Magnetic Resonance Imaging Evaluation of the Effects of Closed Reduction in Infants with Developmental Dysplasia of the Hip
Developmental dysplasia of the hip (DDH) is a common orthopedic condition in infants, characterized by abnormal development of the hip joint, which can lead to dislocation or subluxation of the femoral head. Early diagnosis and treatment are crucial to prevent long-term complications such as avascular necrosis and impaired mobility. Among the various treatment options, manual closed reduction has emerged as the most common and effective method, particularly for infants under 18 months old. This approach minimizes post-operative limitations in the range of motion of the hip joint and reduces the risk of iatrogenic avascular necrosis. To evaluate the therapeutic effects of closed reduction, magnetic resonance imaging (MRI) has proven to be a valuable tool, providing detailed insights into the structural changes in the hip joint post-surgery.
This study aimed to assess the efficacy of closed reduction in infants with DDH using MRI-based parameters, focusing on the acetabular labrum and the contents of the joint space. The study was conducted retrospectively and descriptively, involving 23 patients (4 males and 19 females) under 18 months old who underwent closed reduction surgery at the Third Affiliated Hospital of Southern Medical University between January 2016 and December 2017. All patients were scanned using a 1.5-T MRI scanner (Ingenia, Philips, the Netherlands) with the femurs positioned at an abduction angle of 60°. Clear and qualified MRI data were collected within one week before and after the surgery.
The MRI-based parameters used in this study included the labral angle (LA) and the zone of compressive force (ZCF). The LA is the angle between the labrum and the acetabulum, measured by drawing a horizontal line (Line H) through the superior aspect of the triradiate cartilage, a second line through the bony margin of the acetabulum, and a third line (Line A) representing the direction of the labrum, which is the midline between the inner and outer appendages (points B and C) and the distal apex. The ZCF is a zone determined by drawing a line perpendicular to Line H, tilted inward 16° (the resultant force of partial body weight and the abductor muscle group), and passing through the center of the femoral head. This zone is used to assess the relationship between the affected hip and the compression force acting on it. The upper part of the acetabular bone is divided into three equal areas, numbered as 2, 3, and 4, with zone 1 consisting of the labrum alone. All parameters were measured three times on proton-density-weighted spectral pre-saturation attenuated inversion recovery sequences by two radiologists with over 10 years of experience, and the results were averaged.
The study classified the post-operative conditions of the patients into three categories based on MRI results: concentric reduction, near reduction, and mild subluxation. Concentric reduction was defined as the complete alignment of the femoral head within the acetabulum, near reduction as partial alignment, and mild subluxation as slight misalignment. The results indicated that eight cases achieved complete concentric reduction, eight cases experienced near reduction, and seven cases displayed mild subluxation.
In cases of concentric reduction, the LA values were all less than 0° (average -15°), and all ZCF measures were located in area 3, with transverse acetabular ligaments observed. For near reduction, the LA values were also less than 0° (average -4.5°), with ZCF measures distributed across areas 2, 3, and 4. Transverse acetabular ligaments and fibrous tissue were observed in the hip joint space. In cases of mild subluxation, the average LA value was 1°, with ZCF measures located in areas 3 and 4. Transverse acetabular ligaments, iliac ligaments, and fibrous tissue were embedded within the hip joint gap.
The study demonstrated that MRI could effectively evaluate the curative effects of closed reduction in infants with DDH. The findings suggested that most patients achieved concentric or near reduction, with no significant sequelae or movement defects observed during follow-up surveys. The lower the post-operative LA value, the better the surgical outcome, indicating that the labrum returned to a more normal position after reduction. The epiphyses of the femoral heads were mostly located in area 3 of the ZCF, which is considered the optimal position relative to the acetabulum. If area 3 could not be reached, it was preferable for the femoral head to be located in area 4 rather than area 1 during restoration.
The study also highlighted the importance of analyzing the contents of the joint space via MRI, particularly in cases of refractory or complicated DDH. Materials embedded in the joint space, such as transverse acetabular ligaments, iliac ligaments, and fibrous tissue, could cause reduction failure. By identifying these materials, clinicians can determine the most suitable treatment approach for each patient.
In conclusion, this study demonstrated that MRI is a valuable tool for evaluating the therapeutic effects of closed reduction in infants with DDH. The use of MRI-based parameters, such as LA and ZCF, provided detailed insights into the structural changes in the hip joint post-surgery, helping clinicians assess the success of the procedure and identify potential complications. The findings supported the use of closed reduction as an appropriate method for treating DDH in infants, with most patients achieving favorable outcomes and minimal long-term complications.
doi.org/10.1097/CM9.0000000000001269
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