The humeral head and the scapula are composed of joints and tendons, which are typical ball and socket joints. The joints are small and shallow, and the lips are attached to the edges; the joint capsules are thin and slack, and the biceps are passed through the capsule; the ligaments of the joint capsules, the ligaments of the shoulders and the tendons strengthen the stability. There is no ligament and muscle reinforcement in the lower part of the capsule, which is the weakest. Therefore, when the shoulder joint is dislocated, the humeral head often comes out from the lower part and is taken off the front and the bottom. The size of the articular surface is quite different, the joint capsule is weak and loose, and there are about three ligaments and tendons attached to it. The deltoid muscle is wrapped on three sides of the shoulder.
Ankle joint, which consists of the ankle joint at the lower end of the humerus and the talus block, is also known as the talus calf joint. The lower ankle surface of the humerus and the internal and external ankle joints form a "冂" shaped joint socket that accommodates the talar block (joint head). Since the joint of the pulley is wide and narrow in front, when the foot is dorsiflexed, the wider front enters. In the socket, the joint is stable; but in the case of plantar flexion, the lower part of the trough enters the fossa when the downhill is down, the ankle joint is loose and can be used for lateral movement. At this time, the ankle joint is prone to sprain, and the most common inversion injury is seen. Because the external hemorrhoid is longer and lower than the internal hemorrhoid, it can prevent excessive valgus of the talus.
The knee joint is composed of the medial and lateral femoral condyles and the medial and lateral condyles of the humerus and the humerus. It is the largest joint with the most complicated structure and many opportunities for injury. It belongs to the joint of the trochlear.
It consists of the lower end of the humerus and the upper end of the ulna and the tibia. It consists of three joints, namely the ulnar joint, the ankle joint and the proximal joint of the ulna. It can do forward bend, back stretch movement, also participate in the forearm pronation and pronation movement.