Assessment of inducible fracture micromotion in distal radial fractures using radiostereometry

Objectives: This study examined the potential for measuring dynamic inducible micromotion (DIMM) between fragments in healing distal radial fractures using radiostereometry (RSA). Design: Prospective imaging study. Setting: University teaching hospital. Patients: Nine patients with low-impact distal radial fractures. Intervention: Volar locked plating of the fracture with insertion of tantalum beads into bone fragments. RSA examinations at 1 day and then 2, 6, 26, and 52 weeks. Motion at the fracture site was induced by maximal voluntary hand grip using a Jamar dynamometer. Radiographs were analyzed using locally developed and UMRSA software. Main Outcome Measurements: DIMM and migration were calculated as translations and rotations of the main distal segment. Clinical precision was assessed under repeatability conditions. Results: Precision (as 95% error limit) ranged from 0.06 to 0.13 mm and 0.5 to 0.8 degrees for migration, and from 0.10 to 0.14 mm and 0.6 to 1.0 degrees for DIMM. DIMM was characterized by axial and dorsal compression with dorsiflexion. The median DIMM of patients reached a maximum at 2 weeks: mainly as 0.3 mm axial compression, 0.3 mm dorsal compression, and 2.5 degrees dorsiflexion. DIMM ceased by 26 weeks, indicating union of all fractures. Fracture collapse continued until the 26-week measurement, ranging between 0.2 and 2.8 mm axially. Instability of some intraosseous markers was observed. Conclusions: The precision of this RSA method was sufficient to observe inducible movements occurring during fracture healing. This has the potential for quantifying rates of fracture union and improving understanding of the available treatments.