What Is the Reliability of a New Classification for Bone Defects in Revision TKA Based on Preoperative Radiographs?

Abstract

Background Accurate quantification of bone loss facilitates preoperative planning and standardization for research purposes in patients who undergo revision TKA. The most commonly used classification to rate bone defects in this setting, the Anderson Orthopaedic Research Institute classification, does not quantify diaphyseal bone loss and reliability has not been well studied. Questions/purposes We developed a new classification scheme to rate bone defects in patients undergoing revision TKA and tested (1) the intraobserver and interobserver reliability of this classification for revision TKA based on preoperative radiographs, and (2) whether additional CT images might improve interobserver reliability. Methods This was a preregistered observational study. Interobserver reliability was analyzed using preoperative radiographs of 61 patients who underwent (repeat) revision TKA, and their bone defects were rated by five experienced orthopaedic surgeons. For intraobserver reliability, ratings were repeated at least 2 weeks after the first rating (Timepoints 1 and 2). Directly after the radiographic assessments of Timepoint 2, the observers were provided with CT images of each patient and asked to rate the bone defects for a third time (Timepoint 3), to assess the additional value of CT. Intraobserver and interobserver reliability were tested using Gwet’s agreement coefficient 2, which is a measure of agreement between observers in categorical data. Substantial agreement was defined as coefficients between 0.61 to 0.8 and almost perfect agreement as > 0.8. Results The intraobserver reliability varied between 0.55 (95% CI 0.40 to 0.71) and 0.87 (95% CI 0.78 to 0.96) in the epiphysis, between 0.69 (95% CI 0.58 to 0.80) and 0.98 (95% CI 0.95 to 1) in the metaphysis, and between 0.95 (95% CI 0.90 to 0.99) and 0.99 (95% CI 0.98 to 1) in the diaphysis. The interobserver reliability varied between 0.48 (95% CI 0.39 to 0.57) and 0.49 (95% CI 0.42 to 0.56) in the epiphysis and between 0.81 (95% CI 0.75 to 0.87) and 0.88 (95% CI 0.83 to 0.93) in the metaphysis, and was 0.96 (95% CI 0.93 to 0.99) in the diaphysis at Timepoint 1. The interobserver reliability at Timepoint 2 was similar to that of Timepoint 1. The addition of CT images did not improve reliability (Timepoint 3). Conclusions The bone defect classification was less reliable in the epiphyseal area compared with the metaphysis and diaphysis. This finding may be explained by prosthetic components obscuring this region or the more severe bone defects in this region. The addition of CT scans did not improve reliability. Further testing of reliability with observers from other institutions is necessary, as well as validity testing, by testing the classification in relation to intraoperative findings. Level of Evidence Level III, diagnostic study.

Superior Survival of Fully Cemented Fixation Compared to Hybrid Fixation in a Single Design Rotating Hinge Knee Implant

“…In revision knee surgery, adequate fixation in the metaphyseal and diaphyseal area is strongly advised to obtain fixation in at least 2 of the 3 zones since the epiphyseal area is impaired in most revision cases [25]. New classifications that assess bone loss in all 3 zones might have more clinical implications in knee revision surgery [26].…”

Tibial bone defect prediction based on preoperative artefact‐reduced CT imaging is superior to standard radiograph assessment

“…Engh et al described the epiphysis as a zone above a fictive plane through the tip of the fibular head [ 7 ]. In contrast, the current paper used the level of the fibular head with the largest mediolateral width to distinguish between tibial epiphysis and metaphysis [ 2 ]. Consequently, the epiphyseal zone in the current paper is larger than originally reported by Engh et al, however, it is also less impacted by bone defects of the tip of the fibular.…”

“…The epiphyseal-metaphyseal junction was defined at the widest mediolateral point of the fibular head (Fig. 2 ) [ 2 ]. The volume of the remaining bone in each of these areas was computed relative to the total tibial volume of the zone.…”

Imaging in revision total knee arthroplasty: A novel 3D classification system for tibial bone defects

“…The rule of the square defines epiphysis and metaphysis as a square with a side length that is the same as the widest part of the tibial epiphysis used. A plane through the widest mediolateral point of the fibular head was used to distinguish between tibial epiphysis and metaphyseal anatomic zones [19]. Bones below the square were classified as diaphysis.…”