PARIS (POSTERIOR MALLEOLUS RADIOLOGICAL INVESTIGATION STUDY): STANDARDIZING MANAGEMENT OF UNSTABLE ANKLE FRACTURES WITH A POSTERIOR MALLEOLUS COMPONENT

The PARIS algorithm is used to classify posterior malleolar fractures (PMF) and guide fixation planning based on plain radiographs, with reassessment following pre-operative computed tomography (CT). This study aimed to validate and optimise the PARIS algorithm to determine which ankle fractures with associated PMF require pre-operative CT imaging and fixation. This prospective, pragmatic, observational cohort study was conducted at a large academic trauma centre. Adult patients (≥16 years) presenting with an isolated unstable ankle fracture and associated PMF were recruited. All patients underwent pre-operative CT. Data collected included demographics, fracture classification, and clinical, radiographic, and patient-reported outcomes up to one-year post-surgery. PMF classification and treatment plans based on plain radiographs were recorded and compared with those following CT assessment. A total of 120 patients were included, with a mean age of 51.5 years (22–81); 73.3% were female. Due to the pragmatic design, 98 patients (82%) were managed according to the PARIS algorithm, while 22 (18%) were not. Pre-operative CT altered the radiograph-based classification or treatment plan in only 10% of cases (12/120). In the non-algorithm group, the median PMF size was significantly larger (19.0% vs 9.4%; p<0.001), with a higher fixation rate (90.0% vs 15.3%; p<0.001). However, CT changed the fixation plan in only 7 of these 22 cases. Infection rates were significantly lower in patients managed according to the algorithm (9.2% vs 27.3%, p=0.020). Post-operative reduction and rates of post-traumatic osteoarthritis at six months were comparable between groups. At one year, Olerud Molander Ankle Scores were superior in the algorithm group (85 vs 65), although not statistically significant (p=0.120). Use of the PARIS algorithm resulted in lower complication rates with comparable radiographic and clinical outcomes. Routine CT is not necessary for all PMFs; selective imaging in larger or more complex fractures appears sufficient to guide fixation decisions.