Objectives To evaluate the risk of psoriatic arthritis (PsA) among patients with psoriasis exposed to physical trauma.

Methods A matched cohort study was performed using data from The Health Improvement Network (THIN). Patients with psoriasis exposed to trauma were randomly matched to up to five unexposed psoriasis controls based on gender, age, duration of psoriasis and the date of entry into THIN. Trauma exposure was stratified into subgroups of joint, bone, nerve and skin trauma. Cox proportional hazard models were used to estimate the HRs for developing PsA. For comparison, an identical analysis was performed in the entire THIN population evaluating rheumatoid arthritis (RA) risk following physical trauma.

Results Patients with psoriasis exposed to trauma (N=15 416) and matched unexposed patients (N=55 230) were followed for a total of 425 120 person-years during which 1010 incident PsA cases were recorded. Adjusting for potential confounders, patients with psoriasis exposed to trauma had an increased risk of PsA compared with controls, with a multivariate HR of 1.32 (95% CI 1.13 to 1.54). In our subset analysis, bone and joint trauma were associated with multivariate HRs of 1.46 (95% CI 1.04 to 2.04) and 1.50 (95% CI 1.19 to 1.90), respectively; while nerve and skin trauma were not associated with a statistically significant increase in risk compared with controls. Patients exposed to trauma in the entire THIN population did not have an increased risk of developing RA: HR 1.04 (95% CI 0.99 to 1.10).

Conclusions Patients with psoriasis exposed to physical trauma are at an increased risk of developing PsA.