Introduction

• Hip dysplasia is the underlying diagnosis in a large number of young patients with hip dysfunction.  It is the underlying diagnosis in up to 48% of patients requiring THA for coxarthrosis.
• The additive anomalies of the dysplastic hip concentrate high forces (increased body weight lever arm due to relative hip COR lateralization) over smaller contact areas (due to poor coverage of the femoral head).
• Abnormally high stresses may lead to premature joint destruction. 
• Typical femoral deformities
  • Short, valgus neck
  • Excessive anteversion
  • Posteriorly displaced GT
  • Very stenotic femoral canal 

• Typical pelvic deformities
  • Shallow socket
  • Anteverted (although 1 in 6 may be retroverted)
  • Lateralized hip COR
  • Anterior and lateral (superior) deficiency

Diagnosis

Plain XR

• AP Pelvis
  • Assess for degenerative changes, version, joint congruency, and dysplasia on both the femoral and acetabular side
• False Profile View (Faux Profil)
  • Assess the anterior center-edge angle
• Abduction view (leg in neutral rotation)
  • Assess joint congruency, coverage improvement offere
• Plain XR Evaluation
• Acetabular Index of the Weightbearing Zone [aka the Tönnis angle, aka the horizontal toit externe (HTE) angle]
  • Formed by a line parallel to the weightbearing surface of the acetabulum and a horizontal line.
• Tönnis Classification of Osteoarthritis by Radiographic Changes
  • Grade 0: No signs of OA
  • Grade 1: Increased sclerosis, slight joint space narrowing, no or slight loss of head sphericity
  • Grade 2: Small cysts, moderate joint space narrowing, moderate loss of head sphericity
  • Grade 3: Large cysts, severe joint space narrowing, severe deformity of the head
• Lateral center-edge angle (of Wiberg)
  • Formed by the line CE joining the center of the femoral head to the lateral edge of the acetabulum and a vertical line LC through the center of the head.
  • Normal CEA is > 25 degrees. 20 - 25 degrees is borderline, and < 20 degrees is diagnostic of DDH
• Anterior Center-Edge Angle (de Lequesne et de Seze)
  • The anterior center-edge angle as described by Lequesne and de Seze is shown. It represents a true lateral of the socket and allows assessment of the degree of femoral head anterior (un)coverage.
  • Values are same as the CEA on the AP pelvis. Normal is > 25 degrees, less than 20 degrees is indicative of DDH, and 20 - 25 degrees is borderline. 
  • Values less than 10 degrees are normal. As the value rises above 10 degrees, the hip is more dysplastic.

Nonarthroplasty Options

• Arthroscopy
  • Rule out acetabular version problems
  • Minimal dysplasia
  • Mechanical symptoms
  • Loose bodies, labral tears
  • Incompletely studied, few patients meet strict criteria
• Osteotomy
  • General Indications:
  • Young, symptomatic patients
  • Relatively little proximal migration of COR
  • Relatively well-preserved motion
  • Tönnis Grade 2 or less XR changes
• Pelvic Osteotomy
  • The primary site of deformity is on the acetabular side, and should be the site of correction.
  • Salvage (head coverage is not hyaline cartilage)
• Shelf Procedure
  • Chiari medial displacement osteotomy
  • Reconstructive (hyaline cartilage head coverage)
• Innominate Osteotomies
  • Single, double, triple
• Spherical periacetabular
  • Wagner, Ninomiya
  • Bernese periacetabular (PAO)- Ganz
  • Advantages: Other options
    • Extra-articular cuts
    • Preserved blood supply
    • Intact posterior column
    • Abductor-sparing
    • Can correct anterior and lateral deficient coverage
    • Medialization hip COR
  • Goal Correction:
    •  Medialize head to within 1 cm of ilioischial line
    • Tönnis angle < 15 degrees
    • Anterior and lateral CEA greater than 20 degrees
    • Anteverted socket
• Femoral Osteotomy
  • Less often the primary site of deformity. The ideal candidate has a spherical, congruent head; a valgus neck-shaft angle; and minimal acetabular involvement.
  • Look closely for poor anterior coverage on the false profile view, as minimal correction can be achieved through extension on the femoral side.
• Varus-producing osteotomy
  • Limit correction to no more than 20 - 25 degrees due to concomitant limb shortening and abductor weakness.
• Valgus-producing osteotomy
  • Indicated in patients with large, elliptical heads and large inferomedial osteophytes known as "capital drop" osteophytes (Bombelli). Must have improved congruency demonstrated on adduction views.
•  Arthrodesis
  • If not a candidate for osteotomy or THA
  •  Contra-indicated in: morbid obesity, systemic arthritis, contralateral hip disease, LS spine disease, or ipsilateral knee problems (arthritis, instability, deformity).
• Resection Arthroplasty
• Total Hip Arthroplasty

Crowe Classification

• Used to describe the degree of proximal migration of the femoral head
• first, measure the height of the femoral head
• When the head is deformed, take 20% of the total pelvic vertical height as the estimation of femoral head height.
• Next, measure the distance from the inter-teardrop line to the inferomedial head-neck junction
• Then, divide that distance by the femoral head height
• example: If the head is 40 mm and it has migrated 20 mm proximally (20/40), then the head has migrated 50%.
  • Crowe I: Up to 50% subluxation
  • Crowe II: Between 50 and 75% subluxation
  • Crowe III: Between 75 and 100% subluxation
  • Crowe IV: Beyond 100% subluxation (superior dislocation) 

Treatment Options

These are, of course, very broad recommendations not applicable to every case!

• Crowe I Hips
  • Socket: True hip center
  • Femur: Component, fixation of choice
  • Approach: Surgeon preference
• Crowe IV Hips
  • Socket: True hip center, small component
  • Femur: Shortening subtrochanteric osteotomy from a posterior approach; or, transtrochanteric osteotomy with sequential proximal femoral shortening and GT reattachment
• Crowe II - III Hips Femur: Based on femoral morphology and patient
  • Socket Options:
  • Go for an uncemented hemisphere near the true hip center. If this is not sufficiently supported . . .
  • Medialize into the pelvis (acetabuloplasty)
  • Structural femoral head autograft
  • High hip center
  • Approach: Variable, based on planned reconstruction and need for femoral shortening.
• Results
  • Cemented stems have outperformed cemented sockets in patients with DDH.
  • Placement of the socket outside of the true hip center has been shown to result in higher failure rates of both cemented sockets and stems. The use of autograft femoral head does appear to provide initial implant support and lasting restoration of bone stock, particularly when paired with uncemented implants.
  • Longer-term follow-up of uncemented THA in patients with DDH is needed.

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