Abstract:

Background

Proximal humeral fractures are common upper limb fractures and have a high incidence among middle-aged and older adults， usually caused by low-energy falls. With the intensification of global population aging， the incidence of proximal humeral fractures is also increasing.Recent epidemiological studies have pointed out that the majority of proximal humeral fractures are displaced. Elderly patients， due to osteoporosis and decreased bone density， tend to have more complex fractures when they occur and face more challenges in the treatment process. For displaced and unstable proximal humeral fractures， open reduction and internal fixation remain the preferred treatment methods when bone quality permits. Open reduction and internal fixation not only help restore the anatomical position of the fracture site but also effectively relieve pain and promote early rehabilitation. Proximal humeral fractures are often accompanied by relatively obvious osteoporosis， which makes internal fixation treatment face many difficulties. Osteoporosis leads to bone fragility in the fracture area， which affects the stability of the fixation device and increases the risk of postoperative complications. The most common complication after internal fixation of proximal humeral fractures is the varus deformity of the humeral head. Varus not only affects postoperative shoulder joint function but may also lead to complications such as subacromial impingement， internal fixation failure， and screw protrusion due to changes in the rotation center of the humeral head， resulting in pain and functional disorders in patients. Clinically， for cases with medial cortical fragmentation， methods such as enhancing the internal fixation torque through intramedullary nails or increasing stability through intramedullary fibular bone grafting can prevent the inversion and collapse of the humeral head after surgery. Although these measures can effectively prevent the occurrence of humeral head varus and collapse， the mechanism of changes in the bony structure and internal fixation of the proximal humerus caused by humeral head varus has not been fully clarified so far. The occurrence of varus deformity may be closely related to multiple factors such as fracture type， postoperative reduction condition， bone condition， and the choice of internal fixation. Therefore， in-depth research on the pathological mechanism and imaging manifestations of inversion after proximal humeral fracture surgery has practical clinical significance. Through imaging measurements， especially the evaluation of geometric indicators after humeral head inversion， a basis can be provided for further optimizing the treatment plan.

Objective

To investigate the radiographic characteristics and correlations of varus deformity following locking plate fixation for proximal humeral fractures.

Methods

A retrospective analysis was conducted on patients with locking plate internal fixation of proximal humeral fractures who underwent surgical treatment from September 2014 to September 2024. A total of 53 patients with humeral head inversion after surgery （22 males and 31 females， with an average age of 61.3 years±5.4 years） were screened out. The following parameters were measured by anterior-position X-ray films of the scapula one year after surgery：（1）Humeral head trunk angle （HSA）； （2）Large nodule - acromial distance （GT-AC）； （3）Medial cortical interpolation（MI）； （4）Rotation center height difference（）； （5）Large nodule - humeral head distance. Pearson correlation analysis was used to assess the relationships between various imaging indicators.

Results

HSA was significantly positively correlated with GT-AC （r=0.694， P＜0.001）， HSA was significantly negatively correlated with MI （r= -0.986， P＜0.001）， articular surface-large nodule distance （r=0.063， P=0.656），and （r=0.015， P=0.912） had no significant correlation with the degree of inversion.

Conclusion

The shortening of medial cortical intercalation and the reduction of the distance between the large nodule and the acromion is significantly associated with humeral head inversion. In the clinical assessment of humeral head inversion after proximal humeral fracture surgery， these concomitant pathological mechanisms should be considered.

Key words: proximal humeral fractures, Internal fixation, Varus, Imaging