Ultrasound Guided Interventional Procedures in.4

REVIEWARTICLE

Ultrasound-Guided Interventional Procedures inPain Medicine

A Review of Anatomy, Sonoanatomy, and Procedures. Part V: Knee Joint

Philip W. H. Peng, MBBS, FRCPC, Founder (Pain Medicine),* and Hariharan Shankar, MD†

Abstract: Ultrasound-guided injection in pain medicine is emerging as apopular technique for pain intervention. It can be applied to the intra-articular injection of the knee joint. The first objective of this review wasto describe and summarize the anatomy and sonoanatomy of the kneeand associated structures relevant for intra-articular injection. The secondobjective was to examine the feasibility, accuracy, and effectiveness of in-jections as well as injection techniques.

(Reg Anesth Pain Med 2014;39: 368–380)

A rthritis involving the knee joint is a common cause for painand disability. Conservative management includes weight

loss, physical therapy, and pharmacologic interventions. Patientsunresponsive to conservative management are usually offeredintra-articular (IA) injections, which may be performed blindlyor with image guidance using fluoroscopy or ultrasound. Ultra-sound guidance has provided an additional tool to identify the tar-get pathology, improving accuracy without the harmful effectsof radiation.

This review, focusing on interventions to the knee joint,aimed to describe and summarize the anatomy and sonoanatomyof the knee and associated structures relevant for IA injection.The second objective was to examine the feasibility, accuracy,and effectiveness of injections and injection techniques.

METHODSWe performed a literature search of the MEDLINE database

from January 1980 to June 2013 using the search terms “knee,”“arthritis,” “ultrasound,” “pain,” and “treatment” to identify re-ports of the use of IA injections for the amelioration of knee ar-thritis, the agents used, and the use of image guidance and theiraccuracy and efficacy.

DISCUSSION

Anatomyof Knee Joint and Surrounding StructuresThe knee joint is a complex joint consisting of 3 components:

the femorotibial, patellofemoral, and superior tibiofibular joints.

From the *Department of Anesthesia, Toronto Western Hospital, University ofToronto, Toronto, Ontario, Canada; and †Department of Anesthesiology, ClementZablocki VA Medical Center, Medical College of Wisconsin, Milwaukee, WI.Accepted for publication June 19, 2014.Address correspondence to: Philip W. H. Peng, MBBS, FRCPC, McL 2-405,

Department of Anesthesia, Toronto Western Hospital, 399 Bathurst St,Toronto, Ontario, Canada M5T 2S8 (e‐mail: [email protected]).

Institutional funding was received for this study.P.W.H.P. received equipment support from SonoSite Canada. H.S. received

equipment support from SonoSite, BK Medical, and Philips and anhonorarium from Dannemiller.

Copyright © 2014 by American Society of Regional Anesthesia and Pain MedicineISSN: 1098-7339DOI: 10.1097/AAP.0000000000000135

368 Regional Anesthesia and

Copyright © 2014 American Society of Regional Anesthesia and Pain

This review focuses on the anatomy of the knee relevant to IAknee injections.

Muscles and TendonsMuscles and tendons surrounding the knee joint may

be grouped based on their location or function. The extensormechanism—the most prominent contributor to the knee joint—comprises the quadriceps femoris muscle and the patella. Thequadriceps muscle consists of rectus femoris, vastus medialis,vastus intermedius, and vastus lateralis, forming a common ten-don that is inserted into the tibial tubercle (Fig. 1). The commontendon (quadriceps and patellar tendons) houses the patella,which is a large sesamoid bone spanning the knee joint anteriorly.The quadriceps tendon is a trilaminar structure composed of su-perficial (from rectus femoris), intermediate (from amalgamationof the vastus medialis and lateralis), and deep (from the vastusintermedius) layers, which merge to form a common tendon(Fig. 2). The patellar tendon has high tensile strength and arisesfrom the apex and the medial and lateral sides of the patella.

The knee flexors are located predominantly posteriorly and in-clude the biceps femoris, semimembranosus, and semitendinosusmuscles (Fig. 3). Other flexors include gastrocnemius, which pri-marily plantar flexes the foot, and the gracilis, which is locatedposteromedially and acts as a hip adductor as well as a flexor ofthe knee and hip joints. The only anteriorly located knee flexor isthe sartorius, which functions as a hip flexor as well as abductorand spans from the iliac crest, crossing over medially beforeinserting into the tibia. Pes anserinus (Latin for goose’s foot) isthe insertion of the conjoint tendons of semitendinosus, gracilis,and sartorius onto the anteromedial (AM) aspect of proximal tibia(Fig. 4). Popliteus is also a knee flexor, but only when the knee ishyperextended; in other positions, it functions as a medial rotatorof the tibia on the femur (Fig. 4).

LigamentsThe stability of the knee is maintained primarily by 4 liga-

ments (Fig. 4). Both the anterior and posterior cruciate ligamentsare intracapsular but extrasynovial structures. The anterior cruci-ate ligament originates from the posteromedial aspect of the lat-eral femoral condyle and has its attachment to the front of theintercondylar eminence on the tibia. The stronger posterior cruci-ate ligament originates from the posterolateral surface of the me-dial condyle and is attached to the posterior intercondylar fossaof the tibia. The medial collateral ligament is inserted to the me-dial epicondyle of the femur and the medial tibial condylewith the deep fibers attaching to the medial meniscus (Fig. 4).It is buttressed between the tendons of pes anserinus andsemimembranosus. The lateral collateral ligament spans betweenthe lateral epicondyle of the femur and the head of the fibula.

JointsThe femorotibial joint is composed of 2 compartments: me-

dial and lateral. The fibrocartilaginous medial and lateral menisci

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Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014 US in Pain Medicine: Knee Joint

increase the surface area of contact between the convex femoralcondyles and flat tibia plateau. The articular capsule is reinforcedby various structures surrounding the joint: muscles and tendons,retinaculum, and ligaments. Anteriorly, they are quadriceps andpatella tendons, medial and lateral patellofemoral ligaments, andretinaculum from vastus medialis and lateralis. Medially, it is rein-forced by medial collateral ligament. Laterally, it is strengthenedby iliotibial band, lateral collateral ligament, and the bicep tendonsand their fascial expansion.

There are many recesses to the femorotibial joint, but thewidest is the suprapatellar recess (SPR) (Fig. 4), which originatesfrom the fusion of the subquadriceps bursa with the joint cavityand allows an access for injection into the joint cavity.

BursaAround the knee joint, there are multiple bursae, which serve

to reduce the friction between various structures (bones, tendons,ligaments, or skin), allowing a smooth and independent glidingof these structures during joint movements. The anatomical loca-tions of these bursae are summarized in Table 1 and Figure 4. Ofthese bursae, the most well-known is the semimembranosus orsemimembranosus-gastrocnemius bursa. Abnormal distension ofthis results in Baker’s cyst. Although Baker’s cyst is the most

FIGURE 1. Anterior view of the thigh and knee. Reproduced with perm

© 2014 American Society of Regional Anesthesia and Pain Medicine


common popliteal cyst (defined as a fluid-filled mass in the pop-liteal fossa), the terms should not be used synonymously as thereare other causes of popliteal cysts. In adult, almost all Baker’scysts are secondary, which means that communications exist be-tween the bursae and knee joint.1

SonoanatomyThe kneemay be examined from anterior, medial, lateral, and

posterior surfaces to identify various structures and pathologies. Alinear array transducer at frequencies of 6 to 12 MHz is usuallyideal for the examination of the knee. Higher frequencies are usedto examine the more superficial structures in details.

Anterior KneeWhen examining the knee anteriorly, the patient is placed in

supine position with the knee slightly flexed 20 to 30 degrees on abolster to keep the quadriceps tendon taut. The sequence of exam-ination starts from above the patella to evaluate the quadricepsfemoris (Fig. 5). Just beneath the tendon of the quadriceps femorisis the suprapatellar bursa appearing as a thin hypoechoic line. Vol-untary contraction of the quadriceps may help identify smaller ef-fusions.2 The prefemoral fat pad is located over the femur, and thesuprapatellar fat pad is underneath the quadriceps tendon. The

ission from Dr Philip Peng from Philip Peng Educational Series.

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Peng and Shankar Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014

suprapatellar bursa is commonly chosen as the site for access tothe knee joint. The medial and lateral recesses may be examinedin a transverse view by the side of the patella (Fig. 6). When theknee is fully flexed, the condyles may be visualized as a curvedhyperechoic line with an acoustic shadow beneath it. Lining thecondyles is the hypoechoic hyaline cartilage (Fig. 7).

Scanning longitudinally inferior to the patella helps identifythe patellar tendon inserting into the tibial tuberosity, and beneaththe tendon, the intracapsular Hoffa’s fat pad is located (Fig. 8).The infrapatellar bursa lies over the tibia and the distal portionof this tendon (Fig. 4).

Medial KneeExamination is best performed with the patient’s knee exter-

nally rotated while maintaining 20- to 30-degree flexion. Placingthe ultrasound probe over the long axis of medial collateral liga-ment reveals the superficial layer and the deep meniscofemoraland meniscotibial components of the ligament (Fig. 9). In general,the ligament is examined for the entire length and with dynamicscanning during valgus stress for the possible pathology and as-sessment of integrity. The medial meniscus appears as ahyperechoic triangular structure between the femur and tibia(Fig. 9). Moving the ultrasound probe distally to the AM aspectof the tibial metaphysis, the tendons of sartorius, gracilis, and

FIGURE 2. Lateral view of the knee showed the details of the trilaminar nwas the expanded view of the rectangle over the quadriceps tendon. ReEducational Series.

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semitendinosus are seen blended together, forming the pesanserinus complex (Fig. 9).

Lateral KneeExamination of the lateral knee is performed with the pa-

tient’s knee internally rotated while maintaining 20- to 30-degree flexion. The ultrasound probe is first placed over the longaxis of iliotibial band, with the distal segment best revealed in thecoronal plane. The iliotibial band is seen as a thin, fibrillar struc-ture that inserts onto the Gerdy tubercle, a bony prominence onthe anterolateral (AL) aspect of the tibial epiphysis (Fig. 10).The lateral collateral ligament is best examined by placing thelower part of the ultrasound probe over the fibula head with theproximal part of probe rotating over the femur. When the probeis aligned with the ligament, it gives the longest view of the liga-ment. With a proper scan, the popliteus tendon and the lateral me-niscus can be seen (Fig. 10).

Posterior KneeThe examination is performed while the patient is prone posi-

tion with the knee extended. The ultrasound probe is placed on theposteromedial aspect of the knee over the medial femoral condyle.The following structures are seen from medial to lateral in short-axis scan: sartorius, gracilis, semimembranosus, semitendinosus,

ature of the quadriceps tendon. The insert on the right upper cornerproduced with permission from Dr Philip Peng from Philip Peng




and medial head of gastrocnemius muscle (Fig. 11). The semi-membranosus or semimembranosus-gastrocnemius bursa is locatedbetween the tendons of semimembranosus and the medial head ofgastrocnemius. Moving the probe laterally, the short-axis scan ofthe popliteal fossa reveals the neurovascular bundle (Fig. 11). Mov-ing the probe further laterally, the biceps femoris muscle and tendonare examined in the long-axis scan (Fig. 11).

AccuracyAlthough the knee IA injections are commonly performed

with landmark-based technique by rheumatologists, orthopedic sur-geons, and general practitioners, the accuracy of the landmark-based technique in clinical studies is approximately 79% (range,40%–100%).3 Three factors influence accuracy: use of image guid-ance, experience of practitioners, and approach of injection.

Literature supports the superiority of image guidance interms of accuracy.4 Comparison studies reveal pooled accuracyrates of 81.0% and 96.7% for landmark-based versus image guid-ance (fluoroscopy or ultrasound) techniques, respectively.4 In con-trast to fluoroscopy, ultrasound allows the procedure to beperformed in office-based settings. The accuracies of landmark-based versus ultrasound guidance techniques were also signifi-cantly different, 77.8% and 95.8%, respectively.4 Although thepresence of an effusion greatly enhances the accuracy oflandmark-based IA needle placement in the knee,5,6 loss of resis-tance is not indicative of an IA location. This was supported by a

FIGURE 3. Posterior view of the thigh and knee showed the flexors of thPeng Educational Series.



cadaver study examining the reasons for the failure of thelandmark-based injection, with most of the inaccuracies due tothe injection into the Hoffa’s fat pad (81%).7

Experience can be an important contributor to the accuracy.The only controlled study looking at the influence of practitioner’sexperience in knee injection compares the accuracy of a traineewith 10 months of landmark-based knee injection experienceand a staff physician with 13 years’ experience in the same. Thisstudy demonstrated a huge difference in success rate, 55% versus100% for the trainee and staff physician, respectively.8 However,another important finding of this study was that both achieved100% accuracy with ultrasound-guided technique (the levels ofexperience with ultrasound imaging guidance were 10 monthsand 3 years for the trainee and staff physician, respectively). Thisstudy echoed the improvement in accuracy with ultrasound guid-ance for the less experienced practitioners in another study, inwhich patients who received injections at various sites (shoulder,elbow, wrist, knee, and ankle) were randomized to ultrasound-guided injections or injections using the landmark-based tech-nique.9 The ultrasound technique was exclusively performedby 1 junior trainee with 9 months of rheumatology experienceand 8 sessions of musculoskeletal ultrasound training. Thelandmark-based technique was performed by a group of rheuma-tologists with more training, with approximately two-thirds of in-jections by 9 rheumatologists with median experience of 15 yearsand one-third of injections by 9 senior rheumatology trainees withmedian rheumatology experience of 3 years. The accuracy was

e knee. Reproduced with permission from Dr Philip Peng from Philip

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significantly better for the junior trainee who performed all theultrasound-guided injections (accuracy rates of 83% vs 66% forultrasound and landmark-based technique, respectively). Confi-dence or satisfaction of injection by the practitioner usinglandmark-guided technique did not result in a better success rate.9

FIGURE 4. Four views of the knee showed the ligaments and bursae. A,Mposterior view, the medial head of gastrocnenimus was removed to revepermission from Dr Philip Peng from Philip Peng Educational Series.

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This is similar to the confidence factor of the practitioner in shoul-der injections reviewed previously.10

Accuracy is also influenced by the approaches. When per-forming landmark-based technique knee injections, there aregenerally 6 approaches: superolateral (SL), superomedial, medial

edial view. B, Anterior view. C, Lateral view. D, Posterior view. In theal the IA structures. F indicates fibula; T, tibia. Reproduced with



TABLE 1. Bursae of the Knee

Bursa Location Between

Anserine Pes anserinus Tibia and medial collateral ligamentSubcutaneous prepatellar Skin Anterior surface of patellaSuprapatellar Quadriceps tendon FemurSubcutaneous infrapatellar Skin Tibial tuberosityDeep infrapatellar Patella tendon (ligament) Anterior surface of tibiaSemimembranosus Semimembranosus tendon Medial head of gastrocnemiusPopliteus Popliteus tendon Lateral condyle of tibia


midpatellar (MMP), lateral midpatellar (LMP), AM, and AL(Fig. 12). The details of the approaches are reviewed elsewhere.11

The first 4 approaches are performed with the knee in extension,whereas AM and AL approaches are performed with knee in90-degree flexion with or without the modification of degree of

FIGURE 5. A, Sonogram of the suprapatellar view of the normal knee. ThB, Sonogram of the details of quadriceps tendon. C, Sonogramof the supof effusion fluid filling the space between prefemoral fat pad and quadricepad; P, patella; F, femur. ** indicates the SPR. Reproduced with permiss



flexion as suggested byWaddell et al.12 The SL approach resultedin the highest accuracy of 91% (95% confidence interval [CI],84%–99%). There are also different approaches for ultrasoundguidance. Only 1 study compared the accuracies of differentultrasound-guided approaches.13 The SL and LMP approaches

e insert showed the position of the patient and the ultrasound probe.rapatellar view of a patient with knee effusion. Note the presenceps tendon. SPFP indicates suprapatellar fat pad; PFFP, prefemoral fation from Dr Philip Peng from Philip Peng Educational Series.

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FIGURE 6. A and C, Pictures show the position of the ultrasound probes and themanipulation of the patella by the examiner. The patella waspushed to the medial and lateral sides, respectively in A and C. B and D, The respective sonograms (B and D) show the medial and lateralviews, respectively. MFC indicates medial femoral condyle; LFC, lateral femoral condyle. Stars indicate the Hoffa fat pad; chain of trapezoidindicates the cartilage. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.


were significantly more accurate than MMP approach (accu-racy rates of SL, LMP, and MMP were 100%, 95%, and75%, respectively).

Ultrasound improves accuracy of IA injection, which is im-portant to both outcome and safety. Still, there is some controversyregarding the effect of imaging method for needle placement

FIGURE 7. Sonogram of both femoral condyles. The picture on the left scartilage was marked with trapezoids. QT indicates quadriceps tendon.Dr Philip Peng from Philip Peng Educational Series.

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improved clinical outcome.14 It is important to recognize that kneeinjections can be used to deliver various therapeutic medications(eg, corticosteroids or viscosupplements) or biologic agents (eg,platelet-rich plasma or stem cells) to reduce pain and improvefunction in patients with knee disorders.15,16While therapeutic ef-fect can occur with suboptimal location of corticosteroid in the

hows the position of the knee and the ultrasound probe. The hyaline*Muscle of vastus medialis. Reproduced with permission from



FIGURE 8. Sonogram of the infrapatellar region. The picture on the left shows the position of the ultrasound probe. The arrow indicates thepatella tendon, and * indicates the Hoffa fat pad. T indicates tibia; TT, tibial tuberosity. Reproduced with permission from Dr Philip Pengfrom Philip Peng Educational Series.


knee joint,17,18 other agents require precise deposition in the IAspace. There is sufficient literature evidence showing that im-proved accuracy of IA corticosteroid injection correlated with bet-ter pain relief, functional outcome, and cost-effectiveness.9,19–23

In addition, precise placement of needle minimizes procedure-related pain, tissue trauma, crystal synovitis, hemarthrosis, and ar-ticular cartilage atrophy.4,19,24,25

Efficacy of IA Knee InjectionsThe main indication for IA knee injection is osteoarthritis

(OA), and the injection agents commonly used by practitionersare corticosteroid and hyaluronic acid (HA).15 Efficacy of othermedications and biologic agents has been examined elsewhere,15

but only corticosteroid and HA are reviewed here.Three systematic reviews consistently concluded that IA cor-

ticosteroid was more effective than IA placebo for pain reduction

FIGURE 9. A, Sonogram of long-axis view of the medial collateral ligamligament, which is deep to the superficial fascia (open arrows); closed armeniscus (*) and the femur (F). B, Sonogram of long-axis view of the pesmetaphysis. At this level, the 3 tendons of sartorius, gracilis, and semitendiagram is the color Doppler showing the inferior medial genicular arterpatient as well as the corresponding anatomical structures in the sonogrsmall pillow. Reproduced with permission from Dr Philip Peng from Phili



(weighted mean difference, −21.91; 95% CI, −29.93 to −13.89)and patient global assessment (relative risk, 1.44; 95% CI,1.13–1.82).26–28 However, these reviews also suggested that IAcorticosteroid provided only short-term benefit (<3 weeks), andthere was a lack of evidence for efficacy in functional improve-ment. Research comparing different preparations of corticosteroidsuggests that triamcinolone is more effective than betamethasoneand methylprednisolone, 2 other commonly used corticosteroids.However, not all studies considered using a validated outcomemeasure such as the visual analog scale pain scale.29

Viscosupplementation is indicated for symptomatic OA ofthe knee without complete collapse of joint space.15 The use ofthis in the management of knee OA has become a controversialsubject lately.30 Viscosupplementation refers to IA injection ofHA, which is a natural substance normally found in the synovialfluid of joints. It provides the rheological properties (viscosityand elasticity) of the synovial fluid and functions as a lubricant

ent. Open arrowheads indicate superficial layer of the collateralrow, the deeper meniscofemoral ligament connecting theanserinus complex inserting into the anterolateral aspect of the tibialdinosus cannot be differentiated from each other. The lowery (dark arrowhead). The inserts show the position of the probe andam. Note that the leg was externally rotated and rested on ap Peng Educational Series.

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FIGURE 10. A, Sonogram of the long-axis view of iliotibial band (hyperechoic structures indicated by the arrows) inserting into theGerdy tubercle (GT). The GT and the fibula (F) were marked on the skin. B, Sonogram of the long-axis view of lateral collateral ligament(arrows) inserting into the fibular head. The popliteus tendon (open arrowhead) is seen deep to the collateral ligament at this level andinserted in the small fossa (closed arrowheads) located on the lateral aspect of the lateral femoral condyle. The insert shows the positionof the probe and the position of the patient. The leg was internally rotated resting on a small pillow. Reproduced with permission fromDr Philip Peng from Philip Peng Educational Series.


and shock absorber of the joint. The rheological properties of HAdepend on both the concentration and the molecular weight of theHA in the synovial fluid. There are various products on the marketfor viscosupplementation. These include HA preparations of rela-tively lowmolecular weight (Hyalgan andARTZ), of intermediatemolecular weight (Orthovisc), and a cross-linked hyaluronan ofhigh molecular weight (Synvisc).

Avery detailed evidence-based review on knee injections forarthritis published in 2012 summarized that there were 7 meta-analyses on the effectiveness of IA injection of HA for the treat-ment of knee OA.15 Compared with placebo or IA corticosteroidinjection, 5 of 7 analyses found IA injection of HA efficaciousin the management of OA. In addition, 9 of 10 guidelines on man-agement of kneeOA provide positive recommendations on the useof HA.15 The therapeutic benefit over placebo of IA HA for kneeOAwas more long-lasting than IA corticosteroid. There was a sig-nificant improvement in pain scores from baseline by 26% andfunction by 27% during the period of fifth to 13th week.31 How-ever, the included studies were variable in design and outcomes.31

A closer examination of this review from 2012 revealed thatthe most recent meta-analysis quoted in this article was publishedin 2009, and there were 7 trials published outside of this meta-analysis.32–38 The American Academy of Orthopedic Surgeonsrecently published a meta-analysis that included all those recenttrials. Unlike other systematic reviews, they excluded those stud-ies that recruited fewer than 30 patients in each treatment groupand included only those trials that demonstrated clinical efficacybeyond 4-week treatment period.30 They also interpreted the resultusing the terms “minimum clinically important improvement”,which was expressed as meaningfully important differenceunits. They included 14 studies (3 high-strength studies and 11moderate-strength studies). This was in contrast to the latestCochrane review, which included 40 studies. Although all analy-ses of the WOMAC (Western Ontario and McMaster UniversitiesArthritis Index) pain, function, and stiffness subscales scores re-vealed statistically significant treatment effects, none of these

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improvements met the minimum clinically important improve-ment thresholds. They showed that the overall improvement (painand function outcome) was less than 0.5 meaningfully importantdifference units. This suggested a low likelihood that an apprecia-ble number of patients achieved clinically important benefits inthe outcome.39 When the high- and low-molecular-weight HAswere analyzed separately, they showed that most of the statisti-cally significant outcomes were associated with high-molecularcross-linked HA (Synvisc), but when compared with midrangemolecular-weight HA, statistical significance was not maintained.Based on their review method, they did not recommend the use ofHA for knee OA. The strength of this recommendation was strongand was based on lack of efficacy, not on potential harm

Based on the above information, should we consider knee in-jection in managing patient with OA of knee? Both injection med-ications clearly show benefits in terms of pain and function.However, the clinical benefit of IA corticosteroid is short term.Literature on viscosupplementation supports improvement in painand function as well. The controversy is whether the benefits areclinically significant. In deciding the management options to pa-tients with knee OA, clinician should balance the benefits andrisks of IA injection with the other conservative and surgical op-tions in the management algorithm.

Ultrasound-Guided Injection TechniqueBecause the suprapatellar or SL approach is the most well-

studied ultrasound approach and was shown to have the highestefficacy, this approach is described here.

The procedure is performed with the patient placed in supineposition with the knee slightly flexed and supported. Followingsterile preparation, a high-frequency linear probe (6-13 Hz) isplaced over the patella and quadriceps tendon (Fig. 13). Withproper positioning, the SPR between the suprapatellar andprefemoral fat pads should be revealed. A couple of maneuverscan be used to augment the SPR when the synovial fluid is scant:



FIGURE 11. A, Sonogram showing the various muscles and tendons in the posteromedial region of the knee. Deep to the sartoriusmuscle (Sa), the tendon of gracilis (arrow) and saphenous nerve (line arrows) were revealed. Semitendinosus tendon (closed arrowheads)was seen as a round hyperechoic structure resting on the semimembranosus muscle (SM), similar to “a cherry on the cake.” B, By movingthe ultrasound lateral to the medial femoral condyle (MC), the medial head of gastrocnemius (GH) and its tendon (asterisk) wererevealed. Between the space between the medial head of gastrocnemius and semimembranosus muscle is the semimembranosus orsemimembranosus-gastrocnemius bursa (outlined by dotted line), which is hypoechoic in normal state because of the apposition of synovialwalls. Because of lack of fluid in normal state, one should apply very light pressure to the ultrasound probe to reveal its presence. The hyalinecartilage was indicated by white rhombi. C, Sonogram of the central portion of the posterior knee. Color Doppler shows the poplitealartery (blue structure indicated by the arrow). The sciatic nerve was also revealed posterior to the artery. D, Sonogram of the biceps femorisin the posterolateral region of the knee. The biceps muscle (BFm) continues as a tendon (arrows) inserting into the fibular head (F) as a clearhyperechoic structure. * Indicates lateral meniscus; T, tibia. The inserts in each figure show the position of the patient, the position of theprobe, and the anatomical structures corresponding to the sonogram. Reproduced with permission from Dr Philip Peng from Philip PengEducational Series.


(1) to ask the patient to perform isometric contraction of thequadriceps or (2) to apply pressure in the parapatellar space tosqueeze the synovial fluid to the SPR. Once the SPR is seen,the ultrasound probe is rotated 90 degrees above the patella. A20- or 22-gauge needle is inserted from lateral to medial in-planetoward the SPR. Alternatively, the ultrasound probe is rotated45 degrees with the cephalad end directed to the lateral side (SLposition). The rotation of the probe is to avoid needle trauma tothe quadriceps tendon. Aspiration of synovial fluid should alwaysbe considered. Five milliliters of corticosteroid (40 mg methyl-prednisolone or triamcinolone diluted in 5 mL of local anesthetic)



or viscosupplement is injected following hydrolocation of the lo-cation of the needle (avoid injecting into the fat pad).

CONCLUSIONSKnee IA injections are commonly performed with landmark-

based technique by general practitioners and specialists. The ac-curacy of IA injection is influenced by 3 factors: use of imageguidance, experience of practitioners, and the approach of injec-tion. Literature supports better accuracy with ultrasound guidance

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FIGURE12. Diagram shows the various landmark-based approach. The dark dotsmark the sites of needle entry; the arrows show the directionof needle entry. The knee was put in extension for SL, superomedial (SM), LMP, and MMP approaches. The AM and AL approaches areperformed with knee in 90-degree flexion with or without the modification of degree of flexion as suggested by Waddell et al.12 Reproducedwith permission from Dr Philip Peng from Philip Peng Educational Series.


over landmark-based technique. Better experience of the practi-tioner improves the accuracy of landmark-based technique, butthe use of ultrasound guidance can boost the accuracy of the less ex-perienced. Superolateral approach appears as the most reliableapproach for both the ultrasound-guided or landmark-based tech-niques. Ultrasound enhances the accuracy of knee IA injection,

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which in turns improves the clinical outcome. Literature supportsthe efficacy of IA injection of corticosteroid, but the benefits areof short term (<3 weeks). Viscosupplementation provides signifi-cant improvement in pain scores and function up to 3 months.However, controversy exists on whether the benefits are clini-cally significant. Clinicians should balance the benefits and risks



FIGURE 13. Picture shows the injection technique. The ultrasound probe is placed between the patella and quadriceps tendon initially andthen turned 90 degrees upon visualization of the SPR. The needle is then approached from lateral to medial to avoid puncturing thequadriceps tendon. The needle is indicated by the arrowheads and the SPR by asterisks (****). R indicates retinaculum; Q, quadriceps tendon;F, femur. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.


with the other conservative and surgical options in the manage-ment algorithm.

ACKNOWLEDGEMENTThe authors thank Dr Richelle Kruisselbrink for assisting

with the construction of the sonogram.

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