Long-Term Outcome Measures of Repeated Non-Animal Stabilized Hyaluronic Acid (Durolane) Injections in Osteoarthritis: A 6-Year Cohort Study with 623 Consecutive Patients

PURPOSE: To determine the duration of symptom relief following repeated administration of hyaluronic acid injections for osteoarthritis. PATIENTS AND METHODS: This was a 6-year observational study with 623 consecutive patients who had received hyaluronic acid injections. The primary outcome measure was the mean time between injections measured in days. Classical one-sample 2-sided t-tests, one-way analysis of variances and post-hoc analyses were performed to determine if there were statistically significant differences between age, gender, radiographic severity and the type of joints injected. All patients were invited to complete an online post-treatment experience and satisfaction survey. RESULTS: The analysis included 727 joints (mean Kellgren-Lawrence grade, 2.9 ± 0.8 (range 2–4)) in 623 patients (297 (47.7%) male; mean age at first injection, 57.8 ± 12.7 years (range 21.2–92.1)). Patients ranged from having 1–8 injections per joint. The mean time between injections in days was 466.8 ± 321.7 (2nd injection, 157 joints), 400.5 ± 164.7 (3rd injection, 58 joints), 378.2 ± 223.1 (4th injection, 27 joints), 405.3 ± 216.3 (5th injection, 7 joints), 268.4 ± 104.4 (6th injection, 5 joints), 289.8 ± 99.4 (7th injection, 4 joints), and 272.5 ± 33.2 (8th injection, 2 joints). Patients with grades 2 and 3 compared to grade 4 osteoarthritis experienced a longer time between injections (F (2, 154) = 3.53, p = 0.0316). No statistically significant differences were observed between age, gender, or joint groups. The survey included 233 participants (109 (46.8% male)). A total of 144 respondents (64.9%) recommended hyaluronic acid injections for osteoarthritis. CONCLUSION: Pain relief from hyaluronic acid injections was sustained for on average 466.8 days post initial treatment. Patients who received subsequent 3rd, 4th, and 5th injections also experienced extended duration of benefit. Patients with grades 2 or 3 osteoarthritis are more likely to experience a longer duration of relief.