Presentation on theme: "Total Hip Replacements About 160,000 THRs performed every year 90% of all hip replacements need some sort of revision No. 1 reason for revision is loosening."— Presentation transcript:
Total Hip Replacements About 160,000 THRs performed every year 90% of all hip replacements need some sort of revision No. 1 reason for revision is loosening of the implant
Why Total Joint Replacement???
Cement vs. Cementless Characteristics
Bonding Time: Cemented vs. Cementless Cemented Approximately 10min Cementless One year for good ingrowth Up to two years for 100% of ingrowth bone (30% of the total porous surface) Cemented Approximately 10min Cementless One year for good ingrowth Up to two years for 100% of ingrowth bone (30% of the total porous surface)
Healing Time: Cemented vs. Cementless CementedCementless Weight bearing Next day with crutches Next day depending on stability Walk (crutches) 2 day after surgery 6-12 weeks depending on surgeon Pain Free 5 days in some cases Depends on stability Normal Walk 2 weeks (6 weeks with crutches is recommended) Couple of months to 1 year depending on ingrowth rate Everything good Around six months for a knee replacement 2 years onward
Loosening in Cemented THRs Loosening is caused by several factors Macrophage Phagocytosis of the bone cement Macrophage Phagocytosis of the bone cement Cement Disease – lytic erosions in bone Cement Disease – lytic erosions in bone Microcrack formation in the cement Microcrack formation in the cement All of these result in the spawning of bone cement particles
Abrasive Wear Particles from loose cement cause abrasive wear in the acetabular joint
Bone Cement Stabilization Three ways to try to stabilize bone cement 1) Replace Barium Sulfate component with a more biocompatible material 2) Add additional material to the cement to reinforce it 3) Mix the cement in a vacuum to reduce voids and stress concentrations
Barium Sulfate Substitutes Materials that are expected to promote bone growth, which assists in reinforcing the cement Examples Hydroxyapetite (HA) Hydroxyapetite (HA) Same material found in bone Tricalcium Phosphate Tricalcium Phosphate Good biocompatibility
Reinforcing Materials Reinforcing materials give the PMMA more attachment points which increases the strength of the bone cement Some examples include Glass Fibers Glass Fibers Carbon Fibers or Particles Carbon Fibers or Particles Metal fibers Metal fibers
Vacuum Mixing Vacuum mixing decreases voids in the bone cement which decreases stress concentrations within the hardened cement
Impaction Grafting Loose implant and cement is removed. Extremely thin bone is reinforced with wire mesh. Crushed bone chips are impacted into the canal.