Total Hip Arthroplasty (THA)

Indications

• end-stage degenerative joint disease of the hip, which may result from 1º or 2º OA, AVN and inflammatory arthropathies such as RA
• most authors agree that conservative measures should be tried for 6 months before surgery is recommended
• goals of THA are similar to those of TKA

Types of Hip Arthroplasty

Surgical Approaches

• Lateral (Hardinge)
  • direct approach to the hip with excellent acetabular exposure & low dislocation rate
  • no true internervous plane: fibers of the gluteus medius & vastus lateralis muscles are split in their own line to gain access to anterior face of the hip joint
• Posterior (Moore) a.k.a. Southern Approach
  • acetabular visualization more difficult and higher dislocation rate, but is rarely associated with a post-operative limp
  • no true internervous plane: gluteus maximus split along its fibers

Prosthesis Design

• Acetabular Component
  • composed of a polyethylene cup with metal backing
  • “metal-on-metal” implants consist of a cobalt-chromium
    metal cup or ceramic cup designed to reduce particle
    shedding and osteolysis
  • fixation achieved via PMMA cement, spikes, screws or
    press fit with porous surface for bony ingrowth
• Femoral Component
  • consists of a metal femoral stem (cobalt-chromium or
    titanium alloy) and a metal or ceramic femoral head
  • fixation achieved via PMMA cement or press fit with a
    porous surface for bony ingrowth

PEARL optimal femoral head size of 26-28 mm minimizes wear (>6 mm of polyethylene insert is ideal) while not increasing dislocation risk secondary to small head size

Technical Goals

• femoral component should be in neutral position avoiding excessive valgus or varus angulation
• lateral inclination of acetabular cup 35-45º, 15º anteversion

Complications

• Immediate:
  • improper component placement (varus alignment) or increased acetabular cup inclination
  • dislocation: pts. should avoid combinations of excessive flexion, IR & adduction or excessive extension, ER & adduction
  • nerve injury: sciatic (80%), femoral or obturator
  • infection ? septic loosening (rates vary from 1- 2% depending on centre)
• Long-term:
  • aseptic loosening that causes pain (most common)
  • implant failure/periprosthetic fracture
  • heterotopic ossification

PEARL S. aureus is the most common infecting organism in all orthopaedic procedures, but S. epidermidis is the most common when prostheses are involved

Bipolar Hip Replacement

• cemented hemiarthroplasty in which the acetabular component is free to move within the native acetabulum
• most often indicated in the elderly population after suffering a femoral neck fracture that has compromised the vascular supply of the femoral head

Hip Resurfacing (Birmingham)

• metal-on-metal THA that involves capping the femoral head to preserve bone of the proximal femur for subsequent hip replacements
• intended for younger people with advanced hip disease who would otherwise receive and likely outlive a conventional primary total hip replacement
• no long-term outcome data exists and there is a concern of the possible absorption of circulating metal degradation products

Attachments:

THR Components.jpg (image/jpeg)


Birmingham THA.jpg (image/jpeg)