Hip Resurfacing - Recon

Introduction

History
- prior versions of resurfacing failed in the past due to
  - larger femoral head on polyethylene -> increased volumetric wear -> high osteolysis rate
- modern resurfacing techniques (approved by FDA in 2006) have made the following changes
  - metal-on-metal components
  - larger femoral head
- very popular 10 years ago particularly in younger patients due to less femoral bone resection

Indications

Indications (controversial)
- patients with advanced arthritis and good proximal femoral bone stock
  - best outcomes in younger males with good bone stock
- patients with proximal femoral deformity making total hip arthroplasty difficult
Contraindications
- absolute
  - bone stock deficiency of the femoral head or neck
    - e.g., cystic degeneration of the femoral head
- relative
  - coxa vara
    - increased risk for neck fractures
  - significant leg length discrepancies
    - resurfacing does not allow leg length corrections
  - female sex of child bearing age (controversial)
    - due to fact that metal ions can cross placenta
  - renal failure
    - functional kidneys required to excrete metal ions

Advantages & Disadvantages

Advantages
- preservation of femoral bone stock
- better stability compared to standard small head (22- to 32-mm) THA
- improved restoration of hip biomechanics with lower risk of limb length discrepancy
- revision may be easier than an intramedullary THA
Disadvantages
- lack of modularity with inability to adjust length or correct offset
- requires larger exposure than conventional THA

Outcomes

Variable outcome findings in the literature (79% to 98% success rate)
Better results found in patients young, larger males with excellent bone stock treated for osteoarthritis than for dysplasia or osteonecrosis
Some case series have shown survival comparable to conventional THA, while others have reported higher rates of early revision
- some products have been removed from the market due to early failure
More recent prospective trials have shown few differences between resurfacing and THA

Complications

Periprosthetic femoral neck fracture
- incidence of 0% to 4% (more common than in THA)
- most common early complication (within first 3 years) and frequent cause for revision in acute post-operative period (<20 weeks)
- mechanism thought to be related to osteonecrosis
- fracture pattern
  - vertical fracture line from neck down to lesser trochanter
- risk factors
  - femoral neck notching
    - prevent by placing implant in slight valgus (rather than slight varus)
  - osteoporotic bone
  - large areas of preexisting AVN
  - femoral neck impingement (from malaligned acetabular component)
  - female sex
  - varus positioning of femoral component
- presents as groin pain
- treatment
  - convert to a primary THA
  - place cerclage wire above lesser trochanter to prevent fracture propagation during stem insertion
Implant loosening (aseptic)
- early loosening of the cemented femoral resurfacing component
Heterotopic ossification
- higher incidence of heterotopic ossification compared to THA (from wider exposure)
Metallosis
- may have elevated metal ion levels (cobalt, chromium, and cobalt-chromium ratio)
- found in blood and urine from metal debris
- presentation and laboratory values may mimic infection
  - may present with elevated synovial WBC due to metal debris and corrosion
- most cases related to edge loading of the implant
Dislocation
- risk is <1% (lower than conventional THA)
Pseudotumor
- risk
  - metal-on-metal implants (like resurfacing)
  - young
  - female sex
- may be asymptomatic
- symptomatic patients require revision surgery