Complications following Total Joint Arthroplasty in Patients with Rheumatoid Arthritis

s (263-265) and a look-back period of two years. Additionally, Adjusted Clinical Groups (ACGs), based on diagnosis codes from hospitalizations and physician visits in the 2years before the index TJA admission were used to classify recipients as frail (yes/no)(266). Frailty is associated with a decline in physical activity and muscle strength, as well as immune system dysfunction(127-130). Frailty may therefore increase risk for falls leading to fracture or dislocation and infection following TJA. For each of TKA, the volume of arthroplasties performed for each surgeon and each hospital was defined as the number of primary and revision knee replacement procedures performed in the 365 days prior to the index TKA procedure. This was repeated for each index THA procedure. We defined teaching hospitals as those who were members of the Council of Academic Hospitals of Ontario (www.cahohospitals.com). Surgical Complications All patients were followed from the date of their index TJA to examine for the occurrence of venous thrombo-embolism (VTE), and death within 90days, and infection of the replaced joint, dislocation of the replaced joint (only for THA), peri-prosthetic fracture, and revision of the index arthroplasty within 2years. We also compared groups on the occurrence of a composite outcome encompassing all of the above complications (VTE, death, infection, dislocation, fracture and revision). We limited follow-up to two years, as revision during this period is considered a catastrophic complication (8, 267, 268). We identified death within 90 days of operation using the OHIP Registered Persons Database (Appendix 3.1). Occurrence of a VTE was defined as the presence of a diagnostic code for a deep vein thrombosis or pulmonary 55 embolism in the DAD or National Ambulatory Care Reporting System (NACRS) database. Infections were identified using three methods(269): 1) occurrence of an ICD-10-CA diagnostic code for intra-articular infection, with a confirmatory code for an irrigation and debridement; 2) occurrence of an OHIP code for a spacer insertion; and/or 3) occurrence of a procedure code for a peripheral intravenous central catheter (PICC) line after the TJA, where the referring physician was an orthopaedic surgeon. Dislocations were defined as the occurrence of a diagnostic code for dislocation, or a procedure code for closed/open hip reduction(270). Peri-prosthetic fractures were defined as the occurrence of a diagnostic code for fracture following insertion of an implant. Revision procedures were identified using ICD-10-CA/CCI procedure codes accompanied by the supplementary status attribute “R”(270). Statistical analyses Age-sex standardized rates for each complication by the type of arthritis were determined using indirect standardization. Univariate analysis was used to compare demographics of TJA recipients at the time of their index surgical admission by arthritis type (RA versus OA). Wilcoxon rank-sum tests were used to compare non-normally distributed continuous variables. Chi-square and Fisher exact tests were used to compare categorical variables. Cox proportional hazards models, censored on death and accounting for clustering of patients within surgeons, were used to estimate the hazard of each outcome for patients with RA and IA, relative to those with OA. Age and sex were included in all multivariable models. Other variables were included if in the univariate analyses he covariate was associated with the outcome at a p-value of ≤0.4. Other potential variables included: income quintile, rurality, Charlson co-morbidity score, frailty, surgeon and hospital volume in the year preceding the surgery, and performance of the TJA at a teaching hospital. We performed two sensitivity analyses: 1) repeating the multivariate analysis after excluding persons with a prior code for osteonecrosis, and 2) repeating the 56 analyses after limiting the definition of infection to cases managed specifically by an irrigation and debridement. Where appropriate, unadjusted hazard ratios and adjusted hazard ratios with 95% confidence intervals (95%CI) are reported. All analyses were performed using SAS version 9.2 for UNIX (SAS Institute, Cary NC). The type I error probability was set to 0.05 for all analyses.