X-ray of hip dysplasia

From radlines.org
Jump to navigation Jump to search
Hip dysplasia with right-sided hip dislocation.

Authors: Mikael Häggström; Authors of integrated Creative Commons article[1] [notes 1]

Projectional radiography ("X-ray") of dysplasia of the hip joint (also termed developmental dysplasia of the hip (DDH)) is where the socket portion does not fully cover the ball portion, resulting in an increased risk for joint dislocation.[2]

Planning

Choice of modality

Ultrasonography of hip dysplasia yields better results defining the anatomy until the cartilage is ossified. When the infant is around 3 months old a clear roentgenographic image can be achieved. Unfortunately, the time at which the joint gives a good x-ray image is also the point at which nonsurgical treatment methods cease to give good results.

Image quality checking
Image quality checking.
  • Pelvic rotation can be evaluated by dividing the horizontal diameter of the obturator foramen of the right side and that of the left. In neutral rotation the ratio is 1 but is considered to be acceptable when it is between 0.56 and 1.8.
  • Pelvic volar/dorsal tilt can be evaluated by lines drawn from the highest point of the ischium to the most prominent point of the symphysis, joining at the inside of the pelvis. The range of normal values is from 90 to 135° and is related to the infant’s age.[1]

Measurements in children

The most useful lines and angles that can be drawn in the pediatric pelvis assessing DDH are as follows:[1]

  • (A) Hilgenreiner line. It is considered a basal line joining the top aspect of the triradiate cartilages. This line is used to measure the acetabular angle and as a reference for Perkin line.
  • (B) Perkin line is perpendicular to Hilgenreiner line, touching the lateral margin of the acetabulum. This leads to four quadrants and a normal femoral head has to be located in the inferomedial quadrant. We can measure the lateral displacement of the femoral head with regard to the Perkin line by dividing the width of the head that crosses the Perkin line by the diameter of the head. The value for patients under 3 years must be 0 and in older children this ranges from 0 to 22%.
  • (C) Shenton line is a continuous arc drawn from the inner edge of the femoral neck to the superior margin of the obturator foramen. This should be smooth and undisrupted; otherwise it may indicate a fracture or hip dysplasia.
  • (D) The acetabular index measures the acetabular roof slope. It is the most useful measure of acetabular dysplasia until 6 years of age. It is formed between Hilgenreiner line and the acetabular roof. In newborns, values of 30° ±4° in females and 26° ±5° in males are considered normal. Gradually this angle becomes smaller, with a mean value of 20° ±3° in females and 18° ±4° in males at 1 year of age.
  • (E) The medial articular joint space is measured between the medial border of the femoral head or neck (when epiphysis is not ossified) and the acetabular platform. Normal values range between 5 and 12 mm. Differences greater than 1.5 mm between the two sides are considered abnormal.
Reimer's migration index (crop).png Also, Reimer's migration index can be used to indicate hip dislocation. The migration index (MI) is normally less than 33%.[3]

Measurements in adults

X-ray of the hips of a 40-year-old female, with dysplasia of her right hip.

In the adult hip there are important landmarks to be recognized on plain film radiographs (Figure 5):[1]

  • (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 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. 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 (Figure 5).
  • (D) 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 head.

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.[1]

Table 1: Measurements in adult hip.[1]
Measurement Target Normal value
Acetabular depth ratio Deepness of acetabulum >250
Center-edge angle Coverage of acetabulum 20–40
Tönnis angle Slope of the sourcil 0–10°
Sharp angle Acetabular slope <45°
Crossing ratio Percentage of acetabular walls crossing <20%
Alpha angle Degree of bulging of the femoral head-neck junction
  • Male > 68° 
  • 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 >0.18
Figure 5 (a). Iliopectineal line (red), ilioischial line (yellow), tear drop (blue), acetabular fossa (brown), and anterior (white) and posterior (green) wall of the acetabuli showing mild upper crossover sign.[1]

Figure 6:

Acetabular depth value under 250 characterizes the dysplastic hip.[1]

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.[1]

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.[1]

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.[1]

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.[1]

The Sharp angle is a global way to measure the acetabular slope. Angles over 45° are indicative of acetabular dysplasia.[1]

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%.[1]

Other signs associated with acetabular retroversion are the sciatic spine and posterior wall signs. 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.[1]

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).[1]

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.[1]

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.[1]

Although femoral version or torsion can be measured by radiographs, CT overcomes the inconsistencies demonstrated in the measurements made by biplane radiography.[1]

Notes

  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Radlines:Authorship for details.

References

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 Initially largely copied from: Ruiz Santiago, Fernando; Santiago Chinchilla, Alicia; Ansari, Afshin; Guzmán Álvarez, Luis; Castellano García, Maria del Mar; Martínez Martínez, Alberto; Tercedor Sánchez, Juan (2016). "Imaging of Hip Pain: From Radiography to Cross-Sectional Imaging Techniques ". Radiology Research and Practice 2016: 1–15. doi:10.1155/2016/6369237. ISSN 2090-1941.  Attribution 4.0 International (CC BY 4.0) license
  2. . Your Orthopaedic Connection: Developmental Dysplasia of the Hip (October 2013).
  3. . Hip subluxation and dislocation in cerebral palsy: Outcome of bone surgery in 21 hips (2008).