Illuminating the Complexity of Biology in Syndesmotic Injuries with Ankle Fractures: The Downfalls of Strong Bones

CATEGORY: Ankle INTRODUCTION/PURPOSE: Injury to the syndesmotic ligaments can lead to prolonged functional limitations and thus, long-term ankle mobility dysfunction if not diagnosed and treated appropriately. Obesity has been studied in relation to syndesmotic instability but there is a paucity of literature investigating syndesmotic risk associated with other bone fragility characteristics. Additionally, ankle injury complexity associated with risk of Charcot in patients with a syndesmotic injury remains unstudied. METHODS: This is a large retrospective, database study with structured query of a national insurance claims database (PearlDiver Technologies) for patients treated with ankle fixation from 2015 through 2020 as identified by ICD-10 codes. Patient characteristics associated with obtaining a syndesmotic injury with ankle fracture were analyzed using multivariable logistic regression analysis. In addition to corroborating the increased risk seen with elevated BMI, data included age at time of operation, sex, smoking record, diabetes, and osteoporosis. Likelihood of developing Charcot in patients with an ankle fracture and unstable syndesmosis was also analyzed using univariable logistic regression. RESULTS: Our query yielded 168,359 patients who underwent ankle fixation; 32,502 (23.9%) were treated for syndesmotic injury. On multivariable analysis, obese and male patients had a higher probability of syndesmotic injury (OR 1.39 [95% CI, 1.36-1.43] and OR 1.55 [95% CI, 1.52-1.59], respectively; P<0.001); osteoporotic patients had lower probability of syndesmotic injury (OR 0.64 [95% CI, 0.62-0.67]; P<0.001). Of 13,275 diabetic patients, 2,822 (21.3%) were treated for syndesmotic injury. Diabetic patients had increased probability of developing Charcot (OR 1.54 [95% CI, 1.19-2.00]; P=0.001). A total of 36,883 patients were treated with ankle fixation and unstable syndesmosis. While statistically insignificant, compared to patients with syndesmotic injury treated with bimalleolar ORIF, patients undergoing isolated fibular ORIF had lower probability of developing Charcot (OR 0.71 [95% CI, 0.50-0.99]) versus undergoing trimalleolar ORIF had higher probability (OR 1.24 [95% 0.91-1.69]). CONCLUSION: Among this population derived from a large all-claims database using ICD-10 coding, higher probability of syndesmotic injury was associated with male or obese patients; lower syndesmotic injury probability was associated with osteoporotic patients. This suggests that injuries obtained with a greater force or patients with stronger bone strength are more likely to sustain a syndesmotic disruption while weaker bones are more susceptible to fracture, leaving the syndesmotic structures intact. These findings suggest purposeful evaluation for syndesmotic disruption in patients with these higher risk characteristics. Increasing ankle injury complexity demonstrates a gradient in Charcot risk in patients with syndesmotic instability.