The wide spectrum of anatomic abnormalities that characterize hip dysplasia dictate the need for different reconstructive techniques when hip replacement is required. Multiple factors such as young age and high activity level of this patient population, coupled with the increased complexity of surgery, explain the somewhat elevated historical failure rate of hip arthroplasty in DDH and emphasize the need for careful analysis of each case and selection of the most appropriate reconstruction options. One particular problem specific to acetabular reconstruction is the deficient bone stock that may limit the ability to place the component fully on native bone at the true acetabular region. When standard techniques of reconstruction leave a significant portion of the component uncovered, the alternatives include acetabular augmentation with bone autograft, intentional high placement of the component, or medialization of the component with or without medial wall osteotomy. Uncemented sockets have provided promising midterm results with supplemental bone augmentation and are the authors’ preferred method of treatment for hips with moderate dysplasia and anterolateral acetabular bone deficiency.
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The wide spectrum of anatomic abnormalities that characterize hip dysplasia dictate the need for different reconstructive techniques when hip replacement is required.
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When standard techniques of reconstruction leave a significant portion of the component uncovered, the alternatives include acetabular augmentation with bone autograft, intentional high placement of the component, or medialization of the component with or without medial wall osteotomy.
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Uncemented sockets have provided promising midterm results with supplemental bone augmentation and are our preferred method of treatment for hips with moderate dysplasia and anterolateral acetabular bone deficiency.
Introduction
Developmental dysplasia of the hip (DDH) is the most prevalent developmental childhood hip disorder. Formerly known as congenital dysplasia of the hip, this condition encompasses abnormalities involving the growing hip, from minimal dysplasia to dislocation of the hip joint. Dysplastic hips share a common pathophysiology in which anatomic abnormalities subject the hip to increased contact stress leading to abnormal hip biomechanics, hip instability, impingement, associated labral pathologic condition, and eventually degenerative arthritis. Despite the availability of several nonarthroplastic alternatives, many patients with advanced hip dysplasia eventually require hip replacement surgery. Because of the unique characteristics of these patients, including young age and anatomic abnormalities of the hip, the failure rate after total hip arthroplasty (THA) in patients with DDH is higher than those in the general population. The specific alterations observed in the acetabulum usually include a shallow socket with bone deficiency anteriorly, laterally, and superiorly. Reconstruction during THA, particularly the location of the placement of the acetabular component defines the new center of hip rotation, which in turn influences hip biomechanics, leg length, and femoral reconstruction. This article reviews the different alternatives for the reconstruction of acetabulum during THA in patients with DDH.
Classification
Dysplastic hips can be characterized by the severity of anatomic abnormalities. Classification systems are useful for the assessment of patients and comparison of results using different treatments. The classification by Crowe and colleagues is the most common method to categorize the degree of dysplasia. In the original description, dysplastic hips were categorized radiographically into 4 groups based on the extent of proximal migration of the femoral head. The migration is calculated on an anteroposterior radiograph of the pelvis by measuring the vertical distance between the interteardrop line and the inferior head-neck junction. The amount of subluxation is the ratio between this distance and the vertical diameter of the undeformed femoral head. Thus, if the distance between the head-neck junction and the teardrop is half the vertical diameter of the femoral head, the hip is subluxated 50%. When the femoral head is deformed, the predicted vertical diameter of the femoral head was 20% of the height of the pelvis, as measured from the highest point on the iliac crest to the inferior margin of the ischial tuberosity ( Table 1 ). Because this system is based on the degree of displacement of the femoral head and does not define the acetabular abnormality, other classification systems, such as the Hartofilakidis classification, which divides congenital hip disease in adults into 3 categories: dysplasia, low dislocation, and high dislocation ( Table 2 ), have been proposed. The authors prefer using this classification system because it simply describes the acetabular deformity and is useful in determining the type of acetabular reconstruction that is required. In this system, each category is based on the relationship between the femoral head and the true or false acetabulum. With dysplasia, the femoral head, despite some degree of subluxation, is still contained within the original acetabulum. With low dislocation, the femoral head articulates with a false acetabulum that partially covers the true acetabulum and radiographically appears to be 2 overlapping acetabula; the inferior part of the false acetabulum is an osteophyte that begins at the level of the superior rim of the true acetabulum. With high dislocation, the femoral head migrates superiorly and posteriorly. The true acetabulum is inferior and anterior to the hollow in the iliac wing, with which the femoral head articulates, and may have the appearance of a false acetabulum.
| Group | Description |
|---|---|
| I | Subluxation <50% or proximal dislocation <0.1% of the pelvic height <10% |
| II | Subluxation 50%–75% or proximal dislocation of 0.1%–0.15% of pelvic height 10%–15% |
| III | Subluxation 75%–100% or proximal dislocation of 0.15%–0.20% of pelvic height 15%–20% |
| IV | Subluxation >100% or proximal dislocation of >0.20% of pelvic height >20% |
| Type | Description | Acetabular Deficiencies During Surgery |
|---|---|---|
| Dysplastic hip | The femoral head is contained within the original acetabulum despite the degree of subluxation |
|
| Low dislocation | The femoral head articulates with a false acetabulum that partially covers the true acetabulum to a varying degree |
|
| High dislocation | The femoral head is completely out of the true acetabulum and migrated superiorly and posteriorly to a varying degree |
|
Classification
Dysplastic hips can be characterized by the severity of anatomic abnormalities. Classification systems are useful for the assessment of patients and comparison of results using different treatments. The classification by Crowe and colleagues is the most common method to categorize the degree of dysplasia. In the original description, dysplastic hips were categorized radiographically into 4 groups based on the extent of proximal migration of the femoral head. The migration is calculated on an anteroposterior radiograph of the pelvis by measuring the vertical distance between the interteardrop line and the inferior head-neck junction. The amount of subluxation is the ratio between this distance and the vertical diameter of the undeformed femoral head. Thus, if the distance between the head-neck junction and the teardrop is half the vertical diameter of the femoral head, the hip is subluxated 50%. When the femoral head is deformed, the predicted vertical diameter of the femoral head was 20% of the height of the pelvis, as measured from the highest point on the iliac crest to the inferior margin of the ischial tuberosity ( Table 1 ). Because this system is based on the degree of displacement of the femoral head and does not define the acetabular abnormality, other classification systems, such as the Hartofilakidis classification, which divides congenital hip disease in adults into 3 categories: dysplasia, low dislocation, and high dislocation ( Table 2 ), have been proposed. The authors prefer using this classification system because it simply describes the acetabular deformity and is useful in determining the type of acetabular reconstruction that is required. In this system, each category is based on the relationship between the femoral head and the true or false acetabulum. With dysplasia, the femoral head, despite some degree of subluxation, is still contained within the original acetabulum. With low dislocation, the femoral head articulates with a false acetabulum that partially covers the true acetabulum and radiographically appears to be 2 overlapping acetabula; the inferior part of the false acetabulum is an osteophyte that begins at the level of the superior rim of the true acetabulum. With high dislocation, the femoral head migrates superiorly and posteriorly. The true acetabulum is inferior and anterior to the hollow in the iliac wing, with which the femoral head articulates, and may have the appearance of a false acetabulum.
| Group | Description |
|---|---|
| I | Subluxation <50% or proximal dislocation <0.1% of the pelvic height <10% |
| II | Subluxation 50%–75% or proximal dislocation of 0.1%–0.15% of pelvic height 10%–15% |
| III | Subluxation 75%–100% or proximal dislocation of 0.15%–0.20% of pelvic height 15%–20% |
| IV | Subluxation >100% or proximal dislocation of >0.20% of pelvic height >20% |
| Type | Description | Acetabular Deficiencies During Surgery |
|---|---|---|
| Dysplastic hip | The femoral head is contained within the original acetabulum despite the degree of subluxation |
|
| Low dislocation | The femoral head articulates with a false acetabulum that partially covers the true acetabulum to a varying degree |
|
| High dislocation | The femoral head is completely out of the true acetabulum and migrated superiorly and posteriorly to a varying degree |
|
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