Changes

In the adult hip there are important landmarks to be recognized on plain film radiographs (Figure 5):<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> ==Measurements===*(A) Iliopectineal or iliopubic line is formed by the arcuate line of the ilium and the superior border of the superior pubic ramus up to the pubic symphysis. It conforms to the inner margin of the pelvic ring and it is part of the anterior column of the acetabulum.*(B) The '''Fossa/ilioischial line of Köhler begins at the medial border of the iliac wing and extends along the medial border of the ischium to end at the ischial tuberosity. It is part of the posterior column of the acetabulum.*(C) Acetabular Floor. relationship''': In normal conditions the floor of the acetabular fossa is lateral to the ilioischial line by 2 mm in men and 1 mm in women. When the acetabular floor overlaps or overpasses the ilioischial line, the diagnosis of coxa profunda can be made. Nevertheless, coxa profunda had been found in 76% of asymptomatic hips, mainly in women. Therefore, this as an isolate criterion is not enough to make the diagnosis of pincer-type impingement. A more severe condition is protrusio acetabuli, diagnosed when the femoral head overlaps or overpasses the ilioischial line (.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/><gallery mode=packed heights=150>File:X-ray of coxa profunda.jpg|Figure 5(b).Coxa profunda.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/>*File:X-ray of protrusio acetabuli.jpg|thumb|Figure 5 (Dc) The teardrop represents a summation of shadows. Its medial aspect corresponds to the inner cortex of the pelvis and the lateral edge with the acetabular notch and the anteroinferior portion of the quadrilateral plate. It is not present at birth but gradually develops due to pressure of the femoral headProtrusio acetabuli.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> </gallery>*'''Joint space''': In the adult hip, normal joint space ranges from 3 to 5 mm and must be uniform. Values under 2 mm are consistent with joint space narrowing. The most important measurements are detailed in Figure 6 and Table 1.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/>

|+ Table 1: Measurements Other measurements in adult hip.<ref group="notes">Unless otherwise specified in boxes, reference is the one marked in header.</ref><ref name="Ruiz SantiagoSantiago Chinchilla2016"/>

! Measurement !! Image !! Target !! Normal value

| [[File:Acetabular depth ratio.jpg|170px]]| Deepness of acetabulum . *The width is measured between the inferior margin of the teardrop and the lateral rim of the acetabulum.<ref name="LaborieEngesæter2013">{{cite journal|last1=Laborie|first1=Lene Bjerke|last2=Engesæter|first2=Ingvild Øvstebø|last3=Lehmann|first3=Trude Gundersen|last4=Sera|first4=Francesco|last5=Dezateux|first5=Carol|last6=Engesæter|first6=Lars Birger|last7=Rosendahl|first7=Karen|title=Radiographic measurements of hip dysplasia at skeletal maturity—new reference intervals based on 2,038 19-year-old Norwegians|journal=Skeletal Radiology|volume=42|issue=7|year=2013|pages=925–935|issn=0364-2348|doi=10.1007/s00256-013-1574-y}}</ref>*The depth is measured perpendicularly from the midpoint of the width line.<ref name="LaborieEngesæter2013"/>| >250*Less indicates a dysplastic hip|-! Center-edge angle of Wiberg| [[File:Center-edge angle of Wiberg.jpg|170px|left]]| The superior-lateral coverage of the femoral head. |*>20° (<55 years old)<ref name="wiberg" group="notes">This can also be used in children. At between 5 and 10 years, the minimum normal value is 15°.</ref>*<24° (>55 years old)<ref name="wiberg" group="notes"/>*>40° indicates overcoverage

! CenterReimer's migration index<ref name=Persiani>{{cite web|url=http://www.actaorthopaedica.be/acta/download/2008-5/06-edge angle Persiani%20et%20al.pdf|title=Hip subluxation and dislocation in cerebral palsy: Outcome of bone surgery in 21 hips|author1=Pietro PERSIANI|author2=Iakov MOLAYEM|year=2008|author3=Alessandro CALISTRI|author4=Stefano ROSI|author5=Marco BOVE|author6=Ciro VILLANI|journal=Acta Orthop. Belg.}}</ref>| [[File:Femoral extrusion index.jpg|170px]] | Coverage The percentage of the femoral head that lies outside of acetabulum the acetabular roof. It is also called the ''femoral extrusion index''. || 20–40<25%

| [[File:Tönnis angle of the hip.jpg|170px]] | Slope of the sourcil (the sclerotic weight-bearing portion of the acetabulum) | 0 to 10°*>10° is a risk factor for instability*<0° is a risk factor for pincer impingement|-! Caput-sourcil angle<ref name="FaWang2014">{{cite journal|last1=Fa|first1=Liangguo|last2=Wang|first2=Qing|last3=Ma|first3=Xiangxing|title=Superiority of the modified Tönnis angle over the Tönnis angle in the radiographic diagnosis of acetabular dysplasia|journal=Experimental and Therapeutic Medicine|volume=8|issue=6|year=2014|pages=1934–1938|issn=1792-0981|doi=10.3892/etm.2014.2009}}</ref>| [[File:Caput-sourcil angle.jpg|170px]]| Superior to the Tönnis angle in cases without joint space narrowing or subluxation.<ref name="FaWang2014"/>| 0–10°−6 to 12°<ref name="FaWang2014"/>*>12° is a risk factor for instability*<-6° is a risk factor for pincer impingement

| [[File:Sharp angle of the hip.jpg|170px]]| Acetabular slope || <45°*Greater indicates acetabular dysplasia

! Crossing ratio Cervical diaphyseal angle| Percentage [[File:Cervical diaphyseal angle of acetabular walls crossing |the hip.jpg| <20%170px]]|-! Alpha The angle | Degree of bulging of formed between the femoral head-neck junction |and femoral diaphysis |120° to 140°*Male > 68° Higher indicates coxa valga *Female > 50°|-! Femoral head-neck offset | Offset of the femoral head with regard to most prominent aspect of the femora neck || >10 mm|-! Offset percentage | Femoral head-neck offset related to femoral head diameter || >0.18Lower indicates coxa vara

[[File:Iliopectineal line (red), ilioischial line (yellow), tear drop (blue), acetabular fossa (brown), and anterior (white) and posterior (green) wall of the acetabuli.jpg|thumb|300px|Figure 5 (a). Iliopectineal line (red), ilioischial line (yellow), tear drop (blue)On CT, acetabular fossa (brown), and anterior (white) and posterior (green) wall of the acetabuli showing mild upper crossover sign.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/>]] <gallery mode=packed heights=150>File:X-ray of coxa profunda.jpg|Figure 5 (b). Coxa profunda.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/>File:X-ray of protrusio acetabuli.jpg|thumb|Figure 5 (c). Protrusio acetabuli.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> </gallery> Figure 6: <gallery mode=packed heights=150>File:Acetabular depth ratio.jpg|(a) Acetabular depth ratio.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Center-edge angle of Wiberg.jpg|(b) Center-edge angle of Wiberg.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Femoral extrusion index.jpg|(c) Femoral extrusion index.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Tönnis angle of the hip.jpg|(d) Tönnis angle.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Sharp angle of the hip.jpg|(e) Sharp angle.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Crossing ratio of the hip.jpg|(f) Crossing ratio.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Alpha angle measured in 45 degrees Dunn view.jpg|(g) Alpha angle measured in 45° Dunn view.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Hip offset percentage measured in cross-lateral view.jpg|(h) Offset percentage measured in cross-lateral view.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> File:Cervical diaphyseal angle of the hip.jpg|(i) Cervical diaphyseal angle.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> </gallery> Acetabular depth value under 250 characterizes the dysplastic hip.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> In normal conditions the acetabulum covers 75% of the femoral head. This coverage can be determined by three different measurements: lateral center-edge angle of Wiberg, '''anterior center-edge angle, and femoral extrusion index. Femoral extrusion index measures the percentage of the femoral head that lies outside of the acetabular roof. This percentage must be inferior to 25% in adults.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> Center-edge Wiberg’s angle measures the superior-lateral coverage of the femoral head. It is useful in children older than 5 years and in adulthood. For children between 5 and 10 years the minimum normal value is 15°, and in adults it is about 20°, although after 55 years this minimum increases to 24°. Values over 40° indicate overcoverage.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> Anterior center-edge Lequesne’s angle ''' can be measured in a false profile view of the hip or in a sagittal CT scan. In this case the tangent line touches the anterior rim of the acetabulum. Values under 20° indicate undercoverage of the femoral head.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> The acetabular slope can also be measured by different methods. The Tönnis angle quantifies the slope of the sourcil (the sclerotic weight-bearing portion of the acetabulum). Values over 10° are considered a risk factor for instability, while values under 0° are considered a risk factor for pincer impingement.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> The Sharp angle is a global way to measure the acetabular slope. Angles over 45° are indicative of acetabular dysplasia.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> Normal acetabulum is oriented in anteversion. Its value ranges from 15 to 20° in the equatorial plane of the acetabulum and decreases gradually towards the acetabular roof, where normal values range from 0 to 5°. Retroversion of the upper part of the acetabulum has been related with pincer type impingement. In radiography the presence of a “crossover sign” is produced when the posterior wall of the acetabulum crosses the anterior wall before reaching the acetabular roof. It is a sign of acetabular retroversion and it has been linked with overcoverage and pincer impingement. Nevertheless, this sign has been described in 6% of the normal population. Therefore, more important than its presence is the percentage of crossing. This ratio is considered significant if it is over 20%.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/>

Other signs associated with acetabular retroversion are the The '''sciatic spine and posterior wall signs''' are other signs associated with acetabular retroversion. The first one is considered positive when the sciatic spine is projected medial to the iliopectineal line in an AP radiography of the spine, indicating that it is not just the acetabulum but the whole hemipelvis that is twisted into retroversion. The second sign is considered positive when the posterior wall edge is medial to the center of the femoral head, indicating deficiency of the posterior wall.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> In normal conditions there is a symmetric concave contour at the junction of the anterior and posterior profile of the femoral head and neck. Loss of this concavity or bone bulging may lead to cam type impingement. The degree of this deformity can be measured by the alpha angle. Although it can be measured in the cross-lateral view, the 45° Dunn view is considered more sensitive and the frog leg view more specific in determining pathologic values. Debate about which values are considered normal is still in progress. Based on the Copenhagen Osteoarthritis Study, a recent work defined three ranges of values for the α-angle: pathological (≥83° in men and ≥57° in women), borderline (69° to 82° in men, 51° to 56° in women), and normal (≤68° in men and ≤50° in women).<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> The offset between the neck and femoral head can also be calculated in the lateral projection of the hip. A value of less than 10 mm is considered pathologic. The percentage is calculated by dividing the distance between the femoral head and the neck lines by the femoral head diameter. If this percentage is under 0.18 there is high probability of cam type impingement.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/> The angle formed between the femoral neck and femoral diaphysis ranges from 120° to 140°. Coxa valga is diagnosed if the angle is higher and coxa vara if the angle is lower than this normal range.<ref name="Ruiz SantiagoSantiago Chinchilla2016"/>