Case report of a young man
with bilateral trigger toe

V. PAPATHANASIOU, V. I. SAKELLARIOU, I. P. SOFIANOS
Levadia General Hospital Orthopaedic Department

ABSTRACT
Trigger toe constitutes a clinical manifestation of stenosing tenosynovitis of the flexor hallucis longus tendon at the level of the sustentaculum tali. This is a rare clinical entity, affecting mainly female classic ballet dancers. In this article, we present a 25 year-old man, who attended our clinic, because of intense pain during plantar flexion of both great toes, but especially the right one. During the clinical examination, a palpable node at the medial malleolus that was following the movements of the great toe was revealed, as well as crepitation and a triggering sensation at the ankle. The patient wasn't able to stand on the tips of his toes (en pointe position).
Laboratory evaluation was carried out, including complete blood count, complete biochemical assessment, protein electrophoresis, antibody factors detection, immunological, endocrinological, microbiological and virological control, without any abnormal findings.
The imaging evaluation, with simple X-rays was normal. The MRI imaging revealed a thickening of the tendon of the flexor hallucis longus behind the ankle joint, along with minimal liquid accumulation, an image compatible with tenosynovitis.
The patient underwent surgical intervention consisting of incision of the sheath at the right foot, where symptoms were more intense. Two days postoperatively, he was discharged from the clinic, partial weight bearing of the leg, while 7 days later he begun a gradual progress in weight bearing, along with exercises in order to regain full range of motion. The postoperative period was 8 weeks long and none of the possible complications emerged (infection, skin damage, pain at the site of injury, injury of the neurovascular bundle, tendon loosening).
Any pain at the region of the medial malleolus imposes a differential diagnosis procedure from diseases like rheumatoid arthritis, Reiter Syndrome, infectious bowel diseases, several neoplastic diseases and the os trigonum syndrome.

Κey words: trigger toe, stenosing tenosynovitis, palpable node at the medial malleolus, pain of the medial malleolus

INTRODUCTION
Stenosing tenosynovitis of the tendon of the flexor hallucis longus at the level of the sustentaculum tali (Image 1) is a relatively rare medical entity, that affects primarily female classic ballet dancers[8,16,18,32]. According to Hamilton, the disease is characterized by pain at the anterior and medial surface of the ankle, enhanced by standing in the "en pointe" position. Usually the pain lessens at rest and the condition tends to drag on. This entity was described for the first time in 1940 by Lewin, who successfully treated a classic ballet dancer with trigger toe, without the use of invasive methods[21]. The non-invasive treatment of this condition was first described by Lipscomb[22] in 1944, and Burman[2] in 1953.
The invasive treatment of the condition was first reported in 1950 by Lapidus and Seidenstein. In this study, a male patient managed to return to his former sport activities after the release of the tendon[19]. However, most of the reports of surgical treatment for this condition refer to female classic ballet dancers[1,3,5,6,12,20,24,25,35,41].
As mentioned above, stenosing tenosynovitis of the tendon of the flexor hallucis longus is rarely encountered in the general population. This can explain the relatively high possibility of incorrect or delayed diagnosis of the disease. Even though the effectiveness of the surgical treatment has been pointed out by the preceding writers, we are not aware of any study where the results of the surgical treatment in a patient series, which were operated by the same surgeon, are compared to each other. We also don't have in view any studies presenting a bilateral stenosing tenosynovitis of the flexor hallucis longus, all the more so in a patient who isn't involved in activities that require standing in the en pointe position.

Figure 1. The injury of the tendon is thought to occur at the proximal margin of the fibro-osseous tunnel beneath the sustentaculum tali of the calcaneus.

MATERIALS AND METHODS
A 25 year old man attended our department, because of intense pain during plantar flexion of the great toes in both sides, but mainly at the right foot. The patient was feeling discomfort during long-lasting standing and wasn't able of participating in activities that require standing in the en pointe position or jumping on the spot. The clinical evaluation revealed a palpable node at the region of the medial malleolus, following the movements of the great toe, crepitation and a triggering sensation at the ankle.
His personal history was negative. He didn't mention any previous injury, serious or not, at the region of the ankle or the foot. The family history was also negative. We also examined the patient's parents and brother, but no similar medical condition was found in any member of the family.
Within the limits of the differential diagnosis, that is unfolded in detail below, the patient underwent detailed laboratory control, consisting of blood count, complete biochemical assessment, protein electrophoresis, and antibody detection, immunological, endocrinological, microbiological and virological control, without any abnormal findings.
Imaging with X-rays of the ankles and the feet, of both sides, in anteroposterior, lateral and oblique projection didn't reveal any abnormal findings. No presence of os trigonum was observed.
MRI imaging (Image 2) showed a thickening of the tendon of the flexor hallucis longus behind the talocrural joint, along with minimal liquid accumulation, a picture compatible with tenosynovitis.
After the diagnosis was confirmed, non steroid anti-inflammatory drugs were provided for 15 days. The non-invasive treatment slightly improved the pain of the left leg, where the symptoms were milder from the beginning, but was totally ineffective for the right leg. As a result of it, after discussing with the patient about the possible progress of the clinical condition, his demands regarding the activity level that he wanted to perform, but also the potential complications of the operation, we decided to proceed to surgical incision of the tendon sheath of the right foot and conservative treatment of the left foot.

Figure 2. The tendon of the flexor hallucis longus appears thickened behind the right tibiocalcaneal joint with a small quantity of fluid, which is compatible with tenosynovitis. The same finding, with a smaller thickening, appears at the left tibiocalcaneal joint too.

SURGICAL TECNHNIQUE
After spinal anesthesia administration, the patient was positioned in prone position on the surgical table. We used a tourniquet to prevent bleeding and to improve the appearance of the surgical field during the procedure. We applied antiseptic on the skin of the leg below the knee and we covered the rest of the body with sterilized surgical drapes. Using special magnifying loops, we made a 7 cm long, ellipsoid incision, beginning from the medial malleolus to the inner surface of the subtalar joint, ending up at the predetermined site of maximal strain. Afterwards, an incision of the aponeurosis above the neurovascular bundle was performed, which then was dissected from the surrounding tissue, released and secluded with the use of a medical ribbon. Gentle pulling down the neurovascular bundle, we revealed the tendon of the flexor hallucis longus, while entering the fibrosseous canal under the sustentaculum tali.
The part of the aponeurosis participating in the forming of the canal of the tendon of the flexor hallucis longus was dissected lengthwise at the level of the sustentaculum tali, in order to allow the inspection of the injury area at the proximal entry site of the canal. Flexion and extension of the great toe helps the localization of the tendon abnormality, and the definition of the extent of the canal stenosis. Afterwards, we made an incision at the canal in order to ascertain the free sliding of the tendon (Image 3).
The tourniquet was released, in order to ensure the proper hemostasis before closing the wound and placing anti-adhesion gel (Adcon). The inner part of the aponeurosis was not closed. The subcutaneous tissue edges were approached with absorbable sutures and the suture of the skin was performed by nylon stitches and a continuous American suture. Eventually, compressive gauzes and bandages were placed over the wound.

Figure 3. Division of the fibro-osseous tunnel and the tendon sheath.

RESULTS
Two days following the surgical operation, the patient was discharged with limited weight bearing of the leg (bearing with crutches). The duration of the postoperative monitoring was 8 weeks, a period during witch the patient was performing passive, in the beginning, and then mild active flexion and extension movements of the foot. During the recovery period, exercises were added in order to reinforce the leg so that the patient could gradually return to his previous activities, based on repetitive movements without crutches, while jumping was prohibited. The patient returned to his previous physical activity and his normal way of living within 4 months, without any persisting limitation by his right leg. None of the possible complications emerged (infection, skin lesions, pain at the site of the wound, neurovascular bundle injury, tendon loosening).
As to the left leg, the one with the milder clinical course, we advised a regimen with non-steroid anti-inflammatory drugs and monitoring of the clinical course, in order to decide whether it is necessary or not to continue the conservative treatment or to proceed to operation.
During the regular, every six months, examination of the patient, the operated right leg presented excellent clinical course and full functional rehabilitation. As to the left leg, it continued presenting the sign of the trigger toe, but without any pain, or limitation of the patient's daily activities. On this account, we selected the policy of monitoring the patient and altering the treatment only when there would be a significant change of the clinical course and especially the function of the leg.

DISCUSSION
Stenosis of the tendon sheath of the flexor hallucis longus, which is manifested as trigger toe, is a rare clinical entity. It mainly affects female classic ballet dancers, because of the significant strain bearing the lower extremities. Washington, in a review of 1662 injuries, related to dancing, found out that the lower extremities were the more common site of injury[42], and especially the ankle and the foot. Solomon et al., in a review of 171 injuries, reported 77 injuries of the foot and ankle, 26 injuries of the back and 20 injuries of the knee[39]. Most of the injuries are not severe and recover with time. Standing in the en pointe position, which is a routine exercise for ballet dancers, is related to a larger risk of foot and ankle injury, and frequently leads to tendonitis of the flexor hallucis longus[14,17,27,31].
Standing in the en pointe position requires significant plantar flexion of the ankle joint, as well as physical strength, good balance and muscle synergy. When someone is standing in the en pointe position, the tendon of the flexor hallucis longus may be distended beyond its normal limits. Many factors, such as the decreased ligament elasticity, the improper en pointe position, the pronation of the foot and the wrong position of the hips may augment the stress of the tendon[12]. This repeated distress in combination to the anatomical condition of the fibrosseous canal below the sustentaculum tali, where the tendon's direction is acutely altered, contributes to an increased potential of injury of the tendon at this position.
The structure of the anatomical features of the posteromedial surface of the ankle, from the inside towards outside is as following: tendon of the tibialis posterior, tendon of the flexor digitorum longus, posterior tibial vessels, tibial nerve, and tendon of the flexor hallucis longus. The accessory flexor digitorum longus may also be present in the form of fibers that are in close contact with the neurovascular bundle and the tendon of the flexor hallucis longus. Nathan et al. noticed such a structure in 12 among 100 necrotomic specimen[29]. All the above mentioned anatomical structures deviate from their direct course as they penetrate the subtalar joint and are retained together by the retinaculum of the flexor muscles (laciniate ligament).
The tendon of the flexor hallucis longus passes behind the medial malleolus and deep into the laciniate ligament inside a canal formed between the medial and lateral tubercle of the anterior process of the talus, and then penetrates the plantar canal below the sustentaculum tali. The fibrosseous canal formed by these anatomic features is covered by a membrane. This membrane begins at 1 cm proximally to the subtalar joint and encircles the tendon of the flexor hallucis longus, ending in the plantar side of the tendon sheath of the tibialis posterior[9,11,15,37]. This membranic tissue that covers the fibrosseous canal is the exact site of injury in patients that present stenosing tenosynovitis of the flexor hallucis longus[7].
A range of pathologic lesions are related to stenosing tenosynovitis of the flexor hallucis longus. These lesions consist of thinning and stenosis of the tendon sheath, membranous hypertrophy and symphysis[6,12,13,34]. In several cases, an abnormal muscle interference enables the entry of muscle fibers into the sheath following an intense flexion of the great toe[7,12,28,40]. The tendon itself may develop thinning or even central necrosis[12,31,41]. In more severe cases, trigger toe may be the result of calcificated nodules or a partial transection of the tendon[35].
A patient suffering from stenosing tenosynovitis of the flexor hallucis longus, presents with pain and edema behind the medial malleolus. Symptoms are related to the foot movements, primarily when the patient is trying to raise the arch of the foot, and they become more intense during jumping and en pointe position. In severe cases, crepitation may develop, as well as a triggering sensation at the ankle, when extending the great toe[3,6,12,33,35,41]. When a node gets trapped inside the canal, the distal phalanx of the great toe remains extended. In this setting, the patient isn't able to stand in the en pointe position, while it is impossible for him to hold the interphalangeal joint in a neutral position.
The physical examination reveals sensitivity over the tendon sheath, behind and below the medial malleolus, while nodes may be palpated at the site of the sensitivity. The passive movement of the great toe generates less paint than the active one. By passively extending the interphalangeal joint of the great toe, trapping of a node inside the fibrosseous canal may occur, generating thus the triggering sensation, when the flexor hallucis longus contracts, pulling the node outside of the canal[3,6,12,20,24,31,34,35,36]. Limitation of the dorsal flexion of the great toe may occur when the knee is in full extension and the ankle joint in full plantar flexion. Some writers claim that this finding is suggestive of functional contraction of the tendon of the flexor hallucis longus[12,40].
The evaluation should also include radiological imaging of the ankle joint and the foot. An oblique X-ray of the ankle joint in full flexion will help to identify the presence of the os trigonum. While Lunch and Pupp believe that tomography is essential in the diagnosis of the tendon sheath stenosis, Kolettis et al. claim that this isn't necessary[12,40].
The differential diagnosis of the pain at the posterior surface of the foot or the ankle joint in patients with predisposition to such a medical condition includes any other injury because of mechanical strain, and inflammatory diseases, such as rheumatoid arthritis, gonococcal arthritis, syphilis, tuberculosis, gout arthritis, Reiter syndrome, inflammatory bowel diseases and several neoplastic diseases[1,22,23,24,30]. The os trigonum syndrome is an entity that must always be considered during differential diagnosis. This entity may frequently coexist or even misinterpreted as tendonitis of the flexor hallucis longus. The os trigonum is a distinct part of the lateral tubercle of the talus that may give symptoms either following a direct injury during plantar flexion of the joint, or following irritation of the tendon of the flexor hallucis longus, which passes between this bone and the medial tubercle of the ankle.
Dancers have a greater incidence of os trigonum, as also a greater incidence of symptoms caused by this bone. This tension correlates with the excess plantar flexion of the ankle joint required during the en pointe position. Hamilton[12], in a review of the problems of the foot and ankle, mentions 17 cases in which the release of the tendon of the flexor hallucis longus was combined with the removal of the os trigonum, and also noted the difficulty in evaluating the results of this combined condition. The investigation of an os trigonum that seems to generate symptoms may be mandatory, along with the investigation of the flexor hallucis longus, in every patient complaining of pain during the en pointe position[4,12,13,26,43].
The first therapeutic approach of an isolated tenosynovitis of the flexor hallucis longus consists of administration of non steroid anti-inflammatory drugs (NSAIDs), cold baths, mild extension, massage, hydrotherapy and ultrasound therapy. Training may be continued but without en pointe position. Moreover, patients should avoid triggering factors, such as the use of soft shoes during exercise, pronation of the feet, exercising on hard terrain and landing on the heels after the jumps[3,11,12,31,33].
If symptoms get more intense, we recommend more potent NSAIDs, immobilization for short periods of time (3-4 weeks), and physiotherapy[11,12,13]. Corticosteroid injections are rarely performed due to the risk of impairment or rupture of the tendon.
Surgical release of the flexor hallucis longus is only advisable when symptoms persist despite the preceding conservative treatment. Potential complications of the operation are infection, skin lesions, pain at the injury site, and neurovascular bundle injury. Hardening of the tendon or recurrence of the tenosynovitis may be caused by the postoperative scar, or by an ineffective release of the tendon sheath, or a combination of these two. Moreover, several writers claim that the complete release of the aponeurosis which is a part of the fibrosseous canal may lead to tendon loosening.
In conclusion, surgical release of the tendon of the flexor hallucis longus is mandatory for the treatment of stenosing tenosynovitis at the level of ankle joint, when conservative treatment fails, especially in patients who claim for excellent function of the foot.
Questions and speculation, regarding the investigation of other triggering factors that contribute to the emergence of this clinical entity, still remain. The above case report, with bilateral stenosing tenosynovitis at the level of the ankle, in a person that wasn't straining his feet by working in the en pointe position and didn't have any anatomic abnormality, or any of the triggering factors mentioned above, leads as to further investigations. Genetic, hereditary, environmental - during delivery or during the development of the child - factors, yet unidentified, may contribute, even if we are not capable of revealing them up to this day. Besides, the formation of potent statistical correlations between cause and result becomes very difficult because of the very low incidence of the disease.

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Levadia General Hospital Orthopaedic Department
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e-mail: isoforth@hol.gr