fat-suppressed MR arthrogram shows thickening of the anterolateral capsule (arrow). Despite arthrographic distention, no fluid is seen between the fibula (F) and the irregular capsule. (b) Corresponding arthroscopic image shows the talus (T) with scarring and synovitis (S) of the anterolateral gutter. (Reprinted, with permission, from reference 9.)
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Figure 4b. (a) Axial T1-weighted fat-suppressed MR arthrogram shows thickening of the anterolateral capsule (arrow). Despite arthrographic distention, no fluid is seen between the fibula (F) and the irregular capsule. (b) Corresponding arthroscopic image shows the talus (T) with scarring and synovitis (S) of the anterolateral gutter. (Reprinted, with permission, from reference 9.)
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Another finding in this study was that absence of the recess between the anterolateral soft tissues and the anterior surface of the fibula despite adequate distention of the ankle joint space was always associated with scarring or synovitis at MR arthrography and arthroscopy (Fig 4) (9). This feature was significantly more common in patients with clinical anterolateral impingement but again was not fully sensitive or specific (9). It is suggested that this may occur because adhesions and scar tissue prevent fluid from entering the normal recess between the fibula and joint capsule (Fig 4).
Management
Most patients with anterolateral impingement respond to rehabilitative physiotherapy; however, if this is unsuccessful, surgical treatment may be of benefit (1,7–9,14,15). Orthopedic studies have shown that when synovitis and scarring are débrided in this patient group, there is a considerable improvement in symptoms and ankle function (1,7,14,16).
If MR imaging is to play a role, it should be reserved for cases where there is some clinical uncertainty regarding the diagnosis. A normal MR arthrogram seems to exclude anterolateral synovial scarring (9). In patients with definite clinical impingement, MR arthrography may be of value in determining the extent of soft-tissue abnormality present and detecting any coexisting pathologic condition prior to surgery (16–18).
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Anterior Impingement
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Anatomy and Causes
Anterior ankle impingement is a well-established cause of chronic ankle pain (19,20). Although there have been relatively few radiologic studies of anterior ankle impingement, a number of surgical studies have made a more extensive assessment of overall outcome after treatment (3,21–23).
The condition is characterized by anterior tibiotalar spurs, which were originally thought to be due to chronic traction on the anterior capsule. Spur is the preferred term for these bony outgrowths in the surgery literature, as the term osteophyte is thought to imply conventional osteoarthritis (3,21). However, these spurs are essentially osteophytes forming at a focal area of premature degeneration within the joint (see discussion later in this article) (3,21–23). Surgical research has shown that the spurs have typical positions on the anterior tibia and talus (Figs 5, 6) and are actually within the joint capsule, most commonly at the margin of the articular cartilage rim (3,21).
It is well recognized that supination injuries can cause damage at the anterior and medial margins of the articular cartilage (3,24). It is thought that the cartilage damage repairs with scar tissue and proliferative fibrosis with eventual formation of spurs (3,21).
Damage of the anterior articular cartilage rim also occurs during forced dorsiflexion injuries and with repeated direct microtrauma (21). Dorsiflexion injuries can occur in any athlete but are especially common in ballet and soccer (21,25). Direct trauma from ball kicking is also common in soccer, with analysis of the typical striking action showing a considerable proportion of ball impact over the anterior tibiotalar joint. At this point, there is only subcutaneous fat covering the anterior articular cartilage rim (26,27). Given that all three of the mechanisms described are common occurrences in soccer, it is not surprising that this condition is extremely prevalent among professional soccer players (Fig 7) (19,21,26,27).
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Figure 7. Clinical anterior impingement in a male professional soccer player. Sagittal T2-weighted fat-suppressed MR arthrogram shows anterior tibial and talar spurs (solid arrows) with thickening of the anterior capsule (open arrow).
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However, one survey found that a significant proportion of professional athletes (45%–59%) had anterior tibiotalar spurs at conventional radiography, yet none were symptomatic for anterior impingement (28). It is thought that the associated anterior synovial thickening and scarring, rather than the spurs alone, are critical for producing the clinical syndrome (Fig 7) (21,28).
Clinical Features
The typical clinical symptoms of anterior ankle impingement are pain with a subjective feeling of blocking on dorsiflexion. At examination, there is restricted and painful dorsiflexion and occasionally palpable soft-tissue swelling (21).
A clinical grading system has been designed that depends on the severity of the clinical findings and the size of the spurs at conventional radiography (3). However, studies have shown that despite the clinical grade, overall outcome is more dependent on the degree of degenerative change (cartilage damage, subchondral changes) present in the rest of the tibiotalar joint at the onset of treatment (see later discussion) (21).
Imaging Features
Conventional radiography is the only imaging study necessary in most cases, allowing evaluation of osseous spurs and the tibiotalar joint space (3,23). The tibiotalar spurs occur in the typical positions identified in surgical series (Figs 5, 6) (3). One recent article reported a series of cases where the talar spurs occurred on the medial aspect of the tibiotalar joint and the tibial spurs occurred on the lateral aspect, although such localization may be difficult on radiographs (29).
Isotope bone scanning or CT is rarely necessary (21). To our knowledge, no data on the sensitivity and specificity of MR imaging in this condition have been published, presumably because it is not usually performed. In our practice, we find that conventional MR imaging allows assessment of bony detail and soft-tissue abnormality and also gives information regarding any associated internal derangement. This can be important for management planning prior to arthroscopy.
MR imaging shows the position of the tibiotalar spurs within the capsular margin, although the associated finding of bone marrow edema is uncommon (Fig 7). Synovial thickening usually has low signal intensity on T1-weighted images and low to intermediate signal intensity on T2-weighted images, with an irregular contour or stranding evident if an effusion is present (Fig 7).
Management
Most patients with anterior impingement of the ankle respond to rehabilitative physiotherapy (3,21–23), but in resistant cases surgery has been shown to have a long-term benefit (21). In athletes with symptomatic anterior ankle impingement, arthroscopic resection of the osseous spurs and soft-tissue abnormality with washout of the joint has been shown to yield excellent functional and symptomatic results (21,30). The overall prognosis after surgery has been shown to depend on the degree of degenerative change evident in the rest of the tibiotalar joint at the time of treatment (21). In the largest surgical series of anterior ankle impingement reported to date, patients with a normal joint space or minimal degeneration at radiography had excellent function 6.5 years after surgery (100% and 77%, respectively) (21).
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Anteromedial Impingement
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Anatomy and Causes
The clinical entity of anteromedial ankle impingement is becoming increasingly recognized in the orthopedics literature (5,31). An initial case report described a patient with an anteromedial "meniscoid" lesion at surgery, which caused impingement (31). The original mechanism of injury was not documented, but it was hypothesized to be a pronation (eversion) injury that caused a partial tibiotalar ligament tear.
In reality, the exact mechanism responsible for anteromedial impingement is not fully understood (5). Orthopedic and radiologic studies have found that most patients with anteromedial impingement of the ankle had initially experienced a supination (inversion) injury. Therefore, this condition is probably a rare complication of supination injury with perhaps a rotational component, which leads to tearing of the anteromedial capsule (5,32). As with anterolateral impingement, it is thought that subsequent repeated microtrauma produces synovitis and capsular thickening. In addition, bony injury and cartilage damage may result in anteromedial spurs with associated capsular and synovial thickening.
The largest surgical series to date retrospectively evaluated 11 cases of clinical anteromedial impingement (5). Surgical evaluation showed anteromedial capsular thickening in all 11 cases, anteromedial spurs in two cases, and thickening of the anterior fibers of the deltoid ligament and a medial osteochondral defect of the talus in six cases. Associated lateral ligament and capsular synovitis required débridement in five cases (5). If a supination (inversion) injury is the underlying mechanism of injury in anteromedial ankle impingement, it is probably not surprising that lateral capsular abnormalities and medial osteochondral defects can also occur concurrently.
Clinical Features
In the clinical and radiologic series, patients had chronic focal anteromedial pain that was exacerbated on dorsiflexion. Clinical examination showed anteromedial tenderness and limitation of dorsiflexion and inversion (5,32).
Imaging Features
This condition is sufficiently uncommon that there are no large studies of imaging appearances, to our knowledge. In the surgery literature, MR imaging was performed in only two cases and the results were described as "inconclusive" (5). A radiologic study recently reported the MR arthrographic findings in two surgically confirmed cases of anteromedial impingement. Both cases showed marked focal capsular and synovial thickening in the anteromedial tibiotalar joint anterior to the tibiotalar ligament (Fig 8) (32). Soft-tissue thickening had intermediate to low signal intensity on T2-weighted images with no edema present (Fig 8) (32). One patient had anteromedial tibiotalar bone spurs in addition to the focal anteromedial synovitis (Fig 9). Neither case showed additional significant disease in the remainder of the joint at MR arthrography or subsequent arthroscopic surgery (32).
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Figure 8a. Clinical anteromedial impingement in a male kickboxer. Axial T1-weighted fat-suppressed (a) and sagittal T2-weighted fat-suppressed (b) MR arthrograms show focal thickening of the anteromedial capsule (arrows).
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Figure 8b. Clinical anteromedial impingement in a male kickboxer. Axial T1-weighted fat-suppressed (a) and sagittal T2-weighted fat-suppressed (b) MR arthrograms show focal thickening of the anteromedial capsule (arrows).
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Figure 9. Clinical anteromedial impingement in a female hockey player. Sagittal T1-weighted fat-suppressed MR image shows anteromedial tibiotalar osteophytes (arrows). (Reprinted, with permission, from reference 32.)
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Management
The orthopedic and radiologic studies of anteromedial impingement have described good symptomatic and functional results after arthroscopic resection of the synovitis and any associated bony abnormality (5,32).
Although this condition is relatively rare, it seems that it may commonly occur in combination with other pathologic conditions in the ankle (5). If there is clinical concern regarding the underlying abnormality present, MR arthrography may be particularly valuable to define possible capsular abnormalities and also assess the remainder of the osseous and soft-tissue components in the joint and surrounding tissues of the ankle (17,18,32).
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Posterior Impingement
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Anatomy and Causes
Posterior impingement has been described under a variety of different names, including os trigonum syndrome and posterior tibiotalar compression syndrome (33). The condition arises from compression of the soft tissues between the posterior process of the calcaneus and the posterior tibia on plantar flexion of the ankle (Figs 10, 11) (4,33,34). The lateral posterior process of the talus is also important because if this is prominent or if an os trigonum is present, additional bony impingement with these structures can occur (Figs 12–14) (4,33).
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Figure 11a. Normal posterior ligaments. (a, b) Axial proton-density-weighted MR arthrograms (b obtained superior to a) show a normal posterior talofibular ligament and lateral talar process (P in a) and a normal intermalleolar ligament (arrow in b). (c) Coronal T1-weighted fat-suppressed MR arthrogram shows normal posterior talofibular (curved arrow) and intermalleolar (straight arrows) ligaments.
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Figure 11b. Normal posterior ligaments. (a, b) Axial proton-density-weighted MR arthrograms (b obtained superior to a) show a normal posterior talofibular ligament and lateral talar process (P in a) and a normal intermalleolar ligament (arrow in b). (c) Coronal T1-weighted fat-suppressed MR arthrogram shows normal posterior talofibular (curved arrow) and intermalleolar (straight arrows) ligaments.
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Figure 11c. Normal posterior ligaments. (a, b) Axial proton-density-weighted MR arthrograms (b obtained superior to a) show a normal posterior talofibular ligament and lateral talar process (P in a) and a normal intermalleolar ligament (arrow in b). (c) Coronal T1-weighted fat-suppressed MR arthrogram shows normal posterior talofibular (curved arrow) and intermalleolar (straight arrows) ligaments.
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Figure 12a. Clinical posterior impingement in a professional ballet dancer. (a) Lateral radiograph shows a prominent lateral talar process (arrow). (b) Sagittal T1-weighted MR image shows focal thickening of the posterior capsule (arrow) but normal bone marrow signal intensity in the lateral process. (c) Longitudinal ultrasonographic (US) image shows focal thickening of the posterior capsule (*) adjacent to the posterior talus (T). Palliative injection was performed under US guidance.
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Figure 12b. Clinical posterior impingement in a professional ballet dancer. (a) Lateral radiograph shows a prominent lateral talar process (arrow). (b) Sagittal T1-weighted MR image shows focal thickening of the posterior capsule (arrow) but normal bone marrow signal intensity in the lateral process. (c) Longitudinal ultrasonographic (US) image shows focal thickening of the posterior capsule (*) adjacent to the posterior talus (T). Palliative injection was performed under US guidance.
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Figure 12c. Clinical posterior impingement in a professional ballet dancer. (a) Lateral radiograph shows a prominent lateral talar process (arrow). (b) Sagittal T1-weighted MR image shows focal thickening of the posterior capsule (arrow) but normal bone marrow signal intensity in the lateral process. (c) Longitudinal ultrasonographic (US) image shows focal thickening of the posterior capsule (*) adjacent to the posterior talus (T). Palliative injection was performed under US guidance.
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Figure 14a. Posterior impingement in a professional soccer player. (a) Control radiograph shows an os trigonum (arrow). (b) Postinjection image shows free flow of iodinated contrast material around the os trigonum, confirming disruption of the synchondrosis.
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Figure 14b. Posterior impingement in a professional soccer player. (a) Control radiograph shows an os trigonum (arrow). (b) Postinjection image shows free flow of iodinated contrast material around the os trigonum, confirming disruption of the synchondrosis.
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A secondary ossification center forms at the posterolateral aspect of the talus between the ages of 7 and 13 years and usually fuses within 1 year (33). If this forms a large lateral talar process, it is called a Stieda process (Fig 12) (35). If there is failure of fusion, an os trigonum is formed, which articulates with the talus via a synchondrosis (frequency, 7%–14%) (Figs 13, 14) (33,36,37).
The capsular soft tissues involved in the setting of posterior ankle impingement include the posterior capsule and the posterior talofibular, intermalleolar, and tibiofibular ligaments (Figs 10, 11). The flexor hallucis longus tendon runs in the groove between the lateral and medial processes of the talus (Fig 11) and can also be injured in posterior impingement, resulting in stenosing tenosynovitis (4,33).
The syndrome can develop after a significant acute injury such as avulsion of the posterior talofibular ligament, talar fracture, or disruption of an os trigonum (4,33). However, this is relatively rare and the syndrome usually arises insidiously in predisposed athletes. It is believed that repetitive forced plantar flexion of the foot results in chronic injury to the posterior osseous and soft tissues (4). Ballet dancers are especially prone to this injury, as the ankle is commonly at the extremes of its full range of movement (see the section on anterior impingement) and is maintained in these positions for relatively prolonged periods (Fig 12) (4,38,39). Professional soccer players are also at increased risk because ball kicking leads to repeated sudden forced plantar flexion (Fig 15) (4).
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Figure 15a. Clinical posterior impingement in a professional soccer player. (a) Axial T1-weighted MR image shows focal capsular thickening (*) that involves and displaces the intermalleolar ligament (arrow). (b) Axial T1-weighted fat-suppressed MR image obtained after intravenous administration of gadolinium contrast material shows enhancement of the area of synovitis. (c) Longitudinal US image shows capsular thickening (arrow) at the inferior margin of the tibia (T). Palliative injection was performed under US guidance.
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Figure 15b. Clinical posterior impingement in a professional soccer player. (a) Axial T1-weighted MR image shows focal capsular thickening (*) that involves and displaces the intermalleolar ligament (arrow). (b) Axial T1-weighted fat-suppressed MR image obtained after intravenous administration of gadolinium contrast material shows enhancement of the area of synovitis. (c) Longitudinal US image shows capsular thickening (arrow) at the inferior margin of the tibia (T). Palliative injection was performed under US guidance.
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Figure 15c. Clinical posterior impingement in a professional soccer player. (a) Axial T1-weighted MR image shows focal capsular thickening (*) that involves and displaces the intermalleolar ligament (arrow). (b) Axial T1-weighted fat-suppressed MR image obtained after intravenous administration of gadolinium contrast material shows enhancement of the area of synovitis. (c) Longitudinal US image shows capsular thickening (arrow) at the inferior margin of the tibia (T). Palliative injection was performed under US guidance.
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It is thought that the syndrome usually manifests clinically when a significant soft-tissue component forms (4). The soft-tissue component can consist of synovial thickening throughout the posterior capsule or be more focal, involving the posterior intermalleolar or talofibular ligament (Fig 15) (40,41). A stress fracture of the talar process or os trigonum can also precipitate presentation. Acute injuries elsewhere in the ankle are also significant as they can cause instability in the posterior ankle, which again can precipitate symptoms (4). This is not uncommon in soccer, where tackling can result in relatively minor injuries to the anterolateral ligaments with subsequent presentation of posterior symptoms (4).
Clinical Features
Clinical symptoms in posterior ankle impingement usually consist of posterior ankle pain exacerbated by plantar flexion or dorsiflexion. Clinical examination shows posterior tenderness anterior to and not involving the Achilles tendon (4,38,39). Again, this tenderness is exacerbated by plantar flexion or dorsiflexion (ie, compressing or distracting the injured tissues). Occasionally, there is palpable soft-tissue thickening (4).
Imaging Features
Conventional radiographs may show a prominent lateral talar (Stieda) process or os trigonum, but further evaluation is required to confirm if these are in fact the source of associated symptoms (Fig 12) (4). CT can demonstrate the bony anatomy of the posterior talus and may show a fracture not evident on conventional radiographs (4,33,34). Isotope bone scans have been used in the past with the view that a symptomatic os trigonum will show increased activity, whereas a negative scan excludes this diagnosis (4,33).
However, both of these techniques have been largely superseded by conventional MR imaging (33,34). Bony abnormality manifests as bone marrow edema (Fig 13), a fracture line, or fluid in the synchondrosis (indicating os trigonum fracture) (33,34,42,43). In addition, MR imaging may demonstrate posterior capsular or ligament thickening with intermediate to low signal intensity on T2-weighted images (Figs 12, 15) (34). The integrity of the ligaments can also be assessed (Fig 11) (18,19). We have found that increased signal intensity due to enhancement after intravenous administration of gadolinium contrast material can highlight small focal areas of synovitis around the posterior ligaments (Fig 15). MR imaging can also demonstrate possible associated flexor hallucis longus abnormality or other internal derangement, which can alter any planned surgical approach.
In addition, MR imaging can highlight areas of disease that may benefit from targeted therapy. Imaging-guided injection of a local anesthetic and steroid can confirm the diagnosis and also give palliative pain relief (44,45). Disruption of the os trigonum synchondrosis can be difficult to define on conventional MR images. In this situation, fluoroscopically guided arthrography of the synchondrosis will help define its integrity and also allow therapeutic intervention (Fig 14) (45). In the remaining cases with focal soft-tissue abnormality, ultrasound is a useful technique for accurate real-time guidance of therapeutic injection (Figs 12, 15).
Management
Most cases of posterior impingement of the ankle respond to conservative treatment (physiotherapy) (4). Imaging-guided injection of a steroid or local anesthetic into the area of focal capsular thickening or the os trigonum synchondrosis may provide diagnostic information regarding the origin of the pain (44,45). Such therapy also allows palliative relief in the professional athlete or performer until surgery can be planned.
A number of surgical studies have shown that arthroscopic resection of soft-tissue thickening and any associated bony abnormality with joint washout produces good symptomatic and functional results in resistant cases (4,38,39).
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Conclusions
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Impingement syndromes of the ankle are usually a clinical diagnosis, and complex radiologic evaluation is not always necessary. Conventional radiography plays an important role in the initial assessment of these conditions and may be sufficient as the only imaging study performed, depending on the degree of confidence in the clinical diagnosis. This is especially true in anterior impingement, where conventional radiographs have also been shown to provide prognostic information (21,22).
MR imaging is probably most useful in posterior impingement, where it can identify the relative contributions of the osseous and soft-tissue components. Arthrographic cross-sectional imaging studies (CT or MR arthrography) seem to be the most accurate means of assessing the capsular abnormalities present in anterolateral and anteromedial impingement and for the confirmation of possible concomitant injury.
Although researchers have tried to investigate these conditions in isolation, the precipitating mechanism of injury involved with all of these conditions implies an associated risk of additional concomitant joint abnormalities (eg, cartilage defects, ligament disruption) (5,9). Because of this clinical overlap, MR imaging may be of particular value in assessment of the possible soft-tissue and osseous abnormalities implicated in a particular clinical setting of ankle impingement as well as providing an assessment of the whole joint prior to treatment.
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Footnotes
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See the commentary by Rosenberg
following this article.
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References
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