Adult Dysplasia of the Hip - Recon

Introduction

Overview
- hip dysplasia is a disorder of abnormal development resulting in a shallow acetabulum with lack of anterior and lateral coverage
  - treatment typically involves periacetabular osteotomies (PAO) for those with concentrically reduced hips with congruous joint space and THA for those presenting with end stage osteoarthritis (OA)
Epidemiology
- incidence
  - US: 3-5%
  - estimated that 10% of all THA are performed as a result of dysplasia
Demographics
- females > males
- 2-4x relative risk increase
Risk factors
- breech presentation, female sex, primiparity, and family history
Pathophysiology
- abnormal movement of the femoral head within the acetabulum due to both osseous and soft tissue abnormalities
- leads to overload of the acetabular rim leading to secodnary OA
Associated conditions
- increased femoral anteversion, coxa valga, head-neck junction deformitites, femoral head asphericity, hypoplasia of the femoral intramedullary canal, posterior displacement of the greater trochanter
Prognosis
- 48% of THA in patients <50-years-old are a result of dysplasia

Anatomy

Acetabulum
- normal anteversion 15°, abduction 45°
Proximal femur
- femoral head
  - center of the femoral head should be at level of the greater trochanter
- proximal femur
  - normal femoral neck anteversion: 15° relative to the femoral condyles
  - normal neck shaft angle: 125°

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 with insidious onset
  - exacerbating activitis include hip flexion or external rotation in weight bearing stance
- lateral hip pain and a limp or Trendelenburg gait may occur with abductor fatigue
Physical exam
- insepction
  - evaluation of gait; abductor fatigue or Trendelnburg sign
  - overall ligamentous laxity; Beighton score
- motion
  - increased internal rotation with the hip in flexion
    - increased femoral anteversion
- provocative tests
  - anterior apprehension sign
    - lateral decubitus position, hip placed in extension as examiner applies progressive external rotation and adduction
    - positive with apprehension and/or pain
  - prone external rotation tests
    - anterior-directed force on the posterior greater trochanter

Imaging

Radiographs
- recommended views
  - AP
  - lateral
  - false-profile view
- findings
  - asphericity of the femoral head
  - coxa valga (increase neck-shaft angle)
  - narrow femoral canal
- measurements
  - lateral center-edge angle (LCEA) of Wiberg
    - assesses superolateral coverage of the femoral head on the AP view
    - angle between a verticle line through the center of the femoral head and the acetabular edge
    - dysplastic: <20°
    - 20-25° "borderline"
    - 25-39° normal
  - Tonnis angle
    - inclination of the weight bearing portion of the acetabulum
    - angle formed between the horizontal and a line along the superior acetabulum
    - evaluated on the AP view
    - dysplastic: >10°
    - normal: <10°
  - anterior center-edge angle of Lequesne
    - assesses anterior coverage of the femoral head
    - angle created between a vertical line through the center of the femoral head and the lateral acetabulum
    - evaluated on the false-profile view
    - dysplastic: <20°
    - normal 25-40°
    - >40° indicative of femoroacetabular impingement (FAI)
  - Femoro-Epiphyseal Acetabular Roof (FEAR) index
    - angle formed between the horizontal portion of the central proximal femoral physeal scar and the acetabular index
    - evaluated on the AP view
    - FEAR index <5° indicative of a stable hip not requiring treatment
CT
- indications
  - preoperative planning
  - should only be ordered by treating surgeon
- findings
  - adequate assessment of acetabular and proximal femoral osseous morphology including excessive anteversion or retroversion
    - distal femur should be included in patients with clinical signs of femoral anteversion
    - diameter of femoral canal may be over-estimated on AP radiographs and underestimated on lateral radiographs due to rotational mismatch of the metaphysis and diaphysis

Prevention

Identification and prevention of infantile developmental dysplasia (DDH)
- Pavlik harness, closed and open reductions, spica casting, proximal femoral osteotomies

Treatment

Nonoperative
- supportive measures
  - role of long-term nonsurgical management in symptomatic dysplasia is limited given premature progression of secondary OA
Operative
- hip arthroscopy
  - indications
    - controversial
    - adjunct procedure to PAO for enhanced visualization and management of chondral, labral and proximal femoral cam-type lesions
    - contraindicated in the setting of moderate to severe dysplasia
  - outcomes
    - chondral and labral pathology is a sequelae of osseous instability and may recur or progress if underlying pathology is not corrected
      - associated with accelerated progression of arthritis, hip subluxation, less functional improvement, as well as increased risk of surgical failure and reoperation
- periacetabular osteotomy (PAO)
  - indications
    - symptomatic dysplasia in an adolescent or adult with a concentrically reduced hip and congruous joint space
    - preserved range of motion
    - intraoperative dynamic testing of hip motion is needed to determine the need for femoral osteotomy
      - minimum of 90° flexion and 15° internal rotation to prevent FAI
  - advantages
    - provides hyaline cartilage coverage
    - preserved integrity of the posterior column, which allows patients to weight bear as tolerated postoperatively
    - large multidirectional corrections
    - preserves external rotators
    - delays need for arthroplasty
  - outcomes
    - reliably improves radiographic parameters and symptomatology
    - 92% survivorship at 15 years in avoiding THA
- salvage pelvic osteotomy (Chiari, Shelf)
  - indications
    - unreduced hip
    - recommended for patients with inadequate femoral head coverage and an incongruous joint (a salvage procedure)
  - outcomes
    - 84% survivorship at 17 years with advanced OA as an endpoint
    - advanced DDH and asphericity of the femoral head associated with poor outcomes
- hip resurfacing
  - indications
    - can be used for Crowe type I or II disease
  - outcomes
    - unable to address leg-length discrepancy
    - 10% revision rate at 6 years
    - higher revision and complication rate with hip resufracing in patients with DDH compared to general population
- total hip arthroplasty (THA)
  - indications
    - treatment of choice for patients with end-stage OA secondary to dysplasia
    - may need small acetabular components
  - outcomes
    - improves Harris Hip scores and pain
    - outcomes for Crowe I and II patients are in similar to those of THA for primary OA in the short term
      - revision rates for Crowe III and IV are higher than non-dysplastic hips
    - long term follow up demonstrates a higher revision rate for THA in dysplastic hips
    - increased complication profile: infection, instability and neruovascular injury
      - risk of sciatic nerve injury if limb length changed by >4cm
      - may need to perform femoral shortening (trochanteric or subtrochanteric)

Techniques

Supportive measures
- technique
  - weight loss, NSAIDs, activity modification, intra-articular injections
Hip arthroscopy
- technique
  - should not be performed in isolation as it does not treat underlying pathologic cause
  - hip arthroscopy performed concomitantly with PAO to address labral pathology or evaluate for chondral injuries
    - if significant chondral injury is identified, PAO can be abandoned with minimal morbidity
    - continues to be controversial
Periacetabular osteotomy (PAO) (Ganz, Bernese)
- approach
  - modified Smith-Petersen
- technique
  - involves osteotomies in the pubis, ilium, and ischium near the acetabulum
  - allows significant three-dimensional correction of the acetabulum
- complications
  - hip arthroplasty performed after PAO may lead to increased incidence of a retroverted acetabular cup
Salvage Osteotomies
- Chiari Osteotomy
  - technique
    - make cut above acetabulum to sciatic notch and shift ilium lateral beyond the edge of acetabulum
    - depends on metaplastic bone (fibrocartilge) for successful results.
  - complications
    - shortens limb
- Shelf Osteotomy
  - approach
    - modified Smith-Petersen
  - technique
    - places extra-articular buttress of bone to the lateral acetabulum over the subluxed femoral head
    - increases weight bearing surface
    - cover femoral head with fibrocartilage (metaplastic bone), not articular cartilage
Hip Resurfacing
- technique
  - posterior approach with release from the piriformis to the gluteus maximus tendon
    - partial gluteus maximus tendon release aids in exposure
  - unable to address limb length
- complications
  - postoperative femoral neck fracture
Total Hip Arthroplasty
- approach
  - anterior, lateral or posterior based approaches may be used
- technique
  - trochanteric osteotomy may be needed to improve visualization, especially in Croew type III or IV dysplastics
  - goal is to place the acetabular component in the true acetabulum to restore normal hip center of rotation and biomechanics
    - this may cause significant leg lengthening, which would subsequently require femoral shortening (trochanteric or subtrochanteric)
  - components may need to be medialized or used with augments to gain adequate coverage and stability of the acetabulum
    - can use uncemented cup if there is less than 30% uncoverage
  - a high hip center can be used to gain adequate bony stability, but is less ideal biomechanically
  - modular femoral components allow for correction of rotational deformities
- complications
  - increased risk of loosening with a high hip center
  - increased risk of neurovascular injury and infection

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
Nonunion
- 29% nonunion with greater trochanter osteotomy
- subtrochanteric osteotomy and trochanter advancement lowers nonunion rate
Hip Dislocation
- increased risks of hip dislocation after arthroplasty (5-10%), especially when high hip center is used
Component loosening
- placement of the acetabular component in a high hip position associated with increased risk of loosening
Periprosthetic femur fx
Infection