High prevalence of MRI findings suggestive of occult lateral hinge fractures after open-wedge distal tibial tuberosity osteotomy

Purpose This study aimed to determine the prevalence of magnetic resonance imaging (MRI) findings suggestive of lateral hinge fracture (LHF), including occult lesions undetectable on conventional imaging, after open-wedge distal tibial tuberosity osteotomy (OWDTO), and to evaluate their clinical significance. Methods This single-center observational study included 47 knees that underwent OWDTO. Imaging assessments consisted of plain radiographs obtained immediately post-operatively and at 1 week and 1 month; computed tomography (CT) at 1 week and 2 months; and MRI at 1 month post-operatively. LHF detection was evaluated for each imaging modality. The morphological pattern of MRI findings was classified using the Takeuchi classification, and bone healing status was assessed using CT at 2 months post-operatively. Factors associated with delayed union were analyzed. Results LHF was detected in 1/47 knees (2.1%) on immediate post-operative radiographs, 2/47 knees (4.3%) both on radiographs and CT at 1 week, 4/47 knees (8.5%) on radiographs at 1 month, and 6/47 knees (12.8%) on CT at 2 months. In contrast, MRI at 1 month identified findings suggestive of LHF in all cases (47/47 knees, 100%). Of these, 46 knees (97.9%) were classified as type I and 1 knee (2.1%) as type III, with no type II findings. Most cases with MRI findings suggestive of occult LHF achieved bone union without clinical complications. Delayed union was instead associated with a larger opening width and with an overt LHF that was already evident on radiographs and CT at 1 week post-operatively. Conclusions MRI findings suggestive of LHF were identified in all cases after OWDTO, and many cases previously considered fracture free on conventional imaging may harbor occult structural changes detectable only by MRI. Most cases with MRI findings suggestive of LHF healed uneventfully, suggesting that the mere presence of an occult LHF does not necessarily indicate a clinically significant problem. Whether MRI offers additional clinical value, particularly for the early detection of clinically important Takeuchi type II and type III fractures, remains to be confirmed, as such fractures were rare or absent in this cohort.