Identification of fine wire and half-pin loosening for external fixators: a systematic review

Introduction: This review article discusses the published methods of identification of fine wire and half-pin loosening. The evidence is reviewed and presented for the clinical, radiological and histological analysis of the half-pin and fine wire to bone interface. Materials and Methods: A Preferred Reporting Items for Systematic Reviews and Meta-Analyses compliant systematic review was conducted. Studies investigating the use of external fixators with descriptions on measurement of half-pin and fine wire loosening were included in this review. Results: Eight studies were eligible and included. No randomized controlled trials were identified. Torque measurement was most frequently used to quantify the half-pin to bone interface, histological analysis was performed by three studies, and radiographic analysis was performed by five papers including plain film and micro-computed tomography (CT) techniques. Discussion: The available evidence was of poor quality, with a lack of homogeneity in quantitative data for torque measurements and a prevalence of arbitrary figures for the definition of loosening. There was no mechanical analysis of fire wire loosening, and the most common clinical measure used for loosening was a scale validated for infection. Micro-CT was validated against torque figures and appears to be the most repeatable measure which could be applied clinically, however has only been used in canine studies. We recommend a study to compare the clinically relevant measurement of loosening against a standard model to provide a validated method of identification or prediction of half-pin and fine wire loosening.