The calcaneus epiphysitis, also known as Sever's disease, was first reported in detail by James Warren Sever in 1912. The diseased population is child and adolescent who have emerged and have not closed the calcaneal epiphysis. The clinical manifestations are localized pain and swelling of the heel. The positive medial-lateral compression test is helpful for the diagnosis of the disease. Many factors such as chronic injury, acute strain and cold stimulation can cause pain in the calcaneal nodules, and high-intensity physical activity can aggravate the pain (1). Its pathogenesis is diverse, and the basic pathology is that the calcaneal callus is subjected to repetitive microfracture damage, causing aseptic inflammation of the calcaneal epiphysis, i.e. surrounding soft tissue and ligament (2,3). There is currently no single explanation for all cases of the disease. The X-ray shows an increase in the density of the calcaneal epiphysis, and a radiolucent line of the epiphysis - that is, a fragmentation of the epiphysis (4,5), but this phenomenon can also occur in healthy children and adolescents (6). Because the mechanical structure of the calcaneus is relatively weak, it is prone to injury (7). This study compared the X-ray image of 98 cases of Sever's disease patients and 120 cases of healthy children and adolescents. Among the 98 patients, 6 underwent MRI, the images showed abnormal signal. Statistical analysis and images processing was performed to provide a basis for the diagnosis of Sever's disease.

The results of this study suggested that the X-ray of Sever's disease showed an increase in the density of the epiphysis, a radiolucent line and a statistically significant comparison with the control group, which is consistent with previous studies (9,11-13). However, in the calcaneus epiphysis development of healthy children and adolescents, increased density and radiolucent line is also observed (4,7-9). It has been suggested in the literature that some patients with severe Sever's disease have reduced density and atrophy of the calcaneus epiphysis (4,14). In the present study, patients with thinning and atrophy of the epiphysis have not been observed, which may be related to the small number of samples and the increased attention of parents. Radiolucent lines can also be seen in the developmental period of normal developing children's calcaneus, accounting for about 1/3, usually 1 to 2 lines, and radiolucent lines were observed in all Sever's patients (11), with higher incidence in male than female, higher incidence in those with larger amount of exercise, obesity and in the preferential foot. Sever's disease is mostly bilateral, and the incidence of boys is higher than that of girls (15). The average age of onset of girls in this study was at the age of 10.08 years, and the average age of onset of boys was 11.49 years, which is consistent with the pattern of growth and development of girls earlier than boys.

Due to the high cost of MRI examination and the long waiting time required, there are few patients who choose this examination, and it is impossible to do statistical analysis. The signs and symptoms can only be observed according to a few cases. The nature of Sever's disease is the process of microfracture of bone cells and repairing after ischemic death. MRI has a good soft tissue resolution and is sensitive to bone marrow edema, synovial thickening, joint effusion and soft tissue edema (16). Sever's disease is a self-limiting disease, mainly characterized by pain, swelling, and fewer other symptoms such as fever. It is usually treated conservatively by appropriately limiting physical activity and suggesting rest to relieve the stimulation to the heel from pulling the Achilles tendon, or by physical methods such as scaffold support, cold compress, traction to alleviate the heel pain to achieve self-healing, most patients only need the clinician physical examination and the addition of lateral calcaneal view films, CT or MRI may be required for very few serious cases with poor prognosis from conservative treatment. Given the radioactivity of X-rays, it is still controversial whether Sever's patients need to take a film, but taking X-rays can rule out other lesions of the calcaneus such as fractures, osteomyelitis, calcaneal tumors or tumor-like lesions.

In conclusion, the main clinical manifestation of Sever's disease is local pain of the calcaneus. The X-ray is mainly characterized by increased density of the calcaneus epiphysis, and the appearance of radiolucent line. It is sometimes difficult to diagnose by X-ray film alone, the combination with the medical history or MRI examination is required. MRI is the most accurate imaging examination method for the damage of the epiphysis (17), which can provide more reliable image information for the observation and prognosis of Sever's disease osteophyte soft tissue injury, and provide direction for guiding clinical treatment (18,19). This study was aimed to provide some help for clinical and imaging diagnosis of Sever's disease.