The posterior tibial slope modifies the diagnostic utility of posterior shiny-corner lesions in medial meniscus posterior root tears.

Purpose: A posterior shiny-corner lesion (PSCL) on magnetic resonance imaging (MRI) is an early imaging marker of medial meniscus posterior root tear (MMPRT). However, false-negative PSCL findings may occur even in the acute phase of MMPRT. This study aimed to investigate whether the posterior tibial slope (PTS) modifies the presence of PSCL in surgically treated MMPRT across different MRI timing categories. We hypothesized that higher PTS would be associated with PSCL positivity. Methods: We retrospectively reviewed records of 53 knees in 46 patients (36 women and 10 men; mean age, 66.5 ± 9.4 years) treated surgically for MMPRT who had undergone preoperative MRI. MRI timing from symptom onset was categorized as acute (within 3 weeks), subacute (within 8 weeks but beyond 3 weeks), and chronic (beyond 8 weeks). The presence of PSCL, MRI signs (cleft, giraffe neck and ghost signs), and medial meniscus extrusion were recorded. Multivariable logistic regression analysis was performed to evaluate whether PTS was independently associated with PSCL after adjusting for MRI timing category. Results: The prevalence of PSCL decreased with time from onset (acute, 86.4%, 19/22 knees; subacute, 62.5%, 10/16 knees; chronic, 13.3%, 2/15 knees). PSCL-positive patients had higher PTS than PSCL-negative patients (8.7° ± 3.4° vs. 5.5° ± 2.9°; Conclusion: PSCL is associated with early phase of MMPRT; however, its presence is influenced by PTS and is not solely time-dependent. PSCL may be absent even in acute cases with low PTS and therefore should not be used alone to exclude acute MMPRT. Level of Evidence: Level III.