REVIEW ARTICLE
Ultrasound-Guided Interventional Procedures in Pain 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 a popular technique for pain intervention. It can be applied to the intraarticular injection of the knee joint. The first objective of this review was to describe and summarize the anatomy and sonoanatomy of the knee and associated structures relevant for intra-articular injection. The second objective was to examine the feasibility, accuracy, and effectiveness of injections as well as injection techniques. (Reg Anesth Pain Med 2014;39: 368–380)
A
rthritis involving the knee joint is a common cause for pain and disability. Conservative management includes weight loss, physical therapy, and pharmacologic interventions. Patients unresponsive to conservative management are usually offered intra-articular (IA) injections, which may be performed blindly or with image guidance using fluoroscopy or ultrasound. Ultrasound guidance has provided an additional tool to identify the target pathology, improving accuracy without the harmful effects of radiation. This review, focusing on interventions to the knee joint, aimed to describe and summarize the anatomy and sonoanatomy of 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.
METHODS We 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 reports of the use of IA injections for the amelioration of knee arthritis, the agents used, and the use of image guidance and their accuracy and efficacy.
Muscles and Tendons Muscles and tendons surrounding the knee joint may be grouped based on their location or function. The extensor mechanism—the most prominent contributor to the knee joint— comprises the quadriceps femoris muscle and the patella. The quadriceps muscle consists of rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis, forming a common tendon that is inserted into the tibial tubercle (Fig. 1). The common tendon (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 superficial (from rectus femoris), intermediate (from amalgamation of the vastus medialis and lateralis), and deep (from the vastus intermedius) layers, which merge to form a common tendon (Fig. 2). The patellar tendon has high tensile strength and arises from the apex and the medial and lateral sides of the patella. The knee flexors are located predominantly posteriorly and include the biceps femoris, semimembranosus, and semitendinosus muscles (Fig. 3). Other flexors include gastrocnemius, which primarily plantar flexes the foot, and the gracilis, which is located posteromedially and acts as a hip adductor as well as a flexor of the knee and hip joints. The only anteriorly located knee flexor is the sartorius, which functions as a hip flexor as well as abductor and spans from the iliac crest, crossing over medially before inserting into the tibia. Pes anserinus (Latin for goose’s foot) is the 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 is hyperextended; in other positions, it functions as a medial rotator of the tibia on the femur (Fig. 4).
Ligaments
DISCUSSION Anatomy of Knee Joint and Surrounding Structures The 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 of Toronto, Toronto, Ontario, Canada; and †Department of Anesthesiology, Clement Zablocki 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 an honorarium from Dannemiller. Copyright © 2014 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000135
368
This review focuses on the anatomy of the knee relevant to IA knee injections.
The stability of the knee is maintained primarily by 4 ligaments (Fig. 4). Both the anterior and posterior cruciate ligaments are intracapsular but extrasynovial structures. The anterior cruciate ligament originates from the posteromedial aspect of the lateral femoral condyle and has its attachment to the front of the intercondylar eminence on the tibia. The stronger posterior cruciate ligament originates from the posterolateral surface of the medial condyle and is attached to the posterior intercondylar fossa of the tibia. The medial collateral ligament is inserted to the medial epicondyle of the femur and the medial tibial condyle with the deep fibers attaching to the medial meniscus (Fig. 4). It is buttressed between the tendons of pes anserinus and semimembranosus. The lateral collateral ligament spans between the lateral epicondyle of the femur and the head of the fibula.
Joints The femorotibial joint is composed of 2 compartments: medial and lateral. The fibrocartilaginous medial and lateral menisci
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
increase the surface area of contact between the convex femoral condyles and flat tibia plateau. The articular capsule is reinforced by various structures surrounding the joint: muscles and tendons, retinaculum, and ligaments. Anteriorly, they are quadriceps and patella tendons, medial and lateral patellofemoral ligaments, and retinaculum from vastus medialis and lateralis. Medially, it is reinforced by medial collateral ligament. Laterally, it is strengthened by iliotibial band, lateral collateral ligament, and the bicep tendons and their fascial expansion. There are many recesses to the femorotibial joint, but the widest is the suprapatellar recess (SPR) (Fig. 4), which originates from the fusion of the subquadriceps bursa with the joint cavity and allows an access for injection into the joint cavity.
US in Pain Medicine: Knee Joint
common popliteal cyst (defined as a fluid-filled mass in the popliteal fossa), the terms should not be used synonymously as there are other causes of popliteal cysts. In adult, almost all Baker’s cysts are secondary, which means that communications exist between the bursae and knee joint.1
Sonoanatomy The knee may be examined from anterior, medial, lateral, and posterior surfaces to identify various structures and pathologies. A linear array transducer at frequencies of 6 to 12 MHz is usually ideal for the examination of the knee. Higher frequencies are used to examine the more superficial structures in details.
Anterior Knee Bursa Around 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 gliding of these structures during joint movements. The anatomical locations of these bursae are summarized in Table 1 and Figure 4. Of these bursae, the most well-known is the semimembranosus or semimembranosus-gastrocnemius bursa. Abnormal distension of this results in Baker’s cyst. Although Baker’s cyst is the most
When examining the knee anteriorly, the patient is placed in supine position with the knee slightly flexed 20 to 30 degrees on a bolster to keep the quadriceps tendon taut. The sequence of examination starts from above the patella to evaluate the quadriceps femoris (Fig. 5). Just beneath the tendon of the quadriceps femoris is the suprapatellar bursa appearing as a thin hypoechoic line. Voluntary contraction of the quadriceps may help identify smaller effusions.2 The prefemoral fat pad is located over the femur, and the suprapatellar fat pad is underneath the quadriceps tendon. The
FIGURE 1. Anterior view of the thigh and knee. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series. © 2014 American Society of Regional Anesthesia and Pain Medicine
369
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
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 to the knee joint. The medial and lateral recesses may be examined in a transverse view by the side of the patella (Fig. 6). When the knee is fully flexed, the condyles may be visualized as a curved hyperechoic line with an acoustic shadow beneath it. Lining the condyles is the hypoechoic hyaline cartilage (Fig. 7). Scanning longitudinally inferior to the patella helps identify the patellar tendon inserting into the tibial tuberosity, and beneath the tendon, the intracapsular Hoffa’s fat pad is located (Fig. 8). The infrapatellar bursa lies over the tibia and the distal portion of this tendon (Fig. 4).
Medial Knee Examination is best performed with the patient’s knee externally rotated while maintaining 20- to 30-degree flexion. Placing the ultrasound probe over the long axis of medial collateral ligament reveals the superficial layer and the deep meniscofemoral and meniscotibial components of the ligament (Fig. 9). In general, the ligament is examined for the entire length and with dynamic scanning during valgus stress for the possible pathology and assessment of integrity. The medial meniscus appears as a hyperechoic triangular structure between the femur and tibia (Fig. 9). Moving the ultrasound probe distally to the AM aspect of the tibial metaphysis, the tendons of sartorius, gracilis, and
semitendinosus are seen blended together, forming the pes anserinus complex (Fig. 9).
Lateral Knee Examination of the lateral knee is performed with the patient’s knee internally rotated while maintaining 20- to 30degree flexion. The ultrasound probe is first placed over the long axis of iliotibial band, with the distal segment best revealed in the coronal plane. The iliotibial band is seen as a thin, fibrillar structure that inserts onto the Gerdy tubercle, a bony prominence on the anterolateral (AL) aspect of the tibial epiphysis (Fig. 10). The lateral collateral ligament is best examined by placing the lower part of the ultrasound probe over the fibula head with the proximal part of probe rotating over the femur. When the probe is aligned with the ligament, it gives the longest view of the ligament. With a proper scan, the popliteus tendon and the lateral meniscus can be seen (Fig. 10).
Posterior Knee The examination is performed while the patient is prone position with the knee extended. The ultrasound probe is placed on the posteromedial aspect of the knee over the medial femoral condyle. The following structures are seen from medial to lateral in shortaxis scan: sartorius, gracilis, semimembranosus, semitendinosus,
FIGURE 2. Lateral view of the knee showed the details of the trilaminar nature of the quadriceps tendon. The insert on the right upper corner was the expanded view of the rectangle over the quadriceps tendon. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
370
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
and medial head of gastrocnemius muscle (Fig. 11). The semimembranosus or semimembranosus-gastrocnemius bursa is located between the tendons of semimembranosus and the medial head of gastrocnemius. Moving the probe laterally, the short-axis scan of the popliteal fossa reveals the neurovascular bundle (Fig. 11). Moving the probe further laterally, the biceps femoris muscle and tendon are examined in the long-axis scan (Fig. 11).
Accuracy Although the knee IA injections are commonly performed with landmark-based technique by rheumatologists, orthopedic surgeons, and general practitioners, the accuracy of the landmarkbased technique in clinical studies is approximately 79% (range, 40%–100%).3 Three factors influence accuracy: use of image guidance, experience of practitioners, and approach of injection. Literature supports the superiority of image guidance in terms of accuracy.4 Comparison studies reveal pooled accuracy rates of 81.0% and 96.7% for landmark-based versus image guidance (fluoroscopy or ultrasound) techniques, respectively.4 In contrast to fluoroscopy, ultrasound allows the procedure to be performed in office-based settings. The accuracies of landmarkbased versus ultrasound guidance techniques were also significantly different, 77.8% and 95.8%, respectively.4 Although the presence of an effusion greatly enhances the accuracy of landmark-based IA needle placement in the knee,5,6 loss of resistance is not indicative of an IA location. This was supported by a
US in Pain Medicine: Knee Joint
cadaver study examining the reasons for the failure of the landmark-based injection, with most of the inaccuracies due to the 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’s experience in knee injection compares the accuracy of a trainee with 10 months of landmark-based knee injection experience and a staff physician with 13 years’ experience in the same. This study demonstrated a huge difference in success rate, 55% versus 100% for the trainee and staff physician, respectively.8 However, another important finding of this study was that both achieved 100% accuracy with ultrasound-guided technique (the levels of experience with ultrasound imaging guidance were 10 months and 3 years for the trainee and staff physician, respectively). This study echoed the improvement in accuracy with ultrasound guidance for the less experienced practitioners in another study, in which patients who received injections at various sites (shoulder, elbow, wrist, knee, and ankle) were randomized to ultrasoundguided injections or injections using the landmark-based technique.9 The ultrasound technique was exclusively performed by 1 junior trainee with 9 months of rheumatology experience and 8 sessions of musculoskeletal ultrasound training. The landmark-based technique was performed by a group of rheumatologists with more training, with approximately two-thirds of injections by 9 rheumatologists with median experience of 15 years and one-third of injections by 9 senior rheumatology trainees with median rheumatology experience of 3 years. The accuracy was
FIGURE 3. Posterior view of the thigh and knee showed the flexors of the knee. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series. © 2014 American Society of Regional Anesthesia and Pain Medicine
371
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Peng and Shankar
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
significantly better for the junior trainee who performed all the ultrasound-guided injections (accuracy rates of 83% vs 66% for ultrasound and landmark-based technique, respectively). Confidence or satisfaction of injection by the practitioner using landmark-guided technique did not result in a better success rate.9
This is similar to the confidence factor of the practitioner in shoulder injections reviewed previously.10 Accuracy is also influenced by the approaches. When performing landmark-based technique knee injections, there are generally 6 approaches: superolateral (SL), superomedial, medial
FIGURE 4. Four views of the knee showed the ligaments and bursae. A, Medial view. B, Anterior view. C, Lateral view. D, Posterior view. In the posterior view, the medial head of gastrocnenimus was removed to reveal the IA structures. F indicates fibula; T, tibia. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
372
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
US in Pain Medicine: Knee Joint
TABLE 1. Bursae of the Knee Bursa Anserine Subcutaneous prepatellar Suprapatellar Subcutaneous infrapatellar Deep infrapatellar Semimembranosus Popliteus
Location Between Pes anserinus Skin Quadriceps tendon Skin Patella tendon (ligament) Semimembranosus tendon Popliteus tendon
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 in 90-degree flexion with or without the modification of degree of
Tibia and medial collateral ligament Anterior surface of patella Femur Tibial tuberosity Anterior surface of tibia Medial head of gastrocnemius Lateral condyle of tibia
flexion as suggested by Waddell et al.12 The SL approach resulted in the highest accuracy of 91% (95% confidence interval [CI], 84%–99%). There are also different approaches for ultrasound guidance. Only 1 study compared the accuracies of different ultrasound-guided approaches.13 The SL and LMP approaches
FIGURE 5. A, Sonogram of the suprapatellar view of the normal knee. The insert showed the position of the patient and the ultrasound probe. B, Sonogram of the details of quadriceps tendon. C, Sonogram of the suprapatellar view of a patient with knee effusion. Note the presence of effusion fluid filling the space between prefemoral fat pad and quadriceps tendon. SPFP indicates suprapatellar fat pad; PFFP, prefemoral fat pad; P, patella; F, femur. ** indicates the SPR. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series. © 2014 American Society of Regional Anesthesia and Pain Medicine
373
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Peng and Shankar
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
FIGURE 6. A and C, Pictures show the position of the ultrasound probes and the manipulation of the patella by the examiner. The patella was pushed to the medial and lateral sides, respectively in A and C. B and D, The respective sonograms (B and D) show the medial and lateral views, respectively. MFC indicates medial femoral condyle; LFC, lateral femoral condyle. Stars indicate the Hoffa fat pad; chain of trapezoid indicates the cartilage. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
were significantly more accurate than MMP approach (accuracy rates of SL, LMP, and MMP were 100%, 95%, and 75%, respectively). Ultrasound improves accuracy of IA injection, which is important to both outcome and safety. Still, there is some controversy regarding the effect of imaging method for needle placement
improved clinical outcome.14 It is important to recognize that knee injections 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 improve function in patients with knee disorders.15,16 While therapeutic effect can occur with suboptimal location of corticosteroid in the
FIGURE 7. Sonogram of both femoral condyles. The picture on the left shows the position of the knee and the ultrasound probe. The hyaline cartilage was marked with trapezoids. QT indicates quadriceps tendon. *Muscle of vastus medialis. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
374
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
US in Pain Medicine: Knee Joint
FIGURE 8. Sonogram of the infrapatellar region. The picture on the left shows the position of the ultrasound probe. The arrow indicates the patella tendon, and * indicates the Hoffa fat pad. T indicates tibia; TT, tibial tuberosity. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
knee joint,17,18 other agents require precise deposition in the IA space. There is sufficient literature evidence showing that improved accuracy of IA corticosteroid injection correlated with better pain relief, functional outcome, and cost-effectiveness.9,19–23 In addition, precise placement of needle minimizes procedurerelated pain, tissue trauma, crystal synovitis, hemarthrosis, and articular cartilage atrophy.4,19,24,25
Efficacy of IA Knee Injections The main indication for IA knee injection is osteoarthritis (OA), and the injection agents commonly used by practitioners are corticosteroid and hyaluronic acid (HA).15 Efficacy of other medications and biologic agents has been examined elsewhere,15 but only corticosteroid and HA are reviewed here. Three systematic reviews consistently concluded that IA corticosteroid was more effective than IA placebo for pain reduction
(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 IA corticosteroid provided only short-term benefit (
Ultrasound-Guided Interventional Procedures in Pain 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 a popular technique for pain intervention. It can be applied to the intraarticular injection of the knee joint. The first objective of this review was to describe and summarize the anatomy and sonoanatomy of the knee and associated structures relevant for intra-articular injection. The second objective was to examine the feasibility, accuracy, and effectiveness of injections as well as injection techniques. (Reg Anesth Pain Med 2014;39: 368–380)
A
rthritis involving the knee joint is a common cause for pain and disability. Conservative management includes weight loss, physical therapy, and pharmacologic interventions. Patients unresponsive to conservative management are usually offered intra-articular (IA) injections, which may be performed blindly or with image guidance using fluoroscopy or ultrasound. Ultrasound guidance has provided an additional tool to identify the target pathology, improving accuracy without the harmful effects of radiation. This review, focusing on interventions to the knee joint, aimed to describe and summarize the anatomy and sonoanatomy of 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.
METHODS We 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 reports of the use of IA injections for the amelioration of knee arthritis, the agents used, and the use of image guidance and their accuracy and efficacy.
Muscles and Tendons Muscles and tendons surrounding the knee joint may be grouped based on their location or function. The extensor mechanism—the most prominent contributor to the knee joint— comprises the quadriceps femoris muscle and the patella. The quadriceps muscle consists of rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis, forming a common tendon that is inserted into the tibial tubercle (Fig. 1). The common tendon (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 superficial (from rectus femoris), intermediate (from amalgamation of the vastus medialis and lateralis), and deep (from the vastus intermedius) layers, which merge to form a common tendon (Fig. 2). The patellar tendon has high tensile strength and arises from the apex and the medial and lateral sides of the patella. The knee flexors are located predominantly posteriorly and include the biceps femoris, semimembranosus, and semitendinosus muscles (Fig. 3). Other flexors include gastrocnemius, which primarily plantar flexes the foot, and the gracilis, which is located posteromedially and acts as a hip adductor as well as a flexor of the knee and hip joints. The only anteriorly located knee flexor is the sartorius, which functions as a hip flexor as well as abductor and spans from the iliac crest, crossing over medially before inserting into the tibia. Pes anserinus (Latin for goose’s foot) is the 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 is hyperextended; in other positions, it functions as a medial rotator of the tibia on the femur (Fig. 4).
Ligaments
DISCUSSION Anatomy of Knee Joint and Surrounding Structures The 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 of Toronto, Toronto, Ontario, Canada; and †Department of Anesthesiology, Clement Zablocki 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 an honorarium from Dannemiller. Copyright © 2014 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000135
368
This review focuses on the anatomy of the knee relevant to IA knee injections.
The stability of the knee is maintained primarily by 4 ligaments (Fig. 4). Both the anterior and posterior cruciate ligaments are intracapsular but extrasynovial structures. The anterior cruciate ligament originates from the posteromedial aspect of the lateral femoral condyle and has its attachment to the front of the intercondylar eminence on the tibia. The stronger posterior cruciate ligament originates from the posterolateral surface of the medial condyle and is attached to the posterior intercondylar fossa of the tibia. The medial collateral ligament is inserted to the medial epicondyle of the femur and the medial tibial condyle with the deep fibers attaching to the medial meniscus (Fig. 4). It is buttressed between the tendons of pes anserinus and semimembranosus. The lateral collateral ligament spans between the lateral epicondyle of the femur and the head of the fibula.
Joints The femorotibial joint is composed of 2 compartments: medial and lateral. The fibrocartilaginous medial and lateral menisci
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
increase the surface area of contact between the convex femoral condyles and flat tibia plateau. The articular capsule is reinforced by various structures surrounding the joint: muscles and tendons, retinaculum, and ligaments. Anteriorly, they are quadriceps and patella tendons, medial and lateral patellofemoral ligaments, and retinaculum from vastus medialis and lateralis. Medially, it is reinforced by medial collateral ligament. Laterally, it is strengthened by iliotibial band, lateral collateral ligament, and the bicep tendons and their fascial expansion. There are many recesses to the femorotibial joint, but the widest is the suprapatellar recess (SPR) (Fig. 4), which originates from the fusion of the subquadriceps bursa with the joint cavity and allows an access for injection into the joint cavity.
US in Pain Medicine: Knee Joint
common popliteal cyst (defined as a fluid-filled mass in the popliteal fossa), the terms should not be used synonymously as there are other causes of popliteal cysts. In adult, almost all Baker’s cysts are secondary, which means that communications exist between the bursae and knee joint.1
Sonoanatomy The knee may be examined from anterior, medial, lateral, and posterior surfaces to identify various structures and pathologies. A linear array transducer at frequencies of 6 to 12 MHz is usually ideal for the examination of the knee. Higher frequencies are used to examine the more superficial structures in details.
Anterior Knee Bursa Around 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 gliding of these structures during joint movements. The anatomical locations of these bursae are summarized in Table 1 and Figure 4. Of these bursae, the most well-known is the semimembranosus or semimembranosus-gastrocnemius bursa. Abnormal distension of this results in Baker’s cyst. Although Baker’s cyst is the most
When examining the knee anteriorly, the patient is placed in supine position with the knee slightly flexed 20 to 30 degrees on a bolster to keep the quadriceps tendon taut. The sequence of examination starts from above the patella to evaluate the quadriceps femoris (Fig. 5). Just beneath the tendon of the quadriceps femoris is the suprapatellar bursa appearing as a thin hypoechoic line. Voluntary contraction of the quadriceps may help identify smaller effusions.2 The prefemoral fat pad is located over the femur, and the suprapatellar fat pad is underneath the quadriceps tendon. The
FIGURE 1. Anterior view of the thigh and knee. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series. © 2014 American Society of Regional Anesthesia and Pain Medicine
369
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
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 to the knee joint. The medial and lateral recesses may be examined in a transverse view by the side of the patella (Fig. 6). When the knee is fully flexed, the condyles may be visualized as a curved hyperechoic line with an acoustic shadow beneath it. Lining the condyles is the hypoechoic hyaline cartilage (Fig. 7). Scanning longitudinally inferior to the patella helps identify the patellar tendon inserting into the tibial tuberosity, and beneath the tendon, the intracapsular Hoffa’s fat pad is located (Fig. 8). The infrapatellar bursa lies over the tibia and the distal portion of this tendon (Fig. 4).
Medial Knee Examination is best performed with the patient’s knee externally rotated while maintaining 20- to 30-degree flexion. Placing the ultrasound probe over the long axis of medial collateral ligament reveals the superficial layer and the deep meniscofemoral and meniscotibial components of the ligament (Fig. 9). In general, the ligament is examined for the entire length and with dynamic scanning during valgus stress for the possible pathology and assessment of integrity. The medial meniscus appears as a hyperechoic triangular structure between the femur and tibia (Fig. 9). Moving the ultrasound probe distally to the AM aspect of the tibial metaphysis, the tendons of sartorius, gracilis, and
semitendinosus are seen blended together, forming the pes anserinus complex (Fig. 9).
Lateral Knee Examination of the lateral knee is performed with the patient’s knee internally rotated while maintaining 20- to 30degree flexion. The ultrasound probe is first placed over the long axis of iliotibial band, with the distal segment best revealed in the coronal plane. The iliotibial band is seen as a thin, fibrillar structure that inserts onto the Gerdy tubercle, a bony prominence on the anterolateral (AL) aspect of the tibial epiphysis (Fig. 10). The lateral collateral ligament is best examined by placing the lower part of the ultrasound probe over the fibula head with the proximal part of probe rotating over the femur. When the probe is aligned with the ligament, it gives the longest view of the ligament. With a proper scan, the popliteus tendon and the lateral meniscus can be seen (Fig. 10).
Posterior Knee The examination is performed while the patient is prone position with the knee extended. The ultrasound probe is placed on the posteromedial aspect of the knee over the medial femoral condyle. The following structures are seen from medial to lateral in shortaxis scan: sartorius, gracilis, semimembranosus, semitendinosus,
FIGURE 2. Lateral view of the knee showed the details of the trilaminar nature of the quadriceps tendon. The insert on the right upper corner was the expanded view of the rectangle over the quadriceps tendon. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
370
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
and medial head of gastrocnemius muscle (Fig. 11). The semimembranosus or semimembranosus-gastrocnemius bursa is located between the tendons of semimembranosus and the medial head of gastrocnemius. Moving the probe laterally, the short-axis scan of the popliteal fossa reveals the neurovascular bundle (Fig. 11). Moving the probe further laterally, the biceps femoris muscle and tendon are examined in the long-axis scan (Fig. 11).
Accuracy Although the knee IA injections are commonly performed with landmark-based technique by rheumatologists, orthopedic surgeons, and general practitioners, the accuracy of the landmarkbased technique in clinical studies is approximately 79% (range, 40%–100%).3 Three factors influence accuracy: use of image guidance, experience of practitioners, and approach of injection. Literature supports the superiority of image guidance in terms of accuracy.4 Comparison studies reveal pooled accuracy rates of 81.0% and 96.7% for landmark-based versus image guidance (fluoroscopy or ultrasound) techniques, respectively.4 In contrast to fluoroscopy, ultrasound allows the procedure to be performed in office-based settings. The accuracies of landmarkbased versus ultrasound guidance techniques were also significantly different, 77.8% and 95.8%, respectively.4 Although the presence of an effusion greatly enhances the accuracy of landmark-based IA needle placement in the knee,5,6 loss of resistance is not indicative of an IA location. This was supported by a
US in Pain Medicine: Knee Joint
cadaver study examining the reasons for the failure of the landmark-based injection, with most of the inaccuracies due to the 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’s experience in knee injection compares the accuracy of a trainee with 10 months of landmark-based knee injection experience and a staff physician with 13 years’ experience in the same. This study demonstrated a huge difference in success rate, 55% versus 100% for the trainee and staff physician, respectively.8 However, another important finding of this study was that both achieved 100% accuracy with ultrasound-guided technique (the levels of experience with ultrasound imaging guidance were 10 months and 3 years for the trainee and staff physician, respectively). This study echoed the improvement in accuracy with ultrasound guidance for the less experienced practitioners in another study, in which patients who received injections at various sites (shoulder, elbow, wrist, knee, and ankle) were randomized to ultrasoundguided injections or injections using the landmark-based technique.9 The ultrasound technique was exclusively performed by 1 junior trainee with 9 months of rheumatology experience and 8 sessions of musculoskeletal ultrasound training. The landmark-based technique was performed by a group of rheumatologists with more training, with approximately two-thirds of injections by 9 rheumatologists with median experience of 15 years and one-third of injections by 9 senior rheumatology trainees with median rheumatology experience of 3 years. The accuracy was
FIGURE 3. Posterior view of the thigh and knee showed the flexors of the knee. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series. © 2014 American Society of Regional Anesthesia and Pain Medicine
371
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Peng and Shankar
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
significantly better for the junior trainee who performed all the ultrasound-guided injections (accuracy rates of 83% vs 66% for ultrasound and landmark-based technique, respectively). Confidence or satisfaction of injection by the practitioner using landmark-guided technique did not result in a better success rate.9
This is similar to the confidence factor of the practitioner in shoulder injections reviewed previously.10 Accuracy is also influenced by the approaches. When performing landmark-based technique knee injections, there are generally 6 approaches: superolateral (SL), superomedial, medial
FIGURE 4. Four views of the knee showed the ligaments and bursae. A, Medial view. B, Anterior view. C, Lateral view. D, Posterior view. In the posterior view, the medial head of gastrocnenimus was removed to reveal the IA structures. F indicates fibula; T, tibia. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
372
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
US in Pain Medicine: Knee Joint
TABLE 1. Bursae of the Knee Bursa Anserine Subcutaneous prepatellar Suprapatellar Subcutaneous infrapatellar Deep infrapatellar Semimembranosus Popliteus
Location Between Pes anserinus Skin Quadriceps tendon Skin Patella tendon (ligament) Semimembranosus tendon Popliteus tendon
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 in 90-degree flexion with or without the modification of degree of
Tibia and medial collateral ligament Anterior surface of patella Femur Tibial tuberosity Anterior surface of tibia Medial head of gastrocnemius Lateral condyle of tibia
flexion as suggested by Waddell et al.12 The SL approach resulted in the highest accuracy of 91% (95% confidence interval [CI], 84%–99%). There are also different approaches for ultrasound guidance. Only 1 study compared the accuracies of different ultrasound-guided approaches.13 The SL and LMP approaches
FIGURE 5. A, Sonogram of the suprapatellar view of the normal knee. The insert showed the position of the patient and the ultrasound probe. B, Sonogram of the details of quadriceps tendon. C, Sonogram of the suprapatellar view of a patient with knee effusion. Note the presence of effusion fluid filling the space between prefemoral fat pad and quadriceps tendon. SPFP indicates suprapatellar fat pad; PFFP, prefemoral fat pad; P, patella; F, femur. ** indicates the SPR. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series. © 2014 American Society of Regional Anesthesia and Pain Medicine
373
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Peng and Shankar
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
FIGURE 6. A and C, Pictures show the position of the ultrasound probes and the manipulation of the patella by the examiner. The patella was pushed to the medial and lateral sides, respectively in A and C. B and D, The respective sonograms (B and D) show the medial and lateral views, respectively. MFC indicates medial femoral condyle; LFC, lateral femoral condyle. Stars indicate the Hoffa fat pad; chain of trapezoid indicates the cartilage. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
were significantly more accurate than MMP approach (accuracy rates of SL, LMP, and MMP were 100%, 95%, and 75%, respectively). Ultrasound improves accuracy of IA injection, which is important to both outcome and safety. Still, there is some controversy regarding the effect of imaging method for needle placement
improved clinical outcome.14 It is important to recognize that knee injections 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 improve function in patients with knee disorders.15,16 While therapeutic effect can occur with suboptimal location of corticosteroid in the
FIGURE 7. Sonogram of both femoral condyles. The picture on the left shows the position of the knee and the ultrasound probe. The hyaline cartilage was marked with trapezoids. QT indicates quadriceps tendon. *Muscle of vastus medialis. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
374
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 5, September-October 2014
US in Pain Medicine: Knee Joint
FIGURE 8. Sonogram of the infrapatellar region. The picture on the left shows the position of the ultrasound probe. The arrow indicates the patella tendon, and * indicates the Hoffa fat pad. T indicates tibia; TT, tibial tuberosity. Reproduced with permission from Dr Philip Peng from Philip Peng Educational Series.
knee joint,17,18 other agents require precise deposition in the IA space. There is sufficient literature evidence showing that improved accuracy of IA corticosteroid injection correlated with better pain relief, functional outcome, and cost-effectiveness.9,19–23 In addition, precise placement of needle minimizes procedurerelated pain, tissue trauma, crystal synovitis, hemarthrosis, and articular cartilage atrophy.4,19,24,25
Efficacy of IA Knee Injections The main indication for IA knee injection is osteoarthritis (OA), and the injection agents commonly used by practitioners are corticosteroid and hyaluronic acid (HA).15 Efficacy of other medications and biologic agents has been examined elsewhere,15 but only corticosteroid and HA are reviewed here. Three systematic reviews consistently concluded that IA corticosteroid was more effective than IA placebo for pain reduction
(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 IA corticosteroid provided only short-term benefit (
