Total Hip Arthroplasty (THA) Clinical Trial
Official title:
Vitamin E Stabilized Highly Cross-linked Polyethylene in Reversed Hybrid Total Hip
A prospective randomized controlled study evaluating the wear and migration of cemented acetabular sockets with third generation highly cross-linked vitamin E infused polyethylene and second generation highly crosslinked UHMWPE using Radiostereometric Analysis (RSA).
Background Reducing the rate of polyethylene (PE) wear in acetabular sockets and thereby
increasing the lifespan of Total Hip Arthroplasty (THA) has been a major concern in the
orthopaedic community for decades. Wear of PE and osteolysis followed by late aseptic
loosening of the prosthesis is the main reason for revision surgery after THA in Norway.
During 2008 in Norway 805 out of a total of 1114 revised THA were subjugated to surgery due
to aseptic loosening or osteolysis without loosening. The DRG (Diagnose Related Grouping)
weight is 5.49 for secondary THA and every DRG point has a value of 33.647 NOK adding up to a
direct total cost for revision after aseptic loosening of approximately 27 million USD.
Caput prosthesis with a diameter of 32mm or more has the major advantage to increase the
Range of Motion (ROM) and to reduce the risk of dislocation of the hip but, the larger the
caput prosthesis the more adhesive wear can be expected. This and the relative failure of
metal on PE gave the incentive to develop and take into clinical practise bearings with
increased resilience to wear. Today, there exists a wide range of options with a
substantially lower rate of volumetric wear compared to conventional PE. The biological and
immunological in vivo response to wear particles is very complicated and only partially
understood. It is clear that host response to wear particles and the corrosion products play
a major role in osteolysis around the prosthesis. For metal-on-metal (MoM) bearings the
volumetric wear is a magnitude less but the number of particle debris is massively increased.
MoM also have the problem with possible teratogen effect and allergy or hypersensitivity side
effects. Ceramic on ceramic (cer-cer) has the lowest wear rate of any artificial
articulations, but it is still possible to detect biologically active debris particles.
Cer-cer also has other challenges including fracture of prosthesis, squeaking hip, narrow
margins for placing components and cost.
Polyethylene is a thermoplastic polymer consisting of long chains of the monomer ethylene
(C2H4). The mechanical properties of PE depend on variables such as the extent and type of
branching and the crystal structure etc.
To improve the wear resistance of the PE an increase in the cross-linking between the chains
of polyethylene can be achieved by exposing it to high-energy irradiation. The irradiation
also increases the unpaired free electrons (free radicals). Free radicals can react with
oxygen and start a chain reaction causing an oxidative degradation of the polyethylene and
consequently cause increased wear. 1st generation HXLPE sockets have reduced the mid term
incidence of particle-induced osteolysis but retrieved failed first-generation HXLPE sockets
have shown surface cracking and signs of in vivo oxidative degradation.
In order to enhance the resistance to mechanical fatigue and reduce oxidative potential 2nd
generation HXLPE was developed. To reduce the oxidative potential the polyethylene can be
remelted or annealed. Remelting aggravates the mechanical properties of the polyethylene and
after annealing there are still remaining free radicals capable of oxidation in vivo. By
binding to unpaired free electrons Vitamin E is a scavenger of free radicals. Vitamin E is
hydrophobic and can thereby be infused into polyethylene. 3rd generation HXLPE is
manufactured below the melting temperature to maintain its mechanical properties and contains
Vitamin E to stabilize free radicals. Uncemented Acetabular HXLPE sockets have been shown to
have substantially reduced volumetric wear and excellent clinical mid-term results with this
type of PE. In Scandinavia the majority of sockets are cemented. The different principles of
biological or mechanical stability affects the properties of the socket typically different
E-module and the surrounding interface between implant and bone. Conventional PE cemented
cups have performed better with less aseptic loosening than uncemented cups. However, as the
mechanical properties are changed in highly cross-linked Polyethylene cups, it is not clear
whether the higher elasticity of the bone-cement-polyethylene compound might lead to
fractures of the more brittle polyethylene. It is therefore not possible to extrapolate
clinical results and wear rates from uncemented cups to cemented ones.
Placement of the cup is a crucial parameter for wear and cup survival. Malchau et al. has
shown that even high volume surgeons achieve suboptimal placement in 40% of cases. This may
depend on patient positioning perioperative, surgical instruments or technique. It is not
known whether the surgeon's subjective operative technique directly corresponds to the
postoperative evaluation of the cups position. However, adequate cup positioning is crucial
in the evaluation of wear. CT is the best method to judge cup position postoperatively and
detect osteolysis in the long time perspective.
To the investigators knowledge no randomized controlled study of cemented 3rd generation
HXLPE cups utilizing RSA has been conducted.
Hypothesis There is a mid term in vivo reduction of volumetric polyethylene wear with
cemented acetabular socket 3rd generation E1™ HXLPE compared with 2nd generation HXLPE.
Material: 70 eligible patients will be included following written informed consent. The
participants will be randomized by the envelope method to either E1™ or Marathon™ cemented
acetabular socket. The surgery will be performed at the hospitals in Vestre Viken HF and Oslo
University hospital HF, Ullevål ortopeden.
Implant The investigators will use two different cemented all PE acetabular sockets;
1. MarathonTM is a 1st generation HXLPE. The polyethylene is cross-linked with 5 Mrad that
corresponds to a semi cross-linked PE.
2. The E1™ cemented is an all PE Vitamin E stabilized 3rd generation highly crosslinked
UHMWPE. In vitro tests have shown a 99 % decreased volumetric wear rate comparing E1™
with ArComXL™ HXLPE, (highly crosslinked polyethylene) under high contact stress and a
95% reduction in wear rate comparing E1™ with ArCom™ under high contact area stress.
Wear particle morphology of E1™ is similar to that of the ArCom™ material.
Collared Corail™ (De Puy, Warsaw, Indiana, USA) uncemented femoral prosthesis is a titanium
tapered implant fully coated with 150 micron hydroxyapatite with over 95% survival after 15
years. The caput prosthesis used is the Cobalt Chrome 32 mm Articul/EZE™ (De Puy, Warsaw,
Indiana, USA) Refobacin ™ (Biomet Europe, Berlin, Germany) Bone Cement R is a high viscosity,
x-ray positive bone cement. A sachet of 40 g Refobacin® Bone Cement R contains 0.5 g
gentamicin.
Surgical technique The patient is operated in the position after surgeon's preference and
under spinal anaesthesia. Accordingly the approach is after surgeon's preference. When
posterolateral approach is chosen a repair of the capsule and the external rotators should be
performed. Peroperatively a total of 6 1,0mm tantalum beads are implanted in the perimeter of
the socket and 7 beads in the acetabulum. The acetabular socket is positioned as close to 45◦
abduction and 30◦ anteversion as possible.
The surgeon will postoperative directly grade cup position subjectively as anteverted,
neutral, retroverted, proximalized, distalized.
Postoperative training Postoperatively the patient is mobilized with full weight bearing from
day one.
Radiological analyses Conventional x-ray of pelvis, anterioposterior and lateral projections
of hip preoperatively, postoperatively and at 24 (60, 120) months RSA (Radiostereometric
analysis) postoperatively, 3, 12, 24 (60, 120) months, the RSA will be analysed at Ullevål
University Hospital
Clinical Control Harris Hip Score, EQ-5D and WOMAC will be filled out preoperatively and at
2, 5 and 10 years.
Analysis of data RSA analysis will be performed at the Centre of Implant and
Radiostereometric Research Oslo (CIRRO).
The study analysis is conducted under the guidance of CIRRO.
Storage of data Data will be collected and stored at the server for research at Oslo
University Hospital. All data is stored anonymously. Each patient receives a study ID. The
randomisation key and identity is stored separately.
Statistics Penetration of more than 0,1 mm annually in polyethylene articulations indicates a
wear rate that will lead to future osteolysis1.
Scientific value Firstly, if recently developed manufacturing techniques of polyethylene can
be shown to decrease the wear rate in vivo, and otherwise have a good clinical and
radiological outcome, we have the reason to believe we have the possibility of significantly
reducing the revision rate after THA.
Secondly, new implants should thoroughly be investigated and documented before widespread
use. This could save many patients from possible disastrous failures as the past has taught
us (Boneloc, Carbon compressed Poly).
Safety for the patient. The investigators will follow the normal routines for THA pre, per
and postoperatively. Standardized routines in regards to infection and thrombosis prophylaxis
following the recommendations from the Norwegian national board of orthopaedics will be
followed. Implantation of Tantalum beads has been shown to have negligible side effects.
The E1TM and Marathon PE is clinically tested in uncemented THA, the other components of the
prosthesis has more than 10 years clinical and RSA documentation.
Biomet will cover expenses including:
Extra cost of purchasing and storing prosthesis compared with standard prosthesis. Biomet or
Stryker has no copy right or any other form of ownership to the result of this study.
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