Radiographic Assessment of Bone Union in Proximal Tibia and Distal Femur Osteotomies: A Systematic Review.

Background: Osteotomies around the knee are a well-established treatment option for early and moderate unicompartmental osteoarthritis combined with a lower extremity malalignment. Moreover, osteotomies are often combined with cartilage treatment. Current image-based bone union assessments lack an accepted definition despite widespread use in research and clinical settings. The aim of this systematic review was to identify definitions and classification systems for bone union on radiographs after a proximal tibia or distal femur osteotomy. Methods: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we systematically searched MEDLINE and Embase database, applying specific inclusion and exclusion criteria. Two independent reviewers screened abstracts and full-texts. The modified Cochrane Risk of Bias Tool and Risk of Bias in Nonrandomized Studies of Interventions tool were used. Data extraction included study characteristics, imaging modality, bone union definition, classification systems, assessment of gap fillers, use of modifiers, and osteotomy type. Results: Of the 1,180 screened titles and abstracts, 105 studies were included, with the majority (69 studies [65.7%]) using a retrospective design. Fifty-five studies (52.4%) defined bone union based on one or more criteria, while 50 studies (47.6%) used a classification system. There were 13 different criteria for bone union and 9 different classification systems. Interestingly, none of the classification systems incorporated negative criteria, such as hardware failure. Notably, 137 studies (49.1%) described bone union as either a primary or secondary outcome but do not describe a system for assessing bone union. Conclusion: This systematic review highlights the lack of consensus in the literature in defining bone union after a proximal tibia or distal femur osteotomy, revealing many criteria and different classifications. None of the classification systems were applicable to osteotomies with and without gap filler. This systematic review shows the need for a straightforward, reproducible, and accurate method to assess bone union after a proximal tibia or distal femur osteotomy. Level of Evidence: Level III. See Instructions for Authors for a complete description of levels of evidence.