Does Soft Tissue Envelope Affect Rates of Union in Functional Brace Treatment of Humeral Shaft Fractures?

Abstract

To evaluate the relationship between soft tissue envelope thickness and progression to union for humeral shaft fractures treated with functional bracing. Design: Retrospective cohort study. Single academic institution. Patients with humeral shaft fractures (OTA/AO 12) who underwent at least 6 weeks of functional brace treatment. Demographics, injury characteristics, and treatment outcomes were collected. Failure of nonoperative management was defined as continued fracture site motion after 6 weeks with accompanying lack of progressive callus formation. Soft tissue envelope, including the relative thickness of muscle and fat, was measured at the surgical neck of the humerus and deltoid tuberosity using post-reduction radiographs and those taken at the two-, four-, and six-week follow-up visits. Compared were patients who achieved union with bracing to those who did not. Fifty-eight patients met inclusion criteria, of which 29 (50%) were female. Median age was 46.4 years (range 19.9-89.6). Thirty-five (60.3%) progressed to union with functional brace treatment, whereas 23 (39.7%) underwent surgery for failure of progressive union or had nonunion as their final outcome. Current smoking status was significantly associated with nonunion (43.5% versus 17.1%, p=0.028). Union outcome was not significantly associated with age, sex, body mass index (BMI), endocrine disease, injury mechanism, or AO/OTA classification (all p>0.05).Patients who progressed to union had less muscle at the deltoid tuberosity four weeks after injury (median 12.8mm (IQR 10.3-17.9)) versus those who did not progress to union (median 22.5mm (18.6-23.7); p=0.015). Union outcome was not associated with soft tissue measurements at any other time point (all p>0.05). Four weeks post-injury, patients who progressed to union had 1cm less muscle at the deltoid tuberosity compared to those who failed nonoperative management. However, no association was found at other time points, suggesting the efficacy of functional brace treatment does not reliably depend on soft tissue thickness around the humerus. III.