This 9-year-old girl presented with a painful mass in the posterolateral aspect of her right knee. Excisional biopsy of the mass revealed a juxta-articular myxoma. The differential diagnosis for such an intra- or periarticular mass should include meniscal cyst, parameniscal cyst, ganglion cyst, juxta-articular myxoma, focal nodular PVNS, and desmoid tumor. Current imaging techniques do not allow differentiation between these benign lesions and low grade myxoid-containing sarcoma.

This study was undertaken to determine the accuracy of magnetic resonance image scanning in detecting posterior cruciate ligament injury, and to determine those clinical situations where it can add the most useful information. A retrospective study was conducted on 201 patients who underwent surgery after magnetic resonance scanning of their knees. Two additional patients who did not have surgery but had clinical findings grossly positive for posterior cruciate ligament injury were included in the analysis of magnetic resonance imaging accuracy. In all, there were 190 intact and 13 torn posterior cruciate ligaments. In a review of the clinical findings in the 11 patients with surgically documented tears, we found that all 11 had positive magnetic resonance scans. In 4 of the 11, magnetic resonance imaging provided especially useful information regarding the status of the ligament. For the 190 normal ligaments, there were no false-positive scans; for the 13 torn ligaments, there were no false-negative scans. Therefore, specificity and sensitivity estimates for this group were both 100%. Magnetic resonance imaging proved to be an accurate modality for evaluating the integrity of the posterior cruciate ligament. If used in the proper setting, it can provide useful information for diagnosing posterior cruciate ligament injuries.

Background

Post-arthroplasty infections represent a devastating complication of total joint replacement surgery, resulting in multiple reoperations, prolonged antibiotic use, extended disability and worse clinical outcomes. As the number of arthroplasties in the U.S. will exceed 3.8 million surgeries per year by 2030, the number of post-arthroplasty infections is projected to increase to over 266,000 infections annually. The treatment of these infections will exhaust healthcare resources and dramatically increase medical costs.

Methodology/principal findings

To evaluate novel preventative therapeutic strategies against post-arthroplasty infections, a mouse model was developed in which a bioluminescent Staphylococcus aureus strain was inoculated into a knee joint containing an orthopaedic implant and advanced in vivo imaging was used to measure the bacterial burden in real-time. Mice inoculated with 5x10(3) and 5x10(4) CFUs developed increased bacterial counts with marked swelling of the affected leg, consistent with an acute joint infection. In contrast, mice inoculated with 5x10(2) CFUs developed a low-grade infection, resembling a more chronic infection. Ex vivo bacterial counts highly correlated with in vivo bioluminescence signals and EGFP-neutrophil fluorescence of LysEGFP mice was used to measure the infection-induced inflammation. Furthermore, biofilm formation on the implants was visualized at 7 and 14 postoperative days by variable-pressure scanning electron microscopy (VP-SEM). Using this model, a minocycline/rifampin-impregnated bioresorbable polymer implant coating was effective in reducing the infection, decreasing inflammation and preventing biofilm formation.

Conclusions/significance

Taken together, this mouse model may represent an alternative pre-clinical screening tool to evaluate novel in vivo therapeutic strategies before studies in larger animals and in human subjects. Furthermore, the antibiotic-polymer implant coating evaluated in this study was clinically effective, suggesting the potential for this strategy as a therapeutic intervention to combat post-arthroplasty infections.