Background Musculoskeletal ultrasound (MSK US) is a rapidly developing imaging modality, particularly efficient in the evaluation of soft tissues. Low back pain (LBP) is one of the most frequent complaints of the MSK system. Even though it is often considered that soft tissue pathology could cause or contribute to complaints in many LBP patients, there are very few US studies to prove this. As enthesopathies are the underlying lesions in a lot of MSK disorders, in this pilot US study, we evaluated the caudal entheses of the largest of back muscles: Erector Spinae. Besides, a regional pain syndrome affecting this area of the back (Iliac Crest Pain Syndrome) has been found in more than one third of the patients with LBP but its cause remained unidentified.

Objectives By means of MSK US to evaluate caudal enthesis of the Erector Spinae in patients with “nonspecific” LBP and tenderness over this structure, and in subjects without such complaints.

Methods We studied 15 middle-aged patients (5 males, 10 females) with unilateral, regional LBP of cause unidentified by clinical examination and conventional X-ray and with features of ICPS. The contra lateral, non painful side of the same patients (15 entheses) and both paravertebral sides of another 15 adults of matching sex, age, height and weight (30 entheses) without complaints served as control. Longitudinal and transverse scans of the attachment site of the Erector Spinae muscle to the medial Iliac Crest and Superior Posterior Iliac Spine were obtained with linear 5-12 MHz transducer in all subjects. The following parameters were analyzed: 1. Thickness of the entheses; 2. Echogenicity of the tendon at its bony attachment; 3. Calcification foci; 4. Cortical irregularities of the iliac bone. Enthesopathy was defined when abnormal US findings (according to the OMERACT criteria) were visible in two perpendicular planes.

Results Erector Spinae entheses could be visualized by US in all subjects. The painful entheses were significantly thicker (men 7.38, women: 7.34 mm) than both contra lateral ones in the same patient (men: 5.74, women: 5.14 mm) and those in the individuals without LBP (men: 5.85, woman: 5.16 mm). Other signs of enthesopathy were also more frequent at the symptomatic site: 1. Hypoechoic echo texture was evident in the painful entheses of 4/5 men and 9/10 women, while contra lateral non painful entheses had this character in none of the males (0/5) and in only 1/10 females. In control subjects that sign was present in 1/10 entheses in men and 2/20 of those in women; 2. Calcification foci were observed in 1/5 painful entheses in men and 2/10 of those in women. Calcifications were observed neither in the contra lateral non painful entheses, nor in those of control subjects; 3. Cortical irregularities of the iliac bone were seen in 3 of the painful entheses in men and in 8 of those in women. Contra lateral non painful entheses exhibited cortical irregularities in 1 man and 3 women, and in 1/10 and 5/20 entheses of control men and women respectively.

Conclusions As in other parts of the body, enthesopathy could be an important source of pain in the lower back and it could be demonstrated by means of MSK US. Part of the so called “nonspecific” LBP and ICPS could be in fact caused by enthesopathies and further sonographic study on more patients will allow standardization of US examination for more precise diagnosis.

Disclosure of Interest None Declared