Ultrasound Guided Procedures
Sacroiliac Joint
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Ultrasound-guided intra-articular injections can provide both pain relief and diagnostic information in sacroiliac (SI) joint pain
Pertinent Anatomy
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The SI joint is stabilized by the anterior SI ligament, the interosseous ligament, and the short and long posterior SI ligaments. Secondary stabilizers are the sacrospinous and sacrotuberous ligaments ( Fig. 15.1 ).
Fig. 15.1
Posterior pelvic and sacral ligaments.
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The cranial third of the joint is a fibrous joint, the middle third of the joint is fibrocartilaginous and resembles a symphysis, while the caudal third is synovia. ,
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The anterior joint capsule is contiguous resulting in a “true synovial joint”, while the posterior joint capsule is thin and non-contiguous, made up of a series of ligaments, allowing for diffusion of larger volumes of injectate around the posterior ligaments and soft tissue structures. ,
Common Pathology
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The SI joint (SIJ) is a common source of axial low back pain, with a prevalence of 25%.
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The pathophysiology of SI joint pain is highly debated. Pain generation may be the result of abnormal movement of the SI joint (either laxity or immobility), malalignment of the SI joint, and osteoarthritis of the SI joint.
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Sacroiliitis may be an early symptom of seronegative spondyloarthropathies. Seronegative spondyloarthropathy should be suspected in younger (<45 years) male patients presenting with SI joint or low back pain of insidious onset that improves with activity. ,
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Increased Doppler signal surrounding the SI joint is seen in sacroiliitis.
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In addition to axial pain, pathology of the SIJ can produce variable referred pain patterns, including pain referred into the buttock, the lower lumbar area, and the thigh.
Equipment
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Needle size: 25–22 gauge and 2 to 3.5-inch needle
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Low frequency curvilinear ultrasound transducer
Common Injectates
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Local anesthetics for diagnostics, corticosteroids
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Prolotherapy, Orthobiologics (PRP, bone marrow concentrate, etc.)
Injectate Volume
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0.8–2.5 mL
Technique
Patient Position
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Prone with a pillow under the abdomen to flatten the lumbar curvature.
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Lower extremities should be internally rotated while feet are inverted to help flatten the gluteal region.
Clinician Position
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Sitting or standing by the patient’s side
Transducer Position
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Transverse orientation to identify the sacral hiatus
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Move the transducer laterally to identify the lateral edge of the sacrum
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Keeping the transducer in the transverse orientation, move cephalad until the contour of the ilium is identified ( Fig. 15.2A )
Fig. 15.2
Ultrasound guided sacroiliac joint injection (A) Set-up. The posterior superior iliac spine, superior border of the sacrum, and lateral borders of the sacrum are marked on the model for reference during the procedure. (B) A transverse ultrasonic view of the SI joint with the ilium to the left of the screen and sacrum to the right. The needle approach shown from medial to lateral into the boat-shaped SI joint (arrow) . Dorsal sacral foramina (∗).
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Transducer should end over the caudal third of the SI joint. ,
Needle Position
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In-plane with the transducer, medial to lateral approach with approximately 45–65 degrees of angulation (see Fig. 15.2B )
Target
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The caudal third of the SI joint is targeted advancing the needle past the posterior SI ligament (see Fig. 15.2 ). ,
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Alternatively, the middle third or the cranial third of the SI joint can be targeted with comparable pain reduction.
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A 2%–2.5% rate of vascular uptake in US guided SI joint injection has been reported. ,
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The posterior sacral foramen should be visualized on ultrasound along with the SI joint to confirm injection location lateral to the S2 foramen, and avoid foraminal injection.
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In cadaveric studies, >50% of injections at the caudal third of the SI joint had extra-articular spread. For this reason, it may be worthwhile to consider targeting the cranial third or middle third of the SI joint, as the approach may be technically less challenging with the wider joint space in this area.
The Sacrococcygeal Joint
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Ultrasound can be a useful adjunct to fluoroscopy to locate the sacrococcygeal joint (SCJ) for joint injection or set-up for ganglion impar block. Fluoroscopy is required to confirm needle depth and position.
Pertinent Anatomy
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The SCJ contains the sacrococcygeal disc, which may ossify with age and obscure the SCJ on fluoroscopy.
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The ganglion impar is located ventral to the deep sacrococcygeal ligament and can be accessed through the SCJ.
Common Pathology
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Pain can be traumatic or non-traumatic
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Coccydynia more frequently affects women. Compared to males, the female coccyx tends to be shorter, straighter, and more prone to retroversion.
Equipment
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Needle size: 25–22 gauge and 2 to 3-inch needle.
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High-frequency linear ultrasound transducer
Common Injectates
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Local anesthetics for diagnostics, corticosteroids
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Prolotherapy, Orthobiologics (PRP, bone marrow concentrate, etc.)
Injectate volume
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1–3 mL
Technique
Patient Position
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Prone, with a pillow under the abdomen to flatten the lumbar curve.
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Lower extremities should be internally rotated while feet are inverted to help flatten the gluteal region.
Clinician Position
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Seated or standing next to the patient
Transducer Position
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Start with the transducer transverse across the midline and locate the sacral hiatus.
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Identify the sacral cornua.
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The sacrococcygeal ligament can be identified overlying the sacral hiatus, which is superficial to the base of the sacrum.
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Rotate longitudinally over the SCJ and sacral hiatus, so the proximal part of the transducer rests between the two cornua, and the first cleft caudal to the sacral hiatus is the SCJ ( Fig. 15.3A ).
Fig. 15.3
Ultrasound guided injection of the sacrococcygeal joint. (A) Set up. (B) Ultrasound view of the sacrum (proximal, left ), coccyx (distal, right ), and sacrococcygeal joint (∗) , with needle path (arrow).
Needle position
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In plane with the transducer Fig. 15.3B
Target
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The cleft of the SCJ (the first cleft caudal to the sacral hiatus is the SCJ) (see Fig. 15.3B )
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The tip of the needle can be difficult to visualize in the joint space using ultrasound.
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Fluoroscopy is preferred to confirm needle depth and position.
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The same approach is used for ganglion impar block, passing through the joint to reach the ganglion anterior to the ventral sacrococcygeal ligament with fluoroscopy to confirm needle placement.
Short and Long Dorsal Sacroiliac Ligaments
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The short and long dorsal SI ligaments are able to be visualized superficial to the SI joint using ultrasound guidance and targeted for injection. ,
Pertinent Anatomy
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The SI joint is located in the bony cleft between the sacrum and the contour of the ilium.
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The dorsal ligaments lie within this bony cleft lateral to the sacrum at the S1–S2 level.
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The short dorsal ligament is oriented perpendicular to the joint, while the long ligament runs oblique to it.
Common Pathology
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Disruption or laxity of the ligamentous structures leading to altered joint mechanics is a potential cause of SIJ pain.
Equipment
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Needle size: 25–22 gauge and 2 to 3.5-inch needle.
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High-frequency linear ultrasound transducer
Common Injectates
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Local anesthetics for diagnostics
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Prolotherapy, Orthobiologics (PRP, bone marrow concentrate, etc.)
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Avoid intra-ligamentous corticosteroid injections.
Injectate Volume
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1–3 mL
Technique
Patient Position
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Prone, with a pillow under the abdomen to flatten the lumbar curvature.
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Lower extremities should be internally rotated while feet are inverted to help flatten the gluteal region.
Clinician Position
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Sitting or standing next to the patient opposite the side to be injected (for a medial to lateral approach).
Transducer Position
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Transverse to the SI joint, long-axis to the short ligament
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Obliquely paralleling the lateral border of the sacrum and long-axis to the long ligament
Needle Position
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In-plane to the transducer, medial to lateral approach with needle oriented 45 to 65 degrees.
Target
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Anechoic or hypoechoic signal within the ligaments.
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Marking the posterior superior iliac spine on the skin for reference allows for better transducer positioning during the procedure.
Superficial Posterior Sacrococcygeal Ligament
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In 90% of cases, coccydynia responds to conservative treatment.
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In refractory cases, interventional procedures such as injections have been shown to be effective.
Pertinent Anatomy
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The superficial posterior sacrococcygeal ligament runs posteriorly, spanning from the sacral hiatus and inserting distally to the first inter-coccygeal joint.
Common Pathology
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Pain can be traumatic or non-traumatic
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In non-traumatic cases, ligamentous laxity with excessive motion of the 1st intercoccygeal joint is one proposed mechanism of coccydynia (the second intercoccygeal joint is typically fused).
Equipment
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Needle size: 27–25 gauge and 1.5 to 3-inch needle.
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High-frequency linear ultrasound transducer
Common Injectates
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Local anesthetics for diagnostics
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Prolotherapy, orthobiologics (PRP, bone marrow concentrate, etc)
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Avoid intraligamentous corticosteroid injections.
Injectate Volume
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1–3 mL
Technique
Patient Position
- •
Prone with a pillow under the abdomen to flatten the lumbar curvature.
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Lower extremities should be internally rotated while feet are inverted to help flatten the gluteal region.
Clinician Position
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Seated or standing directly next to the patient
Transducer Position
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Long-axis to the sacrococcygeal ligament ( Fig. 15.4A ).
Fig. 15.4
Ultrasound guided injection of the sacrococcygeal ligament. (A) Setup. (B) Ultrasound view with proximal to the left. The sacrum (S5) , first and second bones of the coccyx (cox1, cox2) , posterior sacrococcygeal ligament (PSCL) , and needle approach (arrowheads) are shown.
Needle Position
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Long-axis to the ligament and in plane to the transducer. A proximal to distal or distal to proximal approach can be used (see Fig. 15.4B ).
Target
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Anechoic or hypoechoic signal within the ligament (see Fig. 15.4B ).
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Interstitial tearing of the ligament can be challenging to identify with imaging. A diagnostic lidocaine injection into the ligament can be used to confirm the ligament as a source of pain, which can guide further workup and treatment decisions.
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Occult interstitial tearing can sometimes be identified during the injection when small aliquots of the injectate are placed in the ligament as the needle is advanced.
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Gauze should be placed in the inter-gluteal or natal cleft just proximal to the rectum to protect the mucosa during skin preparation from the antiseptic cleansing agents.
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Ultrasound allows for direct visualization of the superficial fibers of the sacrococcygeal ligament, but acoustic shadowing from the bone prevents visualization of the deep sacrococcygeal ligament. If there is suspected involvement of the deep sacrococcygeal ligaments (SCL), fluoroscopy guidance should be used to access the superficial and deep fibers .
Sacrotuberous and Sacrospinous Ligaments
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The sacrotuberous ligament is a key point of attachment for the hamstrings and gluteal musculature.
Pertinent Anatomy
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The sacrotuberous and sacrospinous ligaments have a conjoint origin, with interwoven fibers that attach proximally to the posterior superior iliac spine, the long posterior SI ligament, the lateral sacrum, and the coccyx proximally. Fibers of the proximal sacrotuberous ligament serve as attachment sites for the gluteus maximus and piriformis.
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The sacrotuberous ligament narrows and spirals along its length, then broadens toward its distal attachment on the ischial tuberosity. Fibers of the distal sacrotuberous ligament are contiguous with the conjoined tendon of the biceps femoris and semitendinosus. ,
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The sacrospinous ligament attaches distally on the ischial spine.
Common Pathology
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Entrapment between the sacrotuberous and sacrospinous ligaments is a common cause of pudendal neuralgia.
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The sacrotuberous and sacrospinous ligaments are important pelvic stabilizers, and may be injured due to high-energy trau-ma (i.e., motor vehicle collisions, falls, pedestrians struck by a vehicle) with anterior-posterior compression forces across the pelvis.
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Irritation of the sacrotuberous ligament with localized pain, swelling, and reduced echogenicity may be seen at its junction with the conjoined tendon. Fibers of the distal ligament are contiguous with the conjoined tendon of the long head of the biceps femoris and semitendinosus, and they are disrupted in full hamstring tear.
Equipment
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Needle size: 25–22 gauge and 2 to 3.5-inch needle.
- •
Low frequency curvilinear ultrasound transducer
Common Injectates
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Local anesthetics for diagnostics
- •
Prolotherapy, Orthobiologics (PRP, bone marrow concentrate, etc.)
- •
Avoid intraligamentous corticosteroid injections.
Injectate Volume
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1–3 mL
Technique
Patient Position
- •
Prone with a pillow under the abdomen to flatten the lumbar curvature.
- •
Lower extremities should be internally rotated while feet are inverted to help flatten the gluteal region.
Clinician Position
- •
Seated or standing directly next to the patient
Transducer Position
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Start with one end of the transducer positioned along the lateral border of the sacrum and the other pointed toward the greater trochanter over the piriformis, the probe is then rotated toward the ischial spine (lateral edge greater sciatic notch).
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The sacrospinous ligament is visualized as a hyperechoic line extending medially from the ischial spine.
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The sacrotuberous ligament can be seen as a light hyperechoic line parallel and superficial to the sacrospinous ligament. ,
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The transducer may need to be rotated clockwise/counterclockwise to improve visualization of the ligament.
Needle Position
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In-plane with the transducer
Target
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Anechoic or hypoechoic signal within the ligament.
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Patient body habitus is a key factor influencing success visualizing the sacrotuberous and sacrospinous ligaments under ultrasound.
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Resistance can be felt as the needle advances through the sacrotuberous ligament, typically with a loss of resistance as the needle “punches through” the ligament to the soft tissues underneath.
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The sacrotuberous ligament may be confused with the sciatic nerve at the level the sciatic notch. The sciatic nerve can be traced down into the posterior thigh, passing lateral to the ischial spine, while the sacrotuberous ligament can be followed to its attachment on the ischial tuberosity.
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The pudendal nerve is difficult to reliably visualize due to its small size and anatomic variability. One, two, or three nerve trunks may be identified at this level. Doppler ultrasound visualizing the pudendal artery can be a useful guide, although it should be noted that the artery course is highly variable. The pudendal artery may be located medial to the nerve, lateral to the nerve, or with two branches on either side of the nerve.
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