Caused by longitudinal traction with the wrist in pronation, although in a series only 51% of people were reported to have this mechanism, with 22% reporting falls, and patients less than 6 months of age noted to have the injury after rolling over in bed. Cause
This injury has also been reported in babies younger than six months and in older children up to the preteen years. There is a slight predilection for this injury to occur in girls and in the left arm. The classic mechanism of injury is longitudinal traction on the arm with the wrist in pronation, as occurs when the child is lifted up by the wrist. There is no support for the common assumption that a relatively small head of the radius as compared to the neck of the radius predisposes the young to this injury. Pathophysiology
The distal attachment of the annular ligament covering the radial head is weaker in children than in adults, allowing it to be more easily torn. The older child will usually point to the dorsal aspect of the proximal forearm when asked where it hurts. This may mislead one to suspect a buckle fracture of the proximal radius. There is no tear in the soft tissue (probably due to the pliability of young connective tissues).The forearm contains two bones: the radius and the ulna. These bones are attached to each other both at the proximal, or elbow, end and also at the distal, or wrist, end.
The peritoneal cavity is a potential space between the  parietal peritoneum (the peritoneum that surrounds the abdominal wall) and visceral peritoneum (the peritoneum that surrounds the internal organs). The parietal and visceral peritonea are layers of the peritoneum named depending on their function/location. It is one of the spaces derived from the coelomic cavity of the embryo, the others being the pleural cavities around the lungs and the pericardial cavity around the heart. It is the largest serosal sac, and the largest fluid-filled cavity, in the body and secretes approximately 50 ml of fluid per day. This fluid acts as a lubricant and has anti-inflammatory properties. The peritoneal cavity is divided into two compartments – one above, and one below the transverse colon. Compartments
The peritoneal cavity is divided by the transverse colon (and its mesocolon) into an upper supracolic compartment, and a lower infracolic compartment. The liver, spleen, stomach, and lesser omentum are contained within the supracolic compartment. The small intestine surrounded by the ascending, transverse, and descending colon, and the paracolic gutters are contained within the infracolic compartment. Clinical significance
The peritoneal cavity is a common injection site, used in intraperitoneal injection. An increase in the capillary pressure in the abdominal viscera can cause fluid to leave the interstitial space and enter the peritoneal cavity, a condition called ascites.