A prospective study of Charnley low friction arthroplasty in patients under the age of 51 at the time of surgery.

1092 patients, 668 women and 424 men, mean age 41 years (12–51) at the time of surgery had 1434 Charnley low-friction arthroplasties carried out between November 1962 and December 1990. At mean follow-up 14.2 years (1 – 32), 742 patients (973 hips) are still attending and patients’ satisfaction with the outcome is 96.2%. Survivorship was 95.24% at 10 years and 58.67% at 27 years.

Patients who had had previous hip surgery had revision rate 24.8% compared with 14.1%. Patients with rheumatoid arthritis had fewer revisions than those with developmental hip dysplasia or primary osteoarthritis. Large 43 mm diameter cup gave lower revisions for aseptic cup loosening as compared with 40mm cup. Presence and preservation of subchondral plate, rim support compared to medialization of the cup, use of acetabular cement pressurizer and the reduced diameter neck (10mm) all made a contribution to reducing the incidence of revisions for aseptic cup loosening. Closing the medullary canal with bone block reduced the incidence of aseptic stem loosening. Use of the brace reamers did not affect the outcome and there appears to have been no advantage with the flanged stem.

The long-term problem was the increasing incidence of revisions for aseptic cup loosening. This was exponentially related to the depth of cup penetration by the head of the femoral component.

The long term clinical results of the Charnley LFA remain excellent even in young patients. Rim support of the cup, preservation of the subchondral bone of the acetabulum, cup flange and pressurising of the acetabular cement all make a significant contribution. Distal closure of the medullary canal and central position of the stem are of benefit, but reaming the medullary canal to cortex must be avoided. The long-term problem has been highlighted again as: wear and cup loosening.

We retrospectively analysed three hundred and one infected total hip replacements. Infection was defined on the basis of the surgeons clinical impression. This included a thorough history and physical examination, laboratory and radiographic evaluation. Peri operative findings were also taken into consideration.

Despite the overt appearances of sepsis fifty seven of these three hundred and one cases demonstrated no bacterial growth. These were excluded from the microbiological analysis.

The remaining two hundred and forty four cases oven bacteriological evidence of deep infection. Thirty seven cases grew two different organisms both of which were felt to be clinically significant. The remainder grew a single organism. Hence a total two hundred and eighty one bacteriological isolates were grown.

Coagulase negative staphylococcus accounted for 54.8%, staphylococcus aureus 13.5%, streptococci 8.9%, Escherichia coli 6.1% and diptheroids 2.5%.These organisms were plated out in a standard fashion against a variety of antimicrobial agents.

We analysed ten antibiotics and their sensitivity profiles against the spectrum of organisms demonstrated by this series.

Best antimicrobial coverage by a single antibiotic was afforded by fucidic acid (85.3%) and erythromycin (79.6%). Gentamicin was found to be sensitive to only 76.1% of the bacteria present at the time of revision for deep infection.

Combining gentamicin with other antibiotics improved the theoretical coverage. A combination of gentamicin and fucidic acid demonstrated a 97.5% coverage. Gentamicin with erythromycin gave 95.2%.

When treating the infected arthroplasty it may be beneficial to add extra antibiotics to bone cement. This may either be to the cement spacer in a two stage revision or to the definitive cement in a single stage revision. We would suggest that fucidic acid or erythromycin would be good candidates for this. These candidates should also be considered when designing the next generation of combination antibiotic acrylic bone cements.

Bacterial resistance in joint replacement surgery is an emerging problem. A review of the bacteriology from infected revisions performed at Wrightington over the past 5 years has shown that the most common organism is coagulase negative staphylococcus (59%), followed by staphylococcus aureus (17%).

The sensitivity profiles are shown below.

Gentamicin is the most commonly pre formulated antibiotic added to acrylic bone cement. The above data clearly demonstrates that for 32% of infected cases gentamicin alone is inadequate prophylaxis. As a consequence of this the use of additional antibiotics for resistant cases is becoming commonplace.

The aim of this study was to investigate the mechanical properties of additional antibiotics in acrylic bone cement.

The 7 antibiotics listed above were selected on the basis of sensitivity to organisms isolated at revision for deep infection. Each was added at a loading of 1g active to CMW1 RO (plain) and CMW1 G (gentamicin). The antibiotics were mixed with the polymer by hand. The cement was then mixed as per manufacturer’s instructions.

Dough and setting times were noted. Standard samples were produced using ISO approved moulds. Each antibiotic/cement combination was tested for compression strength, impact strength and flexural strength.

All antibiotic/cement combinations performed as well as the control mix when tested for compression and impact strength. The flexural strength results for fusidic acid and erythromycin when added to acrylic cement were comparable to the control mix. Flucloxacillin, clindamycin and teicoplanin did lower the flexural strength to just below acceptable limits. However Vancomycin when added at 1g active reduced the flexural strength of acrylic bone cement significantly.

Although vancomycin may remain one of the last bastions of antibiotic therapy our study suggests that’s its addition to acrylic bone cement significantly weakens its mechanical properties. We would advise caution in its use as this may reduce the chances of long term success when undertaking revision for deep infection.

Objective: To study the incidence of MRSA (Methicillin resistant Staphylococcus aureus) at pre-operative screening and relate this to positive cultures of the tissue in joint replacement surgery.

Setting: Elective joint replacement centre with routine MRSA screening facility.

Design: Retrospective review of MRSA screening and positive tissue samples taken during one year period from 1.11.99 to 31.10.00 in hip and knee replacements.

Results: Eighteen (18) out of the 2867(0.7%) screens performed on patients undergoing joint replacement surgery had MRSA isolated from one source or other. However, no MRSA was found from tissue samples taken during the surgery. But 63 isolates from 499 tissue samples (12.6%) were reported as coagulase negative staphylococcus, out of which 28(44%) were resistant to Methicillin.

After observing the incidence of Methicillin resistant coagulase negative staphylococcus during one year, we reviewed the tissue culture reports in revision hip replacements from May 1974 till July 1999. Two hundred ninety-one (291) positive organisms were isolated from 337 cultures, out of which 57.5% were coagulase negative staphylococcus 11.9% staphylococcus aureus. Methicillin resistance was noted in 30.8% of coagulase negative staphylococcus as opposed to 6% of staphylococcus aureus.

Conclusion: Staphylococcus epidermidis is the most prevalent and persistent species on human skin and mucous membranes, constituting 65–90% of all staphylococci (Mandell, Douglas & Bennett, 2000). Since a majority of isolation in tissue samples constitute methicillin resistant coagulase negative staphylococcus, would it be more appropriate to screen for Methicillin resistant Staphylococcus epidermidis (MRSE), rather than MRSA, in patients undergoing joint replacement surgery?