UTILITY OF THREE-DIMENSIONAL COMPUTED TOMOGRAPHY PELVIS RECONSTRUCTION FOR IDENTIFICATION OF ACETABULAR DEFECTS IN RESIDENCY TRAINING

Introduction The number of complex revision total hip arthroplasties (THA) is predicted to rise. The identification of acetabular bone defects prior to revision THA has important implications on technique and complexity of acetabular reconstruction. Paprosky et al. proposed a classification system including 3 main types with up to 3 subtypes focused on the integrity of the superior rim of the acetabulum and medial wall. However, the classification system is complex and its reliability has been questioned. The purpose of this study was to evaluate the effectiveness of different radiologic imaging modalities (plain radiographs, 2-D CT, 3-D CT reconstructions) in classifying acetabular defects in revision hip arthroplasty cases and their value of at different levels of orthopaedic training. Methods Patients treated with revision total hip arthroplasty for acetabular bone defects between 2002–2012 were identified and 22 cases selected that had plain radiographs, 2-D CT and 3-D reconstructions available. Bone defects were classified independently by two fellowship-trained adult reconstruction surgeons. Representative sections were chosen and compiled into a timed presentation. Thirty-five residents from PGY-1 to PGY-5 and 4 attending orthopaedic surgeons were recruited for this study and received a 15-minute introduction to the classification system. Chi square analysis was utilized to examine the influence of image modality and level of training on the correct classification of acetabular bone loss using the Paprosky classification system with alpha=0.05. Results The correct classification regardless of imaging of PGY levels was 30%. The level of training did not influence the ability to classify an acetabular defect (p=0.918). Correct classification was significantly influenced by the imaging used. Using x-ray led to 37% correctly identified defects, CT scans to 33% and 3D modeling to 30% of correct answers (p<0.001). For Class 1 defects, x-ray imaging had significantly higher number of correct classification (93%) compared to CT scans (67%) and 3D modeling (31%, p<0.001). Similarly, 2A defects were classified correctly with higher frequency on x-ray (49%) compared to CT scans (36%) or 3D modeling (15%, p=0.007). For type 2B, 2C, 3A and 3B defects, the type of imaging did not influence the frequency of correct answer. The level of training did not influence the frequency of correct classification regardless of the type of defect (p<0.05). However, there was a significant difference based on the defect type (p<0.001). Regardless of level of training or imaging, 64% of observers recognized type 1 defects, compared to only 16% correct recognition of 3B defects. Discussion In the current study using different image modalities, residents regardless of the level of training were only able to classify 30% of defects correctly using the Paprosky classification system of acetabular defects. Using plain x-rays led to an increased number of correct classification, while regular CT scan and 3D CT reconstructions did not improve accuracy. The cost for advanced imaging when using this classification may not be justified. The Paprosky classification system of acetabular defects can be used for treatment decisions; however, it is complex and residents may require increased education in its use and identification of defects.