Radiological Imaging of Developmental dysplasia of the hip.

Dr/ ABD ALLAH NAZEER. MD.

Developmental dysplasia of the hip joints:Developmental dysplasia of the hip (DDH) denotes aberrant development of the hip joint and results from an abnormal relationship of the femoral head to the acetabulum. There is a clear female predominance, and it usually occurs from ligamentous laxity and abnormal position in utero. Therefore, it is more common with oligohydramniotic pregnancies. This article describes the commonly used radiographic measurements and lines involved in DDH.EpidemiologyThe reported incidence varies between 1.5 and 20 per 1000 births, with the majority (60-80%) of abnormal hips resolving spontaneously within 2-8 weeks 1 (so-called immature hip).Risk factors include :female gender (M:F ratio ~1:8)family historybreech presentationoligohydramnios

Clinical presentationDDH is usually suspected in the early neonatal period due to the widespread adoption of clinical examination (including Ortolani test, Barlow manoeuvres, Galeazzi sign). The diagnosis is then usually confirmed with ultrasound, although the role of ultrasound in screening is controversial.Radiographic featuresUltrasound is the modality of choice prior to ossification of the proximal femoral epiphysis. Once there is a significant ossification then x-ray examination is required.For some reason, the left hip is said to be more frequently affected. One-third of cases is affected bilaterally .UltrasoundUltrasound is the test of choice in the infant (<6 months) as the proximal femoral epiphysis has not yet significantly ossified. Additionally, it has the advantage of being a real-time dynamic examination allowing the stability of the hip to be assessed with stress views.Some values are used to 'objectively' assess morphology.

Alpha angleThe alpha angle is formed by the acetabular roof to the vertical cortex of the ilium. This is a similar measurement as that of the acetabular angle (see below). The normal value is greater than or equal to 60º.Beta angleThe beta angle is formed by the vertical cortex of the ilium and the triangular labral fibrocartilage (echogenic triangle). The normal value is less than 77º but is only useful in assessing immature hips when combined with the alpha angle (see the sonographic classification of developmental hip dysplasia).Bony coverageThe percentage of the femoral epiphysis covered by the acetabular roof. A value of >50% is considered normalUS criteria for DDH. 1. < 50% coverage of the capital femoral epiphysis.2. Alpha angle < 60 degrees.3. Blunted acetabular margin.

Plain radiographThe key to plain film assessment is looking for symmetry and defining the relationship of the proximal femur to the developing pelvis. The ossification of the superior femoral epiphyses should be symmetric. Delay of ossification is a sign of DDH.Hilgenreiner lineHilgenreiner line is drawn horizontally through the superior aspect of both triradiate cartilages. It should be horizontal but is mainly used as a reference for Perkin line and measurement of the acetabular angle.Perkin linePerkin line is drawn perpendicular to Hilgenreiner line, intersecting the lateral most aspect of the acetabular roof. The upper femoral epiphysis should be seen in the inferomedial quadrant (i.e. below Hilgenreiner line, and medial to Perkin line).

Acetabular angleThe acetabular angle is formed by the intersection between a line drawn tangential to the acetabular roof and Hilgenreiner line, forming an acute angle. It should be approximately 30 degrees at birth and progressively reduce with the maturation of the joint.Shenton lineShenton line is drawn along the inferior border of the superior pubic ramus and should continue laterally along the inferomedial aspect of the proximal femur as a smooth line. If there is a superolateral migration of the proximal femur due to DDH then this line will be discontinuous.

Normal and dysplastic hips. A, Anteroposterior radiographs of right hip with graphic representations in 29-year-old woman (A) with normal acetabular roof with weight bearing forces applied over entire surface and 24-year-old woman (B) with dysplastic shallow acetabular roof with weight bearing forces distributed over smaller area. Arrows indicate acetabular roof and arcs indicate weight bearing forces.

Ultrasound is the reference standard for evaluating the hip in an infant before 6 months, when capital femoral epiphyseal ossification usually occurs. It is a nonionizing, quick, and portable examination that furthermore offers the advantage of dynamic imaging in addition to standard static views.The American College of Radiology recommends that a standard ultrasound examination be performed in two orthogonal planes: a coronal view in the standard plane at rest and a transverse view of the flexed hip with and without stress. Three anatomic landmarks—ilial line, triradiate cartilage, and labrum—are used to measure the α and β angles. A standard plane includes a straight iliac line, the femoral head with maximum diameter, the tip of the echogenic acetabular labrum, and the triradiate cartilage. shows the anatomic landmarks in a normal hip. Meticulous scrutiny of the α angle measurement is necessary because false-positive findings can occur if the imaging plane is suboptimal. When reporting the α angle, the largest angle, not the average angle, should be given.

A, Standard static coronal (A) and transverse (B) ultrasound images of normal hip. Glut = gluteal muscles, Ac = acetabular cartilage, LTP = ligamentum teres/pulvinar complex, FH = cartilaginous femoral head, Tr = triradiate cartilage.

B, Standard static coronal (A) and transverse (B) ultrasound images of normal hip. Glut = gluteal muscles, Ac = acetabular cartilage, LTP = ligamentum teres/pulvinar complex, FH = cartilaginous femoral head, Tr = triradiate cartilage.

A, Ultrasound image shows measurement of α angle (thin diagonal line) in normal hip in 1-month-old boy, which is more than 60°; β angle (thick line) is also within normal range.

B, Ultrasound image in 1-month-old girl with developmental dysplasia of hip shows α angle (dashed line) is abnormal, measuring 43°. Acetabulum is shallow and femoral head is laterally dislocated. There is pulvinar fat hypertrophy (arrowhead) and blunting of bony acetabulum (thick solid arrow).

Real-time coronal sonogram of the hip shows calculation of the acetabular alpha angle. An angle of 60° or greater indicates acetabular maturity.

Real-time coronal sonogram of the hip with calculation of the d/D ratio. Coverage of 58% or greater is considered normal

Radiography: After the child is 4–5 months old, the ossification of the femoral epiphysis begins to obscure sonographic landmarks and radiography becomes more reliable for detection of DDH. This is the standard tool to diagnose DDH after 6 months. An anteroposterior radiograph of the hips in neutral position is used to assess the morphology of the acetabulum, ossification of the femoral head, and position of the femoral head relative to the acetabulum. In early infancy, a normal acetabulum is relatively steeper and straighter. The morphology of the acetabulum changes with age, with the acetabulum becoming more curved inferiorly along the medial and lateral margins. shows the spectrum of normal hips in anteroposterior radiographs in a 6-month-old child and a 2-year-old child, respectively. In DDH, there is delayed ossification of the femoral head and an abnormally shallow acetabulum, thereby predisposing to subluxation and dislocation. Additionally, late complications, such as osteoarthritis and avascular necrosis, can occur. A frog-leg lateral view is sometimes used to determine whether a subluxed hip reduces. Several lines and angles are used to diagnose and further characterize DDH: The first is the Hilgenreiner line, which is a line crossing through both tri-radiate cartilages. The second is the acetabular angle, which is formed by the Hilgenreiner line and a line drawn through the acetabular roof. A neonate should normally have an acetabular angle of less than 30°. The acetabular angle should be less than 22° at and beyond 1 year of age. Acetabular morphology and the degree of femoral head ossification changes with age. The third is the Perkins line, which is a vertical line drawn perpendicular to the Hilgenreiner line and intersecting the lateral rim of the acetabular roof. A normally situated femoral head is in the inferior medial quadrant. The fourth is the Shenton line, which is a C-shaped line drawn along the inferior border of the superior pubic ramus and the inferomedial border of the femoral neck. A normal Shenton line should form a smooth arc. The fifth is the anterior center-edge angle, which is an angle subtended by a craniocaudal line through the center of the ossified femoral head and a line from the center of the femoral head to the lateral margin of the acetabular roof. A center edge angle less than 20° is indicative of dysplasia.

A, Normal anteroposterior radiograph of hips in 6-month-old boy shows acetabular angles in right and left hip (lines) are normal for age, measuring 22° and 24°, respectively.

B, Normal anteroposterior radiograph of hips in 2-year-old boy shows α angles of right and left hips are normal for age, measuring 18° and 20°, respectively. Note how contour of acetabula changes with age. Ossified femoral epiphyses are symmetric and well seated within acetabula. Hilgenreiner (long-dashed line), Perkins (short-dashed line), and Shenton (dotted line) lines are superimposed. Femoral epiphysis is appropriately situated in inferomedial quadrant. Center edge angle is formed by vertical line through center of femoral head and line from center to lateral acetabular roof (solid lines).

A, Anteroposterior radiograph obtained at 6 months of age shows shallow left acetabulum with steep roof, compatible with DDH.

B, Anteroposterior radiograph obtained at 1 year of age shows interval growth of left femoral epiphysis; however, it remains smaller relative to right femoral epiphysis. Left acetabular dysplasia persists.

A, Initial radiograph shows superolateral subluxation of right femoral head, valgus deformity, and acetabular dysplasia.

B, Postoperative radiograph after iliac osteotomy and femoral varus osteotomy shows interval healing and improved acetabular roof coverage of femoral head. Previous valgus deformity has been corrected.

Frontal radiograph of the pelvis in a 1-year-old child with a dislocated right hip. The degree of ossification of the femoral head on the dislocated side is decreased compared with that of the normally located left hip. The abnormally located hip articulates with a false neoacetabulum.

Frontal radiograph of the pelvis obtained with the legs in the frog-leg position indicates that the plane of the femoral projection is toward the triradiate cartilage, suggesting that the hips are reducible.

Healed Salter Osteotomy After three years16M/F

10-week-old female, bilateral DDH.

Bilateral Hip Dislocation. 

Arthrography is typically performed intraoperatively by the orthopedic surgeon at the time of reduction. Obstacles to successful reduction, such as limbus eversion, can be identified. Arthrography during reconstructive osteotomy helps obtain concentric reduction of the hip.

Fluoroscopic image from arthrography in 15-month-old girl with left developmental dysplasia of hip shows contrast material within joint. Femoral head is seated in dysplastic acetabulum.

Arthrogram of congenital hip dysplasia. (A) Arthrogram of the right hip in the neutral position in a 1-year-old girl with congenital subluxation of the hip shows the typical displacement of the hip lateral to, but below the acetabular labrum. There is accumulation of contrast agent in the stretched capsule (arrow), and the ligamentum teres is elongated. (B) In the frog-lateral position, the head moves more deeply into the acetabulum, but subluxation is still present.

Arthrogram of congenital hip dislocation. (A) Anteroposterior radiograph of the right hip in an 8-year-old girl demonstrates complete superolateral dislocation of the femoral head. Note the shallow acetabulum. (B) Arthrogram of

the hip shows a deformed cartilaginous limbus and stretching of the ligamentum teres. The femoral head lies superior and lateral to the edge of the cartilaginous labrum. Note the accumulation of contrast agent in the loose joint capsule.

CT is generally reserved for problem solving in difficult cases and involves a low-dose technique, often in the setting of prior postoperative evaluation. The CT technique at our institution is weight based (Table 4). CT is more commonly used postoperatively after the patient has been placed in a cast to define the success of reduction. Postoperatively, concentric reduction of the femoral head can be confirmed. Preoperative assessment includes evaluation of bony acetabular morphology and the ossified femoral epiphysis as well as the femoral head position relative to the acetabulum.

A, Preoperative radiograph showing left DDH. B, Postoperative CT image was obtained to evaluate relocation of left hip after iliac and femoral varus osteotomy.

CT of congenital hip dislocation. Axial section through the proximal femora and hips of a 6-month-old boy shows posterolateral dislocation of the left hip. The right hip is normal.

Treatment of congenital hip dysplasia. (A) Anteroposterior radiograph of the pelvis in a 1-year-old boy demonstrates the typical appearance of congenital dislocation of the left hip. (B) After conservative treatment with a Pavlik harness at age 2, there is still subluxation. Note the broken Shenton-Menard arc. At age 3, after further conservative treatment by skin traction and application of a spica cast, there is almost complete reduction of subluxation, as demonstrated by contrast arthrography (C). (D) CT scan, however, demonstrates some minimal residual lateral displacement of the femoral head, as evidenced by the medial accumulation of contrast.

Mild right hip dysplasia. AP pelvic view shows lateral CE angle measuring less than 20º (lateral CE angle = 19º, considered diagnostic of hip dysplasia); and axial CT image shows deficient anterior, posterior and global acetabular coverage with decreased AASA, PASA and HASA (AASA = 46º , PASA = 87º ad HASA = 133º).

MRI Findings of the Normal Hip Familiarity with the normal appearance of the pediatric hip on MRI is critical to detect pathology. The ossified and unossified femoral heads, cartilage, and ligaments are clearly depicted. The infantile acetabulum can be categorized into three basic components: bony, cartilaginous, and ligamentous or soft tissue. The bony acetabulum is seen on radiography and is composed of the acetabular parts of the ilium, ischium, and pubis, all of which are held together by the triradiate cartilage. The cartilaginous acetabulum consists of the hyaline cartilage at the articular surface, which is U-shaped and is bridged by the transverse acetabular ligament, and the supporting vascularized growth cartilage, which includes the triradiate cartilage. The labrum, trans-verse acetabular ligament, and the ligamentum teres are the primary ligamentous structures. The labrum is of low to intermediate signal intensity and appears as a small triangular structure along the edge of the acetabulum on axial images. The labrum's intrinsic signal intensity typically increases slightly from T1- to T2-weighted images. It is important to evaluate for normal morphology and position of the labrum when evaluating dysplastic hips. The transverse ace-tabular ligament is located inferiorly, where there is a deficiency of cartilaginous acetabulum. The ligamentum teres originates from the transverse ligament and inserts on the femoral head fovea. The iliopsoas tendon is a low-signal-intensity structure that is seen just anteromedial to the anterior labrum on the axial plane. The intraarticular fat pad, or pulvinar, lies in the central portion of the acetabulum and has the highest signal intensity of all the structures in the hip, paralleling that of subcutaneous fat. It is important to assess for pulvinar hypertrophic changes, which can serve as an obstacle to successful reduction. The pulvinar in the affected hip can be compared with the contra lateral side to determine any relative size asymmetry.

The ossified femoral epiphysis appears as a low-signal-intensity structure within the high-signal-intensity unossified hyaline cartilage. Symmetry between the two ossified femoral heads should be noted. When evaluating for concentric femoral head positioning, a line can be drawn through both triradiate cartilages. After successful reduction, the ossified portion of the femoral epiphyses should lie anterior to this line. The ossified portions of the anterior and posterior columns are low to intermediate in signal intensity, with an interposed band of high-signal-intensity triradiate cartilage. Depending on the degree of acetabular dysplasia, the unossified parts of the anterior and posterior columns affect acetabular depth. The fibrous joint capsule attaches to the acetabular margin peripheral to the labrum. At birth, the femoral attachment is near the metaphysis and migrates inferiorly as the hip develops. By 12 months of age, the capsule is partly fused to the femoral neck periosteum and runs up the femoral neck, attaching to the edge of the cartilaginous femoral head. Normal acetabular development is dependent on concentric positioning of the femoral head within the acetabulum.

MRI Findings of Developmental Dysplasia of the Hip When characterizing DDH using MRI, the dysplastic acetabulum should be evaluated for retroversion and degree of femoral head coverage. There may be associated cartilaginous defects or delamination. Delayed ossification of the femoral head can be determined by comparing the ossific nucleus of the femoral head in the affected hip with the contra-lateral side. A major advantage of MRI is the ability to visualize the cartilaginous acetabulum and determine its contribution to femoral head coverage. MRI depicts the unossified acetabular epiphysis in the ilium and underlying labrum, therefore showing greater and more accurate acetabular coverage than that seen on radiography alone.Recent orthopedic articles have described the utility of bony and cartilaginous acetabular indexes on MRI in the evaluation of DDH. The bony acetabular index can be measured by MRI using an anteroposterior coronal view and is similar to the acetabular index measured on radiography. To obtain the bony acetabular index, the Hilgenreiner line and Perkins line are drawn using the same landmarks as used on radiography. The bony acetabular index line is drawn from the Hilgenreiner line at the lateral part of the triradiate cartilage to the Perkins line at the lateral aspect of the bony acetabulum. The angle subtended by the bony acetabular index line and the Hilgenreiner line is the bony acetabular index angle. The cartilaginous acetabular index is measured by drawing a line from the lateral part of the triradiate cartilage at the Hilgenreiner line to the lateral acetabular cartilaginous margin (the cartilaginous acetabular index line). The cartilaginous acetabular index angle is formed by the cartilaginous acetabular index line and the Hilgenreiner line.

A, Anteroposterior radiograph shows lateral dislocation of right hip. Right acetabulum is steep and shallow. Right femoral head ossification is delayed.

B, MRI was performed immediately after right hip arthrogram, closed reduction, and adductor release. Axial T1-weighted images show interval reduction of right hip with mild persistent posterior subluxation. Acetabulum is shallow. Compared with normal left side (solid arrow, C), right femoral head ossification is delayed (long solid arrow, B). Anterior labrum is mildly inverted (short solid arrow, B). Significant pulvinar hypertrophy (dotted arrow

D, Radiograph obtained 6 months after surgery shows interval improvement with mild persistent subluxation of right hip. However, right acetabulum is still dysplastic with abnormal acetabular angle. Right acetabular angle measures 34° and left acetabular angle is 23°.

C, MRI was performed immediately after right hip arthrogram, closed reduction, and adductor release. Axial T1-weighted images show interval reduction of right hip with mild persistent posterior subluxation. Acetabulum is shallow. Compared with normal left side (solid arrow, C), right femoral head ossification is delayed (long solid arrow, B). Anterior labrum is mildly inverted (short solid arrow, B). Significant pulvinar hypertrophy (dotted arrow, B).

T1-weighted images with fat saturation show superimposed bony acetabular index angle (I) and cartilaginous acetabular index angle (J). Bony acetabular index measures 39.6°, which is fairly concordant with 34° acetabular angle measured on radiographs. Hypertrophic acetabular cartilage contributes to 15° cartilaginous acetabular index, which is still abnormal but relatively closer to normal range (mean cartilaginous acetabular index in 2-year-old is 8.2 ± 1.9 [40]) compared with measured bony acetabular index. This examination served as guide for further orthopedic management. Compared with radiographs, femoral head appears more concentrically located in acetabulum. Surgeon subsequently elected to treat more conservatively.

A, Anteroposterior radiograph shows shallow steep dysplastic left acetabulum (long arrow), lateral subluxation of left hip, and delayed ossification of left femoral head (short arrow). Radiopaque objects seen at bottom of image are buttons overlying patient.

B, Axial T2-weighted image with fat saturation obtained after interval reduction and with spica cast in place shows mild residual subluxation of left femur and fibrofatty pulvinar hypertrophy with small effusion. Note signal intensity loss of fibrofatty pulvinar with fat saturation (long arrow). Anterior labrum is inverted (short arrow). Right hip appears normal with normal-sized spherical femoral head compared with small and aspherical left femoral head.

C, Coronal T1-weighted image shows lateral subluxation of left femoral head and fibrofatty pulvinar hypertrophy (arrow). Note delayed ossification and aspherical shape of left femoral head.

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