Oxford Partial Knee Replacement: A Randomized Clinical Trial of Three Implant Types.

The purpose of this scientific study is to clarify whether there is a relationship between the appearance of radiolucent lines in bone-cement interphase of the tibial component of the different models of the Oxford Uni Knee prosthesis and poor prognosis of these prostheses. This will be accomplished in a series of three different Oxford Uni Knees by studying:

1. Three way randomized comparison of migration (prosthetic fixation) by Model Based RSA with three different Oxford Uni Knee prosthesis (both tibial trays and femoral components will be assessed).
2. Fluoroscopy (screening) roentgenograms for determination of RLL around the tibial component and "overhang" of the tibial trays.
3. Changes in periprosthetic bone mineral density between the three randomized groups evaluated in the proximal tibia and distal femur on the surgical side and on the unaffected tibial condyle area (BMD).
4. Clinical function of the Uni Knee evaluated by a score system using a recent Danish adaptation of the Oxford Knee Score that consists of a questionnaire filled-out by the patient with 12 simple questions on pre-and postoperative assessment of the ADL.
5. Analysis of wear of the mobile polyethylene (meniscus) including a methodical study as to whether the technique requires weightbearing (standing) stereoroentgenograms or whether non-weightbearing stereoroentgenograms can be used (assessed with Model Based RSA).
6. If a fast bone-remodeling increases the risk of aseptic loosening (histomorphometric results combined with RSA results and possible revision)
7. Increased risk of aseptic loosening with cemented (two designs) compared to uncemented im-plants.
8. If bone-remodeling of the proximal tibia is dependent on gender and age.

The study would be considered a success if all designs of the prostheses are firmly fixed and remain so during the entire period of study, that is, no increasing migration is seen using RSA. It would be a success if the appearance of RLL beneath the implant in the proximal tibia is unrelated to bone loss and prosthesis migration.

The hypotheses are:

1. RLL in relation to the tibial component is unimportant for fixation of the Oxford Uni Knee as assessed with DEXA and RSA.
2. There is very little wear of the polyethylene in the course of a 5 year follow-up as assessed with RSA.
3. The femoral component is expected to remain fixed throughout the entire period of follow-up.
4. Function assessment as ROM (range of motion) after UKA is satisfactory and generally better than after TKA.
5. All three prosthetic designs are expected to migrate minimally and remain fixed throughout the follow-up period, but the uncemented design is expected to be superior to the cemented design.
6. No difference in clinical outcome between the three prosthetic types.
7. The bone-remodeling rate in the medial periarticular tibia bone increases the risk of aseptic loosening.