BackgroundLower limb trauma is the most common injury sustained in motorcycle crashes. There are limited data describing this cohort in Australia and limited international data establishing costs due to lower limb trauma following motorcycle crashes. MethodsThis retrospective cohort study utilised administrative hospitalisation data from Queensland, Australia from 2011–2017. Eligible participants included those admitted with a principal diagnosis coded as lower extremity or pelvic fracture following a motorcycle crash (defined as the index admission). Multiply injured motorcyclists where the lower limb injury was not coded as the primary diagnosis (i.e. principal diagnosis was rather coded as head injury, internal organ injures etc.) were not included in the study. Hospitalisation data were also linked to clinical costing data. Logistic regression was used to determine risk factors for 30-day readmission. Costing data were compared between those readmitted and those who weren't, using bootstrapped t-tests and ANVOA. ResultsA total of 3342 patients met eligibility, with the most common lower limb fracture being tibia/fibula fractures (40.8%). 212 participants (6.3%) were readmitted within 30-days of discharge. The following were found to predict readmission: male sex (OR 1.84, 95% CI 1.01–1.94); chronic anaemia (OR 2.19, 95% CI 1.41–3.39); current/ex-smoker (OR 1.60, 95% CI 1.21–2.12); emergency admission (OR 2.77, 95% CI 1.35–5.70) and tibia/fibula fracture type (OR 1.46, 95% CI 1.10-1.94). The most common reasons for readmission were related to ongoing fracture care, infection or post-operative complications. The average hospitalisation cost for the index admission was AU$29,044 (95% CI $27,235-$30,853) with significant differences seen between fracture types. The total hospitalisation cost of readmissions was almost AU$2 million over the study period, with an average cost of $10,977 (95% CI $9,131- $13,059). ConclusionsUnplanned readmissions occur in 6.3% of lower limb fractures sustained in motorcycle crashes. Independent predictors of readmission within 30 days of discharge included male sex, chronic anaemia, smoking status, fracture type and emergency admission. Index admission and readmission hospitalisation costs are substantial and should prompt health services to invest in ways to reduce readmission.