BackgroundIn proximal humeral fractures, the medial calcar is often considered an important stabilizing structure. When the medial calcar is disrupted, some patients may have accompanying humeral lesser tuberosity comminution that has not been noticed. To investigate the impacts of comminuted fragments of lesser tuberosity and calcar on postoperative stability, CT results, number of fragments, cortical integrity, and the variation of neck-shaft angle were compared in patients with proximal humeral fractures.Materials and methodsFrom April 2016 to April 2021, this study included patients with senile proximal humeral fractures diagnosed by CT three-dimensional reconstruction with lesser tuberosity fractures and medial column injuries. The number of fragments in the lesser tuberosity and the continuity of medial calcar were evaluated. Postoperative stability and shoulder function were evaluated by comparing changes in neck-shaft angle and the DASH upper extremity function score from 1 week to 1 year after the operation.ResultsA total of 131 patients were included in the study, and the results showed that the number of fragments of the lesser tuberosity was related to the integrity of the medial cortex of the humerus. That is, when there were more than two lesser tuberosity fragments, the integrity of humeral medial calcar was poor. The positive rate of the lift-off test was higher in patients with lesser tuberosity comminutions 1 year after surgery. In addition, patients with more than two lesser tuberosity fragments and continuous destruction of the medial calcar had large variations in the neck-shaft angle, high DASH scores, poor postoperative stability, and poor recovery of shoulder joint function 1 year postoperatively.ConclusionThe number of humeral lesser tuberosity fragments and the integrity of the medial calcar were associated with the collapse of the humeral head and the decrease in shoulder joint stability after the proximal humeral fracture surgery. When the number of lesser tuberosity fragments was greater than two and the medial calcar was damaged, the proximal humeral fracture had poor postoperative stability and poor functional recovery of the shoulder joint, which required auxiliary internal fixation treatment.