preferred solutions for the purposes of the present invention contain hyaluronic acid or one of its salts , at least one salt selected from calcium salt , magnesium salt , and mixtures thereof , and further one salt of citric acid . typically , in addition to hyaluronic acid or corresponding salt , they contain sodium , potassium , calcium , magnesium , chloride , and citrate ions . typically , the aqueous solutions useful for intra - articular irrigation according to the present invention also contain a phosphate buffer . according to preferred embodiments , they also contain an anti - oxidant tolerated by intra - articular tissues , and in addition a phosphate buffer . the aqueous solutions useful for the purposes of the present invention contain hyaluronic acid or one of its salts having molecular weight of between 0 . 5 and 5 . 0 million daltons , for example of between 1 . 3 and 2 . 2 million daltons , at a concentration more preferably of between 0 . 3 % and 0 . 6 % weight / volume , for example of 0 . 5 % weight / volume . the viscosity of the present solutions is preferably comprised between 30 mpa . sec and 43 mpa . sec ., measured at a shear rate of 10 sec - 1 , at 25 ° c . for the purposes of the present invention , also hyaluronic acid of a molecular weight different from those given above , but not less than 500 , 000 daltons , may be used , in concentrations such as to obtain the desired viscosity . according to a particular embodiment of the present invention , the hyaluronic acid or corresponding salt is the only viscosity - enhancing polymer present in the aqueous solution for intra - articular irrigation according to the present invention . typically , sodium hyaluronate ( naha ) is used , or other alkaline or alkaline - earth salts of hyaluronic acid . the naha may be of extractive origin ( e . g ., from cock &# 39 ; s combs or umbilical cords , etc .) or of fermentative origin ( e . g ., streptococcus , etc .). the solutions for intra - articular irrigation according to the present invention have moreover the advantage of exhibiting a non - newtonian rheological behaviour , showing a reduction of viscosity with the increase in the shear stress , even in the presence of salts , such as calcium and / or magnesium salts , and of other substances , such as sodium citrate , sodium ascorbate and / or glucose , and phosphate buffer . preferably , the solutions for intra - articular irrigation according to the present invention have a substantially neutral ph , for example of between 7 . 0 and 7 . 4 . the phosphate buffer typically contains hpo 4 - ions , typically as sodium or potassium salts , and is preferably added in a sufficient quantity to yield a substantially neutral aqueous solution having the ph above specified . in addition , the aqueous solutions useful for the purposes of the present invention preferably contain a salt of citric acid ( citrate ) in a quantity of preferably between 0 . 7 and 2 . 5 mmol ./ liter , more preferably of between 0 . 7 and 1 . 6 mmol ./ liter . citrate is typically present as alkali metal salt of citric acid , e . g ., trisodium citrate . in addition to glucose , also other anti - oxidants may be used , and in particular salts of ascorbic acid , either alone or associated together . preferably , the solutions for intra - articular irrigation according to the present invention contain glucose ( preferably at least 3 mmol ./ liter ). they may optionally contain sodium ascorbate , in a quantity of preferably at least 0 . 50 mmol ./ liter . preferably , glucose is used as anti - oxidant in quantities of between 3 and 7 mmol ./ liter , optionally associated with sodium ascorbate , the latter in quantities typically of between 0 . 50 and 50 mmol ./ liter , more preferably of between 0 . 50 and 1 . 0 mmol ./ liter . according to particular embodiments of the present invention , the hyaluronic acid - based solutions may contain one or more , preferably all , of the following components , for which the minimum quantities preferably present are indicated alongside : phosphate ions ( in particular hpo 4 2 - ): preferably at least 6 mmol ./ liter ; aqueous solutions further preferred for the purposes of the present invention , in addition to the quantities specified above of hyaluronic acid or of one of its salts , having molecular weight as specified above , contain one or more of the following components , preferably all of them , for which the quantities preferably present are indicated alongside : na + : preferably 40 - 180 mmol ./ liter , more typically 90 - 180 mmol ./ liter ; k + : preferably 12 - 30 mmol ./ liter , more typically 15 - 30 mmol ./ liter ; ca ++ : preferably 0 . 4 - 0 . 9 mmol ./ liter , more typically 0 . 4 - 0 . 8 mmol ./ liter ; mg ++ : preferably 0 . 3 - 1 . 00 mmol ./ liter , more typically 0 . 3 - 0 . 6 mmol ./ liter ; cl - : preferably 50 - 200 mmol ./ liter , more typically 100 - 190 mmol ./ liter ; preferably , in addition to the above - mentioned components , the solutions useful for the purposes of the present invention contain glucose ( preferably 3 - 7 mmol ./ liter ). they may also contain sodium ascorbate ( preferably 0 . 50 - 50 mmol ./ liter , more typically 0 . 50 - 1 . 00 mmol ./ liter ). for example , for the purposes of the present invention , sodium hyaluronate - based aqueous solutions may be used as those described in the patent ep - a - 719 . 559 , the content of which is herein incorporated by reference , and which describes the use of said solutions as masking fluid for photokeratectomy by means of excimer laser . the aqueous solutions useful as liquids for intra - articular irrigation according to the present invention are typically sterile , and are prepared mixing the ingredients in water according to conventional methods . the intra - articular irrigation according to the present invention is , for example , carried out according to the general technique previously described in the present text , with the difference that as lavage liquid a hyaluronic acid - based solution , as described for the purposes of the present invention is used , and with the further difference that the aliquot of solution used for the last irrigation can possibly be left in situ . the number of intra - articular lavages may vary according to the specific purpose of the treatment and of the seriousness of the lesion to be treated ; for example , one or more ravages may be performed , possibly grouped together in cycles . the hyaluronic acid - based aqueous solution for intra - articular irrigation according to the present invention affords the following advantages with respect to bss : it facilitates the entrapping and removal of cartilaginous fragments , thus reducing tissue damage due to the process of aspiration of the lavage liquid in the area of the articulation involved ; after the irrigation , it may be left in situ , thus facilitating the process of repair of the articular cartilage layer ; it protects the cartilage both against progressive cell - dependent inflammatory decomposition and against destruction of the chondrocytes . given below is an example which serves as an illustration of the present invention , without , however , in any way limiting the scope thereof . ______________________________________ g / 100 ml mmol ./ liter______________________________________naha 0 . 50 ( mw 1 . 8 - 2 . 2 million daltons ) nacl 0 . 68 116kcl 0 . 19 26na . sub . 2 hpo . sub . 4 . 12h . sub . 2 o 0 . 33 9na . sub . 3 . citrate 0 . 031 1 . 2mgcl . sub . 2 . 6h . sub . 2 o 0 . 009 0 . 45cacl . sub . 2 . 2h . sub . 2 o 0 . 0087 0 . 6glucose 0 . 09 5______________________________________ we carried out arthroscopy of the knee joint and joint lavage in 10 patients with knee pain and effusion due to trauma who were divided into 2 groups . we performed joint lavage to remove cartilage debris and / or inflammatory cells in both groups of patients . in one group ( 5 patients ) we used bss ( balanced salt solution ) under pressure to wash the joints . at the end of the procedure we removed the bss from the joint . in the other group ( 5 patients ) we used the composition of example 1 ( the composition ) under pressure to wash the joints and left at least 2 ml of the product in the joint at the end of the procedure . the use of medication which might interfere with the assessment of pain ( antidepressants , tranquillizer , etc .) was not permitted during the study . the use of paracetamol was allowed but intake was not allowed for 2 days prior to each assessment . primary efficacy criterion was pain on movement ( evaluated using the vas ). knee joint performance using the lysholm knee scoring scale ( lkss ) ( scoring scale am . j . sports med . 1982 ; 10 : 150 - 154 ) was also assessed . secondary parameters were : joint circumference , analgesic consumption , patient and investigator judgement at the end of the study . 1 ) the composition was well tolerated by the joint tissues during and after joint lavage . no adverse events due to the composition were observed or reported . there were no changes in the laboratory safety parameters . 2 ) during joint lavage , the composition facilitated the removal of cartilaginous debris due to its viscous nature . 3 ) the composition was left in the joint after lavage . in the composition group , patients experienced less pain and increased joint function at week 2 compared to baseline values and to the comparative bss group . pain decreased further in the composition group at weeks 3 and 6 with significant differences compared to baseline and to the control group . 4 ) the baseline lkss could not be taken since it was impossible for the patients to undergo this test owing to the severity of the pain . hence the baseline value was taken as 0 . however , from week 2 onwards , this parameter improved significantly in the composition group compared to baseline and the control group . 5 ) joint circumference decreased in the composition group at week 2 , 3 and 6 compared to baseline values and to the control group . ______________________________________demographic data composition group bss group______________________________________no . patients ( male ) 5 5age ( years ± s . e .) 31 . 5 ± 2 . 2 32 . 7 ± 1 . 9weight ( kg ± s . e .) 69 . 6 ± 2 . 3 69 . 0 ± 2 . 2______________________________________pain on movement ( mm vas ) pain on movement ( mm vas ) composition group bss group______________________________________baseline ( week 0 ) 65 . 8 ± 11 . 6 63 . 3 ± 15 . 9week 2 35 . 3 ± 8 . 9 51 . 9 ± 12 . 1week 3 27 . 4 ± 12 . 8 43 . 7 ± 9 . 3week 6 13 . 0 ± 9 . 3 27 . 8 ± 13 . 2______________________________________lysholm score ( mean ± s . d .) lysholm score ( mean ± s . d .) composition group bss group______________________________________baseline ( week 0 ) 0 0week 2 90 . 3 ± 4 . 3 67 . 9 ± 15 . 2week 3 97 . 4 ± 3 . 8 76 . 3 ± 9 . 3week 6 98 . 6 ± 3 . 7 89 . 8 ± 8 . 7______________________________________ from the above results we can conclude that the intra - articular joint lavage solution of example 1 presents the following significant advantages against bss : 1 ) the composition facilitates the entrapment and removal of cartilage debris . it also protects the cartilage cells from damage . on the contrary , bss has been shown to be harmful to cartilage cells . 2 ) the composition can be left in situ after joint lavage enhancing the repair process of the articular cartilage , decreasing pain and improving joint function . on the other hand , bss must be removed from the joint . 3 ) finally , the composition protects the cartilage from cell - dependent inflammatory process and hence prevents cartilage degradation .