The mean vectorial migration was 0.31 and 0.24 mm and change in inclination 0.2° and 0.2° for the groups. (p>
0.8) Harris Hip Score was 92/96 and the radiological and clinical performance was equal after 2 years.
Post operative stability is of paramount importance to obtain bone in growth and a tight interface in uncemented implants. Although hemispherical press fit cups are widely used different opinions exists according optimal fixation and a variety of principles are preferred. Lab studies show better stability if a cup is augmented by screws or pegs. However, cups with screws and holes increases penetration of joint fluid, pressure and particles to the interface with a risk for osteolyses. HA coating is in many studies favourable to obtain a quick in growth but is by many regarded unnecessary or even a risk for increased wear. This RSA studie was done to investigate stability and wear in cups with different fixation.
Mann-Whitneys U-test was used on signed values for evaluation of group differencies.
Wear was 0.45 mm proximally and in total 0. 6 mm without any sign of differences between the HA and porous coated groups. HA coated cups had less radiolucent lines after 2 years. (p=0.01)
In clinical Orthopaedic research we often need better tools for follow up investigations and evaluation of new methods. One alternative is Radiostereometric analyses (RSA) which can be used for high precision measurements of migration, micro movements and wear. Since developed 25 years ago it has now been used in a few thousand patients and made into a comprehensible computerized, PC based system. Recent development has made it much faster, more accurate and user friendly enough for more common use. RSA can basically measure 3D movements between rigid bodies as bone or implants and is used for many sorts of applications as bone growth, fracture healing, joint kinematics, bone elasticity, spinal fusion etc where a high accuracy is needed. It has, however, mostly been used for research in hip and knee arthroplasty since early migration has been found a good predictor for later implant failure. As also wear in artificial joints can be accurately measured the technique is definitely a useful tool for implant research.
With modern digital x-ray technique we obtain an in vivo precision of about 50 microns longitudinally, 80 horizontally and 200 sagittaly, for rotations 0.1°–0.3°depending on direction, (95% confidence limit).
Some general findings are: In cemented stems the loosening starts at the stem-cement interface and the cement mantles are very well fixed to bone, loosening being a secondary phenomenon. A low temperature curing, non-vacuum mixed cement had equal fixation to bone and stem as a standard vacuum mixed. Some stem designs move a lot inside the cement, possibly with a big risk for cement fractures and abrasion. Especially subsidence and retro version seems ominous. Repeatedly HA coating has shown excellent implant stability, in the same range as cemented components and better than porous coated ones. We have found good and reproducible stability with impaction grafting in both acetabulum and femur using both cemented and uncemented non tapered implants. Structural grafts seem to imply increased migration. Wear has been increased with non irradiated plastic components, in younger patients, if cement contains ZrO as opacifier and together with unstable cemented stems. No correlation has been found between wear and HA coating, head or stem material or weight but decreased wear found for high cross-linked plastics. RSA has been a big asset for Implant research over the years. With the more stable implants and modern bearings of today a high accuracy method is even more needed for to measure fixation and wear, or the actual results will be lost in a lot of noise. The new focus and interest in synergistic effects of implant micro movements, interface stress, hydrostatic pressure and particles for the development of osteolyses is a new area were RSA should be a useful tool to study inducible implant movements and fixation quality in vivo.
We analysed synovial fluid from 88 hips, 38 with osteoarthritis and 12 with well-functioning and 38 with loose hip prostheses. The levels of TNF-α, IL-1ß (71 hips) and IL-6 (45 hips) were measured using the ELISA technique. Joints with well-functioning or loose prostheses had significantly increased levels of TNF-α compared with those with osteoarthritis. Hips with aseptic loosening also had higher levels of IL-1ß but not of IL-6 compared with those without an implant. The levels of TNF-α and IL-1ß did not differ between hips with stable and loose prostheses. Higher levels of TNF-α were found in hips with bone resorption of type II and type III (Gustilo-Pasternak) compared with those with type-I loosening. The level of cytokines in joint fluid was not influenced by the time in situ of the implants or the age, gender or area of the osteolysis as measured on conventional radiographs. Our findings support the theory that macrophages in the joint capsule increase the production of TNF-α at an early phase probably because of particle load and in the absence of clinical loosening. Since TNF-α has an important role in the osteolytic process, the interfaces should be protected from penetration of joint fluid.