Residency · Residency · Orthopedic Surgery
Primary Total Hip Arthroplasty: Bearing Surfaces and Fixation
Introduction
Total hip arthroplasty (THA) is one of the most successful surgical procedures in modern medicine, reliably alleviating pain and restoring function in patients with end-stage hip disease. The selection of bearing surfaces and fixation methods remains a critical decision that influences implant longevity, complication rates, and patient outcomes. Understanding the biomechanical principles and clinical evidence behind these choices is essential for the orthopedic surgeon.
Indications for Primary THA
Osteoarthritis is the most common indication, accounting for over 70% of cases. Other indications include inflammatory arthritis (rheumatoid arthritis, ankylosing spondylitis), osteonecrosis of the femoral head, femoral neck fractures in physiologically active elderly patients, post-traumatic arthritis following acetabular or proximal femur fractures, and failed prior procedures such as hemiarthroplasty or internal fixation.
Bearing Surface Options
| Bearing Surface | Wear Rate | Key Advantages | Key Disadvantages | Current Status |
|---|---|---|---|---|
| Metal-on-HXLPE | ~0.05 mm/yr | Most widely used; excellent longevity; low cost | Polyethylene wear (reduced with HXLPE) | Gold standard |
| Ceramic-on-HXLPE | Lower than MoP | Scratch-resistant head; no metal ions | Cost of ceramic head | Preferred for younger/active patients |
| Ceramic-on-Ceramic | Lowest volumetric wear | No metal ions; lowest wear | Squeaking (1-10%); rare fracture; precise positioning needed | Used selectively |
| Metal-on-Metal | Low volumetric wear | — | ALTR; metal ions; pseudotumors | Largely abandoned |
Metal-on-Polyethylene (MoP)
Metal-on-polyethylene is the most widely used bearing combination in contemporary practice. Highly cross-linked polyethylene (HXLPE) has dramatically reduced wear rates compared to conventional polyethylene, with volumetric wear rates of approximately 0.05 mm per year versus 0.1 to 0.2 mm for conventional. The addition of vitamin E to HXLPE provides oxidative stability without sacrificing mechanical properties. Excellent long-term survivorship exceeds 95% at 15 to 20 years with modern HXLPE.
Ceramic-on-Polyethylene (CoP)
Alumina or alumina-zirconia composite (BIOLOX delta) femoral heads paired with HXLPE produce even lower polyethylene wear than cobalt-chrome heads due to the scratch-resistant ceramic surface. This combination eliminates concern for metal ion release from the femoral head and is preferred in younger, more active patients.
Ceramic-on-Ceramic (CoC)
Ceramic-on-ceramic has the lowest volumetric wear of any bearing combination. The risk of squeaking is reported in 1 to 10% of cases. The risk of catastrophic ceramic fracture is exceedingly rare with modern delta ceramics (less than 0.01%). This bearing does not produce metal ions, which is advantageous in patients with metal sensitivity. However, it requires precise component positioning to avoid edge loading and stripe wear.
Metal-on-Metal (MoM)
Metal-on-metal has been largely abandoned for primary THA due to adverse local tissue reactions (ALTR). It is associated with elevated cobalt and chromium ion levels, pseudotumor formation, and metallosis. Regulatory agencies have issued warnings, and it is no longer recommended for routine use.
Fixation Methods
Cementless (Press-Fit) Fixation
Cementless fixation is currently the most common fixation method in North America for both acetabular and femoral components. It relies on initial mechanical stability (press-fit or interference fit) followed by biological ingrowth. Porous coatings include titanium plasma spray, sintered beads, trabecular metal, and 3D-printed surfaces. Hydroxyapatite coating may accelerate bony ongrowth. This method is ideal for patients with adequate bone quality (Dorr type A and B femora).
Cemented Fixation
Cemented fixation uses polymethylmethacrylate (PMMA) to achieve immediate fixation. It is preferred for the femoral component in elderly patients with osteoporotic bone (Dorr type C). Modern cementing techniques include pulsatile lavage, retrograde cement insertion, distal plug, and cement pressurization. Third-generation cementing techniques have improved long-term survivorship. Cemented acetabular components have fallen out of favor due to higher loosening rates compared to press-fit cups.
Hybrid Fixation
Hybrid fixation combines a cementless acetabular component with a cemented femoral stem. This is common practice in European registries, particularly for elderly patients, and produces excellent long-term results in registry data from Sweden, Norway, and the United Kingdom.
Femoral Stem Design Considerations
The 12/14 taper is the most common taper geometry, with trunnion corrosion being a recognized concern with larger-diameter heads. Stem geometry options include tapered-wedge designs (such as the Corail) and fully coated cylindrical stems (such as the AML). Modularity allows intraoperative adjustment of offset, length, and version but introduces junction corrosion risk. Short stems are metaphyseal-fitting designs that offer bone-sparing fixation, with emerging data supporting their use in select patients.
Acetabular Component Considerations
Dual-mobility constructs significantly reduce dislocation rates and are increasingly used in primary THA for high-risk patients. Shell positioning targets 40 degrees of abduction and 15 to 25 degrees of anteversion (the Lewinnek safe zone). Supplemental screw fixation is used for inadequate press-fit or compromised bone stock. Highly porous metals (trabecular metal, 3D-printed titanium) offer superior initial fixation and ingrowth potential.
Complications Related to Bearing and Fixation Choices
Periprosthetic fracture is more common with cementless stems, particularly during insertion. Trunnionosis involves corrosion at the head-neck junction, especially with large-diameter metal heads. Ceramic fracture is rare but catastrophic, requiring complete synovectomy and component exchange during revision. Cement implantation syndrome results from fat and marrow embolization during pressurization and requires intraoperative monitoring.
Clinical Pearls
Highly cross-linked polyethylene with a ceramic or cobalt-chrome head remains the gold standard bearing surface for the majority of primary THA patients. Cementless fixation is preferred in patients with good bone quality, while cemented femoral stems should be strongly considered in Dorr type C femora to reduce periprosthetic fracture risk. Dual-mobility liners are an effective strategy to reduce dislocation risk and are increasingly used in primary cases, especially in patients with neuromuscular conditions or advanced age. Metal-on-metal bearings are no longer recommended for primary THA, but surgeons should be familiar with surveillance and management of existing MoM implants.
References
- Bozic KJ, Kurtz SM, Lau E, et al. The epidemiology of bearing surface usage in total hip arthroplasty in the United States. J Bone Joint Surg Am. 2009;91(7):1614-1620.
- Devane PA, Horne JG, Ashmore A, et al. Highly cross-linked polyethylene reduces wear and revision rates in total hip arthroplasty: a 10-year double-blinded randomized controlled trial. J Bone Joint Surg Am. 2017;99(20):1703-1714.
- Abdel MP, Watts CD, Houdek MT, et al. Epidemiology of periprosthetic fracture of the femur in 32,644 primary total hip arthroplasties. Bone Joint J. 2016;98-B(4):461-467.
- Australian Orthopaedic Association National Joint Replacement Registry. Annual Report 2023. AOA NJRR.