Ultrasound guided injections

# Overview of Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Although this limit varies from person to person, it is approximately 20 kilohertz (20,000 hertz) in healthy, young adults and thus, 20 kHz serves as a useful lower limit in describing ultrasound. Ultrasound is manually produced in many different fields, typically to penetrate a medium and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the inner structure of the medium. The most well known application of this technique is its use in sonography to produce pictures of fetuses in the human womb. There are a vast number of other applications as well.
Medical sonography (ultrasonography) is an ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs, their size, structure and any pathological lesions with real time tomographic images.  It is one of the most widely used diagnostic tools in modern medicine. The technology is relatively inexpensive and portable, especially when compared with modalities such as magnetic resonance imaging(MRI) and computed tomography (CT). As currently applied in the medical environment, ultrasound poses no known risks to the patient.  Utilizing ultrasound for guidance during injections is a relatively recent development compared to its use in medical diagnosis.  The adoption of ultrasound guidance in clinical practice is increasing however and can be attributed to improvements in imaging technology.

# Clinical Indications
The use of Ultrasound in Medicine has become widespread in recent years. Once only available in a select few Universities advances in technology and price reduction have made this technology more available in both community hospitals and in the office setting. Common uses include as a diagnostic tool in the abdomen, vascular studies including both arteries and veins, a wide array of musculoskeletal applications, and with endocrine disease such as thyroid disorders.  Due to its non ionzing imaging ability, relatively low cost, and ease of portability Ultrasound has become more prevalent as a guidance tool for procedures including biopsy, catheter placement, and aspiration.
Given these advancements it is not surprising that the use of ultrasound guidance for percutaneous tenotomy, joint injection, a variety of nerve blocks, and other soft tissue injections has become more common place as well.  While there is extensive literature on the use of Ultrasound for guidance in spinal injections there is still controversy over its use for spinal conditions. This seems to stem more from previous overstatements of its effectiveness in replacing MRI for spinal conditions then due to the more current literature that make use of it for para and extra spinal conditions and guidance.

# Ultrasound Guided Injections
There has been a significant increase in the use of Ultrasound guidance for injections in the past several years. Initial acceptance was confined to peripheral structures such as nerve, tendon, joint capsule and spaces, and ligament with more recent moves toward plexus and then spinal guidance.  As technology continues to improve image quality the advantages of Ultrasound guidance over other imaging studies such as flouroscopy or CT has become more compelling.   Cost and time savings, ease of access, and non ionizing radiation are a few of the clear benefits.A body of literature now exists that clearly demonstrates the utility of Ultrasound to effectively visualize vertebral bodies, articular processes, lamina, intrathecal and lamaninar spaces. Level 1 support for Ultrasound guidance has been established for lumbar zygoapophysial joint injections, medial branch and dorsal ramus block.

# Safety and Efficacy
Ultrasound enjoys a rather unique position among imaging modalities due to its capabilities that do not rely upon non ionizing radiation as compared to flouroscopy or CT scanning.   The presence of artificial joints or pacemakers are also not a problem  with Ultrasound as compared to MRI. Ultrasound guidance for injections has proven itself to be very safe and offers clinicians in the emergency room, office setting, or in the operating room an opportunity to both identify the target structure accurately while providing a greater level of patient safety through avoidance of traumatizing unintended structures such as near by arteries.

# Controversies in Ultrasound Guidance for Injections
While there is community agreement that certain kinds of spinal injections such as transformanal epidurals require an imaging modality such as flouroscopy despite a rather extensive body of literature supporting the use of Ultrasound guidance for paraspinal, sacroiliac, translaminar epidural steroids and caudal injections.  Ultrasound guidance for spinal injections has still not gained full community support.   None the less the trend is clear and overtime Ultrasound utilization for these procedures has only increased.  It is difficult to understand how on the one had there may be no controversy over Ultrasound's capability to identify the target structure and concurrently on the other hand there are still those who dont embrace Ultrasound's utility in guidance for injection of the same structures.

# Related Chapters
Musculoskeletal Ultrasound
Back Pain
Low back pain
Prolotherapy
Sacrum