Aims. Currently, the most common approach for the management of a chronic PJI is a Two-Stage Replacement; because of success rates exceeding 90% when using an antibiotic impregnated cement spacer. Reliable information regarding the etiologic microorganism and its sensitivities is essential to select the antimicrobial therapy that should be used locally in the bone cement spacer during the first stage surgery as well as to select the appropriate microbiological systemic agent. Diagnostic algorithms focus to the importance of joint aspiration cultures although in the modern literature, preoperative joint aspiration has a broad range of values of sensitivity and the proportion of “dry-aspirations” is not well assessed. This low sensitivity of aspiration fluid samples in chronic-PJI is partly attributable to the fact that the majority of the microorganisms in these infections grow in biofilms attached to the implant. We have developed this biopsy technique in an effort to improve the identification rates of the causative organism. Materials and methods. A sample is harvested through a 4 mm bone trephine and the target is the bone-prosthesis gap. We have compared the results of preoperative PIB with the results of cultures from intra-operative tissue collected during the first stage surgery. In both cases a prolonged culture protocol (10 days) in enrichment media was used. On the basis of this relation, sensitivity, specificity, positive and negative predictive values and accuracy were calculated. Results. Twenty-four PIB were done on the 24 patients (10 hips and 14 knees) who subsequently underwent two-stage revision surgery because of high suspicion of PJI between January 2007 and December 2009. A retrospective analysis was performed in these 24 patients (13 women and 11 men) in the mean age of 70 years (from 63 to 88 years old). Nineteen of the cases were primary and 5 were revision arthroplasty. Nineteen patients (79%) were positive for infection from operative tissue cultures. The sensitivity was 0.79 (95% CI, 0.54–0.93); the specificity was 0.80 (95% CI, 0,30–0.99), the positive predictive value was 0.94 (95% CI, 0.67–0.99), the negative predictive value was 0.50 (95% CI, 17.5–82.5) and the accuracy was 0.79. Conclusion. PIB is a useful test to, preoperatively, isolate the infecting bacteria. The values of sensitivity, specificity and accuracy are on the average of the currently published with joint aspiration or biopsy samples cultures. Although comparative study is necessary we believe that the PIB could be useful in cases with high suspicion of PJI and negative joint aspiration cultures and in cases where no fluid is aspired from the joint, in order to preoperatively isolate the infecting bacteria

Several bisphosphonates are now available for the treatment of osteoporosis. Porous hydroxyapatite/collagen (HA/Col) composite is an osteoconductive bone substitute which is resorbed by osteoclasts. The effects of the bisphosphonate alendronate on the formation of bone in porous HA/Col and its resorption by osteoclasts were evaluated using a rabbit model. Porous HA/Col cylinders measuring 6 mm in diameter and 8 mm in length, with a pore size of 100 μm to 500 μm and 95% porosity, were inserted into a defect produced in the lateral femoral condyles of 72 rabbits. The rabbits were divided into four groups based on the protocol of alendronate administration: the control group did not receive any alendronate, the pre group had alendronate treatment for three weeks prior to the implantation of the HA/Col, the post group had alendronate treatment following implantation until euthanasia, and the pre+post group had continuous alendronate treatment from three weeks prior to surgery until euthanasia. All rabbits were injected intravenously with either saline or alendronate (7.5 μg/kg) once a week. Each group had 18 rabbits, six in each group being killed at three, six and 12 weeks post-operatively. Alendronate administration suppressed the resorption of the implants. Additionally, the mineral densities of newly formed bone in the alendronate-treated groups were lower than those in the control group at 12 weeks post-operatively. Interestingly, the number of osteoclasts attached to the implant correlated with the extent of bone formation at three weeks.

In conclusion, the systemic administration of alendronate in our rabbit model at a dose-for-weight equivalent to the clinical dose used in the treatment of osteoporosis in Japan affected the mineral density and remodelling of bone tissue in implanted porous HA/Col composites.