An ultrasound study of the long posterior sacroiliac ligament in healthy volunteers and in patients with noninflammatory sacroiliac joint pain.

Abstract

To describe the sonoanatomy of the long posterior sacroiliac ligament (LPSL) in healthy volunteers and to assessby ultrasound the LPSL in patients with noninflammatory sacroiliac joint pain (SIP). We assessed 64LPSLs of 32 healthy controls and 40 LPSLs of 40 patients with unilateral noninflammatory SIP and a positive Fortin fingertest. LPSLs in both groups were assessed for the presence of alterations in their structure, continuity and echogenicity andtheir thickness was measured in three predefined points. All patients were examined in prone position following a strict scanningprotocol. Detailed sonoanatomy description and measurement of the LPSL in healthy volunteers are provided(length: 31.32±4.79 mm, width: 8.14±1.28 mm, thickness: 2.05±0.55 mm; 1.64±0.41 mm and 1.51±0.42 mm at the iliac andsacral entheses and in its middle part, respectively). The LPSLs were found to be significantly thicker in the SIP group, withan optimum criterion value of >2.0 mm in its middle part to identify pathologically thickened ligaments. In addition, LPSLs inthe SIP group presented significantly more often hypoechogenicity/altered fibrillar structure (57.5% vs.16%) and/or periligamentousedema (72.8% vs 28%). The combination of either altered structure or periligamentous edema, with thickening of theligament's body showed the best diagnostic accuracy (sensitivity and specificity 83.9% and 94.7% for the first combinationand 100% and 84.6% for the second combination) to identify LPSL pathology in noninflammatory SIP. LPSLcould be assessed by ultrasound and sonopathological lesions could be identified in patients with SIP.