Nicholas M. Bernthal

A Mouse Model of Post-Arthroplasty Staphylococcus aureus Joint Infection to Evaluate In Vivo the Efficacy of Antimicrobial Implant Coatings

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 5×103 and 5×104 CFUs developed increased bacterial counts with marked swelling of the affected leg, consistent with an acute joint infection. In contrast, mice inoculated with 5×102 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.

The Multidisciplinary Management of Osteosarcoma

Opinion statementPatients with suspected or confirmed osteosarcoma should be evaluated and treated at a comprehensive cancer center within a multidisciplinary sarcoma program that includes pediatric, medical and radiation oncologists, orthopedic and surgical oncologists, musculoskeletal pathologists, and radiologists. Successful treatment involves proper diagnosis, neoadjuvant and adjuvant multi-agent chemotherapy, and aggressive surgery with an emphasis toward limb-preserving procedures. Treatment of osteosarcoma should be undertaken within the framework of large cooperative group clinical trials for children, adolescents, and adults. Patients treated with osteosarcoma should be followed closely both for recurrence of disease and for development of late effects of the treatment of their cancer. The treatment of metastatic, recurrent and/or refractory disease is more controversial. Despite advances in systemic treatment, surgical technique, and supportive care, the overall outcome is still poor.

Mouse model of chronic post-arthroplasty infection: noninvasive in vivo bioluminescence imaging to monitor bacterial burden for long-term study

Post‐arthroplasty infections are a devastating problem in orthopaedic surgery. While acute infections can be treated with a single stage washout and liner exchange, chronic infections lead to multiple reoperations, prolonged antibiotic courses, extended disability, and worse clinical outcomes. Unlike previous mouse models that studied an acute infection, this work aimed to develop a model of a chronic post‐arthroplasty infection. To achieve this, a stainless steel implant in the knee joints of mice was inoculated with a bioluminescent Staphylococcus aureus strain (1 × 102–1 × 104 colony forming units, CFUs) and in vivo imaging was used to monitor the bacterial burden for 42 days. Four different S. aureus strains were compared in which the bioluminescent construct was integrated in an antibiotic selection plasmid (ALC2906), the bacterial chromosome (Xen29 and Xen40), or a stable plasmid (Xen36). ALC2906 had increased bioluminescent signals through day 10, after which the signals became undetectable. In contrast, Xen29, Xen40, and Xen36 had increased bioluminescent signals through 42 days with the highest signals observed with Xen36. ALC2906, Xen29, and Xen40 induced significantly more inflammation than Xen36 as measured by in vivo enhanced green fluorescence protein (EGFP)‐neutrophil flourescence of LysEGFP mice. All four strains induced comparable biofilm formation as determined by variable‐pressure scanning electron microscopy. Using a titanium implant, Xen36 had higher in vivo bioluminescence signals than Xen40 but had similar biofilm formation and adherent bacteria. In conclusion, Xen29, Xen40, and especially Xen36, which had stable bioluminescent constructs, are feasible for long‐term in vivo monitoring of bacterial burden and biofilm formation to study chronic post‐arthroplasty infections and potential antimicrobial interventions.

Disappointing Short-Term Results With the DePuy ASR XL Metal-on-Metal Total Hip Arthroplasty

Outcomes of ultralarge-diameter femoral heads used in metal-on-metal (MOM) total hip arthroplasty (THA) are relatively unknown. This study reports on early failures of the ASR XL (Depuy, Warsaw, Ind) and assesses whether a correlation with cup positioning exists. A retrospective review of 70 consecutive MOM THAs with ultralarge-diameter femoral head and monoblock acetabular component was conducted. Minimum follow-up was 24 months. Of 70 THAs, 12 (17.1%) required revision within 3 years for pain (7), loosening (3), and squeaking (2). Three additional THAs noted squeaking, 2 noted grinding, and 3 additional hips had persistent pain. In total, 20 (28.6%) of 70 demonstrated implant dysfunction. Acetabular components for all symptomatic hips were in acceptable range of cup abduction and anteversion. The failures noted with this design do not correlate to cup placement. The high rate of implant dysfunction at early follow-up suggests serious concerns with the concept of MOM THA with an ultralarge-diameter femoral head paired with a monoblock acetabular cup.

Monitoring bacterial burden, inflammation and bone damage longitudinally using optical and μCT imaging in an orthopaedic implant infection in mice.

Background Recent advances in non-invasive optical, radiographic and μCT imaging provide an opportunity to monitor biological processes longitudinally in an anatomical context. One particularly relevant application for combining these modalities is to study orthopaedic implant infections. These infections are characterized by the formation of persistent bacterial biofilms on the implanted materials, causing inflammation, periprosthetic osteolysis, osteomyelitis, and bone damage, resulting in implant loosening and failure. Methodology/Principal Findings An orthopaedic implant infection model was used in which a titanium Kirshner-wire was surgically placed in femurs of LysEGFP mice, which possess EGFP-fluorescent neutrophils, and a bioluminescent S. aureus strain (Xen29; 1×103 CFUs) was inoculated in the knee joint before closure. In vivo bioluminescent, fluorescent, X-ray and μCT imaging were performed on various postoperative days. The bacterial bioluminescent signals of the S. aureus-infected mice peaked on day 19, before decreasing to a basal level of light, which remained measurable for the entire 48 day experiment. Neutrophil EGFP-fluorescent signals of the S. aureus-infected mice were statistically greater than uninfected mice on days 2 and 5, but afterwards the signals for both groups approached background levels of detection. To visualize the three-dimensional location of the bacterial infection and neutrophil infiltration, a diffuse optical tomography reconstruction algorithm was used to co-register the bioluminescent and fluorescent signals with μCT images. To quantify the anatomical bone changes on the μCT images, the outer bone volume of the distal femurs were measured using a semi-automated contour based segmentation process. The outer bone volume increased through day 48, indicating that bone damage continued during the implant infection. Conclusions/Significance Bioluminescent and fluorescent optical imaging was combined with X-ray and μCT imaging to provide noninvasive and longitudinal measurements of the dynamic changes in bacterial burden, neutrophil recruitment and bone damage in a mouse orthopaedic implant infection model.

Long‐term results (>25 years) of a randomized, prospective clinical trial evaluating chemotherapy in patients with high‐grade, operable osteosarcoma

The authors present the long‐term follow‐up (>25 years) data from 1 of the original prospective, randomized trials that compared adjuvant chemotherapy with expectant management in patients with high‐grade, localized osteosarcoma. In addition, the value of pathologic necrosis induced by a single cycle of neoadjuvant chemotherapy was analyzed as a predictive marker of disease‐free and overall survival.

Vancomycin-Rifampin Combination Therapy Has Enhanced Efficacy against an Experimental Staphylococcus aureus Prosthetic Joint Infection

ABSTRACT Treatment of prosthetic joint infections often involves a two-stage exchange, with implant removal and antibiotic spacer placement followed by systemic antibiotic therapy and delayed reimplantation. However, if antibiotic therapy can be improved, one-stage exchange or implant retention may be more feasible, thereby decreasing morbidity and preserving function. In this study, a mouse model of prosthetic joint infection was used in which Staphylococcus aureus was inoculated into a knee joint containing a surgically placed metallic implant extending from the femur. This model was used to evaluate whether combination therapy of vancomycin plus rifampin has increased efficacy compared with vancomycin alone against these infections. On postoperative day 7, vancomycin with or without rifampin was administered for 6 weeks with implant retention. In vivo bioluminescence imaging, ex vivo CFU enumeration, X-ray imaging, and histologic analysis were carried out. We found that there was a marked therapeutic benefit when vancomycin was combined with rifampin compared with vancomycin alone. Taken together, our results suggest that the mouse model used could serve as a valuable in vivo preclinical model system to evaluate and compare efficacies of antibiotics and combinatory therapy for prosthetic joint infections before more extensive studies are carried out in human subjects.

Protective role of IL-1β against post-arthroplasty Staphylococcus aureus infection

MyD88 is an adapter molecule that is used by both IL‐1R and TLR family members to initiate downstream signaling and promote immune responses. Given that IL‐1β is induced after Staphylococcus aureus infections and TLR2 is activated by S. aureus lipopeptides, we hypothesized that IL‐1β and TLR2 contribute to MyD88‐dependent protective immune responses against post‐arthroplasty S. aureus infections. To test this hypothesis, we used a mouse model of a post‐arthroplasty S. aureus infection to compare the bacterial burden, biofilm formation and neutrophil recruitment in IL‐1β‐deficient, TLR2‐deficient and wild‐type (wt) mice. By using in vivo bioluminescence imaging, we found that the bacterial burden in IL‐1β‐deficient mice was 26‐fold higher at 1 day after infection and remained 3‐ to 10‐fold greater than wt mice through day 42. In contrast, the bacterial burden in TLR2‐deficient mice did not differ from wt mice. In addition, implants harvested from IL‐1β‐deficient mice had more biofilm formation and 14‐fold higher adherent bacteria compared with those from wt mice. Finally, IL‐1β‐deficient mice had ∼50% decreased neutrophil recruitment to the infected postoperative joints than wt mice. Taken together, these findings suggest a mechanism by which IL‐1β induces neutrophil recruitment to help control the bacterial burden and the ensuing biofilm formation in a post‐surgical joint.

Recovery of elbow motion following pediatric lateral condylar fractures of the humerus.

BACKGROUND Temporary elbow stiffness is often seen after a lateral condylar fracture of the distal end of the humerus in children. There are scant scientific data available to assess the expected time frame for return of elbow motion after these injuries. The purpose of this study is to provide a prospective, longitudinal evaluation of elbow motion in a large group of pediatric patients undergoing treatment for a lateral condylar fracture of the distal end of the humerus. METHODS We prospectively evaluated 141 patients with lateral humeral condylar fractures at a mean age of 5.2 years and with a mean follow-up of twenty-nine weeks. The patients were treated with cast immobilization, percutaneous pinning, or open reduction and internal fixation on the basis of the initial displacement. Elbow motion was followed longitudinally at clinic visits. Relative arc of motion was calculated as a percentage of the motion of the normal, contralateral elbow. RESULTS The mean relative arc of motion at the time of cast removal was 44%, reaching 84% by week 12. By weeks 18, 24, 36, and 48, the relative arc of motion reached 87%, 90%, 93%, and 97%, respectively. Compared with fractures treated without surgery, those treated surgically had a significantly lower absolute arc of motion from the time of cast removal (p = 0.018) and up to eighteen weeks after the injury (p < 0.001); however, no significant difference was observed at eighteen weeks or beyond. For patients treated surgically, no significant difference in relative arc of motion was observed between the patients with closed or open reductions. The age of the patient (hazard ratio = 0.87, p = 0.008), length of immobilization (hazard ratio = 0.79, p = 0.03), and severity of the fracture (hazard ratio = 0.40, p < 0.0001) were independent predictors of recovery of elbow motion after a lateral humeral condylar fracture in children. CONCLUSIONS An initial rapid recovery in elbow motion can be expected after a lateral humeral condylar fracture in a child, with progressive improvements for up to one year after the injury. This recovery is slower if the patient is older, has a longer period of immobilization, and has a more severe injury.

Lateral spurring (overgrowth) after pediatric lateral condyle fractures.

Background: Bony overgrowth over the lateral condyle, or “lateral spurring,” is commonly identified after lateral condyle fractures of the humerus in children. Despite its frequent recognition, no prior study has defined the phenomenon, established an incidence rate, explored a correlation with any fracture or treatment characteristics, nor assessed whether it is of functional significance. Methods: We retrospectively analyzed information on 212 consecutive lateral condyle fractures in children. Spurring was defined as an overgrowth of bone over the lateral aspect of the lateral condyle resulting in an irregularity of the metaphyseal flare. The magnitude of the spurring was classified by measuring the increase in maximum interepicondylar width of the distal humerus on the latest follow-up radiograph. Results: Of the 212 fractures, 55% were treated with cast immobilization, 11% with closed reduction and percutaneous pinning, and 34% with open reduction and internal fixation. Of all fractures, 73% developed a lateral spur. Of those, 43% had a mild spur, 38% a moderate spur, and 19% a severe spur. Fractures that developed a spur had a mean initial displacement of 3.3 mm, as compared with 1.1 mm in those that did not develop spurring (P<0.0001). The amount of initial displacement was higher for fractures that developed mild (2.4 mm, P=0004), moderate (3.6 mm, P<0.00001), and severe (4.9 mm, P<0.00001) spurs, as compared with fractures with no spur. At the latest follow-up, patients that developed lateral spurring had a mean relative arc of motion of 93.7% of the normal contralateral elbow, whereas patients without a spur had a relative range of motion of 94.3% (P=0.4). Conclusions: Lateral spurring is an extremely common sequela of lateral humeral condyle fractures in children. The development of a spur correlates with initial displacement and surgical treatment. The size of the spur is associated with the amount of initial fracture displacement. Despite concerns from patients, families, and physicians alike, neither the presence nor the size of the lateral spur seems to influence the final outcome. Level of Evidence: Level II—retrospective study.