Shoulder joint is the joint with the largest range of movement. The shoulder joints structure is complex and plays an extremely important role in people's daily life. The complex type of proximal humerus fractures has always been a complex disease in the treatment of traumatic orthopedics. The type of proximal humerus fractures and the shape of displacement depend on the mechanism of injury and the pulling of muscle around the fractures. The clinical classification of proximal humeral fractures includes Neer classification and AO classification. Neer classification is based on the affected part and displacement for fracture classification. The proximal of humerus is divided into four parts: humeral head, greater tuberosity, lesser tuberosity and humeral shaft. The classification is based on the number of fractured parts (displacement > 1 cm or > 45°) , and the degree of fracture displacement refers to the position of the other three fracture blocks relative to humeral head. AO classification: type A fracture, as one fracture outside the joint; type B fracture as two fractures outside the joint; type C fracture as intra-articular (anatomical neck) fracture. As the two types of classification are compared, AO classification is used relatively lesser in the clinical due to its large number of subtypes. On the other hand, Neer classification is most commonly used in clinical application. Neer classification can evaluate the complexity of proximal humeral fractures, determine the damage of humeral head blood supply, and guide clinical treatment plan to determine the prognosis of fractures. After more and more clinical cases, however, a special type of fracture was found. According to the Neer classification, it may be only a two-part fracture or a three-part fracture, but the complexity of fractures, the degree of damage to fracture block and the poor prognosis are as bad as the four-part fracture. We call it "head-cap" fracture.

In the Department of Trauma and Orthopedics, Peking University People's Hospital, a total of 76 cases of proximal humeral fractures were diagnosed from January 2016 to December 2017, including 18 cases of "head-cap" type fractures. According to the patient's imaging data, it was found that the humeral head fracture line was located in anatomical neck, and the humeral head had different degrees of compression fracture. The distance between the central region of humeral head anatomical neck plane and the humeral head cartilage surface was less than 17.7 mm, and the average thickness of radial head fracture block was (15.6±1.2) mm. To find a suitable diagnosis and treatment program, we studied the special of the "head-cap" fracture of proximal humerus.

According to the Neer classification, there were 2 cases of two-part fracture, 5 cases of three-part fracture and 11 cases of four-part fracture. Among them, 9 cases were treated with artificial joint replacement, and 9 cases were treated with open reduction and internal fixation. Of the 9 cases treated with open reduction and internal fixation, 2 cases (22%) had different degrees of humeral head absorption. The thickness of radial head fracture block was thinner, and the prognosis of shoulder joint was poor. In the 9 cases of artificial joint replacement, no complication that the shoulder mobility was limited was found.

The risk of humeral head necrosis, malunion and greater tuberosity absorption is very high after the operation of humeral proximal "head-cap" fracture. The orthopedic surgeons should not simply develop a treatment plan based on traditional fracture classification when the corresponding type of fractures is met. According to the specific fracture condition of patients, the surgical treatment should be adjusted. The high risk of humeral head necrosis and malunion after operation for such type of fractures should be taken seriously. The depth of nail should be controlled during internal fixation operation. The screw tip must be strictly 5 mm within joint surface as close as possible, and the crossing of joint surface should be avoided. At the same time, the exact stable fixation of greater and lesser tuberosity is particularly important. The possibility of tuberosity absorption after non-exactly fixation is very high, which may result in serious consequences that cannot be repaired. Arthroplasty is a good treatment option to avoid the complication of humeral head absorption after proximal humeral "head-cap" fracture.