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19th EFORT Annual Congress in Barcelona: Selecting an implant for total hip arthroplasty in 2018
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When treating a patient who is considering having his/her hip replaced with an artificial total hip arthroplasty, the main goal of any orthopaedic hip surgeon is to find the best solution for both the implant and the bearings to make the “new hip” work perfectly for the rest of the patient’s life. However, evidence has shown this is an impossible promise to make to patients. Science, research and especially long-term national registry investigations have all given good guidance on when the risk of THA failure is higher compared to other implants/situations. By focusing on all the keys aspects to consider for the decision-making process, Prof. Per Kjaersgaard-Andersen, from Vejle Hospital in Denmark, will present his experienced rationale used when selecting an implant for primary THA and set a clear strategy to adopt within a specialty that is constantly evolving.
Strategy When Selecting Implant in Primary Total Hip Replacement in 2018
Instructional Lecture – Friday 1 June 2018
To select an implant, the main basic traits of the patient’s medical history should first be considered: age; sex; quality of bone; and mental health. In many medical centers, a cut-off of 70 years of age is used to decide on fixation type for the femoral stem, with cemented stems used in the “elderly” group and non-cemented stems used in the “younger” group. This choice is settled based on two aspects. As the elderly have a shorter life expectancy, they can be treated with cemented stems which are less expensive but still have a good survival rate. Secondly, because they have weaker bone stock, elderly patients have a higher risk of early periprosthetic femoral fractures, especially if they receive a non-cemented stem. These points are very significant based on data from all Nordic THA registries. The type of cemented stem to use should always be related to proven designs with long-term, good results. Therefore, assessing different implants/concepts is a necessity. The Orthopaedic Data Evaluation Panel (ODEP) rating system developed in the United Kingdom is a helpful tool with quotes and rates for implants from data reports, registries and scientific publications. For example, an implant rated ODEP 10A reflects an implant with survival greater than 95% (not revised) after 10 years. This type of implant should be used for most patients, leaving a minority of the patients to enter controlled studies of new implants/concepts to ensure there is continued research in finding newer and better designs.
On the acetabular side, a global phenomenon has gradually developed as fewer cemented components are being inserted. Most acetabular implants today are non-cemented titanium shells, mainly with highly crosslinked (HXL) polyethylene inserts or, more rarely, a ceramic insert. Consequently, several hip surgeons have limited experience with cemented acetabular components, raising the failure rate of these types of surgeries. Industry has reacted by developing more designs with titanium shells. Besides correct positioning during surgery, key considerations for quality/survival of non-cemented, titanium acetabular components are: thickness of the shell, surface roughness to secure fast bony ingrowth, the backside polishing and the locking mechanism of the polyethylene/ceramic insert. In the past, some positive outcomes from animal studies introduced hydroxyapatite-coated (HA) cups and the use of other bony-ingrowth factors for consideration in THA. However, large registry data have shown no benefit from HA on risk of revision in comparable implants with and without HA. Studies have even questioned whether HA coating of implants may increase the risk of revision for aseptic loosening (ASL).
Dual-mobility acetabular components developed in France decades ago helped to overcome THA dislocation in elderly, senile patients and in patients who had repeated THA dislocations. These implants need special attention as this concept proved to reduce the risk of dislocation, but their use in patients whose indications differ from the ones mentioned above is still questioned. Indeed, there are no long-term studies about the potential wear of the large polyethylene insert sliding freely in the large, smooth metal shell.
In the early days of THA use, conventional polyethylene was known to wear out with time regardless of its thickness. The newer generation of HXL polyethylene implants, some of which were implemented more than 10 years ago, have nevertheless shown promising results as no or very limited wear has been seen after 10 or more years of use. Actually, the question of whether this limited wear has any clinical, negative influence at all has been raised because wear particles from the “older” types of polyethylene induced osteolysis, which frequently caused failure of the implant with massive loss of bone. Important institutions and registry reports highlight the fact that there is no or only limited risk of revision due failure of HXL polyethylene inserts.
Ceramic inserts have been through an analogous development, with either total or partial breakage of the inserts being a main issue of concern. Other complications are failure due to third-body wear from foreign particles, such as metal or cement particles, that impinge between the ceramic head and insert. The issues have mainly been associated with a few implant designs and seem to have been overcome. However, noise from loaded ceramic-on-ceramic bearings is still debated as a risk of this THA design. Newer designs of ceramic heads and inserts have shown very low failure rates with a risk of breaking that is less than 10 in 100,000 implants.
As shown by the Australian Orthopaedic Association National Joint Replacement Registry, metal femoral head size has a significant impact on the risk of revision for ASL. Metal heads with a diameter of 36 mm or more are frequently revised, probably because of increased forces in the taper junction, leading to trunnionosis. In contrast, large ceramic heads do not result in this situation, which has led to an increasing number of clinics using ceramic heads in cases when a head size of 36 mm or more is needed.
Metal-on-metal (MoM) bearings in resurfacing THA or stemmed THA with large heads do not need a deeper discussion. Diverse studies worldwide have confirmed the increased revision risk with MoM bearings and several of these implants have been withdrawn from the market. In Denmark, health authorities and the Danish Orthopaedic Society agreed on a “full stop” and “time-out” of MoM THA bearings in 2012.
On top of all the aforementioned aspects related to implant survival, there are also various details related to the patient and the surgery. For instance, elderly patients are more prone to deep infection due to a reduced immune system response. Patients who have a very high BMI or a very recent femoral neck fracture are more prone to dislocation and infection. Surgeons who perform only a limited number of THAs annually are faced with dislocations more often than high-volume surgeons, an observation also related to the fact that more experienced surgeons frequently place the components in a safer position.
Some specific recommendations to consider for a THA surgical strategy can be listed as follows:
- Elderly patients aged 70 years or older: Non-cemented titanium cup; HXL polyethylene; cemented stem (smooth, bi-tapered); antibiotic-loaded bone cement; 36-mm metal head;
- Senility; neuromuscular diseases; severe mental diseases: Dual-mobility acetabular component (cemented/non-cemented); HXL polyethylene; cemented stem (smooth, bi-tapered); antibiotic-loaded bone cement; 28-mm metal head;
- Patients younger than 70 years old: Non-cemented titanium cup; HXL polyethylene; non-cemented stem without HA; 32-mm or 36-mm ceramic head; and
- Patients younger than 50 years old: Non-cemented titanium cup; HXL polyethylene/ceramic liner; non-cemented stem without HA; 32-mm ceramic head.
Despite these preoperative considerations and extensive treatment planning, the final selection of an implant is always done during the surgery. When closing the wound and leaving the OR, implants must simply be correctly positioned and well-fixed.
The Instructional Lecture entitled “Strategy When Selecting Implant in Primary Total Hip Replacement in 2018” can be attended by any participant who is fully-registered for the EFORT Congress. All details to sign-up will be available on our registration platform as of January 2018. Remember to visit our 2018 congress website regularly.
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- 19th EFORT Congress in Barcelona | 30 May to 1 June 2018