Introduction 12 4 Viscosupplementation (VS) is the administration of hyaluronan and/or hyaluronic acid preparations to joint synovial fluid for the treatment of OA in order to restore the biologic properties of normal hyaluronic acid (HA). 14 14 2 The results of a trial comparing three formulations of HA were presented. All patients were candidates for THA. The time of satisfactory pain relief, improved functionality obtained with each infiltration of HA and the delay in surgery were evaluated. Patients and methods Patient selection ® ® ® 1 Table 1 Characteristics of infiltrated population  Period of treatment Patients Gender Age Adant 27-11-02 till 23-02-05 91 35 ♂ and 65 ♀ 61.8 ± 12.8 Synocrom 19-01-04 till 04-10-04 20 7 ♂ and 13 ♀ 62.1 ± 14.5 Synvisc 15-03-01 till 24-04-03 15 7 ♂ and 8 ♀ 61.9 ± 15.3 Eligibility criteria Age between 30 and 70 years and suffering idiopathic radiologically confirmed hip OA. Visual Analogue Scale (VAS) score for pain greater then 30 (on a 100-point scale; 0 no pain and 100 “the worst pain imaginable”) Have persistent pain for longer than 1 month despite use of analgesics or NSAID’s. continuous hip pain, also during the night, requiring daily intake of NSAID’s or pain medication disabled gait pattern and need of walking aid Be able to understand the information relative to viscosupplementation and to give informed consent. Exclusion criteria Pregnancy Contraindications to intra-articular hyaluronic-acid preparations Major hip dysplasia or congenital abnormality of the hip Patients with systemic corticosteroids or intra-articular corticosteroid injections in the last 6 months Contra-lateral THA or hip arthroscopy in the last 6 months Oral or parenteral anticoagulant therapy Previous hyaluronic acid hip infiltrations Skin diseases or infections Signs of haemarthrosis History of allergy or hypersensitivity to iodated contrast Treatment ® 1 Fig. 1 a b  After resting for 2 h, the patient was allowed to walk and to return home. The patient was advised to rest at home until the next morning. Oral symptomatic slow acting drugs for osteoarthritis were authorized if they were taken at a stable dose for more than 3 months prior to inclusion in the study. These analgesics were continued at a stable dose during the VS treatment. Evaluation All patients were assessed at baseline and 6 weeks after each infiltration. During this consultation in the outpatient clinic, the pain and functionality were evaluated using the VAS pain during walking score (100-point scale) and the Harris Hip Score (HHS). The latter is a clinical scoring system on a total of 100 points whereby the following subscales are rated: function (47 points), pain (44 points), range of motion of the hip (5 points) and absence of muscle contractures and length discrepancy (4 points). All side effects and complications of viscosupplementation were noted. In April 2005, all patients were contacted for follow-up assessment over the phone VAS and HHS. Statistical analysis ® t t The second comparison was made between the three groups (Synvisc, Synocrom and Adant). The differences in HHS and VAS evolution between the three groups were checked by the analysis of variance statistics with Tukey extension, which also was used for controlling if the groups were initially homogeneous. P Results P P P 2 2 Table 2 Evolution in average HHS score  HHS pre HHS post Difference P Adant 64.8 ± 13.8 71.1 ± 15.7 + 6.3 < 0.001 Synocrom 66.8 ± 13.8 77.4 ± 14.7 + 10.6 < 0.05 Synvisc 66.3 ± 13.5 72.4 ± 14.5 + 6.1 > 0.05 P P P 2 3 Fig. 2 a b c  3 Fig. 3 Kaplan-Meier survival curve of the duration of effect of the first infiltration in days for the three different treatment groups  2  P 4 Fig. 4 Kaplan-Meier survival curve of the duration of effect of the first infiltration in days (three treatment groups together)  4 Table 3 Evolution in average VAS pain during walking score  VAS pre VAS post Difference  P Adant 51 ± 23 39 ± 27 − 12 < 0.0001 Synocrom 43 ± 22 29 ± 23 − 14 < 0.02 Synvisc 47 ± 26 30 ± 29 − 17 > 0.05 Pre: at first infiltration Post: at follow-up 4 5 Fig. 5 Kaplan-Meier survival curve for the delay to surgery in days for the three groups confounded  Discussion 6 9 Table 4 Duration of treatment effect after first infiltration  Patients Average duration (days) Effect of 1st infiltration still going on 46  352 ± 258 (range 6–886) Effect of 1st infiltration terminated 80 174 ± 163 (range 13–724) N 13 We could identify two groups of responders, the ongoing responders who last on average for 352 days after the first infiltration. The second group, where patients either received a second infiltration or THA had an average duration of effect of 174 days. 1 3 6 7 9 11 1 2 8 10 11 7 9 3 Of all the reports published, we have the longest follow-up, up to approximately 3 years. The analysis by means of the Kaplan-Meier survival curve learns that there is a 50% probability of long-term effect (more than 2 years). 7 7 6 5 15 8 Viscosupplementation with hyaluronic acid seems to be a valuable technique for the management of painful OA of the hip that may delay the need for surgical intervention. Further prospective randomised placebo controlled studies are necessary to draw definite conclusions.