"Functional Pain," Functional Outcomes, and Quality of Life After Hyaluronic Acid Intra-articular Injection for Knee Osteoarthritis

Objective: To compare the effect of hyaluronic acid (HA) intra-articular knee injections on pain and functional outcomes in persons with knee osteoarthritis (OA) over 6 months, and to determine whether or not changes in functional pain are related to improvements in quality of life. Design: A prospective cohort study. Setting: A research laboratory in an academic medical center. Participants: Patients with knee OA (N = 53) who were receiving medical care for OA. Interventions: Intra-articular knee injections of HA (3 injections, each separated by 1 week) and a comparative noninjection group. Main Outcome Measurements: Functional pain and outcomes assessments during chair rise, stair climbing, and a 6-minute walking test (by using 0-10 point numerical pain ratings during each test); gait parameters; Medical Outcomes Short Form-36 (SF-36) scores and subscores; the Western Ontario McMaster University Osteoarthritis Index (WOMAC). Results: Six months after HA, the completion times for the chair rise and stair climb tasks, and the distance covered during the 6-minute walk were not different between the groups. However, functional pain ratings during stair climbing decreased in the HA-treated group (P = .05). Six-month changes in gait velocity, cadence, stride length, step length, and the percentage of the gait cycle spent in single support were all higher after HA injection at month 6 (all P < .05). Significant group-by-time interactions existed for total WOMAC scores. SF-36 Vitality subscores improved by 13%, and Role Physical scores were higher in patients treated with HA injection compared with participants in the noninjection group (P < .05). Regression analyses revealed that changes in the functional pain measures did not correspond with SF-36 scores. Conclusions: HA is associated with lower functional pain severity, with minimal impact on functional test scores. We interpreted this finding to represent an increase in the quality of the movement and functional activity. The change in functional pain did not correspond to changes in SF-36 quality-of-life scores.