Background: A continuing controversy in total knee arthroplasty is the question whether the posterior cruciate ligament should be retained or substituted. This report reviews a series of total knee arthroplasties with a fixed bearing posterior cruciate ligament retaining implant (Nex Gen^© CR, Zimmer Inc., Warsaw, IN).

Methods: Between May 1997 and April 2001 197 patients were provided with 218 primary implants. There were 142 females and 55 males with an average age of 71 years (range 53–88 years) and a BMI of 28,9 kg/m² (range 19,1–41,2 kg/m²). The diagnosis was osteoarthritis in 212 patients, 3 cases of aseptic osteonecrosis, 1 fracture of the tibia plateau, 1 prior infection and 1 psoriatic arthritis. 84 knees had prior operations including high tibial osteotomies and menisectomies.

The operations were performed by 11 surgeons, with more than 80% done by 5 surgeons. 162 (74%) femur components and 181 (83%) tibia components were cemented. Patella resurfacing was performed in 135 (62%) cases.

We evaluated the results prospectively with a clinical inspection, radiographs (AP and lateral, longleg standing, patella sunrise view), and the use of the Knee Society Score, Quality-of-Life Short Form-36 and WOMAC rating score.

149 patients were examined at a mean follow up of 5,9 years (range 4,1–8,2 years). 29 were questioned on the telephone, 29 deceased, 7 revisions had to be performed and 4 (2%) were lost to follow up.

Results: The range of motion improved from 101° to 115° (range 80°–140°). All knees had sufficient antero-posterior and mediolateral stability. The Knee society score improved from 35 to 83 (good result) and the function score improved from 52 to 76 (good result).

Early complications included 12 haematoma, 10 wound healing problems, 5 early infections, 2 thrombosis and 1 non lethal pulmonary embolism. 7 revisions had to be performed: 3 late infections (2 one-stage revisions with synovectomy and exchange of polyethylene inlay, one two-stage revision with semi-constrained implant LCCK© Zimmer Inc.), 3 patella resurfacing due to anterior knee pain and 1 exchange of cemented tibia plateau due to aseptic loosening. Survivorship at 6 years including any reason of failure was 96,5%.

Conclusion: At a mid term follow up of 6 years this fixed bearing posterior cruciate retaining implant achieved a reasonable survivorship with good clinical results, kinematics and patient satisfaction.

Introduction: Irradiation crosslinking of UHMWPE has been developed as an improvement over conventional UHMWPE to provide improved wear resistance, demonstrated during in-vitro studies as well as in early clinical results [1, 2]. The analysis of explants made of highly crosslinked UHMWPE yields valuable information about their clinical utility.

Material: 26 explanted highly crosslinked UHMWPE inlays (Durasul, Zimmer) from various sources were surgically retrieved and analyzed. All inlays articulated with 28 mm CoCr heads except one (32 mm) and had an implantation time from 3 to 43 months (mean 14 months). The reasons for revision were: 9 for infection, 2 for ossification, 4 for luxation, 2 for pain, 4 for bone fracture and 5 for aseptic loosening.

Results: On all explants, scratches on the articulation area as well as machining marks were visible; the latter have sometimes been smoothed out in the loaded area. There were no signs of delamination or oxidation. The loaded area, analyzed by SEM, exhibits microscopic changes in the morphology which have been reported to be potential microcracks [3]. When analyzed by TEM, it was seen that these surface features are ripples and folds, which are induced by normal adhesive-abrasive wear behavior and have a maximum size of 5 m [4]. Mechanisms like folding are reported also from conventional UHMWPE [5]. In order to separate wear from deformation, the shape memory behavior of UHMWPE was employed. After thermal treatment, smoothed machining marks were observed to recover. After about two years in-vivo, some of the machining marks in the loaded area do not recover, which indicates that minimal wear in the range of the height of the machining marks (approx. 10 m) has occurred. In comparison, after this time, 200–600 m of wear would be expected for conventional UHMWPE [6].

Conclusions: The findings from the retrievals showed that there is no adverse wear or material failures due to delamination or cracks at 3 to 43 months. The accumulated scratches are due to the fact that the wear of this highly crosslinked polyethylene is very small. The scratches do not polish out over time as with conventional UHMWPE and do not show adverse effects on the long-term behaviour of the implant. These results are consistent with the performed in-vitro studies.

Aims: To solve the major problems of osteolysis due to particle debris in total hip arthroplasty, highly cross-linked UHMWPE were developed. Investigations on early retrieved components of Durasul™ (Centerpulse Orthopedics Ltd.) provide the opportunity to evaluate the highly crosslinked components for wear damage or other effects on the material. Methods: 12 Durasul™ alpha cups were surgically retrieved and analyzed. The range of in-vivo duration of the cups was between 3 and 15 months. The reasons for revision were not related to material failure. The investigations were made by microscopy and CMM measurement. To differentiate between creep and wear, the memory effect was used. Results: In the articulation, machining marks look partly flattened, or show a highly scratched surface. The loaded area shows some microscopic changes of the morphology like ripples and folds, which are shear-induced ripple formations and material overlappings. In some cases the retrieved cups show a yellow discoloration, indicating the in-vivo absorption of synovial liquid proteins. Conclusion: The findings from the retrievals showed that there is no adverse wear at 3–15 months and there were no material failures due to wear, delamination or cracks. All the effects are accumulating on the articulating surface and lead to the dull scratched morphology. Mechanisms like material overlapping and yellowing are reported also from conventional UHMWPE and do not show adverse effects on the long-term behaviour of the material.