The Importance of Different Implant Surfaces of the Tibial Component for Migration and Adaptive Bone Remodeling in Uncemented Total Knee Arthroplasty (Vanguard Versus Regenerex)
Condition: Artrosis of the Knee
Study type: Interventional
Phase: Phase 4

Summary: 
      In a prospective randomised study two uncemented tibial components with different coating
      (Vanguard® porous coating, Biomet and Regenerex® Primary Tibial Tray, Trabecular Metal
      coating, Biomet) used for total knee arthroplasty (TKA) are evaluated. Both tibial component
      coatings are designed to provide excellent conditions for bone ingrowth.

      The differences between the two tibial components are evaluated by measurements of migration
      of the tibial component assessed by Radiostereometric analysis (RSA) and measurements of the
      adaptive bone remodeling of the proximal tibial assessed by dual energy X-ray absorptiometry
      (DEXA).
    

Detailed description: 
      In general a primary TKA is a durable and well-functioning solution with a 10-year implant
      survival of more than 90 %. However, new techniques are developed and the patients´ demands
      for increased durability of the implants are increasing. It is believed that the new implant
      Regenerex, planned to be tested in the present study, with the new surface coating will
      facilitate bone ingrowth and secure a better fixation to the host bone, thus increasing the
      implant survival and improving the function of the prosthesis.

      One of the implants (Vanguard) has been used for routine clinical use abroad, but also in
      Denmark for some years, and so far the results have been good.

      The other type coating (Regenerex) is a micro-casting of the structure of normal trabecular
      bone, but made from metal alloy, in the element Titanium. Titanium is also very biocompatible
      (Hoffman 1993, Hahn, H 1970) and have been used with great success in e.g. uncemented total
      hip arthroplasy for several years (Marshall et al. 2004, Meding et al, 2004).

      Trabecular metal has a porosious structure close to that of normal trabecular bone, and the
      biomechanical characteristics such as e.g. compressive strength and elastic modulus are very
      close to that of normal trabecular bone (Krygier et al. 1999, Zardiackas 2001). These
      characteristics are the reason why trabecular metal within the past decade have been used for
      production of different orthopedic implants, and the early clinical results so far have been
      very promising (Bobyn et al. 2004, Nasser & Poggie 2004, Nehma et al. 2004, Nelson et al.
      2003).

      Quantitative measurements of the implant migration and adaptive bone remodeling of the bone
      close to the implants are generally accepted as suitable methods for an objective evaluation
      of the effect of joint replacement surgery and have been proposed as mandatory important
      examinations that must bee performed before new implants are distributed for wide-spread use
      (Bobyn et al. 2004, Petersen & Schrøder 2004, Østgaard & Nielsen 2004).

      Very small movements between an implant and the bone can be measured by special RSA X-rays
      after implantation of small (0.8-1.0 mm) Tantalum markers attached to the implant and in the
      bone (Selvik 1989), while changes in bone mineral or bone mineral density (BMD) of the bone
      in close relation to the implant can be measured by DEXA (Glüer et al. 1990, Mazess & Barden
      1988).

      Micromovements with migration of the tibial component are seen after both cemented and
      uncemented TKA during the first postoperative year. Subsequently most implants stabilize,
      while a minority migrate continuously beyond the first postoperative year (Ryd et al. 1995).
      The implants that continues to migrate are those with a high risk of later aseptic loosening.
      Several studies have evaluated the influence of different parameters such as mode of fixation
      (cemented/uncemented), surface coating e.g. hydroxyapatite, metal alloys, and design of the
      prostheses on the migration of the tibial component in primary TKA (Ryd 1986), but whether
      the use of a surface coating of trabecular metal (Titanium) will result in significant
      differences has not yet been evaluated.

      In studies using different bone densitometric techniques for measurements of changes in bone
      mineral of the proximal tibia after primary TKA a significant decrease in BMD is seen in most
      studies (Hvid et al. 1988, Karbowski et al. 1999, Levitz et al. 1995, Petersen et al. 1995,
      Regnér et al. 1999). In some of the studies the decrease in BMD reaches 20% - 36% (Hvid et
      al. 1988, Levitz et al. 1995, Petersen et al. 1995, Regnér et al. 1999), however, in other
      studies BMD remains unchaged (Bohr & Lund 1987, Li & Nilsson 2000, Spittlehouse et al. 1999)
      or shows a minor increase (Petersen et al. 2005).
    

Intervention name(s): Vanguard; Regenerex
Intervention type(s): Device; Device
Intervention description(s): A prospective randomized study where the patients are randomized to receive one of two prostheses (tibial components) with different coating: Vanguard pourous coating, Biomet and Regenerex® Primary Tibial Tray, Biomet. Both prostheses are available and approved by the FDA. The main difference between the implants is the coating of the tibial tray
Allocation: Randomized
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Knee prosthesis