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Introduction
  • Hip dysplasia is a disorder of abnormal development or dislocation of the hip secondary to capsular laxity and mechanical factors
  • Adult and adolescent dysplasia can come in two forms
    • dysplasia that was previously treated
    • dysplasia that was not treated
      • if left untreated it can progress to early arthritis
  • Pathoanatomy
    • acetabular retroversion is most common factor
  • Epidemiology
    • dysplasia is attributable to 1/3rd of all cases of hip osteoarthritis
Classification 
 
Crowe Classfication   
Grade Proximal displacement  Femoral head subluxation
I <10% vertical height of pelvis proximal migration of head neck junction from inter-teardrop line <50% of femoral head vertical diameter
II 10-15%  50-75%
III 15-20%  75-100%
IV  > 20%  >100%
 
Hartofilakidis Classification
Dysplasia (Type A) Femoral head within acetabulum despite some subluxation. Segmental deficiency of the superior wall. Inadequate true acetabulum depth.
Low dislocation (Type B) Femoral head creates a false acetabulum superior to the true acetabulum. There is complete absence of the superior wall. Inadequate depth of the true acetabulum.
High dislocation (Type C) Femoral head is completely uncovered by the true acetabulum and has migrated superiorly and posteriorly. There is a complete deficiency of the acetabulum and excessive anteversion of the true acetabulum.


Presentation
  • Symptoms
    • hip or groin pain, especially in flexion activities
    • often insidious onset
  • Physical exam
    • increased internal rotation before arthritis sets in
      • due to increased femoral anteversion
    • decreased internal rotation may represent osteoarthritis
    • increased external rotation with ambulation
    • positive anterior impingement test (pain with passive flexion, internal rotation and adduction)
    • may have instability with extension, abduction and external rotation
Imaging
  • Radiographs
    • recommended views
    •  
      • AP
      • lateral
    • findings
    •  
      • decreased femoral head sphericity
      • crossover sign
        • results from increased retroversion
      • acetabular protrusio
        • decreased lateral center-edge angle < 20°
        • angle between vertical line + line from femoral head to lateral acetabulum
        • assess on AP view
        • normal 25-40°
      • increased tonnis angle > 10°
        • angle between horizontal line + line along superior acetabulum
        • measures inclination of weightbearing zone
        • assess on AP view
        • normal 0-10°
      • decreased head-neck offset ratio
        • distance between line parallel to femoral neck through anterior femoral neck + anterior femoral head divided by diameter of femoral head
        • assess on lateral view
        • normal > 0.15
      • increased femoral neck-shaft angle 
        • angle created by anatomic axis of the femur and the femoral neck
        • coxa valga
      • decreased vertical center anterior margin angle (anterior center edge angle) 
        • obtained on false profile radiograph
        • angle between the vertical line through the center of the femoral head to the lateral acetabulum
        • assessment of anterior undercoverage
  • CT
    • useful in accessing structural abnormalities of the femoral head and neck
Treatment
  • Nonoperative
    • supportive measures
      • indicated as first line of treatment
  • Operative
    • periacetabular osteotomy +/- a femoral osteotomy
      • indications 
        • symptomatic dysplasia in an adolescent or adult with
        • concentrically reduced hip
        • congruous joint with good joint space
      • advantages
        • provides hyaline cartilage coverage
        • posterior column remains intact and patients can weight bear
        • preserves external rotators
        • delays need for arthroplasty
    • salvage pelvic osteotomy (chiari, shelf)
      • indications
        • unreduced hip
        • recommended for patients with inadequate femoral head coverage and an incongruous joint (a salvage procedure)
    • hip resurfacing
      • indications
        • can be used for Crowe type I or II disease
    • total hip arthroplasty (THA)
      • indications
        • treatment of last resort for those with severe arthritis
        • preferred treatment for older patients (>50) and those with advanced structural changes
        • in a patient with bilateral hip dysplasia, there are significant technical challenges that need to be addressed to ensure a successful total hip arthroplasty.
Surgical Techniques
  • PAO (Ganz, Bernese)  
    • technique
      • involves multiple osteotomies in the pubis, ilium, and ischium near the acetabulum. This allows improved three-dimensional correction of the acetabulum configuration. It is technically the most challenging
    • complication
      • complication rate as high as 15% in experienced hands
      • hip arthroplasty performed after PAO may lead to increased incidence of a retroverted acetabular cup
  • Shelf Osteotomy 
    • goal
      • to increase the weight bearing surface by placing extra-articular buttress of bone over the subluxed femoral head
      • cover femoral head with fibrocartilage (NOT articular cartilage)
    • technique
      • add bone to the lateral aspect of acetabulum. Depends on metaplastic (fibrocartilage) for successful results.
  • Chiari Osteotomy   
    • technique
      • make cut above acetabulum to sciatic notch and shift ilium lateral beyond edge of acetabulum. Depends on metaplastic bone (fibrocartilge) for successful results.
  • Total Hip Replacement
    • technique
      • may need trochanteric osteotomy to improve visualization in Crowe type III or IV patients
      • in a patient with bilateral hip dysplasia, there are significant technical challenges that need to be addressed to ensure a successful total hip arthroplasty
      • acetabular cup is ideally placed where the center of the true acetabulum would be
      • restoring the center of the hip may cause significant lengthening and require femoral shortening.
      • a high hip center can be used when there is inadequate bone stock in the acetabulum to achieve adequate host bone coverage. 
      • a modular femoral implant may be used for a dysplastic hip with significant rotational deformity. 
      • can use uncemented cup if there is less than 30% uncoverage 
Complications
  • Sciatic nerve palsies
    • 10 times increased incidence of sciatic nerve palsy (5-15%)
    • lengthening of greater than 4 cm can lead to sciatic nerve palsy that will present clinically as a foot drop. 
  • Hip Dislocation
    • increased risks of hip dislocation after arthroplasty (5-10%)
  • Periprosthetic femur fx
  • Infection
 

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