I. Anatomical features The Achilles tendon is formed by the union of gastrocnemius and flounder tendon fibers from the middle of the calf to the distal end. The two tendon fibers are connected by a tendon membrane with varying degrees of rotation and end at the midpoint behind the heel tuberosity. The Achilles tendon does not have a tendon sheath like other tendons, but is surrounded by a thin, elastic, loose fibrous tissue called peritendinous tissue. The Achilles tendon is the longest and most powerful tendon in the body, about 15 cm long, and can withstand a force of 7000 Newtons. However, during more strenuous sports activities, the Achilles tendon can be subjected to forces up to 7 times the body weight. In addition, the Achilles tendon can be subjected to greater stress due to the movement of the subtalar joint and the excessive rotation of the foot forward. Anatomical studies have proved that the Achilles tendon is a relatively ischemic area within 2-6 cm from the Achilles stop, and the circumference of the Achilles tendon is the thinnest at 4 cm from the stop, and this area is the most prone to injury. It is the intrinsic cause of non-stop Achilles tendinitis. The most common external cause is inflammation of the peritendinous tissue and degeneration and partial rupture of the Achilles tendon itself after excessive stress and repeated minor injuries. Clement reported that overtraining, functional anterior rotation of the foot and reduced elasticity of the triceps are the most common causes of Achilles tendonitis. Astrom concluded that there is no relationship between histopathological changes in the Achilles tendon and exercise, and that exercise only exacerbates the symptoms of Achilles tendinitis, not its cause. Factors associated with Achilles tendonitis include age-related decreased blood flow and reduced tissue elasticity; muscle weakness and muscle imbalance; poor limb force lines; incorrect training; improper shoeing and the effects of medications such as quinolones and hormones. Puddu divides Achilles tendinitis into three stages: stage 1, normal Achilles tendon itself with inflammation of the peritendinous tissue and peritendinitis. stage 2, peritendinitis and degeneration of the Achilles tendon, manifested by calcification within the tendon, nodular hyperplasia and loss of normal luster. stage 3, rupture of the tendon fibers. Pathological changes were seen in the altered collagen structure of the Achilles tendon and an increased amount of aminoglucan within the tendon fibers. However, no inflammatory changes of the tendon were found. Clinical manifestations Non-stop Achilles tendinitis mostly occurs in male athletes aged 35 to 45 years old, but can also develop in the general population of non-athletes. There is pain in the posterior part of the heel, 2-6 cm from the Achilles tendon stop, and there may be local swelling. In the early stages of Achilles tendinitis, pain is felt in the Achilles tendon area when walking or moving around a lot. When the disease worsens, the Achilles tendon may become stiff in the morning and pain may be felt at rest. Limping may occur. The patient should be asked about the type and amount of exercise, the nature and degree of pain, and previous treatment, and whether hormones have been used systemically or locally. Examination reveals swelling of the Achilles tendon over the Achilles tendon stop and increased localized pain on passive dorsiflexion of the ankle joint. Dorsal extension of the ankle joint may be limited. However, some patients may have increased dorsiflexion of the ankle joint due to lengthening of the Achilles tendon. When the thumb and index finger are squeezed along the medial and lateral side of the Achilles tendon, local pain is noted. Thickening or nodularity of the Achilles tendon surface may be palpable. In patients with pure periarthritis of the Achilles tendon, the Achilles tendon pressure site remains the same during ankle extension and flexion activities, while in patients with partial rupture of the Achilles tendon and Achilles tendonitis, the pressure point changes with ankle extension and flexion activities, a manifestation also known as the painful arc of the Achilles tendon sign. The foot should also be examined for inversion and valgus deformity and high arch or flatfoot deformity. MRI can show the extent and degree of degeneration of the Achilles tendon. Clancy divided the Achilles tendonitis into 3 stages: 1. acute stage, the duration of the disease is shorter than 2 weeks; 2. subacute stage, the duration of the disease is between 3 and 6 weeks; 3. chronic stage, the duration of the disease is more than 6 weeks. Treatment 1. Non-surgical treatment (1): Reduce the activity. Severe cases may need to be fixed. (2), physical therapy, ice. Achilles tendon stretching exercises to enhance the elasticity of muscles and tendons. (3), braces, orthopedic shoes to correct the poor force line of the foot. Heel padding of 1.5 cm to relieve Achilles tendon tension. (4).Non-steroidal anti-inflammatory and pain-relieving drugs (NSAIDS). Hormonal drugs should not be injected into the Achilles tendon to avoid affecting the synthesis of collagen in the Achilles tendon, affecting the healing and occurring Achilles tendon rupture. 2.Surgical treatment When the symptoms are not reduced after 6 months of non-surgical treatment, surgical treatment can be taken. About 25% of the patients are treated surgically. Older age, longer history and recurrence of symptoms are common reasons for surgical treatment. The inflamed peritendinous tissue and degenerated Achilles tendon are removed and small Achilles defects can be directly sutured. Larger defects that cannot be directly sutured need to be repaired with other tissues.