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.

Purpose of the study: Theoretically, in first-intention total hip arthroplasty (THA), restoration of femoral offset (distance between the femoral axis and the joint centre) enables optimal function. The purpose of this study was to determine acceptable limits for variation in femoral offset without loss of function.

Material and method: We studied 122 hips (108 patients) who had THA with a straight cemented stem and a modular cone which could be adapted to enable three dimensional adjustment of the offset (more than 100 configurations). Mean patient age was 64 years. Most had primary or secondary degenerative disease (n=80) of the hip joint or osteonecrosis of the femoral head (n=21). The preoperative PMA score was 11.9 and the Harris score 49. Clinical and radiographic assessment was noted at mean 4.5 years follow-up. The radiographic femoral offset was measured semiautomatically in comparison with the healthy hip using the method described by Steinberg and Harris.

Results: At last follow-up, the mean PMA score was 16.4 and the mean Harris score 89. These clinically scores were statistically different depending on the degree of variation of the femoral offset. Outcome was better for offset increased 0 to 5 mm (PMA 17 and Harris 93). They were less satisfactory for decreased offset (PMA 15.9 and Harris 83) (p=0.01). They were also less satisfactory for an offset increased more than 8 mm, but non significantly.

Discussion: It has been established that increasing the femoral offset decreases the rate of dislocation, reduces the incidence of limping, the use of crutches, and increases the force of the gluteus medius, as well as range of motion and abduction. However, there is no known limit value.

Conclusion: It is advisable to increase the femoral offset during total hip arthroplasty; the increase should be to the order of 0 to 5 mm, and never be too great.

Purpose of the study: Use of the metal-on-metal bearing has been validated in total hip arthroplasty (THA) for conventional diameters and for resurfacing but not with large-diameter implants. The purpose of our study was to establish the short-term clinical validity of large diameter implants.

Material and methods: This was a retrospective study of a consecutive series of 106 press-fit cups (Durom^®) in 102 patients with minimum two years follow-up. Mean age at surgery was 66 years. Aetiologies were primary degenerative diseases (n=83), aseptic osteonecrosis (n=11), secondary degeneration (n=7), degeneration on acetabular dysplasia (n=2), rapid destructive osteoarthritis (n=1), fracture of the femoral neck (n=1) rheumatoid disease (n=1). Patients were reviewed with mean 30 months follow-up with the PMA and Harris scores. Radiographic measurements were made on semi-automatically (Imagicka^®) and included the ratio of prosthesis head to native head diameter, acetabular offset, and any implant migration, gap or lucency.

Results: There were two traumatic dislocations due to falls with regressive tendonitis of the gluteus medius with no later consequence. The mean Harris score was 91.6 and the mean PMA score 17. Outcome was excellent (n=70), good (n=31), fair (n=3) and poor (n=2). The ratio showed that head diameter had been restored for 65 hips (0.95 to 1.05). There were no cases of cup migration. Acetabular offset showed a mean lateralization of 1.1 mm. For 67 immediate posterior gaps, including ten measuring > 2mm, only two had not filled at review. None of the radiographic measurements had an effect on the clinical outcome.

Discussion: These results are comparable with those published for metal-on-metal bearings with 28mm heads and press fit cups. We did not find any mechanical or medical cause explaining the persistent pain observed in our patients with fair or poor outcome. The low level of dislocation (1.8%) confirms the improved prosthetic stability compared with 28 mm heads.

Conclusion: In our opinion, these early results demonstrate a clear improvement in stability, but at the cost of possible unexplained pain. Long term clinical and radiographic surveillance is needed to validate this option in terms of implant wear and survival.