Prospective RCT Using Roentgen Stereophotogrammetric Analysis (RSA) to Evaluate Fixation of the Biofoam Advance Total Knee Arthroplasty Components With and Without Screw Augmentation

Hip and knee replacement arthroplasty are profoundly successful operative interventions, however, some joint replacements do fail and the life expectancy of a hip or knee arthroplasty is finite. This fact has largely been responsible for the continued development of new devices and techniques for joint arthroplasty surgery. Unfortunately, the introduction of new technologies and devices is not a benign process, and even subtle changes to existing implants can have a disastrous effect on patient outcome.

The fact that new technologies and devices can lead to poor results has led some authors to advocate a phased introduction of new technologies. A key component of the phased introduction approach advocates the use of roentgen stereophotogrammetric analysis (RSA) early in the testing process.

RSA is a highly accurate radiographic technique developed in Lund, Sweden and has for some time been the gold standard in Europe for assessing the stability of implants within bone. It is at least ten times more accurate than conventional radiography. RSA involves the insertion of small tantalum markers (0.8mm) into the bone and prosthesis at the time of surgery. By using a calibrated cage with additional markers and simultaneous bi-planar x-rays, micromotion at the prosthesis-bone interface can be very precisely determined. Two types of micromotion can be investigated: migration, i.e. gradual motion over time, and inducible displacement, i.e. instant motion in response to external forces. The pattern of micromotion exhibited by various prostheses and fixation techniques within the first post-operative year has been shown to be predictive of the long-term fixation of the component to bone, especially when considering the tibial prosthesis-bone interface. The value of this precise radiographic technique is that new technologies and techniques can be introduced in vivo while limiting their exposure to as few patients as possible. RSA is a proven, safe and invaluable method for assessing methods of knee component fixation as well as different design concepts.

DEXA bone densitometry has been demonstrated as a reliable method for determination bone mineral density about knee and hip implants. This technique provides further detail about the quality of fixation of knee and hip prostheses and implant induced bone remodeling.

The foam metal backed Advance Knee Arthroplasty components utilize a porous titanium coating on the non-articulating surface of the components to enhance the implant-bone interface. This 3-dimensional scaffold should promote bone in-growth that may provide a more robust bone-implant interface. The high coefficient of friction provides initial fixation negating the need for bone cement which should reduce duration of surgery. There is also a version of the Biofoam Advance that incorporates screwed fixation that allows for augmented fixation with up to four titanium screws, however, it is not clear that this augmentation is necessary.