Abstract
Summary
Quantification of Three-Dimensional Computed Tomography (Q3DCT) is a reliable and reproducible technique to quantify and characterise ankle fractures with a posterior malleolar fragment (www.traumaplatform.org). This technique could be useful to characterise posterior malleolar fragments associated with specific ankle fracture patterns.
Introduction
Fixation of posterior malleolar fractures of the ankle is subject of ongoing debate1. Fracture fixation is recommended for fragments involving 25–30% of articular surface1. However, these measurements -and this recommendation- are based on plain lateral radiographs only. A reliable and reproducible method for measurements of fragment size and articular involvement of posterior malleolar fractures has not been described. The aim of this study is to assess the inter-observer reliability of Quantification using Three-Dimensional Computed Tomography (Q3DCT) –modelling2,3,4,5 for fragment size and articular involvement of posterior malleolar fractures. We hypothesize that Q3DCT-modelling for posterior malleolar fractures has good to excellent reliability.
Patients & Methods
To evaluate inter-observer reliability of Q3DCT-modelling, we included a consecutive series of 43 patients with an ankle fracture involving the posterior malleolus and a complete radiographic documentation (radiographs and computed tomography) Fractures of the tibial plafond (pilon type fractures) were excluded. These 43 patients were divided in 3 different types (Type I, II or III) as described by Haraguchi6. Five patients of each type were randomly selected for an equal distribution of articular fragment sizes. 3D models were reconstructed by 1) creating a mask for every respective slice; 2) select the appropriate dots that separate fracture from tibialshaft; 3) connect masks of each respective slice; and 4) reconstruct a 3D-mesh. After reconstruction of 3D-models, 1) fragment volume; 2) articular surface of the posterior malleolar fragment; 3) articular surface of intact tibia and 4) articular surface of the medial malleolus were calculated by all three observers. A summary of this technique is shown on www.traumaplatform.org. The inter-observer reliability of these measurements was calculated using the ICC, which can be interpreted as the kappa coefficient.
Results
Measurements of the volume of posterior malleolar fracture fragments ranged from 357 to 2904 mm3 with an ICC of 1.00 (Confidence interval (CI) 0.999 – 1.000) Measurements of the articular surface of the posterior malleolar fracture fragment ranged from 25 to 252 mm2 with an ICC of 0.998 (CI 0.996 – 0.999); the articular surface of the intact tibia plafond ranged from 375 to 1124 mm2 (ICC 0.998, CI 0.996 – 0.999); and the articular surface of the medial malleolus ranged from 79 to 149 mm2 (ICC 0.978, CI 0.978 – 0.911). The categorical ratings for all ICC's were defined as almost perfect according to the system of Landis7.
Discussion/Conclusion
This study showed that our Q3DCT-modelling technique2,3,4,5 is reliable and reproducible to reconstruct ankle fractures, in order to assess fracture characteristics of posterior malleolar fracture fragments. Future research will focus on the association between overall ankle fracture patterns according to Lauge-Hansen, and characterization of posterior malleolar fragment morphology. We hypothesise that supination-exorotation type fractures are associated with smaller (in volume and involved articularsurface) “pull-off” fragments, while pronation-exorotation type ankle fractures are associated with larger (in volume and involved articular surface) “push-off” fragments. The clinical relevance might be that smaller “pull-off” type fractures benefit from positioning screws, while larger “push-off” type fractures require direct open reduction and internal fixation of the posterior malleolar fragment.
