Clin Orthop Surg.  2011 Sep;3(3):202-210. 10.4055/cios.2011.3.3.202.

MR-based Parameters as a Supplement to Radiographs in Managing Developmental Hip Dysplasia

• Kim HT
• Kim IB
• Lee JS

• KMID: 1743910
• DOI: http://doi.org/10.4055/cios.2011.3.3.202

Abstract

BACKGROUND
Some dysplastic hips with favorable radiographic parameters fail to develop normally, suggesting that we should consider cartilaginous or soft tissue structures for further information regarding the condition of the hip. The purpose of this study was to provide a clear definition of concentric reduction in developmental dysplasia of the hip (DDH) based on magnetic resonance imaging (MRI), and to determine how radiographic and MR-based parameters could be used together to treat dysplastic hips.
METHODS
We studied range of motion (ROM)-MRI of 25 patients with unilateral hip dysplasia (mean age at the time of MR imaging, 44.1 months). Each ROM-MRI consisted of a set of bilateral hip scans in the following positions: neutral; abduction; abduction- internal rotation; abduction-internal rotation-flexion; and adduction. Before MR scanning, the 25 patients received the following primary treatments: closed reduction (n = 15; at a mean age of 14.5 months); and open reduction (n = 10; at a mean age of 10.0 months). The following new parameters appear to be useful in treating DDH: 1) the labral angle, the angle the labrum makes with the acetabulum; 2) the uncorrected labral deformity (ULD), the "residual deformity" (deflection of the labrum) when the affected labrum is freed from pressure in abduction; and 3) the zone of compressive force (ZCF), the region of the acetabulum through which the body weight acts on the femoral head.
RESULTS
A concentrically-reduced hip is one in which the labrum points downward in the neutral position, at the same angle as that of the normal side; and in which the ZCF is zone 3, the inner acetabular zone as defined herein. The ULD and the ZCF may be determined precisely as we have done, or the physician may simply observe the changes in the orientation of the labrum and compare the changes qualitatively to the unaffected side, and likewise for the medial joint space.
CONCLUSIONS
Detailed analysis of the labrum as permitted by ROM-MRI, together with acetabular index and other parameters measured from radiographs, provides important information for physicians treating childhood hip dysplasia.

Keyword

Developmental hip dysplasia; Dysplastic hip; Magnetic resonance imaging; Concentric reduction; Labrum

MeSH Terms

Child, Preschool
Female
Hip Dislocation, Congenital/*diagnosis/physiopathology/radiography/surgery
Hip Joint/pathology/physiopathology/radiography
Humans
Infant
*Magnetic Resonance Imaging
Male
Range of Motion, Articular

Figure

• 

  Fig. 1 Measurement of labral angle (LA). LA is defined as the angle that the labrum makes with the acetabulum (that is, with the line that is used for measurement of acetabular index [AI]). Line A is the midline of the labrum: that is, it passes through a point midway between the outer and inner attachment points of the labrum (points B and C) and the distal apex of the labrum. Line H is Hilgenreiner's line. The figure shows a dysplastic hip in neutral; such hips have LA values that are high in neutral and low in abduction.

• 

  Fig. 2 Determination of the zone of compressive force (ZCF). The superior portion of the bony acetabulum is subdivided into three equal zones (numbered 2, 3, and 4); the portion of the roof consisting of the labrum alone is zone 1. ZCF is the acetabular zone which is entered by a line, tilted medially at 16° off the vertical (the vertical is a line perpendicular to the line of Hilgenreiner) and passing through the center of the femoral head. The circle is the smallest one that will completely contain the outer margin of the bony head; the point in the circle is its center. The figure shows a dysplastic hip in abduction; in such hips, the ZCF is usually zone 2 in the neutral position, shifting to zone 3 in abduction.

• 

  Fig. 3 Femoral osteotomy. (A) This 25-month-old girl had left hip dysplasia at initial presentation. (B) On the serial range of motion-magnetic resonance imaging (SROM-MRI), her uncorrected labral deformity (ULD) value was -3°; thus she was a candidate for a single femoral or pelvic osteotomy. Femoral varus osteotomy was performed when she was 29 months old. (C) After implant removal, she underwent a second SROM-MRI at 4 years and 2 months of age. Even though her ULD value following surgery was 3°, the zone of compressive force continued as zone 3 even in the neutral position (previously it was zone 2). (D) The radiograph, taken when he was 6 years and 2 months of age, showed improved condition of the hip. NEUT: neutral, ABD: abduction.

• 

  Fig. 4 Pelvic osteotomy. This boy had a right hip dislocation, and he underwent closed reduction when he was 13 months old. (A) At the age of 4 years and 5 months (3 years and 4 months after reduction), his right hip was still dysplastic. (B) On the serial range of motion-magnetic resonance imaging (SROM-MRI), the uncorrected labral deformity (ULD) value was 4° and the zone of compressive force (ZCF) shifted from zone 2 to 3; thus he was a candidate for single femoral or pelvic osteotomy. We performed a Salter innominate osteotomy when he was 4 years and 8 months old. (C) In a second SROM-MRI scan taken when he was 9 years and 1 month old, ZCF was zone 3 in both the neutral (NEUT) and abduction (ABD) positions and his ULD value was -6°. (D) The follow-up radiograph, taken at this time, showed improved condition of the hip.

• 

  Fig. 5 Borderline case (single vs. dual osteotomy). This girl had a right hip dislocation, and she underwent closed reduction when she was 13 months old. (A) However, at the age of 4 years and 5 months, her right hip was still dysplastic. (B) On the serial range of motion-magnetic resonance imaging (SROM-MRI), her uncorrected labral deformity value was 6° and the zone of compressive force did not move medially on abduction, but remained at zone 2-3. Thus, we could have chosen to perform just one osteotomy (hip or pelvis) or both. To be on the safe side, we performed a dual femoral and pelvic osteotomy. (C) The follow-up radiograph, taken at the age of 9 years and 3 months, showed much improved condition of the hip. NEUT: neutral, ABD: abduction.

• 

  Fig. 6 Failure of unilateral osteotomy to reverse pathology. This girl had a left hip dislocation, and was treated with open reduction when she was 21 months old. (A) Two years after reduction (at 3 years and 9 months of age), the left hip was still dysplastic with a widened superior gap; at this time we performed a Dega-type periacetabular osteotomy. (B) Four years after the periacetabular osteotomy (at 7 years and 9 months of age), the left hip was still dysplastic and the superior gap was still wider than normal. At that time, the condition of the hip was checked by range of motion magnetic resonance imaging: (C) neutral and (D) abduction, which revealed a thickened medial acetabular wall and irregular ossification in the hypertrophied acetabular cartilage. (E) The final radiograph, taken at 13 years and 8 months of age, showed progress in the ossification at the widened superior joint gap, although it was not enough to lead to a normal hip joint (note the dysplasia, particularly the upward direction of the lateral end of the sourcil and the broken Shenton's line).

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