Relationships among hip instability, iliofemoral ligament, and pain in patients with developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is one of the most common causes of secondary hip osteoarthritis (OA) [1,2]. Previous studies have shown that DDH patients have hip instability, causing hip pain, and degenerative changes in the hip joint [2,3]. Furthermore, patients with borderline hip dysplasia (BDDH), classically defined as a lateral center edge angle (LCEA) between 20° and 25° [4] remain a challenging population in which to differentiate significant instability leading to OA [5,6]. Hip instability is defined as painful physiological mobility of the hip with architectural and functional abnormalities that impair joint stability [[7], [8], [9], [10]]. Hip instability exerts abnormal stress on the acetabular rim, which leads to acute pain, impaired function, and degenerative changes in the hip joint [11].

As a pathology contributing to hip instability, the bony anatomy has been considered as the primary factor. However, the importance of the soft tissues such as the ligamentous teres, labrum, and capsular ligament has recently been demonstrated [12]. The capsular ligament comprises the iliofemoral, ischiofemoral and pubofemoral ligaments, and the zona orbicularis, which limit hip rotation, translation, and distraction [13,14]. Myers et al. reported that the iliofemoral ligament (ILFL) plays a notable role in limiting hip external rotation and anterior femoral head translation, whereas the acetabular labrum is a secondary stabilizer for these motions in a cadaveric study [15,16]. However, detailed knowledge on the pathology of the capsular ligament and the clinical relationship between hip instability and ILFL has been insufficient, particularly in DDH and BDDH patients.

For assessing hip instability, the diagnosis is based on a combination of clinical symptoms and radiographic parameters, although with significant variability in diagnostic criteria. Historically, plain radiographs have been commonly used for their ease and simplicity. However, there are several disadvantages of having a variable in the radiographic technique, such as low repeatability due to the pelvic inclination and position of the lower extremities. Moreover, other evaluation modalities such as computed-tomography (CT) and magnetic resonance imaging (MRI) assessments are costly and make evaluating the real-time motion of the hip joint difficult. Recently, ultrasonography (US) is increasingly used mainly to detect intraarticular joint effusion and to aid joint aspiration in a variety of clinical settings. US is also an extremely efficient imaging modality to evaluate peri-articular masses, tendon, and nerve disorders, and to evaluate the dynamic joint motion without radiation exposure. Cheng et al. and Yeap et al. [17,18] reported the sufficient reliability of the ultrasound measurements in assessing the anterior humeral translation. For the dynamic evaluation of the hip joint, D'Hemecourt et al. [19] reported that femoral head translation can be reliably measured using a simple office-based ultrasonography examination in a healthy subject, and there is anterior instability when dynamically stressing as the anterior apprehension test. However, there has been no detailed report on hip instability in patients with DDH and BDDH using US. Here, we evaluated hip instability and ILFL morphology in patients with normal and dysplastic hip using US modality and evaluated the relationships among the hip instability, pain, and ILFL morphology.

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