Proximal humeral fractures are relatively common clinically, accounting for about 5% of total body fractures. The epidemiology of hospitalized patients with periarticular fractures in the key projects of national science & technology pillar program during the thirteenth five-year plan period led by the department of orthopedics and traumatology, peking university people's hospital showed that the proximal humeral fractures accounted for 13.5%. 70% of proximal humeral fractures occur in the elderly over 60 years old, most of which are related to osteoporosis. The incidence of proximal humeral fractures ranks third in elderly osteoporotic fractures, second only to hip fractures and distal radial fractures, and is usually caused by low-energy injuries such as standing falls and limb traction. Among young people, the occurrence of proximal humeral fractures is mainly related to high-energy violence such as traffic injuries and fall injuries. With the development of internal fixation technology and the maturity of surgical techniques, the proximal humeral anatomical locking plate is widely used in clinical treatment. The 9 nail holes at the proximal end provide good angular stability and can improve the firmness of fracture fixation, especially Neer part-3 and part-4 fractures. Biomechanical studies reveals that placing the tip of the screw on the subchondral bone of the humeral head can enhance the pullout resistance. However, due to the anatomical and bony characteristics of the humeral head, screw penetration has become the most common complication in the treatment of proximal humeral fractures with anatomical locking plates, of which up to 64% occurred during surgery, resulting in the damage of articular surfaces of humeral head glenoid and thus affecting the recovery of shoulder joint function. At present, intraoperative fluoroscopy technology cannot completely avoid the occurrence of screw penetration. Therefore, how to accurately determine the effective length of the inserted screw and avoid intraoperative screw penetration is an urgent problem for clinicians. Objective To explore the use of ultrasound to determine whether the screw penetrates the articular surface of humeral head during the plate fixation of proximal humeral fracture.

Two cadaver shoulder joints were used as the research objects. Nine-nail hole penetration models of humeral head were made after the proximal humeral anatomical locking plate fixation. The articular surface penetration of humeral head were explored with ultrasound, and the ranges of motion and the positions of the ultrasonic probe on the surface of the shoulder joint were recorded.

During the detection of penetrations of No.1 to No.9 holes, the ranges of motion of right shoulder joint were 45° of adduction with 90° of internal rotation, 30° of external rotation, 15° of external rotation, 90° of internal rotation, neutral position, 60° of external rotation with 45° of abduction, 90° of internal rotation with neutral position, and 30° of external rotation respectively. The corresponding ultrasonic probe were respectively positioned on the posterosuperior, anterosuperior, anterior, posterior, posterior, anterior, anterior, posteroinferior and anteroinferior surface of right shoulder. During the detection of penetrations of No.1 to No.9 holes, the ranges of motion of left shoulder joint were 30° of external rotation, 45° of adduction with 90° of internal rotation, 15° of external rotation, neutral position, neutral position, 60° of external rotation with 45° of abduction, 30° of external rotation and 90° of internal rotation with neutral position respectively. The corresponding ultrasonic probe were respectively positioned on the anterosuperior, posterosuperior, posterior, anterior, anterior, posterior, anterior, anteroinferior and posteroinferior surface of left shoulder.

Using intraoperative ultrasound to detect the screw penetration of humeral head is a convenient, economical, and simple method. It can reduce unnecessary iatrogenic damage to the shoulder joint while reducing radiation exposure, which is worthy of clinical promotion.