Purpose: The objectives of this study are to propose a reliable radiologic method for detecting static inferior subluxation of humeral head, to calculate the relative intra- and inter-observer reliability, and to evaluate its presence pre- and post-surgery.
Methods: This is a retrospective observational study of patients surgically treated for a fracture of the proximal humerus. Fractures were classified using Codman-Lego criteria (radiographic, CT images), osteoporosis was assessed. To identify inferior subluxation, an original method is proposed. This measurement was done pre-operatively, at three and 12 month post-operatively. Clinical evaluation was recorded at final follow-up using Constant Score.
Results: One hundred fifty fractures surgically treated were studied. Intra- and inter-observer reliabilities were excellent and high, respectively. In pre-operative x-rays, a significant inferior subluxation was noted in 17/150 cases (11.3%), with significant correlation with fracture pattern (p=0.045), female sex (p=0.038), age older than 70 (p=0.003), obesity (BMI>30, p=0.03), and local osteoporosis (p=0.002). At three month of follow-up, 22 cases (14.6%) had inferior subluxation, with significant correlation with female sex (p=0.04), age older than 70 (p=0.002), obesity (p=0.02), pin or screw articular surface perforation (p<0.001). At 12 month of follow-up, seven cases showed persistent inferior subluxation, with significant correlation with age older than 70 (p=0.032), obesity (p=0.041), screw joint perforation and lower Constant Score (p<0.001).
Discussion: Inferior subluxation was mostly found in osteoporotic fractures of the elderly, obese, and of female sex both pre- and post-operatively. The intra- and inter-observer reliabilities of proposed radiographic measurement were high and excellent, respectively.
Conclusions: In the early postoperative months, we found a high correlation between inferior subluxation and articular surface perforation; when persisting at later follow-ups, we might speculate that it could represent an early phase of avascular necrosis of the humeral head.
Level of evidence: Level III, observational study.
Keywords: Avascular necrosis; Osteoporosis; Proximal humerus fractures; Screw joint perforation; Static inferior subluxation.