Ultrasound can be used to guide joint and soft tissue interventions to improve accuracy, efficacy, patient satisfaction, and to minimize complications. This article summarizes the rationale supporting ultrasound-guided injections and explains how to safely and effectively set up and perform these procedures.
Key points
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Ultrasound can be used to guide joint and soft tissue interventions to improve accuracy, efficacy, patient satisfaction, and to minimize complications.
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An understanding of ultrasound principles and techniques is critical to performing any ultrasound-guided procedure.
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Appropriate preparation allows the physician to safely and effectively perform ultrasound-guided procedures.
Introduction
Ultrasound use has expanded exponentially in the musculoskeletal arena in recent years for several reasons, including improved safety, portability, decreased cost, and lack of ionizing radiation. In regard to joint and soft tissue injuries, ultrasound is useful for differentiating between acute injuries, chronic disease, and normal anatomic variations. Further, the practitioner can guide a procedure for the treatment of musculoskeletal disease by following the placement of the needle in real time. However, to appreciate and understand the benefit and rationale of ultrasound-guided (USG) injections, the practitioner must have a basic understanding of the ultrasound machine system.
The process of obtaining an ultrasound image begins with the reverse piezoelectric effect. The ultrasound machine sends a pulsed electrical signal to the transducer crystals, which transforms that energy into an intermittent acoustic wave, a form of mechanical energy. These sound waves are then transmitted to the tissues via a sonoconductive gel. The acoustic waves interact with tissue and some waves will be reflected back to the transducer, whereas others are absorbed and refracted. The reflected intermittent acoustic waves return to the transducer and are then converted via the direct piezoelectric effect to an electrical signal. This electrical signal is then translated into an image on the ultrasound screen. Different transducers with varying crystal properties and thickness determine the frequency of the acoustic wave (see later discussion).
Structures that are perpendicular to the transducer will create an angle of insonation of approximately 90°, optimizing the image. Maximizing the reflection produces a bright (hyperechoic) image. Structures with less reflective interfaces will produce a darker (hypoechoic) image. The interface between structures that have very different impedances may also appear hyperechoic, whereas structures with similar impedances may be isoechoic, or of similar echogenicity (overall brightness in sonographic appearance). Furthermore, it is important to realize that ultrasound images are based on the relative material properties of a tissue and its adjacent tissues rather than solely on the properties of that tissue in isolation. Finally, some structures, such as bone, allow no echoes to extend deep to their surfaces and, therefore, the area beneath the surface, or acoustic interface, will appear black from shadowing, also referred to as anechoic (absence of echoes).
Rationale for Ultrasound Guidance for Procedures
Joint and soft tissue injections have been a cornerstone of musculoskeletal medicine and the growth of ultrasound has made many of those injections more accurate and efficacious. Injection accuracy is defined as placing the needle tip and, if desired, injectate into the intended structure. Palpation-guided (PG) injections are more likely to result in adverse effects, including hemarthrosis, septic joint, postinjection pain, and systemic effects. Accuracy may be particularly important when injecting an orthobiologic substance, such as platelet-rich plasma or mesenchymal stem cells, in which precise accuracy of injectate placement is paramount to achievement of its proposed benefit.
Limitations of Palpation-Guided Injections
In addition to potential inaccuracy relative to USG injections, a limitation of PG injections is a possible greater risk of injury to nearby structures. For example, PG injections into the glenohumeral joint are at risk of penetrating the long head of the biceps tendon. Although many clinicians may be confidant in their PG injection technique, many structures are surprisingly difficult to palpate accurately. For example, the accuracy rate for palpation of the biceps tendon in a small group of physicians was only 5%. This investigation found that physicians typically palpated medial to the biceps tendon, often over the subscapularis tendon, making a PG injection in this region potentially unfavorable for both intended therapeutic effect and safety. Furthermore, accuracy rates for PG biceps tendon sheath injections have been found to be 27% compared with 87% with USG injections.
The hip joint is a common source of disease and lies in close proximity to significant neurovascular structures. Injecting the hip joint without imaging carries risk of injury to the femoral nerve, among other vital structures. In PG intra-articular hip injections via the anterior approach, the needle pierced or contacted the femoral nerve in more than a quarter of injections and came within 5 mm in almost two-thirds of the injections.
In the literature, even many superficial, seemingly easy to palpate, structures have poor accuracy rates when injected with a PG technique, and the accuracy of palpation does not always increase with provider experience. In 1 study, physical medicine and rehabilitation resident physicians palpated the acromioclavicular joint with 17% accuracy. The knee is a fairly superficial joint that is often injected without ultrasound guidance. However, ultrasound guidance enables the practitioner to have better visualization of the joint recess, especially in patients with a large body habitus or in the context of degenerative changes that may alter anatomic landmarks. Even in a nonarthritic knee, the accuracy rate for palpation of the lateral knee joint was found to be 58%. The subacromial-subdeltoid bursa is also frequently injected via PG but it has been found that the injectate frequently reaches not only the bursa but also neighboring, potentially unintended structures. For a particularly challenging injection, such as into an interdigital neuroma of the foot, ultrasound guidance ensures accuracy.
Contraindications
There are no contraindications to the use of diagnostic ultrasound. However, general procedural considerations apply, including the use of aseptic technique and use of the as low as reasonably achievable (ALARA) principle, wherein no ultrasound scanning is performed on a patient beyond what is necessary.
Efficacy
Efficacy of USG injections is complex and depends on the outcome scale used, the disease process being treated, the structure injected, individual patient factors, concomitant diagnoses and treatments, and the injectate used. In a group of subjects with inflammatory arthritis, USG injections were more accurate and there was a greater improvement in function if accuracy was improved. However, there was no difference in outcome when comparing USG and PG injections at 2 and 6 weeks following the procedures. This is representative of the idea that extra-articular steroid injections may still be efficacious, due to a regional effect, in patients with inflammatory arthritis.
Studies show USG injections have reduced procedural pain, reduction in pain scores, increase in responder rate, reduction in nonresponder rate, and an increase in therapeutic duration. It has been speculated that less procedural pain is secondary to the ability to direct the needle away from pain-sensitive structures while under ultrasound guidance. Further, decreased postprocedural pain is associated with less intra-articular bleeding.
Ultrasound was also associated with increased detection of effusion and increased volume of aspirated fluid. This may result in a decreased number of procedures that are required, exposing the patient to less risk as well as improving the efficacy of the procedure. In a systematic review comparing USG to PG injections, the ultrasound group showed greater short-term improvement.
Although there are limited data on functional outcomes, patient satisfaction plays a large role in efficacy. Glenohumeral joint USG injections were less painful and enable accuracy of 94% compared with 72% with fluoroscopy-guided injections. Injections performed under ultrasound guidance were also associated with better self-reported health-related quality of life.
Cost-Effectiveness
USG injections have shown to result in a cost reduction for patient per year and an even greater reduction is cost for responder per year. In fact, USG injections reduced the cost per patient per year by 8% compared with PG injections. Notably, the cost-effectiveness of USG injections will depend on the skill of the clinician performing the injection, underscoring the need for proper training for those performing these procedures. A clinician with insufficient training in the performance of USG injections may be more likely to perform an inaccurate injection or damage nearby neurovascular structures. Procedural complications may result in pain, discomfort, and more health care expenditure.
Limitations of Ultrasound-Guided Injections
Perhaps the greatest limitation to USG injections is the training, including correct instruction, sufficient practice, and time commitment involved to become a proficient musculoskeletal sonographer. However, as ultrasound training is incorporated into more residency and fellowship curricula, physicians who complete their training will be more proficient in ultrasound. Not only will physicians improve the accuracy and efficacy of standard joint and soft tissue injections, practitioners will be able to expand their injection repertoire. They will be able to perform procedures that were previously considered unsafe or were only done via fluoroscopy, which may be more costly and has more contraindications than ultrasound. For example, specialized tendon procedures, such as percutaneous needle tenotomy, are only feasible and safe because of the development of these techniques using ultrasound guidance. Although some clinicians believe fluoroscopically-guided injections are easier to learn than USG injections, and in many cases provide similar accuracy, fluoroscopy has several drawbacks, including increased costs, radiation exposure, lack of portability, and general lack of availability at the point-of-care or office setting. However, some injections are more safely and effectively performed with fluoroscopic guidance than USG, such as certain spine procedures (see Hurdle MFB: Ultrasound-Guided Spinal Procedures for Pain: A Review , in this issue).
Introduction
Ultrasound use has expanded exponentially in the musculoskeletal arena in recent years for several reasons, including improved safety, portability, decreased cost, and lack of ionizing radiation. In regard to joint and soft tissue injuries, ultrasound is useful for differentiating between acute injuries, chronic disease, and normal anatomic variations. Further, the practitioner can guide a procedure for the treatment of musculoskeletal disease by following the placement of the needle in real time. However, to appreciate and understand the benefit and rationale of ultrasound-guided (USG) injections, the practitioner must have a basic understanding of the ultrasound machine system.
The process of obtaining an ultrasound image begins with the reverse piezoelectric effect. The ultrasound machine sends a pulsed electrical signal to the transducer crystals, which transforms that energy into an intermittent acoustic wave, a form of mechanical energy. These sound waves are then transmitted to the tissues via a sonoconductive gel. The acoustic waves interact with tissue and some waves will be reflected back to the transducer, whereas others are absorbed and refracted. The reflected intermittent acoustic waves return to the transducer and are then converted via the direct piezoelectric effect to an electrical signal. This electrical signal is then translated into an image on the ultrasound screen. Different transducers with varying crystal properties and thickness determine the frequency of the acoustic wave (see later discussion).
Structures that are perpendicular to the transducer will create an angle of insonation of approximately 90°, optimizing the image. Maximizing the reflection produces a bright (hyperechoic) image. Structures with less reflective interfaces will produce a darker (hypoechoic) image. The interface between structures that have very different impedances may also appear hyperechoic, whereas structures with similar impedances may be isoechoic, or of similar echogenicity (overall brightness in sonographic appearance). Furthermore, it is important to realize that ultrasound images are based on the relative material properties of a tissue and its adjacent tissues rather than solely on the properties of that tissue in isolation. Finally, some structures, such as bone, allow no echoes to extend deep to their surfaces and, therefore, the area beneath the surface, or acoustic interface, will appear black from shadowing, also referred to as anechoic (absence of echoes).
Rationale for Ultrasound Guidance for Procedures
Joint and soft tissue injections have been a cornerstone of musculoskeletal medicine and the growth of ultrasound has made many of those injections more accurate and efficacious. Injection accuracy is defined as placing the needle tip and, if desired, injectate into the intended structure. Palpation-guided (PG) injections are more likely to result in adverse effects, including hemarthrosis, septic joint, postinjection pain, and systemic effects. Accuracy may be particularly important when injecting an orthobiologic substance, such as platelet-rich plasma or mesenchymal stem cells, in which precise accuracy of injectate placement is paramount to achievement of its proposed benefit.
Limitations of Palpation-Guided Injections
In addition to potential inaccuracy relative to USG injections, a limitation of PG injections is a possible greater risk of injury to nearby structures. For example, PG injections into the glenohumeral joint are at risk of penetrating the long head of the biceps tendon. Although many clinicians may be confidant in their PG injection technique, many structures are surprisingly difficult to palpate accurately. For example, the accuracy rate for palpation of the biceps tendon in a small group of physicians was only 5%. This investigation found that physicians typically palpated medial to the biceps tendon, often over the subscapularis tendon, making a PG injection in this region potentially unfavorable for both intended therapeutic effect and safety. Furthermore, accuracy rates for PG biceps tendon sheath injections have been found to be 27% compared with 87% with USG injections.
The hip joint is a common source of disease and lies in close proximity to significant neurovascular structures. Injecting the hip joint without imaging carries risk of injury to the femoral nerve, among other vital structures. In PG intra-articular hip injections via the anterior approach, the needle pierced or contacted the femoral nerve in more than a quarter of injections and came within 5 mm in almost two-thirds of the injections.
In the literature, even many superficial, seemingly easy to palpate, structures have poor accuracy rates when injected with a PG technique, and the accuracy of palpation does not always increase with provider experience. In 1 study, physical medicine and rehabilitation resident physicians palpated the acromioclavicular joint with 17% accuracy. The knee is a fairly superficial joint that is often injected without ultrasound guidance. However, ultrasound guidance enables the practitioner to have better visualization of the joint recess, especially in patients with a large body habitus or in the context of degenerative changes that may alter anatomic landmarks. Even in a nonarthritic knee, the accuracy rate for palpation of the lateral knee joint was found to be 58%. The subacromial-subdeltoid bursa is also frequently injected via PG but it has been found that the injectate frequently reaches not only the bursa but also neighboring, potentially unintended structures. For a particularly challenging injection, such as into an interdigital neuroma of the foot, ultrasound guidance ensures accuracy.
Contraindications
There are no contraindications to the use of diagnostic ultrasound. However, general procedural considerations apply, including the use of aseptic technique and use of the as low as reasonably achievable (ALARA) principle, wherein no ultrasound scanning is performed on a patient beyond what is necessary.
Efficacy
Efficacy of USG injections is complex and depends on the outcome scale used, the disease process being treated, the structure injected, individual patient factors, concomitant diagnoses and treatments, and the injectate used. In a group of subjects with inflammatory arthritis, USG injections were more accurate and there was a greater improvement in function if accuracy was improved. However, there was no difference in outcome when comparing USG and PG injections at 2 and 6 weeks following the procedures. This is representative of the idea that extra-articular steroid injections may still be efficacious, due to a regional effect, in patients with inflammatory arthritis.
Studies show USG injections have reduced procedural pain, reduction in pain scores, increase in responder rate, reduction in nonresponder rate, and an increase in therapeutic duration. It has been speculated that less procedural pain is secondary to the ability to direct the needle away from pain-sensitive structures while under ultrasound guidance. Further, decreased postprocedural pain is associated with less intra-articular bleeding.
Ultrasound was also associated with increased detection of effusion and increased volume of aspirated fluid. This may result in a decreased number of procedures that are required, exposing the patient to less risk as well as improving the efficacy of the procedure. In a systematic review comparing USG to PG injections, the ultrasound group showed greater short-term improvement.
Although there are limited data on functional outcomes, patient satisfaction plays a large role in efficacy. Glenohumeral joint USG injections were less painful and enable accuracy of 94% compared with 72% with fluoroscopy-guided injections. Injections performed under ultrasound guidance were also associated with better self-reported health-related quality of life.
Cost-Effectiveness
USG injections have shown to result in a cost reduction for patient per year and an even greater reduction is cost for responder per year. In fact, USG injections reduced the cost per patient per year by 8% compared with PG injections. Notably, the cost-effectiveness of USG injections will depend on the skill of the clinician performing the injection, underscoring the need for proper training for those performing these procedures. A clinician with insufficient training in the performance of USG injections may be more likely to perform an inaccurate injection or damage nearby neurovascular structures. Procedural complications may result in pain, discomfort, and more health care expenditure.
Limitations of Ultrasound-Guided Injections
Perhaps the greatest limitation to USG injections is the training, including correct instruction, sufficient practice, and time commitment involved to become a proficient musculoskeletal sonographer. However, as ultrasound training is incorporated into more residency and fellowship curricula, physicians who complete their training will be more proficient in ultrasound. Not only will physicians improve the accuracy and efficacy of standard joint and soft tissue injections, practitioners will be able to expand their injection repertoire. They will be able to perform procedures that were previously considered unsafe or were only done via fluoroscopy, which may be more costly and has more contraindications than ultrasound. For example, specialized tendon procedures, such as percutaneous needle tenotomy, are only feasible and safe because of the development of these techniques using ultrasound guidance. Although some clinicians believe fluoroscopically-guided injections are easier to learn than USG injections, and in many cases provide similar accuracy, fluoroscopy has several drawbacks, including increased costs, radiation exposure, lack of portability, and general lack of availability at the point-of-care or office setting. However, some injections are more safely and effectively performed with fluoroscopic guidance than USG, such as certain spine procedures (see Hurdle MFB: Ultrasound-Guided Spinal Procedures for Pain: A Review , in this issue).
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