S-27 Radiostereometric Analysis Detects Interfragmentary Micromotion in Healed Intra-Articular Fractures of the Distal Radius Treated with a Volar Locking Plate

Abstract

A large number of different volar plate designs have emerged into the market without evidence-based data on their relative efficacy in the stabilization of unstable fractures of the distal end of the radius. One of the obstacles is the lack of suitable methods for quantitative assessment of fracture union. The aim of this study was to perform a critical evaluation of radiostereometric analysis (RSA) in the measurement of three-dimensional interfragmentary micromotion in patients with intra-articular fractures of the distal radius treated with a volar locking plate. Fifteen consecutive adult patients with AO type-C fractures of the distal end of the radius were recruited into the study. All fractures were treated with one type of volar fixed-angle plate. During operative treatment, tantalum RSA markers were inserted into proximal and distal fracture fragments of the radius. Assessment of the treatment outcome included functional tests, Patient-Rated Wrist Evaluation questionnaire (PRWE), conventional radiography and static RSA imaging performed at two, six, twelve, eighteen, and fifty-two weeks postoperatively. In order to study inducible interfragmentary micromotion, dynamic RSA imaging was performed during maximal voluntary grip at the follow-up visits starting at six weeks. Interfragmentary migration and inducible micromotion were measured for three axes of translation and rotation, and the total translation and rotation were calculated. The precision of measurements along individual axes was between 0.08–0.17mm and 0.70–0.94° for migration and between 0.04– 0.07mm and 0.29–0.86° for inducible micromotion. The fractures underwent significant translational and rotational migration (p =0.004 for both) during the first two weeks after surgery, but not thereafter. Maximal grip caused significant translational and rotational interfragmentary micromotion (p < 0.03 for both). Inducible micromotion was detectable up to eighteen weeks even after achievement of radiographic union. Application of RSA in the measurement of fracture fragment migration and inducible interfragmentary micromotion is feasible but technically demanding. RSA may be a unique tool for randomized clinical trials in defining the progress of fracture union.