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DOI: 10.1148/radiol.2362040835
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(Radiology 2005;236:974-982.)
© RSNA, 2005

Musculoskeletal Imaging

The Flexor Hallucis Longus: Tenographic Technique and Correlation of Imaging Findings with Surgery in 39 Ankles1

Jae-Boem Na, MD2, A. Gabrielle Bergman, MD3, Lawrence M. Oloff, DPM and Christopher F. Beaulieu, MD, PhD

1 From the Department of Radiology, Stanford University Medical Center, 300 Pasteur Dr, S-056, Stanford, CA, 94305-5105 (J.B.N., A.G.B., C.F.B.); and Sports, Orthopaedics and Rehabilitation, Redwood City, Calif (L.M.O.). Received May 7, 2004; revision requested July 20; revision received September 29; accepted October 26. Address correspondence to C.F.B. (e-mail: beaulieu{at}stanford.edu).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
PURPOSE: To examine the use of tenography for evaluation of the flexor hallucis longus (FHL) sheath.

MATERIALS AND METHODS: Institutional review board approval was waived, patient consent was obtained, and the study was HIPAA compliant. Retrospective review of 192 FHL tenograms and associated surgical records identified 39 ankles in 37 patients (17 male, 20 female; mean age ± standard deviation, 38 years ± 13.8; range, 14–68 years) in which both tenography and surgery had been performed. Two radiologists reviewed tenographic findings, including contrast agent extravasation, synovial irregularity, stenosis, fibrous bands, sheath outpouching, extent of opacification, and communications with adjacent structures. Alterations in pain after anesthesia of the tendon sheath were also recorded. Surgical reports were reviewed.

RESULTS: Thirty-four of 39 tenograms were diagnostic. Some extravasation occurred in nine (45%) of 20 injections with an initial injection method and in two (11%) of 19 with a new injection technique. Synovial irregularity was present in all 34 studies (15 mild, 16 moderate, three severe). Stenoses were identified in 23 (68%) of 34 ankles, fibrous bands were seen in 16 (47%) of 34 ankles, and outpouching of the sheath above a stenosis was present in 13 (38%) of 34 ankles. Communication of the FHL sheath with the ankle, flexor digitorum longus, or subtalar joint occurred in half the cases. Most patients with pain reported relief; relief was complete (100% reduction from preprocedural pain) in eight of 27, moderate (50%–90% reduction) in nine of 27, and mild (<50% reduction) in eight of 27 patients.

CONCLUSION: Tenography of the FHL sheath produced diagnostic images in almost all patients and effectively demonstrated abnormalities of the tendon sheath. Pain relief with anesthetic injection helped confirm the FHL sheath as the pain generator.

© RSNA, 2005


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Chronic ankle pain is common and may arise from a variety of causes, including derangements of joints, ligaments, or tendons. Disorders of the posterior tibial, Achilles, and peroneal tendons are relatively common and widely recognized (1,2). In patients with posteromedial ankle or arch pain, abnormalities of the flexor hallucis longus (FHL) tendon and its sheath must also be considered in the differential diagnosis. Pain or mechanical symptoms related to the FHL are often confused with plantar fasciitis or tarsal tunnel syndrome (3) and may be inadequately treated, leading to chronic pain and disability (4–7).

Stenosing tenosynovitis is the development of fibrous adhesions within a tendon sheath, often as the sequela of trauma such as a malleolar or calcaneal fracture or because of chronic repetitive trauma, typically in athletes (8). Such adhesions interfere with the normal tendon gliding motion and may be associated with pain, limitation in range of motion, and/or snapping sensations. Stenosing tenosynovitis of the FHL sheath has been well described in ballet dancers and to a lesser extent in running and jumping athletes, and it may be associated with posterior ankle impingement (9–12).

For the posterior tibial (13) and peroneal (14,15) tendons, as well as for certain tendons in the hand and wrist (16,17), opacification of the tendon sheath with radiographic contrast material, or tenography, has been described. Disorders such as synovitis, tendon entrapments, discontinuities, and indirect evidence of injuries to lateral ankle ligaments may be detected (13–15,18–20). In contrast, FHL tenography has not received much attention in the published literature. This may be because FHL dysfunction is relatively underrecognized and is hence thought to be less common than other tendon disorders. Also, the FHL tendon runs deep, and its course, immediately adjacent to the medial neurovascular bundle, makes for challenging localization and potential complications during needle placement. Magnetic resonance (MR) imaging has typically been relied on in the diagnosis of pathologic conditions of the FHL because of these difficulties (21).

We have successfully performed FHL tenography for over 10 years. Thus, the purpose of our study was to illustrate imaging findings and injection methods in a group of patients undergoing surgery.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Data Collection
One of the authors (J.B.N.) performed a retrospective search of our radiology information system for all patients who had undergone tenography of any ankle tendon(s) between April 1992 and June 2003. There were a total of 408 ankle tenography examinations performed in 321 patients. Of the 408 total tenography examinations, there were 192 FHL examinations in 150 patients (79 male, 71 female; age range, 14–70 years; mean age, 37 years ± 11.9 [standard deviation]). Thirty of these patients had received bilateral injections. Ten patients underwent repeat examinations, two of which were bilateral examinations. Inclusion in the present study required surgical exploration of the FHL sheath, which will be described further in a later paragraph.

Most patients were referred for evaluation of pain of uncertain origin in the posteromedial ankle or foot that was suspected to be related to the FHL tendon or its sheath. A minority of patients were referred primarily because of, or also had, limitation of range of motion of the ankle or great toe or an abnormal snapping or clicking sensation thought to be related to the FHL.

According to our university's guidelines, all patients undergoing tenography signed informed consent, which included permission for their images to be used for research. All personal health information was blinded during review in accordance with the U.S. Health Insurance Portability and Accountability Act. Given the retrospective nature of the study, our institutional review board provided a waiver from formal review as long as all data were anonymous during analysis and no follow-up patient contact was made.

Information on surgery performed was obtained by searching medical records for surgical reports (J.B.N.). Of the 150 patients who underwent FHL tenography, a total of 40 patients were identified who underwent surgical exploration of the FHL sheath. One patient was excluded from further analysis because of chronic tenosynovitis due to a large ganglion cyst. We were unable to locate the tenograms in two patients, which left 37 patients for analysis. Of these patients, two underwent bilateral tenography and surgery; therefore, the final study group consisted of 39 ankles with tenograms and surgical correlation. The surgical group consisted of 17 male patients and 20 female patients, with a mean age of 38 years ± 13.8 (age range, 14–68 years).

Surgery
All ankles were operated on by a single podiatric surgeon (L.M.O.) who was aware of the tenographic findings and had reviewed the images preoperatively. Fourteen ankles were operated on within 1 month and 19 ankles between 1 and 6 months of tenography. Three ankles were operated on between 6 months and 1 year and three ankles between 1 and 2 years. Surgical findings were derived from the surgical reports, which contained comments on the presence of stenosis or fibrosis of the tendon sheath, synovitis, intrinsic tendon abnormality, low-lying muscle, and the presence of accessory muscles.

Tenography Technique
The procedures reported were performed mainly by two of the authors (A.G.B., C.F.B.).

Patient positioning.—Proper positioning of the affected ankle is critical for determining the trajectory of the injection needle. Patients are placed in a lateral decubitus position with the medial aspect of the ankle of interest facing upward (Fig 1). The nonaffected knee is bent to move the opposite foot out of the procedure field. A pillow placed between the knees is helpful to improve patient comfort. Rotation of the foot approximately 15° toward the supine position is very helpful for successful needle placement (discussed further in a subsequent paragraph); this is accomplished by placing a folded towel under the forefoot to lift the lateral aspect of the foot from the table (Fig 1). It may help to place an additional towel under the knee to effect an overall rotation of the leg toward the supine position and to allow the patient to relax on the fluoroscopy table.



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  		Figure 1. Patient positioning for FHL tenography. For right FHL injection, patient lies in a right decubitus position with foot at an approximately 15° oblique angle to the fluoroscopy table. Towels (T) under the forefoot and right knee and a pillow (P) between the knees are helpful for maintaining position and for patient comfort.

 
Tendon anatomy.—The FHL is the deepest of the three posteromedial ankle muscle-tendon units, normally transitioning from muscle to tendon at the level of the distal tibia (22). The tendon abuts the posterior capsule of the ankle joint and talus almost in the midline of the leg. It then courses under the sustentaculum tali of the calcaneus as it passes toward the great toe or hallux (Fig 2). The neurovascular bundle, containing the posterior tibial nerve, artery, and paired veins, courses immediately superficial to the medial aspect of the FHL tendon.



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  		Figure 2. Diagram of medial ankle tendons shows FHL coursing under the sustentaculum tali (ST). Note also the knot of Henry (H), the point where the FHL and flexor digitorum longus (FDL) normally cross. A = Achilles tendon, PT = posterior tibial tendon. (Modified, with permission, from reference 22.)

 
Radiographic landmarks and needle placement.—In our first several years of performing FHL tenography, needle placement was based on palpation of the tendon in the retrotibial region. The patient was asked to repeatedly flex and extend the great toe while one palpated for the tendon behind the medial malleolus, adjacent to the posterior tibial arterial pulse. Palpation was often difficult in large patients or in those with edema, and in many cases multiple needle adjustments were necessary to opacify the tendon sheath. In addition, this needle trajectory was extremely close to the neurovascular bundle, increasing the risk of puncturing one of these structures.

Given the limitations of the initial approach, we developed a technique based on a combination of palpation and radiographic landmarks, relying heavily on the latter. With the patient as positioned in Figure 1, the posterior tibial artery is palpated and marked on the skin as illustrated in Figure 3. Next, the skin entry site is marked by using fluoroscopic guidance with a hemostat projected over the pre-Achilles tendon region, approximately 1 cm posterior to the artery and 1 cm above the upper border of the calcaneus. Next, a second mark is made on the skin at a location approximately one-third of the way along the sustentaculum tali. This point, together with the skin entry point, determines the orientation of the needle in the anteroposterior and cephalocaudal directions.



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  		Figure 3. Illustration of needle insertion technique shows the skin entry site (dot), posterior tibial artery (dotted line), and sustentaculum tali (long curved line) marked at fluoroscopy. Smaller curved line across the sustentaculum tali represents the target site, below the level of the posterior subtalar joint. Note the examiner's left hand stabilizes the foot to prevent inadvertent movement.

 
With the foot in the oblique position described, fluoroscopy is usually effective in profiling the sustentaculum tali, as shown in Figure 4a. If it is not well seen, small adjustments in the degree of obliquity are useful to delineate the sustentaculum tali. Another effect of the foot positioning is that the medial surface of the calcaneus is oriented slightly off horizontal. This is an advantage in determining the mediolateral orientation of the needle; the needle must pass close to, but on the deep aspect of, the neurovascular bundle to reach the tendon sheath (Fig 4b). By orienting the needle approximately 15° off horizontal, with the tip toward the floor, needle advancement will preferentially result in contact with the calcaneus rather than with the more superficial neurovascular bundle.



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  		Figure 4a. (a) Lateral projection fluoroscopic image shows needle trajectory toward FHL tendon sheath with landmarks as in Figure 3. Skin entry site is indicated with an arrowhead. Needle target is expected position of sheath under sustentaculum tali (white arrows), approximately one-third of the anteroposterior length along this structure and away from the posterior subtalar joint (black arrow). (b) Transverse intermediate-weighted MR images (repetition time msec/echo time msec, 2200/14) illustrate important anatomy related to needle positioning. Left image shows approximate needle trajectory (arrow) toward the FHL sheath; the actual entry site would be in a more caudal cross section on the basis of the angulation seen in a. Right image illustrates the close proximity of the neurovascular bundle (NV) to the FHL.

 


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  		Figure 4b. (a) Lateral projection fluoroscopic image shows needle trajectory toward FHL tendon sheath with landmarks as in Figure 3. Skin entry site is indicated with an arrowhead. Needle target is expected position of sheath under sustentaculum tali (white arrows), approximately one-third of the anteroposterior length along this structure and away from the posterior subtalar joint (black arrow). (b) Transverse intermediate-weighted MR images (repetition time msec/echo time msec, 2200/14) illustrate important anatomy related to needle positioning. Left image shows approximate needle trajectory (arrow) toward the FHL sheath; the actual entry site would be in a more caudal cross section on the basis of the angulation seen in a. Right image illustrates the close proximity of the neurovascular bundle (NV) to the FHL.

 
Injection setup and materials.—For convenience, and because of its relatively low cost, we typically use a commercially available lumbar puncture tray (4824–20; Portex, Keene, NH). This contains skin preparation sponges and povidone iodine, drapes, 2 x 2 gauze, adhesive bandage, lidocaine 1% (without epinephrine), a 5-mL syringe, and a 25-gauge 0.5-inch needle used for skin anesthesia. To this we add a 12-mL syringe, extension tubing, and a 25-gauge 1.25-inch needle that is used for the tendon sheath injection. We originally used iothalamate meglumine (Conray 43; Mallinckrodt Medical, St Louis, Mo) radiographic contrast medium but currently use nonionic iohexol (Omnipaque 240; Nycomed Amersham, Princeton, NJ) contrast medium in 10-mL vials. We did not encounter any complications thought to be related to ionic contrast medium, but we believed that the use of nonionic contrast medium would minimize the risk, and the availability in a suitable-sized vial was an added convenience. Six milliliters of contrast medium is mixed with 4–6 mL of bupivicaine 0.25%, a long-acting anesthetic. If asked by the referring clinician to inject corticosteroids into the tendon sheath, we use 0.5–1.0 mL (2–4 mg) of dexamethasone sodium phosphate (Decadron phosphate, 4 mg/mL; Merck, Whitehouse Station, NJ). This is a short-acting, water-soluble preparation, the use of which does not preclude surgery within (several) weeks after the procedure and which does not leave crystalline deposits in the tendon sheath. The dexamethasone is drawn into a 1.0-mL syringe and injected only after access to the tendon sheath has been obtained.

Injection technique.—The skin entry site is anesthetized by using an intradermal wheal of 1% lidocaine. Note that this is the only local anesthesia used outside of the tendon sheath. The primary reason for this is the need to avoid infiltration of the anesthetic agent around the posterior tibial nerve and thereby cause a nerve block. Nerve block markedly diminishes the reliability of assessment for changes in pain after FHL sheath injection. Fortunately, most patients do not experience substantial pain as the needle is advanced through the subcutaneous fat toward the FHL sheath.

The 1.25-inch, 25-gauge needle (without tubing or a syringe connected) is then inserted to a depth of approximately 1 cm by using the orientation described previously (Figs 3, 4a). Fluoroscopy is used to check the orientation of the needle relative to the desired target, and adjustments are made as needed. After the skin is entered, there should be little resistance to needle insertion on traversing the subcutaneous fat toward the tendon sheath or calcaneus (Fig 4b). The degree of resistance is easily determined when holding the needle hub. If the patient reports "electrical" pain in a radiating pattern along the medial and plantar area of the foot, the needle may be in contact with the posterior tibial nerve or one of the plantar nerves. Redirecting to a slightly steeper needle approach (aiming more laterally, toward the midline of the ankle) usually alleviates this sensation.

As the tendon sheath is encountered, needle resistance takes on a rubbery sensation if the tendon is contacted or a firm, bony contact if the calcaneus is contacted. In the case of bone contact, fluoroscopy is used to determine if the needle tip is adjacent to the sustentaculum tali (Fig 5a). If it is not, retraction and assumption of a less steep approach is needed so as to allow the needle to pass superficial to the calcaneus. Regarding the posterior subtalar joint, it is important to place the needle tip distal to the joint; otherwise, inadvertent direct injection into the joint may occur. Once the needle is in position, the contrast medium–bupivicaine mixture is connected to the needle via extension tubing, and a minimal amount—one or two drops—of this mixture is injected. If the needle is in the sheath, this mixture should track immediately along the tendon sheath, as in Figure 5a and 5b. If the contrast medium remains localized with a rounded or irregular shape, this indicates extravasation, and needle repositioning is necessary. In addition, resistance to injection in the sheath should be low; high resistance may indicate that the needle tip is in the tendon itself. Retraction by 1–2 mm will usually lower the resistance to injection. Sometimes, simply twisting the needle by 180° will reorient the tip so as to reduce the resistance and allow injection into the sheath.



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  		Figure 5a. Normal lateral projection FHL tenograms in a 35-year-old woman with plantar foot pain related primarily to plantar fasciitis. (a) On initial image during injection, contrast agent travels along course of the sheath (arrowheads) rather than pools at the needle tip. If pooling occurs, tip is outside the sheath and needs repositioning. (b) Early image shows continued opacification of the sheath up to the level of the ankle joint, where it appears somewhat irregular (arrows) but incompletely filled. At this stage, corticosteroid is injected if requested. Passive motion of the great toe will confirm motion of the FHL tendon at this point. (c) Further opacification. Note that sheath above level of the posterior talus is further distended (white arrowhead). Under the sustentaculum tali, smooth filling of the sheath in the fibro-osseous tunnel occurs (black arrowheads). More distally, distention of the sheath again occurs (arrows); the latter is a common normal finding. (d) After needle withdrawal, lateral projection image with plantar flexion of the ankle and great toe shows mild irregularity of tendon sheath at level of posterior talus. This short zone of underfilling and possible small diverticulum (arrowhead) could indicate adhesions but needs confirmation on other views. Further distention of distal sheath is again visible. (e) Ankle and toe dorsiflexion. Sheath behind talus is better distended than in d. In this position, slight widening (arrowheads) of the proximal aspect of tendon is visible in the sheath. Larger amount of fusiform widening of tendon in this location may reflect low-lying or hypertrophied muscle belly. (f) Ankle dorsiflexion and great toe plantar flexion. Note that tendon retracts proximally and opacified sheath is relatively smooth, except where projecting over anterior aspect of the calcaneus, where extravasation is relatively common with aggressive attempts at sheath distension.

 


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  		Figure 5b. Normal lateral projection FHL tenograms in a 35-year-old woman with plantar foot pain related primarily to plantar fasciitis. (a) On initial image during injection, contrast agent travels along course of the sheath (arrowheads) rather than pools at the needle tip. If pooling occurs, tip is outside the sheath and needs repositioning. (b) Early image shows continued opacification of the sheath up to the level of the ankle joint, where it appears somewhat irregular (arrows) but incompletely filled. At this stage, corticosteroid is injected if requested. Passive motion of the great toe will confirm motion of the FHL tendon at this point. (c) Further opacification. Note that sheath above level of the posterior talus is further distended (white arrowhead). Under the sustentaculum tali, smooth filling of the sheath in the fibro-osseous tunnel occurs (black arrowheads). More distally, distention of the sheath again occurs (arrows); the latter is a common normal finding. (d) After needle withdrawal, lateral projection image with plantar flexion of the ankle and great toe shows mild irregularity of tendon sheath at level of posterior talus. This short zone of underfilling and possible small diverticulum (arrowhead) could indicate adhesions but needs confirmation on other views. Further distention of distal sheath is again visible. (e) Ankle and toe dorsiflexion. Sheath behind talus is better distended than in d. In this position, slight widening (arrowheads) of the proximal aspect of tendon is visible in the sheath. Larger amount of fusiform widening of tendon in this location may reflect low-lying or hypertrophied muscle belly. (f) Ankle dorsiflexion and great toe plantar flexion. Note that tendon retracts proximally and opacified sheath is relatively smooth, except where projecting over anterior aspect of the calcaneus, where extravasation is relatively common with aggressive attempts at sheath distension.

 


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  		Figure 5c. Normal lateral projection FHL tenograms in a 35-year-old woman with plantar foot pain related primarily to plantar fasciitis. (a) On initial image during injection, contrast agent travels along course of the sheath (arrowheads) rather than pools at the needle tip. If pooling occurs, tip is outside the sheath and needs repositioning. (b) Early image shows continued opacification of the sheath up to the level of the ankle joint, where it appears somewhat irregular (arrows) but incompletely filled. At this stage, corticosteroid is injected if requested. Passive motion of the great toe will confirm motion of the FHL tendon at this point. (c) Further opacification. Note that sheath above level of the posterior talus is further distended (white arrowhead). Under the sustentaculum tali, smooth filling of the sheath in the fibro-osseous tunnel occurs (black arrowheads). More distally, distention of the sheath again occurs (arrows); the latter is a common normal finding. (d) After needle withdrawal, lateral projection image with plantar flexion of the ankle and great toe shows mild irregularity of tendon sheath at level of posterior talus. This short zone of underfilling and possible small diverticulum (arrowhead) could indicate adhesions but needs confirmation on other views. Further distention of distal sheath is again visible. (e) Ankle and toe dorsiflexion. Sheath behind talus is better distended than in d. In this position, slight widening (arrowheads) of the proximal aspect of tendon is visible in the sheath. Larger amount of fusiform widening of tendon in this location may reflect low-lying or hypertrophied muscle belly. (f) Ankle dorsiflexion and great toe plantar flexion. Note that tendon retracts proximally and opacified sheath is relatively smooth, except where projecting over anterior aspect of the calcaneus, where extravasation is relatively common with aggressive attempts at sheath distension.

 


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  		Figure 5d. Normal lateral projection FHL tenograms in a 35-year-old woman with plantar foot pain related primarily to plantar fasciitis. (a) On initial image during injection, contrast agent travels along course of the sheath (arrowheads) rather than pools at the needle tip. If pooling occurs, tip is outside the sheath and needs repositioning. (b) Early image shows continued opacification of the sheath up to the level of the ankle joint, where it appears somewhat irregular (arrows) but incompletely filled. At this stage, corticosteroid is injected if requested. Passive motion of the great toe will confirm motion of the FHL tendon at this point. (c) Further opacification. Note that sheath above level of the posterior talus is further distended (white arrowhead). Under the sustentaculum tali, smooth filling of the sheath in the fibro-osseous tunnel occurs (black arrowheads). More distally, distention of the sheath again occurs (arrows); the latter is a common normal finding. (d) After needle withdrawal, lateral projection image with plantar flexion of the ankle and great toe shows mild irregularity of tendon sheath at level of posterior talus. This short zone of underfilling and possible small diverticulum (arrowhead) could indicate adhesions but needs confirmation on other views. Further distention of distal sheath is again visible. (e) Ankle and toe dorsiflexion. Sheath behind talus is better distended than in d. In this position, slight widening (arrowheads) of the proximal aspect of tendon is visible in the sheath. Larger amount of fusiform widening of tendon in this location may reflect low-lying or hypertrophied muscle belly. (f) Ankle dorsiflexion and great toe plantar flexion. Note that tendon retracts proximally and opacified sheath is relatively smooth, except where projecting over anterior aspect of the calcaneus, where extravasation is relatively common with aggressive attempts at sheath distension.

 


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  		Figure 5e. Normal lateral projection FHL tenograms in a 35-year-old woman with plantar foot pain related primarily to plantar fasciitis. (a) On initial image during injection, contrast agent travels along course of the sheath (arrowheads) rather than pools at the needle tip. If pooling occurs, tip is outside the sheath and needs repositioning. (b) Early image shows continued opacification of the sheath up to the level of the ankle joint, where it appears somewhat irregular (arrows) but incompletely filled. At this stage, corticosteroid is injected if requested. Passive motion of the great toe will confirm motion of the FHL tendon at this point. (c) Further opacification. Note that sheath above level of the posterior talus is further distended (white arrowhead). Under the sustentaculum tali, smooth filling of the sheath in the fibro-osseous tunnel occurs (black arrowheads). More distally, distention of the sheath again occurs (arrows); the latter is a common normal finding. (d) After needle withdrawal, lateral projection image with plantar flexion of the ankle and great toe shows mild irregularity of tendon sheath at level of posterior talus. This short zone of underfilling and possible small diverticulum (arrowhead) could indicate adhesions but needs confirmation on other views. Further distention of distal sheath is again visible. (e) Ankle and toe dorsiflexion. Sheath behind talus is better distended than in d. In this position, slight widening (arrowheads) of the proximal aspect of tendon is visible in the sheath. Larger amount of fusiform widening of tendon in this location may reflect low-lying or hypertrophied muscle belly. (f) Ankle dorsiflexion and great toe plantar flexion. Note that tendon retracts proximally and opacified sheath is relatively smooth, except where projecting over anterior aspect of the calcaneus, where extravasation is relatively common with aggressive attempts at sheath distension.

 


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  		Figure 5f. Normal lateral projection FHL tenograms in a 35-year-old woman with plantar foot pain related primarily to plantar fasciitis. (a) On initial image during injection, contrast agent travels along course of the sheath (arrowheads) rather than pools at the needle tip. If pooling occurs, tip is outside the sheath and needs repositioning. (b) Early image shows continued opacification of the sheath up to the level of the ankle joint, where it appears somewhat irregular (arrows) but incompletely filled. At this stage, corticosteroid is injected if requested. Passive motion of the great toe will confirm motion of the FHL tendon at this point. (c) Further opacification. Note that sheath above level of the posterior talus is further distended (white arrowhead). Under the sustentaculum tali, smooth filling of the sheath in the fibro-osseous tunnel occurs (black arrowheads). More distally, distention of the sheath again occurs (arrows); the latter is a common normal finding. (d) After needle withdrawal, lateral projection image with plantar flexion of the ankle and great toe shows mild irregularity of tendon sheath at level of posterior talus. This short zone of underfilling and possible small diverticulum (arrowhead) could indicate adhesions but needs confirmation on other views. Further distention of distal sheath is again visible. (e) Ankle and toe dorsiflexion. Sheath behind talus is better distended than in d. In this position, slight widening (arrowheads) of the proximal aspect of tendon is visible in the sheath. Larger amount of fusiform widening of tendon in this location may reflect low-lying or hypertrophied muscle belly. (f) Ankle dorsiflexion and great toe plantar flexion. Note that tendon retracts proximally and opacified sheath is relatively smooth, except where projecting over anterior aspect of the calcaneus, where extravasation is relatively common with aggressive attempts at sheath distension.

 
Once contrast material flows along the tendon sheath, 1–2 mL of the mixture is injected to more specifically confirm that the FHL sheath has been entered (as opposed to the adjacent flexor digitorum longus muscle). The FHL sheath is confirmed by its characteristic location under the sustentaculum tali (Fig 5b). Another technique we often use to confirm the FHL sheath has been entered is slight (approximately 1.0 cm) flexion and extension movement of the great toe (motion performed passively, by the radiologist, so as to minimize damage of the tendon by the injection needle). If corticosteroid injection has been requested, we perform this immediately after confirmation of FHL sheath access (Fig 5b), replacing the extension tubing for the 1-mL syringe directly on the injection needle. Given the precise and delicate positioning of the needle, it is helpful to stabilize the hub of the needle carefully with one hand while injecting the steroid with the other hand. We have not found that using a three-way stopcock is helpful, and we do not want to add the steroid directly to the contrast medium–bupivicaine mixture, for two reasons. The first reason is that if early attempts at sheath injection are in fact outside the sheath, the steroid would also be outside the sheath. The second reason is that one cannot determine a priori the total fluid volume the sheath will accommodate, which could lead to delivery of a lower dose of steroid than desired. Typically, we inject a total of 6–8 mL of the contrast medium–bupivicaine mixture. Between six and 12 spot images are obtained during a typical examination. Aggressive attempts to distend the sheath with fluid, or motion of the ankle and great toe after injection, often result in contrast material tracking along the musculotendinous junction. After needle withdrawal, it is not unusual to encounter a small amount of extravasation at the sheath puncture site; therefore, it is important to acquire some images before needle withdrawal and before excessive ankle or toe motion. Images to document the extent of opacification along the sheath and with the ankle and great toe in positions of plantar and dorsiflexion are routinely obtained, as shown in Figure 5d –5f. Additional views with varying obliquity can also be helpful in delineating all portions of the tendon sheath.

Image Analysis
Tenograms were reviewed by two musculoskeletal radiologists (J.B.N., C.F.B.) in consensus. One (C.F.B.) had 9 years of experience with tenogram interpretation, while the other (J.B.N.) had approximately 1 year of experience, based primarily on the current study. Images were interpreted for each of the following features: (a) synovial irregularity, defined on a qualitative spectrum of none (perfectly smooth margins), mild, moderate, and severe, where severe is defined as marked irregularity over a segment of sheath at least 1 cm long (the length criterion helps differentiate from focal stenosis); (b) stenosis, defined as a less than 1-cm-long circumferential constriction to contrast medium opacification that persists on all views and during all phases of injection; (c) fibrous bands, defined as thin linear septations across the sheath that do not cause a circumferential stenosis; (d) outpouching, defined as abnormal globular distention of the tendon sheath immediately proximal to an area of stenosis (compared with normal gradual dilation of the sheath proximally along the myotendinous junction, outpouching is more abrupt and is described only when there is also a stenosis); (e) extent of opacification, in terms of distance above and below the ankle joint or injection site, measured relative to where the opacified sheath projected adjacent to the distal tibia or over the foot; and (f) communications, such as with other tendon sheaths or the ankle or subtalar joints.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Procedural Success and Image Quality
Of the 39 tenograms with surgical correlation, five were suboptimal because of inadequate opacification of the sheath or extensive extravasation of contrast medium. Twenty studies were performed with the original palpation-based technique and 19 studies were performed with the newer fluoroscopy-based technique. Of the suboptimal tenograms, four were obtained with the original technique and one was obtained with the newer technique. This left 34 diagnostic tenograms on which each of the imaging findings could be categorized and compared with surgical findings. Limited contrast medium extravasation in the region of the posterior ankle joint was present on images from nine studies performed with the original technique and two with the new technique. In these cases it was usually possible to catalog other features such as synovial irregularity and extent of filling; therefore, these findings are included in the tabulations that follow.

Imaging Findings
Synovial irregularity.—All 34 ankles showed at least mild synovial irregularity, with proportions as follows: mild in 15 ankles, moderate in 16, and severe in three. The spectrum of irregularity is illustrated in Figure 6. One must be careful to identify contrast medium extravasation (Fig 7), as this rather easily tracks along the neurovascular bundle and, as such, may be misinterpreted as marked sheath irregularity.



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  		Figure 6a. Lateral projection tenograms show spectrum of synovial irregularity. (a) Mild irregularity in 20-year-old male gymnast with posterior ankle pain. Sheath fills out nearly uniformly along course of tendon, which itself is evident as filling defect (arrowheads) in the contrast material column. Mild undulation in sheath contour is evident at level of posterior talus (arrows). Symptom relief was minimal after injection; majority of pain was attributed to edema in posterior aspect of talus identified on MR images. (b) Moderate irregularity in 50-year-old woman with plantar heel and medial ankle pain. Relative underfilling of sheath and moderate contour irregularity (arrows) are seen. Lucent oval distally (arrowhead) represents small air bubble. Initial symptom relief was indeterminate because patient required exercise to experience pain. (c) Severe irregularity (arrows) in 42-year-old woman with chronic medial ankle pain. Marked lobulations and underfilling of sheath extend from posterior talus to under sustentaculum tali. Mild decrease in pain occurred after injection.

 


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  		Figure 6b. Lateral projection tenograms show spectrum of synovial irregularity. (a) Mild irregularity in 20-year-old male gymnast with posterior ankle pain. Sheath fills out nearly uniformly along course of tendon, which itself is evident as filling defect (arrowheads) in the contrast material column. Mild undulation in sheath contour is evident at level of posterior talus (arrows). Symptom relief was minimal after injection; majority of pain was attributed to edema in posterior aspect of talus identified on MR images. (b) Moderate irregularity in 50-year-old woman with plantar heel and medial ankle pain. Relative underfilling of sheath and moderate contour irregularity (arrows) are seen. Lucent oval distally (arrowhead) represents small air bubble. Initial symptom relief was indeterminate because patient required exercise to experience pain. (c) Severe irregularity (arrows) in 42-year-old woman with chronic medial ankle pain. Marked lobulations and underfilling of sheath extend from posterior talus to under sustentaculum tali. Mild decrease in pain occurred after injection.

 


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  		Figure 6c. Lateral projection tenograms show spectrum of synovial irregularity. (a) Mild irregularity in 20-year-old male gymnast with posterior ankle pain. Sheath fills out nearly uniformly along course of tendon, which itself is evident as filling defect (arrowheads) in the contrast material column. Mild undulation in sheath contour is evident at level of posterior talus (arrows). Symptom relief was minimal after injection; majority of pain was attributed to edema in posterior aspect of talus identified on MR images. (b) Moderate irregularity in 50-year-old woman with plantar heel and medial ankle pain. Relative underfilling of sheath and moderate contour irregularity (arrows) are seen. Lucent oval distally (arrowhead) represents small air bubble. Initial symptom relief was indeterminate because patient required exercise to experience pain. (c) Severe irregularity (arrows) in 42-year-old woman with chronic medial ankle pain. Marked lobulations and underfilling of sheath extend from posterior talus to under sustentaculum tali. Mild decrease in pain occurred after injection.

 


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  		Figure 7. Lateral projection tenogram of extravasation of contrast material in 68-year-old woman with plantar heel pain. Injection performed with original approach based primarily on palpation rather than radiographic landmarks. Beginning near site where the needle contacted FHL sheath (black arrow), moderate amount of contrast material tracked posteriorly and cephalad (white arrows), making it difficult to assess sheath for stenosis or irregularity. Patient reported 90% reduction in pain, which could be due to actual decrease in pain related to FHL sheath or due to nerve block.

 
Stenoses and fibrous bands.—Focal stenoses (Fig 8) were radiographically identified in 23 of 34 ankles (68%) (Table 1). Fibrous bands (Fig 9) were seen in 16 of 34 ankles (47%) (Table 1).



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  		Figure 8a. Lateral projection tenograms of stenosis and outpouching. (a) Image in 32-year-old woman with medial foot pain shows stenosis (arrow) at level of the ankle joint. Band of contrast agent (arrowhead) posterior to sheath below stenosis represents small amount of extravasation after needle withdrawal. (b) High-grade focal stenosis (arrow) in 25-year-old ballerina with loud and palpable snapping sensation behind ankle joint with great toe motion. Above stenosis, sheath is markedly dilated, which represents outpouching (arrowheads). Note that injection into sheath is successful even with needle tip along posterior aspect of sheath below sustentaculum tali.

 


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  		Figure 8b. Lateral projection tenograms of stenosis and outpouching. (a) Image in 32-year-old woman with medial foot pain shows stenosis (arrow) at level of the ankle joint. Band of contrast agent (arrowhead) posterior to sheath below stenosis represents small amount of extravasation after needle withdrawal. (b) High-grade focal stenosis (arrow) in 25-year-old ballerina with loud and palpable snapping sensation behind ankle joint with great toe motion. Above stenosis, sheath is markedly dilated, which represents outpouching (arrowheads). Note that injection into sheath is successful even with needle tip along posterior aspect of sheath below sustentaculum tali.

 

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  		TABLE 1. Findings on FHL Tenograms in 34 Ankles

 


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  		Figure 9. Lateral projection tenogram of fibrous bands in 17-year-old girl with calf and medial ankle pain shows relatively thin linear bands (arrows) crossing partially across the tendon sheath. Patient experienced moderate pain reduction after injection.

 
Outpouchings and communications.—Outpouching (Fig 8) of the sheath proximal to a stenosis was identified in 13 of 34 patients (38%) (Table 1). The FHL sheath communicated with the ankle joint in six ankles (Fig 10a), with the flexor digitorum longus sheath in eight ankles (Fig 10b), and with the posterior subtalar joint in three ankles.



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  		Figure 10a. Lateral projection tenograms. (a) Image in 21-year-old female soccer player with medial foot pain shows communication with ankle joint (*). Note that needle tip is a considerable distance from the ankle, indicating that communication is indirect. (b) Image in 42-year-old woman shows FHL tendon sheath (arrowheads) communicating with flexor digitorum longus tendon sheath (arrows).

 


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  		Figure 10b. Lateral projection tenograms. (a) Image in 21-year-old female soccer player with medial foot pain shows communication with ankle joint (*). Note that needle tip is a considerable distance from the ankle, indicating that communication is indirect. (b) Image in 42-year-old woman shows FHL tendon sheath (arrowheads) communicating with flexor digitorum longus tendon sheath (arrows).

 
Extent of opacification.—Because of the structure of the foot and the positioning during the study (eg, Fig 6a), we find it convenient to refer to projections of the sheath relative to the lateral bony structure of the foot, even though the tendon sheath courses medially. The distal extent of the sheath was projected over the calcaneocuboid joint in three ankles, over the cuboid in 20 ankles, over the cuboid-metatarsal joint in seven ankles, and over the first metatarsal base head in four ankles. The proximal extent of opacification averaged 1.7 cm ± 0.9 above the ankle joint (range, 0.1–4.0 cm).

Comparison with surgical findings.—On review of the surgical reports, all patients who had udergone surgery had a postoperative diagnosis of stenosing tenosynovitis. Since this was a retrospective study, details regarding the exact features of each stenosis were not available for direct correlation with images. All stenotic segments were located at the posterior ankle joint or posterior talar process level. We could not quantitatively compare tenographic features of synovial irregularity with information from the surgical reports, which often simply recorded the presence or absence of synovitis. Some surgical findings in the surgical subgroup were not amenable to correlation with tenographic findings, including the presence of a low-lying FHL muscle belly (n = 18), an accessory muscle (n = 5), tendonitis or a fibrillated tendon (n = 2), or a partial tendon tear (n = 1).

Symptomatic Findings
We graded initial symptom relief as follows: none (0%), mild (<50%), moderate (50%–90%), and complete (100%; relief was estimated in 10% increments). Of the 34 ankles with diagnostic images, symptom relief was complete in eight ankles, moderate in nine ankles, and mild in eight ankles, and there was no symptom relief in two ankles (Table 2). In the other seven ankles, patients could not evaluate for pain relief because pain was minimal or absent at the time of the procedure. Given the potentially greater diagnostic importance of symptom relief in patients who had only mild abnormalities at imaging, we looked specifically at the 15 patients with only mild synovial irregularity. This group had complete symptom relief in three ankles, moderate relief in five ankles, mild relief in three ankles, no relief in one ankle, and indeterminate results in three ankles. There were no identified complications reported by any of the patients in the surgical subgroup.


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  		TABLE 2. Pain Relief after Anesthetic Injection of the FHL Tendon Sheath

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
The present work represents an example of re-establishing and expanding on the technique of tenography, which can play an important complementary diagnostic and therapeutic role to noninvasive imaging (23). Our experience with FHL tenography is substantial, as we have performed this procedure on approximately 200 ankles over the past 10 years. Prior reports described opacification of the FHL sheath only in cadavers (13) or indirectly via communication with the flexor digitorum longus sheath (18).

Tenographic Techniques
We currently use the radiographic landmark technique rather than the former palpation technique for a variety of reasons: more diagnostic images obtained, less extravasation, increased ease with which puncture can be performed on large patients or on those with edema, and an easier time teaching the procedure to new operators compared with palpation. Careful patient positioning and initial injection of only minimal amounts of contrast medium are critical to success with the new technique. An alternative, and possibly even easier, method of FHL sheath opacification has been recently reported by Gelbart et al (24). These authors describe a relatively direct puncture nearly perpendicular to the FHL sheath, immediately under the sustentaculum tali. We have used a similar approach only once, on a patient in whom our current method was unsuccessful. We have been somewhat reluctant to directly approach this area because of components of the neurovascular bundle that may course superficial to the sustentaculum tali, although initial experience suggests that these structures can be safely avoided (24). Determining exactly which method will be most easily learned and proved most effective will require further clinical experience.

Imaging Findings
The normal FHL sheath has a smooth curvilinear contour. Normally, there are no adhesions between the sheath and the tendon, which allows for circumferential opacification of the sheath around the tendon. Proximally, the sheath broadens to a conelike fascia and then blends in with muscle fibers at the myotendinous junction. In the midfoot, the FHL tendon crosses the flexor digitorum longus tendon at a point called "the knot of Henry" (25). Contrast medium opacification distal to this point occurs only rarely from the usual proximal injection site, so evaluation of the sheath distal to this point would require a separate injection site.

Proliferation of inflamed synovium leads to varying degrees and extents of nodularity along the sheath. We graded sheath irregularity as mild, moderate, or severe on the basis of clinical experience, as there are no set surgical or imaging definitions to distinguish between various degrees of abnormality. Either tenosynovitis (ie, inflammatory change) or scarring along the tendon sheath may cause the observed irregularity, and tenography is unable to help distinguish between these pathologic conditions. In the subgroup reported in this study, there were no sheaths that were completely smooth or normal; the majority had either mild (44%) or moderate (47%) irregularity. Unlike the reported experience in other tendon sheaths, the FHL sheath does not appear as likely to form sacculations or long stenoses; therefore, grading of tenosynovitis is more subjective (20). Fibrosis or scarring of the tendon sheath may occur if tenosynovitis is chronic, leading to a variety of appearances. Bandlike linear filling defects within the sheath, which we term fibrous bands, were common, occurring in 47% of sheaths. These are partial septations across the sheath that do not result in circumferential sheath underfilling. Surgically, these structures appear as areas of frank synovial sheath hypertrophy, with or without adhesions to the underlying tendon. A more advanced form of fibrosis occurs in a stenosis, defined as a circumferential and relatively concentric adhesion of the sheath around the tendon.

In our retrospective study, stenosis was demonstrated in 68% of the tendon sheaths, although all patients were considered to have stenosing tenosynovitis in their final surgical diagnosis. This apparent discrepancy likely reflects a broader definition of stenosis used by the surgeon that included cases we categorized as having fibrous bands or moderate to severe irregularity as opposed to focal, concentric stenosis. A prospective study would be better for determining the sensitivity and specificity of tenography for various discrete imaging findings relative to their surgical correlates. In their most severe form, stenoses may cause obstruction to flow of contrast material. In our experience, however, blockage is almost always incomplete, such that further contrast material injection is usually successful in opacifying the sheath beyond the stenosis. In rare cases where complete obstruction is present, repositioning of the needle tip may be used to opacify the other segment of the sheath. Focal stenosis of the FHL sheath is almost always located at the level of the posterior talus. Here, chronic friction against the posterior talus, or in some patients an os trigonum, may incite a local inflammatory reaction eventually resulting in fibrosis (9). Typically, FHL stenoses are short, on the order of 5 mm in length. Immediately proximal to a stenosis, the sheath is often dilated, resulting in outpouching of contrast medium around the tendon and distal muscle belly. Visualization of outpouching relies on a sufficient volume of injected contrast medium–anesthetic mixture. When excess tenosynovial fluid is present, MR images may show increased fluid as a useful indirect sign of FHL stenosis. This is supported by an analysis of 12 patients with FHL entrapment reported by Lo and co-workers (21), who found a strong correlation between excess FHL sheath fluid above an os trigonum and impingement of the tendon.

Symptomatic Findings
Recording any changes in pain after the anesthetic injection is also part of tenographic assessment of FHL dysfunction. In the current study, we analyzed only immediate pain relief due to long-acting local anesthetic, and we found that 76% of patients had at least mild symptom relief. Given the relatively small number of patients in this surgical group, we could not draw direct correlations between pain relief and the degree of synovial irregularity. This is analogous to an experience reported with the peroneal and posterior tibial sheaths, in which about half of the patients had moderate symptom relief, although there was not a clear correlation with the degree of sheath irregularity (20). If symptoms occur only with provocative maneuvers such as running or standing for a period of time, we often ask the patient to test for relief of such symptoms after leaving the radiology department. There is clearly a group of patients who have sustained relief beyond the anesthetic phase of tenography. We can only speculate on the mechanism of this benefit. Whether it was an adhesiolysis effect from mechanical distention of the contained environment of the sheath or whether it may be an anti-inflammatory or fibrinolytic effect of the corticosteroids (or a combination of effects) is difficult to determine. In patients with an intermediate or partial response to tenography, we sometimes repeated tenography after a period of a few months as a means of accurately targeting the administration of the corticosteroid for (we hope) long-term therapeutic benefit. Failures with tenography to establish lasting relief would establish these patients as potential surgical candidates. Finally, documentation and description of communications with other structures are important because pain relief needs to be interpreted in this context.

Complementary Imaging
After radiography, MR imaging remains the most useful imaging method for ankle and foot pain (26). With either MR imaging or ultrasonography (US) (27), normal and abnormal tendons are well depicted and tenosynovial effusions can be identified. However, relatively increased fluid in the FHL sheath can be nonspecific (28), and stenosis of the tendon sheath, which may occur without excess fluid, may be invisible. Accordingly, provocative tests such as tenography can play a very useful role in helping refine a differential diagnosis after clinical evaluation and MR imaging. Possible complications of tenography include infection, bleeding, nerve block, and tendon injury. Injection of the steroid directly into the tendon is to be avoided. Results in earlier studies in the literature have shown that local steroid injection into tendons has been associated with collagen necrosis and biomechanical weakness and may increase the risk of tendon tears (29,30). In general, this complication of tenography appears to be exceedingly rare (20), but care to avoid intratendinous injection needs to be taken. We also minimize any risk of long-term tendon weakening by using only a short-acting water-soluble steroid and by avoiding steroids altogether if MR imaging or US shows severe tendinopathy or a tear. Interestingly, when compared with the peroneal or posterior tibialis tendons, it is uncommon to develop intrinsic tendon abnormalities in the FHL, in our experience, with only two of 39 tendons showing partial tear or fibrillation in this surgical group. The preponderance of the disease appears related to the tendon sheath.

Limitations
Our study had several limitations. The patient population was biased, since only patients undergoing surgery were analyzed. Some patients also underwent surgery more than 1 year after the tenography study, so the disease may have changed during this interval. Since the analysis was retrospective, we could not clearly correlate each of the tenographic findings with surgical findings, as would be possible prospectively. We also do not have a surgically proved example of a normal FHL sheath, as this did not occur in the surgical subgroup. Conversely, there were surgical findings for which we did not or could not seek a tenographic correlate, such as intrinsic tendon abnormalities. We also did not review the long-term benefits of the surgical procedures themselves, although others have reported good outcomes in the majority of patients undergoing surgical tenolysis (4,7). An improved ability to correlate tenographic findings with MR imaging findings would also be very helpful, and that analysis is ongoing.

In conclusion, we have described our technique for FHL tenography and illustrated imaging abnormalities of the tendon sheath. We hope this information will be helpful to radiologists in working with specialists and patients with foot and ankle pain.


   FOOTNOTES
 

Abbreviations: FHL = flexor hallucis longus

2 Current address: Gyeongsang National University Hospital, Jinju, Korea Back

3 Current address: Franklin and Seidelmann Virtual Radiologists, El Dorado Hills, Calif Back

Authors stated no financial relationship to disclose.

Author contributions: Guarantor of integrity of entire study, C.F.B.; study concepts, C.F.B., A.G.B.; study design, J.B.N., C.F.B.; literature research, J.B.N., C.F.B.; clinical studies, all authors; data acquisition, C.F.B., J.B.N.; data analysis/interpretation, all authors; manuscript preparation, J.B.N., C.F.B.; manuscript definition of intellectual content, C.F.B., A.G.B.; manuscript editing, revision/review, and final version approval, all authors


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

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A. Mehdizade and R. S. Adler
Sonographically Guided Flexor Hallucis Longus Tendon Sheath Injection
J. Ultrasound Med., February 1, 2007; 26(2): 233 - 237.
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