Defining the Mean Angle of Diaphyseal Long Bone Nonunions-Does Shear Prevail?

OBJECTIVES

To define the mean angle of a series of diaphyseal nonunions based on radiographic analysis.

DESIGN

A retrospective cohort study.

SETTING

Two level-1 trauma centers.

PATIENTS: One hundred twenty patients presenting with nonunion.

INTERVENTION: A mean nonunion angle was calculated from a series of AP and lateral X-rays using a standardized technique. The nonunion angle was then estimated in a single plane by considering the greater of the 2 measured angles. Additional data collected included patient age, sex, nonunion site, initial fracture angle, and original fracture pattern.

MAIN OUTCOME MEASUREMENT: Single plane nonunion angle.

RESULTS

The mean angles of all nonunion in coronal plane was 42 degrees (SD 17 degrees) and 42 degrees in sagittal plane (SD 18 degrees) and 48 degrees (SD 15 degrees) in single plane. The single plane nonunion angle in fractures which were originally multiplanar was steeper to those occurring in originally single plane fractures (P 0.002) although both were close to 45 degrees. There was no significant difference in the nonunion angles on subgroup analysis of cohort location, sex, or anatomic location.

CONCLUSIONS

This study demonstrates the mean angle of diaphyseal nonunions from long bones of the lower limb approaches 45 degrees. This is noted in all types of fractures and is irrespective of anatomic location or sex. This confirms the hypothesis that shear is likely to play a role in the development of a nonunion. This study provides further evidence that nonunions occur primarily because of mechanical instability.

LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.