LAMBDA sign can be used as an indicator to predict long-term prognosis of ankle injury: a ten-year follow-up retrospective study based on MRI

Background : The LAMBDA sign on ankle MRI suggests distal tibiofibular syndesmosis injury. This study evaluated whether the LAMBDA sign predicts long-term outcomes in patients undergoing anterior talofibular ligament (ATFL) surgery. Methods : We retrospectively reviewed patients who underwent ATFL repair or reconstruction at a single institution (2014–2016). A transparent cohort flow was documented, comparing included and excluded patients to assess for selection bias. The primary endpoint was defined as the Foot and Ankle Outcome Score (FAOS) at final follow-up. At surgery, all were diagnosed clinically as isolated ATFL injuries without chondral lesions; the syndesmosis was not explored. Preoperative MRIs were re-read and patients classified by presence/absence of the LAMBDA sign. LAMBDA-positive patients were additionally stratified by distal tibiofibular joint effusion height (DTJEH ≥8 mm vs <8 mm). Baseline characteristics and long-term patient-reported outcomes (FAOS, Karlsson, Tegner) were collected. Adjusted effects with 95% CIs were reported. Rater reliability (ICC/κ) for LAMBDA and DTJEH was assessed with CIs and exact methods. Results : Seventy-nine patients were included (mean follow-up 112.2±8.0 months): 46 LAMBDA-positive and 33 LAMBDA-negative. Compared with the negative group, LAMBDA-positive patients had higher preinjury Tegner scores (6.0 [6.0–7.0] vs 5.0 [4.5–6.5]; p<0.05) but worse final outcomes: FAOS 80.0 [75.0–85.0] vs 86.0 [81.5–88.0] (mean difference -6.1; 95% CI, -9.3 to -3.0; p<0.001), Karlsson 80.0 [75.0–85.0] vs 85.0 [84.0–90.0] (mean difference -6.1; 95% CI, -9.5 to -2.7; p=0.001), and greater Tegner decline 2.0 [1.0–3.0] vs 1.0 [0.5–2.0] (p<0.05). While statistically significant, these differences did not reach established MCID thresholds (FAOS: 11.7, Karlsson: 10.0). Conclusion : The presence of a positive LAMBDA sign on preoperative MRI is associated with poorer long-term clinical outcomes. However, DTJEH is not significantly correlated with overall long-term outcomes. The LAMBDA sign can serve as a valuable preoperative prognostic indicator. Level of Evidence: III (retrospective cohort).