aspiration of the knee joint may be performed for the diagnosis of an unexplained effusion , or the evacuation of a painful effusion1 ) . injection of the knee can be undertaken for radiological investigation of the knee2 ) , for the injection of corticosteroid into a joint suffering from a non - infectious inflammatory process3 ) , or for the injection of viscosupplementation4 ) . of these indications for aspiration or injection of the knee joint , the most common is the injection of corticosteroid in cases of osteoarthritis ( oa ) of the knee , and is performed as an office procedure . a recent article5 ) examined the choice and utilisation of corticosteroid agents for injection into the osteoarthritic knee , and suggested that it is traditional clinical orthopaedic surgery and rheumatology teaching which determines the likelihood of utilisation of one corticosteroid ( and dosing regimen ) over another . similarly , disagreement also exists among practitioners as to the ' best ' approach portal for knee aspiration and injection . this article examines the different approach portals for aspiration or injection of the knee joint with the aim of : describing the available approach portals for aspiration or injection of the knee joint ; determining if indeed there is a ' best ' approach portal ; determining whether the ' best ' approach portal for knee joint aspiration is the same as that for injection ; and examining the possible problems encountered with each approach portal . the first reported use of intra - articular ( ia ) corticosteroid in knee oa was by hollander6 ) in 1953 , and the first clinical trial of ia steroid use for knee oa was reported by miller et al.7 ) in 1958 . six major portals of approach to the knee joint for its aspiration or injection have been described : the lateral and medial mid - patellar ( mmp ) and patellofemoral ; the superolateral and superomedial ; and anterolateral and anteromedial ( inferolateral and inferomedial ) approaches . a recent on - line video series by garcia - rodriguez8 ) demonstrates injection of the knee joint by several of these approaches . each portal of approach has its own advantages and disadvantages , and each of the major techniques is discussed below . table 1 provides a summary of the efficacy of each of the major injection approaches . the traditional approach to knee injection the patella is pulled medially or laterally and a needle is advanced under the patella . the patellofemoral joint , via the lmp and mmp approaches can then be used for joint aspiration and/or injection . when performing a procedure via the lmp approach , the needle is directed at a 45 angle towards the middle of the medial aspect of the joint . injection via the mmp approach is undertaken with the needle entering the medial aspect of the knee joint under the middle of the patella ( midpole ) , and is directed towards the lateral patellar midpole3 ) . it is reported that most ( us ) rheumatologists prefer the medial approach with the knee extended and the patient lying down because the lateral patellofemoral cleft is narrower , and the joint capsule is tougher laterally than medially3 ) . a survey of us radiologists by shortt et al.4 ) found that the lateral patellofemoral approach was the most commonly utilized technique for knee arthrography ( 41/64 respondents , 64% ) , mirroring previous work by freiberger1 ) and esenyal et al.2 ) the medial patellofemoral approach was preferentially utilized by only 16/64 respondents ( 25% ) . reasons for preferring a medial patellofemoral approach included difficulty with lateral access secondary to patellofemoral oa . esenyal et al.2 ) reported in their study of knee joint injection that the mmp approach is the least accurate of all tested ia approaches ( 56% ) . toda and tsukimura9 ) found that they achieved an accuracy of 55%-86% for the lmp approach and that accuracy was directly proportional to severity of radiographic oa assessment ( kellgren - lawrence grading)10 ) . esenyal et al.2 ) reported an accuracy of 76% , and jackson et al.11 ) reported an accuracy of 93% ( 74/80 ) for the lmp approach . aspiration or injection via the lmp or mmp approaches has been reported to be uncomfortable for patients , and can be painful if access is difficult . these approaches can be difficult when patients tense the thigh extensors ; in the obese ; and in patients with patellofemoral arthrosis12 ) . wind and smolinski13 ) have suggested that , as lateral joint line injections ( ie lmp ) may not be reliable for routine injections of low volumes of fluid into the knee joint as it results in good ia delivery less than half the time with a high incidence of soft - tissue infiltration , a superomedial or superolateral approach should be used instead . although the usual site of entry to the knee joint is via either an lmp or mmp approach , an approach lateral and superior to the patella can be used , especially if there is a large effusion in the suprapatellar bursa14 ) ( fig . sher16 ) advocates the use of the superolateral approach ( with the knee extended ) , for aspiration . this technique aims for the suprapatellar pouch , and allows the needle to pass underneath the articular surface of the patella . hermans et al.17 ) determined that the superolateral approach results in the highest pooled accuracy rate of 91% ( 95% ci 84%-99% ) , although this approach still results in a substantial amount of extra - articular needle placements . in their study observing the effect of combined joint lavage and corticosteroid injection upon ninety - eight patients with symptomatic knee oa , ravaud et al.18 ) performed aspiration and injection of the joint via the superolateral approach . more recently , ucar et al.19 ) used the same approach in their study of hyaluronic acid injection into the osteoarthritic knee . the superomedial approach is poorly studied with only a single trial , and a reported accuracy of 93%13 ) . accidental collision of the needle tip with the superolateral or superomedial poles of the patella during attempted aspiration or injection of the knee joint have led to problems with pain , as well as damage to the chondral cartilage of the patella . these problems may be avoided by using the inferolateral or inferomedial poles of the patella ( ie an anterior or arthroscopic approach ) as a needle insertion site20 ) . 3 ) are an alternative to the classic patellofemoral approaches , and are used less often for knee joint injection and aspiration14,21 ) . shortt et al.4 ) reported that only 7/64 ( 11% ) of surveyed north american musculoskeletal radiologists preferentially utilised an arthroscopic approach for injection of the knee joint . anterior techniques utilise an entry approach analogous to the portals used for knee arthroscopy12,21 ) . these approaches are useful when the knee can not be extended , or when there is only a minimal amount of fluid in the knee joint14 ) . with the knee flexed , the needle is introduced either lateral or medial to the patella tendon15 ) , and is directed upwards towards the femoral notch2,22 ) . these approaches traverse only hoffa 's fat pad and they avoid the extensor mechanism and major blood vessels . with correct technique , the anterior horns of the menisci and the transverse patellar ligaments are easily avoided12,21 ) . jackson et al.11 ) examined the accuracy of knee joint injection by a single orthopaedic surgeon using these approach portals . they reported an accuracy of 71% ( 57/80 attempts ) for the anterolateral approach and 75% ( 60/80 attempts ) for an anteromedial approach ( compared to the 93% accuracy for lmp approach ) . toda and tsukimura9 ) reported an accuracy of only 55% ( 6/11 attempts ) for a seated anteromedial approach . esenyal et al.2 ) compared the accuracy of the anterolateral , anteromedial , lmp and mmp approaches . they determined that the anterolateral approach was the most accurate ( 85% ) but that this was not statistically significant compared to the anteromedial ( 73% ) and lmp ( 76% ) approaches . the major problem with these approaches has been reported to be difficulty in obtaining fluid from an affected joint14 ) . waddell et al.22 ) used a technique that placed the knee into 30-40 flexion , and inserted the needle 1 - 1.5 cm proximal from the anterolateral arthroscopy port , aiming the needle towards the anterior contact point between the femoral condyle and the tibial plateau . toda and tsukimura9 ) reported an accuracy of 86% utilising a modified waddell 's approach , which moved the knee into 30 flexion with concurrent traction upon the ankle , and injecting the knee from a point 1 - 1.5 cm above the anteromedial injection site , aiming towards the anterior contact point between the femoral condyle and the tibial plateau17 ) . cohn and shapiro20 ) described an anterior approach that utilized injection through the patellar tendon . however , despite the ease of approach , they determined that the technique led to adverse outcomes related to injection into hoffa 's fat pad , or into the anterior cruciate ligament . cardone and tallia3 ) have described an anterior approach , which aims the needle parallel to the tibial plateau . however , this technique risks meniscal damage by the needle . sambrook et al.23 ) described an interesting variation of access of corticosteroid to the ia space . they used a peripatellar injection of corticosteroid , as they considered ia injection of corticosteroid to be of uncertain efficacy and duration of effect . their technique provided results that were not significantly different from that achieved with their control group , who had received standard ia corticosteroid injection . the patella is pulled medially or laterally and a needle is advanced under the patella . the patellofemoral joint , via the lmp and mmp approaches can then be used for joint aspiration and/or injection . when performing a procedure via the lmp approach , the needle is directed at a 45 angle towards the middle of the medial aspect of the joint . injection via the mmp approach is undertaken with the needle entering the medial aspect of the knee joint under the middle of the patella ( midpole ) , and is directed towards the lateral patellar midpole3 ) . it is reported that most ( us ) rheumatologists prefer the medial approach with the knee extended and the patient lying down because the lateral patellofemoral cleft is narrower , and the joint capsule is tougher laterally than medially3 ) . a survey of us radiologists by shortt et al.4 ) found that the lateral patellofemoral approach was the most commonly utilized technique for knee arthrography ( 41/64 respondents , 64% ) , mirroring previous work by freiberger1 ) and esenyal et al.2 ) the medial patellofemoral approach was preferentially utilized by only 16/64 respondents ( 25% ) . reasons for preferring a medial patellofemoral approach included difficulty with lateral access secondary to patellofemoral oa . esenyal et al.2 ) reported in their study of knee joint injection that the mmp approach is the least accurate of all tested ia approaches ( 56% ) . toda and tsukimura9 ) found that they achieved an accuracy of 55%-86% for the lmp approach and that accuracy was directly proportional to severity of radiographic oa assessment ( kellgren - lawrence grading)10 ) . esenyal et al.2 ) reported an accuracy of 76% , and jackson et al.11 ) reported an accuracy of 93% ( 74/80 ) for the lmp approach . aspiration or injection via the lmp or mmp approaches has been reported to be uncomfortable for patients , and can be painful if access is difficult . these approaches can be difficult when patients tense the thigh extensors ; in the obese ; and in patients with patellofemoral arthrosis12 ) . wind and smolinski13 ) have suggested that , as lateral joint line injections ( ie lmp ) may not be reliable for routine injections of low volumes of fluid into the knee joint as it results in good ia delivery less than half the time with a high incidence of soft - tissue infiltration , a superomedial or superolateral approach should be used instead . although the usual site of entry to the knee joint is via either an lmp or mmp approach , an approach lateral and superior to the patella can be used , especially if there is a large effusion in the suprapatellar bursa14 ) ( fig . sher16 ) advocates the use of the superolateral approach ( with the knee extended ) , for aspiration . this technique aims for the suprapatellar pouch , and allows the needle to pass underneath the articular surface of the patella . hermans et al.17 ) determined that the superolateral approach results in the highest pooled accuracy rate of 91% ( 95% ci 84%-99% ) , although this approach still results in a substantial amount of extra - articular needle placements . in their study observing the effect of combined joint lavage and corticosteroid injection upon ninety - eight patients with symptomatic knee oa , ravaud et al.18 ) performed aspiration and injection of the joint via the superolateral approach . more recently , ucar et al.19 ) used the same approach in their study of hyaluronic acid injection into the osteoarthritic knee . the superomedial approach is poorly studied with only a single trial , and a reported accuracy of 93%13 ) . accidental collision of the needle tip with the superolateral or superomedial poles of the patella during attempted aspiration or injection of the knee joint have led to problems with pain , as well as damage to the chondral cartilage of the patella . these problems may be avoided by using the inferolateral or inferomedial poles of the patella ( ie an anterior or arthroscopic approach ) as a needle insertion site20 ) . 3 ) are an alternative to the classic patellofemoral approaches , and are used less often for knee joint injection and aspiration14,21 ) . shortt et al.4 ) reported that only 7/64 ( 11% ) of surveyed north american musculoskeletal radiologists preferentially utilised an arthroscopic approach for injection of the knee joint . anterior techniques utilise an entry approach analogous to the portals used for knee arthroscopy12,21 ) . these approaches are useful when the knee can not be extended , or when there is only a minimal amount of fluid in the knee joint14 ) . with the knee flexed , the needle is introduced either lateral or medial to the patella tendon15 ) , and is directed upwards towards the femoral notch2,22 ) . these approaches traverse only hoffa 's fat pad and they avoid the extensor mechanism and major blood vessels . with correct technique , the anterior horns of the menisci and the transverse patellar ligaments are easily avoided12,21 ) . jackson et al.11 ) examined the accuracy of knee joint injection by a single orthopaedic surgeon using these approach portals . they reported an accuracy of 71% ( 57/80 attempts ) for the anterolateral approach and 75% ( 60/80 attempts ) for an anteromedial approach ( compared to the 93% accuracy for lmp approach ) . toda and tsukimura9 ) reported an accuracy of only 55% ( 6/11 attempts ) for a seated anteromedial approach . esenyal et al.2 ) compared the accuracy of the anterolateral , anteromedial , lmp and mmp approaches . they determined that the anterolateral approach was the most accurate ( 85% ) but that this was not statistically significant compared to the anteromedial ( 73% ) and lmp ( 76% ) approaches . the major problem with these approaches has been reported to be difficulty in obtaining fluid from an affected joint14 ) . waddell et al.22 ) used a technique that placed the knee into 30-40 flexion , and inserted the needle 1 - 1.5 cm proximal from the anterolateral arthroscopy port , aiming the needle towards the anterior contact point between the femoral condyle and the tibial plateau . toda and tsukimura9 ) reported an accuracy of 86% utilising a modified waddell 's approach , which moved the knee into 30 flexion with concurrent traction upon the ankle , and injecting the knee from a point 1 - 1.5 cm above the anteromedial injection site , aiming towards the anterior contact point between the femoral condyle and the tibial plateau17 ) . cohn and shapiro20 ) described an anterior approach that utilized injection through the patellar tendon . however , despite the ease of approach , they determined that the technique led to adverse outcomes related to injection into hoffa 's fat pad , or into the anterior cruciate ligament . cardone and tallia3 ) have described an anterior approach , which aims the needle parallel to the tibial plateau . however , this technique risks meniscal damage by the needle . sambrook et al.23 ) described an interesting variation of access of corticosteroid to the ia space . they used a peripatellar injection of corticosteroid , as they considered ia injection of corticosteroid to be of uncertain efficacy and duration of effect . their technique provided results that were not significantly different from that achieved with their control group , who had received standard ia corticosteroid injection . numerous studies have shown that a variable proportion of ia injections are placed correctly into the target joint space2,9,11,13,24,25 ) and the injection of ia corticosteroid has been shown to be more effective when it is correctly placed in the joint25,26 ) . the inaccurate placement of injecting needles can result in damage to ia structures secondary to soft tissue infiltration by corticosteroid13,25 ) . clinical experience has shown that ia injection of the knee joint is more painful when the tip of the needle is in hoffa 's fat pad . chavez - chang et al.27 ) have suggested that the length of the needle used for ia injection may influence ia accuracy , as the standard 3.8 cm needle may be too short to reach the synovial space overlying the medial femoral condyle . a review by berkoff et al.28 ) has suggested that the accuracy of ia injection may be improved by the utilization of ultrasound guidance , with an accuracy of 95.8% ( versus 77.8% for anatomical guidance [ p<0.001 , or 6.4 { 95% ci : 2.9 - 14 } ] ) . park et al.29 ) reported an accuracy raging from 95% ( medial midpatellar approach ) to 100% ( superolateral approach ) for the use of ultrasound guidance using a long axis in plane technique . maricar et al.30 ) stated that injection under ultrasound guidance may improve the likelihood of response to ia corticosteroid injection , and sibbitt et al.31 ) reported that ultrasound - guided aspiration and injection of the knee resulted in improved aspiration success , greater synovial fluid yield , more complete joint decompression , and improved clinical outcomes . it has been suggested that accuracy of ia knee injection can be further improved by the use of mini - air arthrography32 ) , or by the combined use of air injection into the target joint with concurrent use of an ultrasound probe33,34 ) . despite their presumed efficacy , these two techniques would appear to be beyond the usual expertise and resources of those medical practitioners that commonly aspirate and/or inject the knee joint . examination of the literature investigating the various approach portals for knee joint aspiration and/or injection determined that there are six major techniques . there is no evidence for an optimal or ' best ' technique , although there is some suggestion that one or two techniques may be inferior to others . particular portals of approach may be more efficacious for particular knee joint pathologies , for example a medial patellofemoral approach may be easier to perform in a patient suffering from patellofemoral subluxation . available evidence suggests that , in the hands of experienced practitioners , it is of no clinical consequence which approach portal is used for the anatomical guidance of aspiration or injection of the knee joint - any of the described approaches may be utilised depending upon the experience and preference of the practitioner . however , practitioners must bear in mind that no approach has 100% efficacy for either aspiration or injection of the knee joint , and incorrect use of any of the techniques may cause pain , or damage internal knee structures . although techniques are available that can enhance the accuracy of ia aspiration or injection , access to the required equipment and familiarity with its use may be beyond the resources , capabilities , and expertise of most practitioners and their practices . this paper demonstrates that the traditional approaches to aspiration or injection of the knee are easily performed and are generally safe , but also highlights the need for practitioners to continuously refine and practice their preferred aspiration and injection technique of the knee joint .
aspiration and injection of the knee joint is a commonly performed medical procedure . 
 injection of corticosteroid for the treatment of osteoarthritis is the most common reason for knee joint injection , and is performed as an office procedure . 
 debate exists among practitioners as to the ' best ' approach portal for knee injection . 
 this paper examines the various approach portals for injection and/or aspiration of the knee joint , as well as the accuracy of each approach . 
 searches were made of electronic databases , and appropriate papers were identified and hand - searched . 
 although there is some evidence that particular approach portals may be more efficacious in the presence of specific knee joint pathologies , generally , in experienced hands , it is of no clinical consequence as to which approach portal is utilised for aspiration or injection of the knee joint . 
 no approach portal is 100% accurate , and the accuracy of injection of the knee joint may be enhanced by the use of techniques such as ultrasound . 
 practitioners are reminded that they should continuously refine and practice their preferred technique . 
 knee joint aspiration and injection is a common , simple , and generally safe office procedure .