Chronic ankle pain in adolescents cannot be diagnosed? Beware of tarsal fusion!

Author: Mo Yueqiang, attending physician, Children's Hospital Affiliated to Fudan University

Reviewer: Xu Ping, deputy chief physician, Children's Hospital Affiliated to Fudan University

Xiao Ming is a 12-year-old middle school student. Two years ago, he began to experience repeated pain on the inner side of his ankles after exercising or standing for a long time. He went to many hospitals for treatment, but the cause was not found. Finally, the doctor highly suspected that Xiao Ming had a rheumatic disease and admitted him to the hospital. After admission, a three-dimensional CT scan of the ankle joint was performed, which showed that the bilateral calcaneus and talus were fused. After consultation with the orthopedic doctor, Xiao Ming underwent a resection surgery on the fusion site of the calcaneus and talus. After one month of plaster fixation after the operation, Xiao Ming recovered well and no longer had pain.

The above-mentioned foot and ankle pain in adolescents is quite common in pediatric orthopedic clinics and has become a common reason for patients to visit. The causes of pain are diverse, including navicular bone, calcaneal epiphysis, tarsal fusion, etc. Despite the variety of causes, most patients can be relieved through conservative treatments such as reducing activities, hot compresses, taking non-steroidal anti-inflammatory drugs (analgesics), and using braces/plaster immobilization. Some patients who fail conservative treatment need further clarification of the cause or even surgical treatment.

1. What are tarsal bones?

The tarsal bones include the calcaneus, talus, cuboid, navicular and three cuneiform bones, a total of seven bones, which are located between the distal end of the tibia and fibula and the sole of the foot (i.e. metatarsals) (the yellow coil part in Figure 1). They are the main load-bearing part of the foot and play a role in buffering shock when walking, running and jumping. Problems in this part can easily cause foot pain.

Figure 1 Copyright image, no permission to reprint

What is tarsal fusion? Why does it cause pain?

Under normal circumstances, each tarsal bone is independent and connected to the surrounding tarsal bones by ligaments. Tarsal fusion refers to the abnormal connection between two or more tarsal bones through bone, cartilage or fiber. This connection weakens or eliminates the buffering effect between the tarsal joints, which can lead to ankle injuries and pain in the long run. Just like a car, if there is no shock absorption system, it is easy to be damaged by the slightest bump. Common tarsal fusions include fusion of the calcaneus and talus and fusion of the calcaneus and navicular bone.

Is tarsal fusion common?

Tarsal fusion often occurs during adolescence. Literature reports that the incidence of tarsal fusion in the population is between 1% and 13% [1], but the actual incidence may be higher because not all tarsal fusions cause pain. If there is no pain, tarsal fusions may not be discovered.

Why is tarsal fusion difficult to diagnose?

Since there is a lot of overlap between the images of the tarsal bones in X-ray films, it is difficult to detect tarsal fusion through X-ray examination, a routine orthopedic examination method, so it is easy to miss the diagnosis.

5. What symptoms should be considered tarsal fusion? How to confirm the diagnosis?

When adolescents repeatedly experience pain in the foot and ankle after standing for a long time or exercising, it is necessary to pay attention to whether there is tarsal fusion. If the pain is located on the dorsum of the foot or slightly outside the dorsum of the foot, it is often suspected that the fusion of the calcaneus and the navicular bone is present. For such patients, anteroposterior and oblique X-rays of the foot can be taken. Abnormal connection between the calcaneus and the talus can often be found on the oblique X-ray of the foot, which manifests as the "anteater nose sign" (Figure 2). If the pain is near the inside of the ankle (that is, the medial malleolus in medicine, with the part close to the midline of the body as the inside), especially if a protruding bone is found under the medial malleolus, and it hurts when pressed, it is necessary to consider the fusion of the calcaneus and the talus, but this fusion is easy to miss in X-ray examinations, and careful search for clues is required to find it. At the same time, children with tarsal fusion are often accompanied by heel valgus, flat feet, etc.

Figure 2 Copyright image, no permission to reprint

After the X-ray examination results are found, the diagnosis can be further clarified through the "gold standard" for diagnosing tarsal fusion - ankle CT examination (Figure 3) to guide subsequent treatment. So can we skip the X-ray examination and directly let all children with ankle pain do CT examination? The answer is obviously no! Because although CT examination is the gold standard, its radiation dose is much higher than that of X-ray examination, and the specific operation is not as convenient as X-ray examination. If all children with ankle pain are required to undergo CT examination, not only will the children be exposed to unnecessary radiation, but it will also cause a waste of medical resources.

Figure 3 Copyright image, no permission to reprint

In addition to X-ray and CT examinations, magnetic resonance imaging (MRI) can also be used as a tool for diagnosing tarsal fusion, especially when diagnosing tarsal fusion caused by cartilage or fibrous connection, magnetic resonance imaging has more advantages than CT examination. However, magnetic resonance imaging has disadvantages such as high examination cost and long examination time.

6. How to treat after diagnosis?

When patients with tarsal fusion experience frequent or persistent pain, treatment is necessary. The first is conservative treatment, including the use of orthopedic insoles, changing the way of activity, braces/plaster fixation, oral nonsteroidal anti-inflammatory drugs to relieve pain, etc. In daily life, you can wear shoes with arch pads, high uppers and relatively hard shoes to improve the shape of the foot during activities, thereby reducing pain.

If conservative treatment is ineffective or the pain recurs, surgery may be necessary. It is recommended that you go to a professional medical institution for treatment.

【References】

[1]SONI JF, VALENZA W, MATSUNAGA C. Tarsal coalition [J]. Curr Opin Pediatr, 2020, 32(1): 93-99.