It is widely recognised that femoroacetabular impingement is a cause of chronic pain in young people and may also be a precursor to osteoarthritis. Femoroacetabular impingement is essentially the abnormal movement that occurs between the femur and the acetabulum at the hip joint. This mechanism is a three-dimensional phenomenon that can sometimes be difficult to demonstrate with conventional radiographic methods. This applies particularly to pincer-type femoroacetabular impingement, which concerns the shape and orientation of the acetabulum, a structure with a 360° circumference; diagnosis by two-dimensional means, that is by plain radiographs, therefore remains a matter of debate.
A number of radiographic markers are of course in use, the most important of them being the crossover sign, the posterior wall sign and the ischial spine sign. In the international literature, however, there are serious questions about the accuracy of these radiographic signs. Indeed, many publications have noted considerable variability in the way these findings are interpreted between different observers (interobserver reliability).
Other studies have examined CT arthrography and magnetic resonance arthrography (MRA) and assessed their accuracy against intraoperative findings, tears of the labrum or chondral lesions, which are what confirm the condition. Some studies have shown magnetic resonance arthrography (MRA) to be markedly superior to conventional radiographic methods, while others have found that CT and MR arthrography give equally reliable results. Recent studies have also shown that pelvic tilt can significantly alter the measurement of the markers on plain radiographs, which are the ones most commonly used. Even where radiographs are standardised for pelvic tilt (for example, a standard distance of 3 to 4cm between the pubic symphysis and the sacrococcygeal joint), the normal orientation of the acetabulum changes significantly when the plain anteroposterior radiograph is taken standing rather than supine. For these reasons a level IV systematic review was carried out in order to look for evidence on the particular radiographic signs on which we rely for the diagnosis of pincer-type femoroacetabular impingement.
A review of the literature was carried out in 2016 using the Cochrane, PubMed and Embase databases. All the articles examined focused on the radiographic diagnosis of pincer-type femoroacetabular impingement. For every article the level of evidence and the type of radiographic marker used were recorded.
A total of 44 studies were included in the final review. Most of them were level IV (26 articles), and there were also 12 level III articles and 6 level II articles. The crossover sign was the most frequently used radiographic sign (27 of the 44), followed by the lateral centre-edge angle (22 of 44). The anteroposterior radiograph of the pelvis and hips was the most commonly used view (33 studies).
It was found that the evidence supporting the most commonly used radiographic signs is of low quality; these include the crossover sign, the lateral centre-edge angle, the posterior wall sign, the ischial spine sign, coxa profunda, acetabular protrusion and the acetabular index. The data on the use of the herniation pit for diagnosing pincer-type femoroacetabular impingement are of poor quality and contradictory. Several novel measurements have also been proposed, such as the β-angle, the acetabular roof ratio and the acetabular retroversion index, but none of them has adequate support in the literature.
The conclusion of this study was that there is no strong evidence to support any particular set of radiographic markers as the best for diagnosing pincer-type femoroacetabular impingement, chiefly because of the lack of high-quality studies, that is levels I and II, comparing conventional radiographic findings with the intraoperative findings at arthroscopy. More specialised imaging, such as computed tomography and magnetic resonance imaging with arthrography, is needed in order to diagnose pincer-type femoroacetabular impingement, and these examinations are sufficiently accurate for assessing pathology of the labrum or of the articular cartilage of the acetabulum.
Source: Rhee C, Le Francois T, Byrd JWT, Glazebrook M, Wong I. Radiographic Diagnosis of Pincer-Type Femoroacetabular Impingement: A Systematic Review. Orthop J Sports Med. 2017
