External fixation versus locking plate osteosynthesis for displaced Neer three- and four-part proximal humerus fractures: a retrospective comparative cohort study

The optimal fixation strategy for displaced three- and four-part proximal humerus fractures remains controversial. This study compared clinical, radiological and functional outcomes after locking plate osteosynthesis versus external fixation in adult Neer three- and four-part proximal humerus fractures. This single-center retrospective comparative cohort study included 68 adult patients who underwent surgery between January 2012 and December 2020. Thirty-seven patients were treated with locking plate osteosynthesis and 31 with external fixation. Fractures were classified according to Neer and AO/OTA systems. Final follow-up assessment included union time, complications, revision surgery, range of motion, Constant-Murley, ASES, UCLA and DASH scores. A multivariable linear regression model was used to examine Constant-Murley score after adjustment for treatment group, fracture severity, age, sex, comorbidity and follow-up duration. The cohort comprised 33 women and 35 men, with a mean age of 51.8 years. Baseline characteristics are presented by treatment group; age, comorbidity prevalence and follow-up duration differed between groups. The multivariable model was statistically significant and explained 56.3% of the variability in Constant-Murley score (R2 = 0.563; adjusted R2 = 0.520; F(6,61) = 13.08; p < 0.001). Fracture severity was the strongest independent predictor: Neer four-part fractures had Constant-Murley scores 12.66 points lower than Neer three-part fractures (95% CI -14.92 to -11.40; p < 0.001). After adjustment for fracture severity, age, sex, comorbidity and follow-up duration, treatment method was not an independent predictor of Constant-Murley score (adjusted mean difference 2.39 points favoring external fixation; 95% CI -0.04 to 4.83; p = 0.054). UCLA score, DASH score, union time and overall complications did not differ significantly. In this retrospective comparative cohort, no statistically significant or clinically meaningful difference was detected between locking plate osteosynthesis and external fixation after adjustment for clinically relevant baseline variables. Fracture severity remained the principal independent determinant of functional outcome. Although external fixation demonstrated a small numerical advantage in Constant-Murley score, the estimated treatment effect was modest, below published MCID thresholds, and should not be interpreted as evidence of treatment superiority.