Courtesy: Dr D Padgett, Ashok Shyam TV, Ortho
Limitations of Cemented Fixation
-
Cement fatigue fractures may:
-
Lead to implant loosening
-
Contribute to particle-induced osteolysis
-
-
Certain patient groups historically performed poorly with cemented fixation:
-
Heavy, highly active males
-
-
Ideal goal:
-
Direct bone–implant fixation
-
Avoidance of an intermediary cement layer
-
Elimination of a second mechanical interface
-
Biologic Fixation: Mechanism
Biologic fixation resembles fracture healing:
-
Mesenchymal cell infiltration
-
Woven bone formation
-
Remodeling into mature lamellar bone
Three Essential Requirements for Successful Bone Ingrowth
-
Intimate bone–implant contact
-
Appropriate implant surface texture
-
Immediate rigid stability at implantation
Failure to meet these principles may result in:
-
Fibrous tissue formation
-
Poor osseointegration
-
Early failure
Early Cementless THA: Lessons Learned
Initial cementless designs (including early-generation systems):
Acetabular Component (Socket)
-
Line-to-line reaming technique
-
Routine use of supplemental screw fixation
-
High fixation rates at 10–15 years (~96%)
However, failures occurred due to:
-
Polyethylene wear
-
Inferior locking mechanisms
-
Backside wear
-
Particle-induced osteolysis
Femoral Component (Stem)
Early-generation stems:
-
Proximally porous-coated
-
Limited coating (patch coating)
-
Designed to reduce stress shielding
Problems encountered:
-
Suboptimal fixation with limited coating
-
High intraoperative fracture rates
-
Variable fixation outcomes
-
Loosening with or without radiographic instability
-
Contributing factor: poor-quality polyethylene during that era
Modern Cementless THA (Contemporary Era)
Improvements Achieved
-
Highly crosslinked polyethylene
-
Improved locking mechanisms
-
More advanced implant surface textures
-
Better instrumentation and surgical techniques
Current Acetabular Preparation Strategy
-
1–2 mm under-reaming
-
Press-fit cup insertion
-
Reduced reliance on supplemental screws
Technique-Related Failures (Surgeon-Controlled Factors)
Three key issues impacting outcomes:
-
Incomplete cup seating
-
Malposition of the implant
-
Iatrogenic periprosthetic acetabular fracture
Incomplete Seating
-
Occurs when the cup is not fully engaged
-
More common with less stiff shell designs
-
Liner–shell mismatch or improper seating may occur
-
Reported rates up to ~10% in some reviews
Malpositioning Consequences
-
Abnormal load distribution on bearing surfaces
-
Increased stress on liners
Specific concerns:
-
Crosslinked polyethylene has lower ultimate tensile strength
-
Fatigue fractures have been reported
-
High abduction angles in metal-on-metal bearings:
-
Associated with early and accelerated wear
-
Under-Reamed Socket Risks
Advantages:
-
Achieves press-fit fixation
-
Often eliminates need for screws
Risks:
-
Dependent on intact cortical bone
-
Risk of iatrogenic acetabular fracture
-
Often related to excessive force or improper preparation
Modern Femoral Stem Considerations
Positive Developments
-
Improved porous surface textures
-
More extensive coating
-
Better instrumentation systems
Technical Principles for Stem Fixation
-
Thorough knowledge of the implant system
-
Careful bone preparation
-
Strict axial alignment
Why Alignment Matters:
-
Prevents varus/valgus malposition
-
Reduces risk of:
-
Cortical perforation
-
Intraoperative fracture
-
Implant subsidence
-
Intraoperative Best Practices
-
Maintain lateralization during preparation
-
Respect femoral cortical dimensions
-
Test broach stability with rotational torque
-
Avoid excessive malleting to compensate for poor preparation
-
Insert implant only after adequate canal preparation
Avoiding Complications
-
Do not over-ream or over-manipulate bone
-
Prevent unrecognized fractures
-
Assess initial stability carefully
Key principle:
Initial mechanical stability ? Predictable long-term biologic fixation
Clinical Take-Home Messages
-
Cementless fixation can be highly successful when biologic principles are respected
-
Implant design has improved significantly, but technique remains critical
-
Most modern failures are technique-related and preventable
-
Attention to detail determines success in cementless total hip arthroplasty
Leave a Reply