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Sonoanatomy and Injection Technique of the Iliolumbar Ligament

While history and physical examination are important in the assessment of back pain, injection of small volumes of local anesthetic into the structure considered the source of pain increases the specificity of the diagnostic workup—in this case, the iliolumbar ligament.
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The iliolumbar ligament plays an important biomechanical role in anchoring the spine to the pelvic ring and stabilizing the sacroiliac joint. 1 Iliolumbar syndrome is a painful condition caused by pathology of the iliolumbar ligament. It commonly occurs in people lifting Figure 1. In the ultrasound guided iliolumbar injection technique, the ultrasound transducer is initially placed over the iliac crest in a sagital plane.heavy loads while rotating laterally (manual workers, golf players, etc). The pathology is believed to be ligament strain. The pain is localized to the posterior/medial portion of the iliac crest, may be constant, and is aggravated by activity (especially bending to the contralateral side). Pain may refer to different areas—e.g., hip, groin and perineal structures. There is tenderness on palpation of the posterior/ medial aspect of the iliac crest. In differential diagnosis, one has to consider other sources of pain—for example, the quadratus lumborum muscle, erector spinae muscle, the facet joints, the sacroiliac joint, the hip. A combination of history, physical exam, and imaging, in conjunction with appropriate diagnostic injections, can lead to the correct diagnosis. 

The iliolumbar ligament runs between the transverse process of L5 and the medial deep iliac crest. The ligament lies deep to the following structures: skin, subcutaneous tissue and the erector spinae muscle. The diagnosis of iliolumbar syndrome is difficult without image-guided injection. Ultrasound offers many advantages in this setting.


Our objective was to perform an ultrasound-guided diagnostic injection of the iliolumbar ligament in a patient with a working diagnosis of iliolumbar syndrome. We planned to assess the patient pre- and post-injection by recording pain scores at rest, range of motion, and on provocation. 

Case Report

A 46-year old male patient (BMI 28) presented with persistent, debilitating right-sided lower back pain. The onset of pain was associated with lifting a heavy weight 12 months previously. His pain averaged 7 out of 10 (numerical rating scale). The pain was centered on the right iliac crest and was associated with tenderness to palpation in this region. There was pain also in the right lateral hip region and the medial aspect of the right groin. Lumbar lateral flexion to the left exacerbated pain. Neurological exam was normal. X-ray and magnetic resonance imaging (MRI) of the lumbar spine were normal.

Conservative measures of anti-inflammatory drugs and physical therapy had failed to resolve symptoms. As a result, the patient was unable to fulfill all of his work commitments. He had to opt for light duties and decreased hours in his work as a warehouse general operative.

Figure 2. Sagital ultrasound image of the iliac crest (‘I’ marks location).The patient consented for an ultrasound-guided right iliolumbar ligament injection. He was placed in the prone position. A pillow was placed under the abdomen to straighten the lumbar lordosis. The operator and the ultrasound screen were positioned on the side to be injected. The skin was disinfected with antiseptic solution and draped. A high frequency (10 MHz), linear transducer ultrasound transducer (Sonosite ® , Micromaxx, Bothwell, Wash.) was inserted into a sterile sheath (CIVCO Medical Instruments, Kalona, Iowa) containing ultrasound gel. Sterile ultrasound gel was placed between the patient and the transducer. 

Figure 3. The orientation of the ultrasound transducer is oblique, over the course of the iliolumbar ligament from the L5 transverse process to the deep aspect of the medial iliac crest. The needle is introduced from the medial side aspect of the transducer using an in-line approach.Figure 4. Ultrasound image of iliolumbar ligament injection. The needle (arrows) is seen traversing the subcutaneous tissue and erector spinae muscle (ES). Note the hypoechoic area around the needle tip depicting the spread of local anaesthetic (*) between the erector spinae and the iliolumbar ligament.(key: I=iliac crest, ST=subcutaneous tissue, ES=erector spinae muscle, IL=iliolumbar ligament, S=sacrum).The ultrasound transducer was placed over the right iliac crest and oriented in a caudad–cephalad direction (see Figure 1). The iliac crest was identified (see Figure 2). The transducer was moved medially and caudad while the orientation was changed to oblique (see Figure 3). This allowed visualization of the erector spinae muscle (see Figure 4). The hyperechoic structure below this muscle is the iliolumbar ligament. Moving the transducer medially and caudally and rotated to a transverse orientation allows visualization of the transverse and spinous process of L5. An aseptic injection technique was used. After infiltrating the skin with 1% lidocaine, a 25G spinal needle (Becton Dickinson S.A., Madrid, Spain) was used to perform the iliolumbar ligament injection. We used an in-line approach from the medial side of the transducer—i.e., the needle was advanced laterally and cephalad (see Figure 3). Real time imaging was used to advance the needle tip deep to the erector spinae muscle and confirm local anesthetic spread along the iliolumbar ligament (see Figure 4). A total of 3mL of local anesthetic was injected. 


The patients’ pain intensity decreased to a 2 out of 10 (numerical rating scale). When asked to perform the contralateral lumbar flexion test, the patient demonstrated increased range of movement and a decreased pain score. A diagnosis of iliolumbar syndrome was made. The patient was referred to physiotherapy with this diagnosis. Subsequently, the patient underwent ultrasound-guided prolotherapy to the right iliolumbar ligament. He obtained persistent pain relief and returned to full work duties.


Back pain is a significant cause of disability. While there may be many pain sources, soft tissue injury (i.e. related to muscles, ligaments, etc.) and consequent pain are believed to be very common. 2 History and physical examination are important in the assessment of back pain but they lack sufficient specificity. 3 Injection of small volumes of local anesthetic into the structure considered to be the source of the pain (i.e., facet or sacroiliac joint injections and, indeed, the iliolumbar ligament) increases the specificity of the diagnostic workup. 3

Our findings suggest that an ultrasound-guided iliolumbar ligament injection is a viable (and probably better) option compared to the classic blind injection technique. 4 The topographic anatomy of the iliolumbar ligament is well described. 5 As there are multiple anatomical structures in close proximity to the medial iliac crest, the specificity of the blind injection technique must therefore be questioned. This may also explain why the blind injection technique or the diagnosis of this syndrome have not become more popular. 

As compared with other imaging modalities—e.g., fluoroscopy, CT, MRI—ultrasound has significant advantages in terms of accessibility, ease of use, safety, cost and quality of visualization of the soft tissues in real time. While it is believed soft-tissue back pain is very common, the true frequency is not well defined. Ultrasound-guided diagnostic blocks can help to accumulate data regarding the incidence of such conditions and thus to assess the real extent of the problem.


This is a case report of a new technique based on knowledge of the topographic anatomy and sonoanatomy of the area injected. Further study confirming the spread of injectate (for example, by MRI) and a clinical feasibility study are needed.


Injection techniques have a significant role in the diagnosis and treatment of back pain. 

Ultrasound guidance may offer advantages in diagnostic and therapeutic injections of back pain. Ultrasound guidance allows the selective deposition of small volumes of local anesthetic into structures believed to cause soft tissue back pain and thus to confirm or exclude the working diagnosis.

Last updated on: March 7, 2011
First published on: January 1, 2011