Nonunion After Nonoperative Treatment of a Proximal Humeral
Researchers aimed to estimate the rate of nonunion in nonoperatively treated patients and to produce a clinical model for its prediction. The prevalence of nonunion after a proximal humeral fracture (PHF) and the risk factors for its occurrence are poorly defined.

2230 adult patients with a PHF underwent assessment of fracture union using standard clinical evaluation and conventional radiographs. The prevalence of nonunion was assessed and the effect of 19 parameters on healing was measured. The PHF assessment of risk of nonunion model (PHARON) was externally validated in a subsequent prospectively collected population of 735 patients, treated by the same protocol in our institution.

--Overall, 231 of 2,230 patients developed nonunion. Only 3 of 395 patients with a head-shaft angle (HSA) of more than 140° developed nonunion; in this cohort, none of the measured candidate variables were independently predictive of nonunion on multivariate logistic regression analysis.

--In the larger cohort of 1,835 patients with an HSA of less than 140°, 228 developed nonunion.

--Decreasing HSA, increasing head-shaft translation (HST), and smoking were independently predictive of nonunion on multivariate analysis.

--The prevalence of nonunion was very low in the majority with both an HSA of more than 90° and HST of less than 50%, whereas the risk was much higher in the 8.3% with an HSA of less than 90° and HST of more than 50%.

--In both groups, the prevalence of nonunion was much higher in smokers.

Finally, after PHF there is a greater rate of nonunion than described earlier. Most patients have favorable estimations of the risk factor, and a very low risk, but there is a much increased risk of a smaller subset. With PHARON, standard clinical evaluation instruments can precisely measure the risk.