Replacing the Dysplastic Hip via the Direct Anterior Approach

John L. Masonis

Frederick Laude

J. Bohannon Mason

Mark Hood

Introduction

Developmental dysplasia of the hip (DDH) encompasses a wide spectrum of structural variants resulting from atypical hip development. Because of its impact early in hip development, significant bone deficiencies are frequent in both the acetabulum and the femur, which can often lead to leg length inequality and early structural failure of the native hip articulation, resulting in chondral demise and early-onset hip arthritis. This chapter is specifically directed at reconstruction of the dysplastic hip at the time of direct anterior approach (DAA) total hip arthroplasty (THA).

Optimal biomechanical reconstruction of the hip can be difficult in dysplasia due to acetabular size, acetabular bone deficiencies, acetabular version anomalies, femoral size, femoral bone deficiencies, and femoral version anomalies, in addition to chronic shortening of the limb and vital soft tissue structures surrounding the hip.

DDH presents multiple challenges of varying difficulty depending on the severity of the disease and the presence of the associated neurologic and musculoskeletal abnormalities. For this reason, it is imperative for the surgeon to perform a complete preoperative evaluation of the patient including the following:

Radiographic evaluation (standing anteroposterior pelvis, Dunn lateral view, standing full-length hip to ankle, and computed tomography or magnetic resonance imaging as needed)
Gait evaluation (with and without gait aids)
Skeletal maturation evaluation based on radiographs (physeal status)
Leg length evaluation (both radiographic and clinical)
Neurovascular evaluation (with particular attention to spasticity)

Classification of Hip Dysplasia

Total Hip Arthroplasty in Crowe I and II Developmental Dysplasia of the Hip

THA reconstruction in Crowe I and II DDH creates a spectrum of challenges primarily involving acetabular fixation and alignment (Table 30.1).

TABLE 30.1 Crowe Classification

Grade	Proximal displacement	Femoral head subluxation
I	<10% vertical height of pelvis	Proximal migration of the head-neck junction from interteardrop line <50% of femoral head vertical diameter
II	10%-15%	50%-75%
III	15%-20%	75%-100%
IV	>20%	>100%

Acetabulum

It should be noted that all DDH reconstructions frequently require small-diameter acetabular and femoral implants and that acetabular diameters below 45 mm can be common. Surgeon preparation for the microanatomy is paramount, and implant selection should be planned accordingly. It should also be noted in cases of high dislocation (Crowe III or IV) that the inferior border of the acetabulum, as indicated by the transverse acetabular ligament, will be significantly distal from the original capsular exposure (Figure 30.1).

FIGURE 30.1 A model of the hemipelvis illustrating the hip location in Crowe classification.

Acetabular bone deficiency in DDH is most commonly located superiorly/anteriorly. This deficiency can create fixation challenges for the surgeon when using cementless acetabular components. Preoperative radiographs, computed tomography, and digital templating can help the surgeon determine the volume of bone available for fixation in Crowe I and II cases. Frequently, medialization of the acetabular component by medial reaming in the anatomic hip center can help create a full acetabular rim for hemispherical fixation, which can effectively solve the need for bone or structural grafting of the acetabulum (Figures 30.2, 30.3 and 30.4).

FIGURE 30.2 Crowe I or II preoperatively.

FIGURE 30.3 Crowe I or II with THA, screws, and no augment.

FIGURE 30.4 Socket fixation without augmentation.

In cases with minimal retroacetabular bone volume, the ability to ream medially in the anatomic hip center is limited and the acetabular bone “hemisphere” is not feasible. When this situation occurs, a decision for augmentation of the dysplastic acetabulum needs to be made. Hemispherical titanium acetabular components have demonstrated a strong clinical history, including cases with limited bone contact. The location of the bone contact appears to be one critical factor in the initial stability of the acetabular component.

Opposing fixation (180° apart) leads to increased cup stability and is desirable in cases with dysplasia. In addition, supplemental screw fixation through the acetabular component can provide improved initial stability and is recommended in cases with reduced bone implant contact. When deciding on cup and screws versus augment, cup, and screws, the authors prefer to prepare the acetabulum using a reamer and then place a trial cup that is 1 mm larger than the last reamer. If the trial cup is “stable,” it will maintain its position with the weight of the insertion handle still attached when the surgeon removes their hands. This is referred to as the trial cup test. In this case, the authors prefer to use a hemispherical cup using the 1-mm press fit and screws to augment fixation. No additional graft or augment is required.

Cases of Crowe I or II acetabular deficiency and minimal retroacetabular bone volume frequently require augmentation of the acetabular fixation to achieve stability. For cases in which the trial cup test (described previously) fails, structural augmentation of the cup is required. Augmentation can be accomplished using either autologous bone graft or porous metal augments.

Autologous Bone Grafting for Acetabular Defect

Primary hip arthroplasty in cases of DDH provides the option of an autologous bone graft from the femoral head. In cases in which grafting is anticipated (Figure 30.5), care should be taken to avoid destruction of the femoral head at the time of the initial surgical exposure. The choice between autologous graft versus porous metal augments is surgeon driven, and both options have demonstrated excellent survivorship.¹^,²^,³

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