Five-year Migration Pattern and Bone Mineral Density for the Tri-Lock and Summit Femoral Stems.
Condition: THA
Study type: Interventional

Summary: 
      The incidence of primary hip joint prosthesis is 180 per. 100,000 inhabitants. In male
      patients younger than 50 years the 10-years survival of the prosthesis is 89 % and 82 % over
      15 years. In women younger than 50 years the 10-years survival of the prosthesis is 87 % and
      78 % over 15 years.

      As revision surgery is associated with higher complication risk for the patient and poorer
      out-come and implant survival it is necessary to examine possible methods that may increase
      long-term survival of the primary hip prosthesis or facilitate better outcomes after revision
      of hip joint prostheses for younger patients.

      In younger patients the prosthesis often is inserted without the use of cement. When not
      using cement, it is crucial for the final result, that there is a direct bone ingrowth of the
      prosthesis. The chance of getting bone ingrowth depends firstly on a good immediate
      mechanical fixation at surgery and secondly on osteoconductive abilities of the prosthetic
      surface.

      This study investigates a new bone sparing implant with a new surface compared to a
      conventional implant.
    

Detailed description: 
      BACKGROUND

      According to the Danish Hip Arthroplasty Registry 201 approximately 10.400 primary hip joint
      prostheses in Denmark are implanted annually, and the incidence is relatively stable. The
      incidence of primary hip joint prosthesis in population was 180 per. 100,000 inhabitants in
      2014, with a slight predominance of female patients (60%). The average age for women is 70
      and for men 67 years. Idiopathic arthritis is diagnosed in 80% of all patients receiving a
      hip joint prosthesis [1,2]. For older patients, the risk of later revision of a hip joint
      prosthesis is small. The overall survival of the primary hip joint prostheses is for all
      diagnoses 82% after 19 years. The prosthesis survival is poorer for younger patients, and for
      women. In male patients younger than 50 years the 10-years survival of the prosthesis is 89 %
      and 82 % over 15 years. In women younger than 50 years the 10-years survival of the
      prosthesis is 87 % and 78 % over 15 years. [2]. As revision surgery is associated with higher
      complication risk for the patient and poorer outcome and implant survival it is necessary to
      examine possible methods that may increase long-term survival of the primary hip prosthesis
      or facilitate better outcomes after revision of hip joint prostheses for younger patients.

      In younger patients the prosthesis often is inserted without the use of cement. When not
      using cement, it is crucial for the final result, that there is a direct bone ingrowth of the
      prosthesis. The chance of getting bone ingrowth depends firstly on a good immediate
      mechanical fixation at surgery and secondly on osteoconductive abilities of the prosthetic
      surface. From a theoretical point of view it is also important that elastic properties of the
      prosthesis differ as little as possible from the elastic properties of the bone, in order to
      prevent a subsequent loss of bone.

      INVESTIGATED IMPLANTS

      The Tri-Lock femoral implant from Depuy ® is in its basic design a well-known implant that
      has been used since 1981 with documented good long-term results. It is an implant with
      bone-preserving properties and proximal coating, providing a predominantly metaphyseal
      anchoring. The Summit femoral implant from Depuy ®, is newer to the marked, and has a longer
      diaphyseal support but is predominantly metaphyseally fixed. A proximal porous implant
      coating will increase the surface area in contact with the metaphyseale bone and increase the
      coefficient of friction compared to mid-coated implants [3,4,5]. Proximal coatings may on the
      positive side lessen periprosthetic bone stress shielding, however, on the negative side,
      proximal coatings may reduce primary prosthesis fixation and lead to fibrous membrane
      formation with consequently implant micromotions that will eventually causing aseptic
      loosening of the im-plant. Hypothetical extensively coated implants have a larger porous
      surface and thus provide better and faster primary fixation, but there are no publications of
      randomized prospective clinical studies to support this. There are different porous coatings
      on the two investigated femoral components. Summit is coated with Porocoat porous coating,
      whereas Tri-Lock in the latest version is coated with the new GRIPTION technique for an even
      larger surface for bone ingrowth (Gription) with a new ultra-porous surface marketed as an
      improved immediate im-plant fixation in the bone. The total surface of the metaphyseal
      implant part is increased by approximately 25% with the Gription coating technique. The
      Gription technique may provide consistent implant seating height and additional initial
      stability, and these qualities may in long term ensure an improvement on implant survival.

      Both femoral implants are made of Titanium. The Tri-Lock stem is designed with a reduced
      lateral shoulder to preserve bone in the greater trochanter, and with a shorter stem and an
      oblique cut stem tip, as compared to the Summit stem, in order to enhance stem insertion
      through minimally invasive approaches.

      PRIMARY OUTCOME Mechanical loosening of a prosthesis may be suspected if the prosthesis
      migrates with respect to the surrounding bone [6;7]. Therefore, there is now consensus that
      the introduction of new implant designs including coatings and also new surgical methods
      should be evaluated in migration studies before they can be recommended for use in general
      [8;9]. Using Radiostereometric Analysis (RSA), it is now possible to get a very accurate
      assessment of prosthesis migration with a precision of at least 0.11 mm [10]. Clinical
      studies have shown that early migration of uncemented prostheses is related to the subsequent
      loss of the prosthesis [11;12]. For RSA tantalum beads are inserted in the prosthesis and
      surrounding bone. Immediately post-operatively stereoradiographs (RSA images) are made, and
      the initial position of the prosthesis relative to the fixed bead markers of the bone is
      determined. At defined time intervals new RSA images are taken. By comparison of the images
      the prosthesis migration in relation to the bone fixing points is determined in three
      dimensions, as a function of time.

      Bone mineral density (BMD) around the inserted implants can be quantified by Dual Energy
      X-ray absorptiometry (DXA), which is an accurate method for the measurement of even small
      changes in BMD around femoral components [13]. DXA has been used to detect decreased bone
      resorption around implants with a lower stiffness [14]. A recent study from Finland
      demonstrated increased stem subsidence in patients with low BMD, and it is therefore
      advisable to screen studied patients for osteoporosis preoperatively. [15].

      MATERIAL & METHODS

      Design: Prospective randomized clinical study. Logistics: All newly referred patients with
      hip pain diagnosed with primary osteoarthritis and scheduled for hip replacement will be
      screened for elegibility in the study according to the study criteria. Assessed patients to
      be a candidate for project participation, given oral information for participants at the
      clinic the same day and handed over documents relating to the project. 1-2 weeks prior to
      surgery the patient participates in a general information session about the surgery and
      post-operative recovery. Here, the selected patients who wish to partici-pate in the project
      sign the consent form. Patients will at information day after signed consent be given an
      Ipad, in order to answer our questionnaires. Furthermore, there will also be conducted
      preoperative DXA scan.

      After informed consent and using the following inclusion criteria, patients are randomized to
      insertion of metafysial fixed femur implant with proximal porous coating porocoat (Summit,
      Depuy®) or proximal Grip Tion coat (Tri-Lock, Depuy®). All patients are inserted dan same
      uncemented acetabular component (Pinnacle cup Depuy®). Randomization is done intraoperatively
      in a sealed envelope system.

      RSA analysis: We will use CAD models for the femur implants, and we expect to use EGS-RSA to
      the acetabulum implants.

      POWER:

      Based on the primary endpoint (RSA) and using the following values: α= 0.05, β= 0.10 (power
      90), SD = 0.6 mm, and MIREDIF: minimum relevant difference = 0.6 mm [16], sample size is 23
      patients for each arm in the study.

      Taking into account the risk of dropout and death in the study group inclusion is set at 25
      patients per group in order to ensure that a minimum of 2 x 23 patients (46 patients) will
      have full follow-up of efficacy parameters at 2 years of follow-up.

      ON RADIATION DOSE

      Measurements were taken for the radiation dose, which shows that the stereo x-ray of the hip
      provides a radiation dose of 0.015 mSv [18]. This represents approximately 50% of a
      conventional recording of the hip. It is shown that a typical DXA measurement of the femur or
      spine (osteoporosis control) produce an effective dose equivalent to 0.015 mSv [19].
      Conventional X-ray of the hip, gives a dose of 0.85 mSv. Normally, our hip prosthesis
      patients not included in this study have taken radiograph least one time within the first
      postoperative year. Patients in this study will have taken the same number of conventional
      radiographs, and in addition to 5 times DXA scan and seven times the stereoradiography. Taken
      from above radiation dose, patients included in this study were subjected to an additional
      radiation dose of 1.93 mSv. This corresponds to have taken three additional conventional
      radiographs of the hip, and it provides an additional risk of fatal cancer of 0.01%. This
      places the subjects in group IIb, where the overall risk of the irradiated individual is 1 to
      10,000. [19]

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        4. Baad-Hansen T, Kold S, Olsen N, Christensen F, Søballe K. Excessive distal migration of
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        6. Karrholm J, Snorrason F. Subsidence, tip, and hump micromovements of noncoated ribbed
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        7. Mjoberg B, Brismar J, Hansson LI, Pettersson H, Selvik G, Onnerfalt R. Definition of
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       19. Appendiks 5. Retningslinier om anvendelse af ioniserende stråling i biomedicinske
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Intervention name(s): Tri-Lock; Summit
Intervention type(s): Device; Device
Intervention description(s): Implant Stem; Implant Stem
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Randomized clinical trial
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: THA; Hip; RSA; Cementless; Radiostereometric analysis