Abstract
Introduction:
While indications for total knee (TKA) and hip arthroplasty (THA) have expanded over the last 35 years, implant labeling has largely remained stagnant, with conditions including obesity, developmental dysplasia, and many others (Table 1) still considered as contraindications. Implant labeling has not co-evolved with surgical indications, as most orthopaedic implants are cleared through the 510(k) process, which conserves the labeling of the predicate device. While surgeons can legally use devices for off-label indications, the scrutiny regarding off-label use of orthopaedic implants has intensified. The objective of this study was to determine the incidence of off-label use at our institution, define the risk in terms of revision rate associated with off-label use, and to compare activity level, functional outcomes, and general health outcomes for on- and off-label TKA and THA patients.
Methods:
Patients who underwent primary TKA or THA at a large academic tertiary referral center between January 1, 2010 and June 30, 2010 were considered for the study (n = 705). Of this cohort, a convenience sample of 283 patients were selected for the study based on the presence of baseline outcomes data. Patients were contacted via mail and/or phone to collect details regarding potential revision surgeries, UCLA activity scores, short form-12 (SF-12), Knee Injury and Osteoarthritis Outcome Score (KOOS) or Hip Disability and Osteoarthritis Outcome Score (HOOS). Using labeled contraindications from the product inserts from multiple orthopaedic implant manufacturers, procedures were categorized as on-label or off-label. Outcomes including revision rate, activity score, and SF-12, KOOS, and HOOS scores were adjusted for age, gender, and BMI by fitting a logistic model and analyzed using the Wald chi-square test (SPSS, Chicago, IL).
Results:
225 patients responded to the survey (79.5% follow-up), with an average follow-up of 2.4 years (± 0.24). Demographics, including age (p = 0.07) and gender (p = 0.31), were not significantly different between the 2 groups. Since obesity was a contraindication, the off-label group was significantly heavier (mean BMI = 34.0) than the on-label group (mean BMI = 26.0; p < 0.001). The overall rate of cases defined as off-label was 68.4% (154/225), the majority of which were due to obesity (118/154; 76.6%), followed by patients who used steroids, immunosuppressive drugs, or diabetes medication (37/154; 24.0%). Adjusting for age, gender, and BMI, the revision rate for on-label (4/71; 5.6%) compared with off-label (11/154; 7.1%) was not significantly different (p = 0.62). Adjusted UCLA activity scores were not significantly different between on-label (5.9 ± 2.0) and off-label (5.7 ± 2.0) patients (p = 0.56). When comparing the adjusted improvements (i.e. difference between preoperative and postoperative) in SF-12, KOOS, and HOOS scores, only the SF-12 role physical subscore was statistically lower for off-label patients (Table 2; p = 0.03).
Discussion:
These pilot data suggest that on- and off-label use of THA and TKA implants result in similar short-term revision rates, activity levels, and functional and general health outcomes. In addition, the improvements realized by off-label patients, as reflected by SF-12 composite scores and KOOS/HOOS quality of life, support the use of these devices in previously contraindicated conditions, with no discernible increased risk of revision.
