Acetabular dysplasia

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Acetabular dysplasia is referred to as a shallow acetabulum, not being able to provide sufficient coverage for the femoral head and thus leading to instability of the hip joint.

Terminology

Acetabular dysplasia is a form of developmental dysplasia of the hip (DDH) often referred to in the adolescent and adult population .

Epidemiology

Adult hip dysplasia has an estimated prevalence of 0.1% and is more common in women . Male sex is apparently associated with posterosuperior deficiency .

Risk factors

Risk factors for acetabular dysplasia include the following :

Clinical presentation

Patients usually present with hip pain or groin pain especially with extreme positions e.g. high hip flexion and hyperextension. In addition, there may be limping or signs and symptoms of hip instability . Clinical signs include a positive anterior apprehension test and/or anterior impingement tests .

Complications

25-50% of patients with acetabular dysplasia will develop early hip osteoarthritis if left untreated .

Other complications include:

Pathology

Acetabular dysplasia is characterized by a smaller weight-bearing surface than the normal acetabulum, which ultimately leads to increased contact stress and static overload due to under-coverage of the femoral head and to structural instability. This adds to cartilage and/or labral injury as well as damage to the joint capsule .

Etiology

Acetabular dysplasia might be the result of abnormal growth after treatment or missed developmental dysplasia of the hip during childhood, the etiology of which is multi-factorial in nature. It may be also due to other hip pathologies that have occurred during childhood as septic arthritis, trauma or Legg-Calve-Perthes disease .

Subtypes

Acetabular dysplasia can be divided into different patterns with respect to the 3-D morphology. One grading scheme subdivides the acetabular dysplasia into the following patterns with lateral acetabular deficiency being constantly present :

  • global acetabular deficiency
  • anterosuperior acetabular deficiency
  • posterosuperior acetabular deficiency

Other schemes differentiate anterior, posterior and global or lateral deficiencies .

Associations

Acetabular dysplasia is associated with the following conditions :

Radiographic features

Radiographic assessment of acetabular dysplasia or adult hip dysplasia includes plain radiographs of the pelvis and additional planes as the false profile view of Lequesne, cross-table lateral or frog-leg lateral views.

Cross-sectional imaging is advised for better three-dimensional characterization, preoperative planning and the detection of chondral and labral lesions.

Plain radiograph

The most common measurement in acetabular dysplasia is the lateral center-edge angle on a plain anterior-posterior radiograph of the pelvis .  Patients should be in the supine position with both legs in 15° of internal rotation to maximize femoral neck length .

A value of ≤25° is considered abnormal or borderline and a value of ≤20° as an indicator for dysplasia . The cut-off should be also adapted to the measurement and whether the lateral bony acetabular rim or the lateral edge of the acetabular sourcil was taken to measure the lateral center-edge angle .

Further measurements to confirm insufficient acetabular coverage are the following :

CT

The main role of CT is improved characterization of the three-dimensional acetabular morphology in a setting of preoperative planning. It should also comprise the assessment for excessive acetabular anteversion or acetabular retroversion. Other than the crossover sign on the anterior-posterior view of the pelvis, CT can also differentiate posterior under-coverage in the setting of acetabular dysplasia from anterior overcoverage in the setting of pincer morphology or plain acetabular retroversion and it can better assess the grade of posterior deficiency than the posterior wall sign .

CT measurements for the assessment of acetabular dysplasia include the following and are conducted one cut above the greater trochanters :

MRI

In addition to the three-dimensional assessment of the acetabular and femoral morphology, which highly benefits from 3D imaging in this situation, MRI allows for assessment of concomitant labral, chondral or ligamentum teres injury as well as the evaluation of the joint capsule .

Radiology report

The radiological report should include the description of the following :

Treatment and prognosis

Treatment options of acetabular dysplasia include in particular periacetabular osteotomy and other acetabular osteotomies (e.g. Salter) which reorient the acetabulum in a fashion that it provides better coverage for the femoral head. Other surgical options are acetabuloplasties, that alter the morphology of the acetabulum (e.g. Pemberton) . Periacetabular osteotomy is in particular indicated in patients with a preserved range of motion.

Salvage osteotomies (e.g. Chiari or shelf osteotomy) do not preserve articular cartilage and can be considered if the hip needs to be stabilized in incongruous joints .

In case of a severely arthritic hip, joint replacement surgery might be considered and include total hip replacement and resurfacing arthroplasty .

The role of conservative management is limited due to the early progression to osteoarthritis and should decrease pain and can be chosen in very mild dysplasia with mild symptoms.  Non-operative treatment includes weight loss, activity and lifestyle modifications as well as nonsteroidal anti-inflammatory drugs, specialized physical therapy intra-articular injections .

Treatment complications

Operative complications include the following:

Differential diagnosis

See also