Objective:
 To evaluate the safety of an intra-articular injection of non-animal stabilised hyaluronic acid (NASHA) in patients with osteoarthritis (OA) of the knee. Design and setting: Non-blind prospective study conducted at five centres in Sweden. Patients and participants: 103 patients aged at least 50 years with OA of the knee (128 knees).
 Methods:
 A single intra-articular injection of NASHA (60mg/3ml) was administered, and patients were followed up for 3 months. In an extension to the study, 53 patients (72 knees) who had participated in the first study received a second intra-articular injection of NASHA(60mg/3ml) approximately 6 months after the first injection. Patients in the study extension were followed up over a 1-month period. Outcome measures: The primary outcome measure in both the primary study and the study extension was the frequency of device-related, unanticipated adverse events. Anticipated adverse events were defined as local reactions such as transient knee pain, swelling, tenderness and heat sensation at the injection site during the first 3 weeks after injection. The following efficacy criteria were also measured: knee pain [measured with a visual analogue scale (VAS)], knee swelling and tenderness, patient’s overall disease condition, and overall treatment satisfaction.
 Results:
After the first injection, 51 local reactions that were possibly related to the study product or injection procedure were reported. Of these, seven events, all described as knee pain and swelling, fulfilled the definition of device-related, unanticipated adverse events, giving an event frequency of 5% in 128 injections. Following the second injection, 11 events were considered potentially related to the study product or the injection procedure, of which three were classed as device-related, unanticipated adverse events, giving an event frequency of 4% in 72 injections. A statistically significant reduction in knee pain (p < 0.0001) was seen after both injections, and tenderness to palpation was significantly reduced at 3 months after the first injection compared with baseline (p = 0.0003). The proportion of knees with swelling was unchanged after either injection. No significant change in patient’s assessment of overall disease condition was noted following either injection, although the physician’s assessment indicated a trend towards a reduction in overall disease condition after the first injection. A clear majority of patients (80%, 76/95) regarded their overall satisfaction with treatment to be very good/good or fair after the first injection. Conclusions: No safety concerns were raised in either the primary study or in the study extension.
NASHA as an intra-articular therapy for OA of the knee appears to have an  acceptable safety profile and thus merits further  investigation regarding its long- term clinical efficacy.
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