Purpose of the study: Staphylococcus lugdunensis, described in Lyon in 1988 by Freney, appears to be a member of the cutaneous perineal flora. Since the first description, S. lugdunensis infections are regularly reported. The germ has been reported as the causal agent for endocarditis on valve prostheses with a very severe prognosis, requiring surgery in addition to medical management. We wanted to ascertain the prognosis of such infections on joint prostheses and to determine if it is different from that with other staphylococcal species.

Material and methods: Since 1991, seven S. lugdunensis infections on a joint prosthesis (three total hip prostheses and four total knee arthroplasties) were identified in our department. The Api Id 32 staph (BioMérieux SA) test battery was used for identification. All patients underwent surgical treatment and were given a prolonged antibiotic regimen. Simple joint cleaning was performed in three cases, one requiring a one-stage prosthesis replacement. There were four two-stage prosthesis replacements. The antibiotic regimen was always long (3–8 months) and was continued as a palliative treatment in two patients who underwent simple cleaning.

Results: One elderly woman with multiple co-morbid conditions died after prosthesis removal before the replacement procedure could be performed. There were no cases of recurrent infection at 16 months and 6 years for the four prosthesis replacements (one- and two-stage procedures). Arthroscopic cleaning without removal of the TKA was a failure in one patient who required prosthetic replacement later. Two simple cleanings in elderly patients were failures and required continuous palliative antibiotics.

Discussion: Staphylococcus lugdunensis is generally considered to be very susceptible to antibiotics in vitro. In our experience, search for minimum inhibitory concentrations and minimum bactericidal concentrations have shown cures with rapid shifts which must be taken into consideration when choosing an antibiotic. With surgical removal of the prosthesis and adapted antibiotics, the prognosis of these infections is not different from other staphylococcal infections of joint prostheses. We did however note two cases of secondary infections, probably related to hematogeneous spread, which developed from an unidentifiable point in time.

Conclusion: Staphylococcus lugdunensis is a coagulase-negative staphylococcus with poorly known virulence properties. In our very small series of joint prostheses infections, therapeutic failure occurred when the infected prosthesis was not removed.

Purpose of the study: The Alpina unicompartimen-tal knee prosthesis (Biomet) is an anatomic prosthesis inserted with a femoral cut, a tibial base plate made of titanium and a flat modular polyethylene insert. Cemented and non-cemented versions are available with hydroxyapatite ceramic (HAC) coating.

Material and methods: We retrospectively reviewed the radiological outcome at more than five years (fie to eight years follow-up) in a consecutive series of patients who had an Alpina HAC prosthesis with tibial fixation completed with a titanium screw. Clinical and radiological findings were recorded. Radiologically: pre- and postoperative angles, implant position, reliability of the instrument set. At last follow-up, we studied the presence of lucent lines, polyethylene wear easily measured on the flat insert, and bone remodeling around the tibial fixation screw.

Results: At last follow-up (5 to 8 years), three patients were lost to follow-up and three had died. Radiological outcome was thus assessed for 44 implants (41 medial and 3 lateral). One patient required an early total knee prosthesis (diagnostic error). Three patients underwent revision at 5–7 years (for rupture of the polyethylene insert in two very active patients, and for significant polyethylene wear in the third). Two had a revision procedure for a partial knee prosthesis and the third for a total knee prosthesis. For the 40 other patients, the following observations were made: partial lucent line along the tibial polyethylene plate with no functional impact (n=1), polyethylene wear visible but measuring less than 1 mm (n=12), remodeling around the tibial fixation screw probably corresponding to a granuloma but not threatening the implant (n=10).

Discussion: The clinical results of partial knee prostheses are well known. Mid-term radiographic results of non-cemented unicompartmental prostheses with a flat tibial plateau producing a minimal contact surface has shown: good reliability of the instrument set, excellent bony integration of the HAC-coated implants, but measurable polyethylene wear on more than one quarter of the prostheses, with two ruptures of the polyethylene insert at 5 and 6 years.

Conclusion: A study currently under way will examine finished pieces on a simulator to study wear and failure as a function of several parameters: polyethylene thickness, lateral restraint with a metal rim, presence of a basal stem fixing the polyethylene on the metal base, importance of the femur-polyethylene surface contact.

Purpose: The double mobility of the G. Bousquet cup—head-polyethylene,polyethylene metal cup—considerably reduces the risk of total hip arthroplasty displacement.

Material and methods: We observed seven cases of “intra-prosthetic” displacement in patients with this type of cup. Progressive wear of the polyethylene retention ring allowed displacement of the femoral head. These displacements occurred in six patients (one bilateral case) aged 43–58 years, on the average ten years after the implantation (range 3.5 – 15 years).

All patients underwent revision.

Results: The polyethylene retention ring was worn in all cases allowing the femoral head to escape. Revision surgery was performed very early in six hips to change the modular base and the polyethylene ring and re-establish retaining capacity. A satisfactory result was achieved in all cases. One patient required revision five years later to change the prosthesis subsequent to haematogenous infection. Another patient underwent a late revision to change the modular base and the entire cup of a press fit implant. This hip was in excellent condition but revision was decided on because of four dislocations.

Discussion: Intra-prosthetic displacement of the polyethylene head of a double-mobility cup is exceptional in our experience. Wear of the retention ring is favoured by different elements: 1) direct phenomena: neck and head diameter causing early contact between the neck and the cup; 2) indirect phenomena: factors limiting the mobility of the polyethylene metal cup couple (fibrosis, repeated interventions, ossification).

In our experience, intra-prosthetic displacement occurs more readily in patients with favouring conditions (alcoholism, muscle deficiency, psychiatric disorder, obesity) observed in six of our seven cases.

Conclusion: Intra-prosthetic displacement of a double-mobility cup is a possible but exceptional complication requiring a technically simple revision. Some teams use this type of cup systematically and for us is an essential element for preventive treatment in high-risk patients and for curative revision of recurrent dislocation.