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Decreased interposition after closed reduction in the hip joint: a case of developmental dislocation of the hip observed by MRI
J Orthop Sci (2002) 7:397–399
Decreased interposition after closed reduction in the hip joint: a case of developmental dislocation of the hip observed by MRI Wataru Watanabe1, Eiji Itoi1, Shin Yamada1, and Ryuji Sashi2 1 2
Department of Orthopedic Surgery, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan Department of Radiology, Akita University School of Medicine, Akita, Japan
Abstract A 4-month-old Japanese girl with a developmental dislocation of the right hip was treated with manual reduction under general anesthesia followed by cast immobilization. Serial magnetic resonance imaging (MRI) revealed that a large interposition of fat tissue in the acetabulum, observed immediately after cast immobilization, became remarkably small in size as the congruity improved after 3 weeks. These MRI findings demonstrate the mechanism of a “squeezing phenomenon” after reduction of the hip. Key words Magnetic resonance imaging · Developmental dislocation of the hip · Interposition · Shrinkage of the interposition
Introduction In developmental dislocation of the hip, the congruity of the hip after reduction improves during immobilization in a cast. This phenomenon is known as a squeezing phenomenon, based on Severin’s description that “the head squeezes into the socket after one or two weeks”.5 The mechanism of this phenomenon has not been clarified. We observed this phenomenon by serial magnetic resonance imaging (MRI) to obtainthe the interesting findings described in this case report.
Case report A 4-month-old girl with a developmental dislocation of the right hip was referred to our clinic (Fig. 1). Because application of the Pavlik harness for 4 weeks had failed, a manual reduction under general anesthesia was attempted after 1 month of skin traction. Arthrography immediately before the reduction revealed hypertrophy Offprint requests to: W. Watanabe Received: June 6, 2001 / Accepted: December 5, 2001
of the ligamentum teres and an inverted limbus (Fig. 2). The femoral head in the acetabulum was stable in the position of the hip flexed 90° and within an arc of 20°– 90° of horizontal abduction. The hip was immobilized in a double hip spica at approximately 120° of flexion, 60° of horizontal abduction, and 20° of internal rotation. However, the distance between the acetabulum and the medial margin of the femoral head was 4 mm wider than on the contralateral side. The hip redislocated 4 days after the first cast immobilization. A hip spica cast was applied again after reduction at 100° of flexion and 80° of horizontal abduction. The distance between the acetabulum and femoral head was still 4 mm wider in the right hip joint than on the other side. MR images (spin echo T1; proton density-weighted and T2-weighted images; T5 Gyroscan, 0.5 T, Philips, Best, Netherlands) were obtained after the second cast immobilization to confirm the reduction and to detect any potential causes of redislocation. MR images in the coronal plane showed that the right femoral head was within the acetabulum, but a large mass with high signal intensity on the T1-weighted image was observed between the femoral head and the acetabulum (Fig. 3a). Proton density-weighted images in the axial plane revealed the inverted limbus interposed into the joint space. Medial to the limbus was an interposition with isosignal intensity and high intensity at the center of a large substance, the same intensity as the subcutaneous fat tissue (Fig. 3b). This fat-like interposition seemed to be surrounded by synovial fluid (isosignal intensity on proton density-weighted image and high signal intensity on T2-weighted image). The interposition together with the inverted limbus seemed to push the femoral head out of the acetabular fossa (Fig. 3b,c). After 3 weeks of immobilization, the interposition decreased remarkably in size, and accordingly the congruity of the femoral head to the acetabulum was improved (Fig. 4a). Although the limbus remained
398
Fig. 1. Anteroposterior radiography of the hip joint at the first visit to our clinic
W. Watanabe et al.: Decreased interposition
a
b Fig. 2. Arthrogram of the hip joint before manual reduction under anesthesia
inverted, the femoral head was successfully “squeezed into the acetabulum” (Fig. 4b). After 4 weeks of casting, the spica cast was replaced with an abduction brace. When it was removed after 6 months of application, the right femoral head was thought to be in acceptable position although the secondary ossification center was still small compared with the normal side (Fig. 5).
Discussion Johnson et al.3 and Krancy et al.4 reported MR images of the normal infantile hip joint. The large interposition seen in our case could not be found in their reports. On the other hand, there are several reports describing the anatomical abnormality detected by MRI in developmental dislocation of the hip. Johnson et al.2 reported a case of developmental dislocation of the hip with an infolded capsule that obstructed reduction of the femoral head. Bos et al.1 have outlined several factors that may obstruct reduction, such as an inverted limbus, thickening or adhesion of the capsule, hypertrophied fat
c Fig. 3a–c. Follow-up magnetic resonance imaging (MRI) 3 days after reduction. a Coronal view, T1-weighted image. A large high-intensity mass indicates fat tissue at the acetabular fossa. b Axial view, proton density-weighted image. The femoral head rests on the inverted limbus. Large amounts of substance showing the same intensity as adjacent cartilage (arrow) just medial to the femoral head and high intensity (arrowhead) at the center occupy the acetabulum. c Axial view, T2-weighted image. Substance that showed isointensity in proton density image has high intensity signal (arrow). Material in the center of the mass has fat-like intensity (arrowhead)
pad, and compression by the psoas tendon over the capsule. Most of the interposition seen in our case might have been hypertrophied fat tissue such as Bos et al.1 had described.
W. Watanabe et al.: Decreased interposition
399
a Fig. 5. Right hip joint seems to have obtained good congruity in this roentogenogram
b Fig. 4a,b. MRI 3 weeks after reduction. a Coronal view, T1weighted image. The high-intensity mass has decreased. b Axial view, T1-weighted image. Congruity of the right hip joint has improved
The interposition, probably consisting of the hypertrophied fat tissue and surrounding synovial fluid, seemed to occupy the acetabulum and looked as if it was preventing the complete reduction of the femoral head at the beginning of casting. However, according to the arthrography performed before the reduction, hypertrophy of the ligamentum teres and an inverted limbus already existed. Therefore, these were one of the interpositions that primarily obstructed reduction. Hypertrophied fat tissue seen in our case might be a secondary reaction after the long-lasting dislocation. The interposition decreased in size 3 weeks after reduction. Accordingly, the femoral head obtained a rela-
tively better congruity. Severin et al.5 demonstrated by arthrography that the femoral head “squeezed into the socket” after 1–2 weeks following reduction. He speculated that a compressive force produced by the reduced head contributed to decrease the size of the interposition. In the present case, MRI clearly demonstrated that the interposing fat tissue reduced in size and synovial fluid disappeared as the head gained better congruity in the acetabulum. One of the mechanisms of the “squeezing mechanism” proposed by Severin might be explained by the shrinkage of the hypertrophied fat tissue and absorption of the synovial fluid.
References 1. Bos CFA, Bloem JL, Obermann WR, et al. Magnetic resonance imaging in congenital dislocation of the hip. J Bone Joint Surg Br 1988;70:174–8. 2. Johnson ND, Wood BP, Jackman KV. Complex infantile and congenital hip dislocation: assessment with MR imaging. Radiology 1988;168:151–6. 3. Johnson ND, Wood BP, Noh KS, et al. MR imaging anatomy of the infant hip. AJR 1989;153:127–33. 4. Krancy R, Prescher A, Botschek A, et al. MR-anatomy of infants hip: comparison to anatomical preparations. Pediatr Radiol 1991; 21:211–5. 5. Severin E. Congenital dislocation of the hip. J Bone Joint Surg Am 1950;32:507–18.
Decreased interposition after closed reduction in the hip joint: a case of developmental dislocation of the hip observed by MRI Wataru Watanabe1, Eiji Itoi1, Shin Yamada1, and Ryuji Sashi2 1 2
Department of Orthopedic Surgery, Akita University School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan Department of Radiology, Akita University School of Medicine, Akita, Japan
Abstract A 4-month-old Japanese girl with a developmental dislocation of the right hip was treated with manual reduction under general anesthesia followed by cast immobilization. Serial magnetic resonance imaging (MRI) revealed that a large interposition of fat tissue in the acetabulum, observed immediately after cast immobilization, became remarkably small in size as the congruity improved after 3 weeks. These MRI findings demonstrate the mechanism of a “squeezing phenomenon” after reduction of the hip. Key words Magnetic resonance imaging · Developmental dislocation of the hip · Interposition · Shrinkage of the interposition
Introduction In developmental dislocation of the hip, the congruity of the hip after reduction improves during immobilization in a cast. This phenomenon is known as a squeezing phenomenon, based on Severin’s description that “the head squeezes into the socket after one or two weeks”.5 The mechanism of this phenomenon has not been clarified. We observed this phenomenon by serial magnetic resonance imaging (MRI) to obtainthe the interesting findings described in this case report.
Case report A 4-month-old girl with a developmental dislocation of the right hip was referred to our clinic (Fig. 1). Because application of the Pavlik harness for 4 weeks had failed, a manual reduction under general anesthesia was attempted after 1 month of skin traction. Arthrography immediately before the reduction revealed hypertrophy Offprint requests to: W. Watanabe Received: June 6, 2001 / Accepted: December 5, 2001
of the ligamentum teres and an inverted limbus (Fig. 2). The femoral head in the acetabulum was stable in the position of the hip flexed 90° and within an arc of 20°– 90° of horizontal abduction. The hip was immobilized in a double hip spica at approximately 120° of flexion, 60° of horizontal abduction, and 20° of internal rotation. However, the distance between the acetabulum and the medial margin of the femoral head was 4 mm wider than on the contralateral side. The hip redislocated 4 days after the first cast immobilization. A hip spica cast was applied again after reduction at 100° of flexion and 80° of horizontal abduction. The distance between the acetabulum and femoral head was still 4 mm wider in the right hip joint than on the other side. MR images (spin echo T1; proton density-weighted and T2-weighted images; T5 Gyroscan, 0.5 T, Philips, Best, Netherlands) were obtained after the second cast immobilization to confirm the reduction and to detect any potential causes of redislocation. MR images in the coronal plane showed that the right femoral head was within the acetabulum, but a large mass with high signal intensity on the T1-weighted image was observed between the femoral head and the acetabulum (Fig. 3a). Proton density-weighted images in the axial plane revealed the inverted limbus interposed into the joint space. Medial to the limbus was an interposition with isosignal intensity and high intensity at the center of a large substance, the same intensity as the subcutaneous fat tissue (Fig. 3b). This fat-like interposition seemed to be surrounded by synovial fluid (isosignal intensity on proton density-weighted image and high signal intensity on T2-weighted image). The interposition together with the inverted limbus seemed to push the femoral head out of the acetabular fossa (Fig. 3b,c). After 3 weeks of immobilization, the interposition decreased remarkably in size, and accordingly the congruity of the femoral head to the acetabulum was improved (Fig. 4a). Although the limbus remained
398
Fig. 1. Anteroposterior radiography of the hip joint at the first visit to our clinic
W. Watanabe et al.: Decreased interposition
a
b Fig. 2. Arthrogram of the hip joint before manual reduction under anesthesia
inverted, the femoral head was successfully “squeezed into the acetabulum” (Fig. 4b). After 4 weeks of casting, the spica cast was replaced with an abduction brace. When it was removed after 6 months of application, the right femoral head was thought to be in acceptable position although the secondary ossification center was still small compared with the normal side (Fig. 5).
Discussion Johnson et al.3 and Krancy et al.4 reported MR images of the normal infantile hip joint. The large interposition seen in our case could not be found in their reports. On the other hand, there are several reports describing the anatomical abnormality detected by MRI in developmental dislocation of the hip. Johnson et al.2 reported a case of developmental dislocation of the hip with an infolded capsule that obstructed reduction of the femoral head. Bos et al.1 have outlined several factors that may obstruct reduction, such as an inverted limbus, thickening or adhesion of the capsule, hypertrophied fat
c Fig. 3a–c. Follow-up magnetic resonance imaging (MRI) 3 days after reduction. a Coronal view, T1-weighted image. A large high-intensity mass indicates fat tissue at the acetabular fossa. b Axial view, proton density-weighted image. The femoral head rests on the inverted limbus. Large amounts of substance showing the same intensity as adjacent cartilage (arrow) just medial to the femoral head and high intensity (arrowhead) at the center occupy the acetabulum. c Axial view, T2-weighted image. Substance that showed isointensity in proton density image has high intensity signal (arrow). Material in the center of the mass has fat-like intensity (arrowhead)
pad, and compression by the psoas tendon over the capsule. Most of the interposition seen in our case might have been hypertrophied fat tissue such as Bos et al.1 had described.
W. Watanabe et al.: Decreased interposition
399
a Fig. 5. Right hip joint seems to have obtained good congruity in this roentogenogram
b Fig. 4a,b. MRI 3 weeks after reduction. a Coronal view, T1weighted image. The high-intensity mass has decreased. b Axial view, T1-weighted image. Congruity of the right hip joint has improved
The interposition, probably consisting of the hypertrophied fat tissue and surrounding synovial fluid, seemed to occupy the acetabulum and looked as if it was preventing the complete reduction of the femoral head at the beginning of casting. However, according to the arthrography performed before the reduction, hypertrophy of the ligamentum teres and an inverted limbus already existed. Therefore, these were one of the interpositions that primarily obstructed reduction. Hypertrophied fat tissue seen in our case might be a secondary reaction after the long-lasting dislocation. The interposition decreased in size 3 weeks after reduction. Accordingly, the femoral head obtained a rela-
tively better congruity. Severin et al.5 demonstrated by arthrography that the femoral head “squeezed into the socket” after 1–2 weeks following reduction. He speculated that a compressive force produced by the reduced head contributed to decrease the size of the interposition. In the present case, MRI clearly demonstrated that the interposing fat tissue reduced in size and synovial fluid disappeared as the head gained better congruity in the acetabulum. One of the mechanisms of the “squeezing mechanism” proposed by Severin might be explained by the shrinkage of the hypertrophied fat tissue and absorption of the synovial fluid.
References 1. Bos CFA, Bloem JL, Obermann WR, et al. Magnetic resonance imaging in congenital dislocation of the hip. J Bone Joint Surg Br 1988;70:174–8. 2. Johnson ND, Wood BP, Jackman KV. Complex infantile and congenital hip dislocation: assessment with MR imaging. Radiology 1988;168:151–6. 3. Johnson ND, Wood BP, Noh KS, et al. MR imaging anatomy of the infant hip. AJR 1989;153:127–33. 4. Krancy R, Prescher A, Botschek A, et al. MR-anatomy of infants hip: comparison to anatomical preparations. Pediatr Radiol 1991; 21:211–5. 5. Severin E. Congenital dislocation of the hip. J Bone Joint Surg Am 1950;32:507–18.