Purpose of the study: Restrained implants with intrinsic stability guaranteed by a large central stem have been developed for revision knee arthroplasty, irrespective of the underlying cause. Successful restraint implies excellent fixation of the prosthetic implants which can be obtained using press-fit centromedullary stems. The purpose of this work was to assess the long-term results of this mode of fixation in this indication and to search for clinical correlations with potential radiological images around the stems.

Material and methods: We report 46 cases of Sigma^®PFC TC3 revision total knee prostheses reviewed retrospectively at two years with a mean follow-up of eight years. Mean age at surgery was 68 years. Revision was indicated for aseptic loosening (n=24) and septic loosening (n=22). The knee society criteria were used for the clinical evaluation. Radiographic measurements were made semiautomatically with the Imagika^® software.

Results: The mean clinical score improved from 42 points preoperatively to 84.7 at two years and 83.7 at last follow-up. Outcome was excellent (n=30), good (n=7), fair (n=1) and poor (n=1). The mean function score improved from 34.3 preoperatively to 69.1 at two years and 64.2 at last follow-up. Radiographic alignment was correct in all cases. The press-fit effect was observed for 63% of the femoral implants and 76% for the tibial implants. Around the stems, 57% of the implants exhibited condensation lines and 23% lucent lines measuring less than 2 mm. There was no relation between radiological findings and the clinical or functional scores. There were two failures, one for frontal instability at six years and the other for aseptic loosening at eight years. Excepting these two cases, there was one case of femoral implant migration with no clinical expression. For all other patients, the radiographic image remained unchanged between the two year check-up and the final follow-up.

Discussion: Thee presence of lucent lines or condensation lines is well known for this type of implant with long centromedullary stems. Nevertheless, this is the first clinical series evaluating the clinical impact of these radiographic images. In our opinion, these images are related to the relative mobility of these implants which should be checked regularly, although no long-term clinical expression occurs. For us, this type of implant enables good function and long-term stability.