Viktor E. Krebs

Diagnosis of Periprosthetic Infection

Periprosthetic infections are rare, but there is evidence to suggest that their frequency may be underestimated. No single laboratory test has perfect sensitivity and specificity for diagnosing infection. Most tests have better specificity when they are performed for patients in whom infection is suspected clinically rather than when they are used as screening tests. Screening test results that may suggest the possibility of infection include elevation of the erythrocyte sedimentation rate and/or serum C-reactive protein level more than three months after an arthroplasty. Most serologic tests are difficult to interpret when the patient has an underlying inflammatory arthropathy. Cultures of aspirated joint fluid can be especially helpful for patients who have symptoms suggestive of infection, but their results are best interpreted two weeks after administration of antibiotics has been discontinued. Joint fluid cell counts may also be helpful, but Gram stains of joint fluid have poor sensitivity and specificity. Criteria for diagnosing infection on the basis of frozen sections of implant membranes have not yet been standardized, but in many laboratories more than five neutrophils per high-power field in five or more fields (excluding surface fibrin) has been found to be suggestive of infection. Most polymerase chain reactions that detect the universal 16S rRNA bacterial gene have problems with false-positive results, but combining a universal polymerase chain reaction with subsequent bacterial sequencing can help improve specificity. Polymerase chain reactions can detect necrotic bacteria, so the clinical importance of positive results of this analysis in the absence of other features of infection remains to be determined.

Simultaneous Detection of Staphylococcus aureus and Coagulase-Negative Staphylococci in Positive Blood Cultures by Real-Time PCR with Two Fluorescence Resonance Energy Transfer Probe Sets

ABSTRACT A real-time PCR assay that uses two fluorescence resonance energy transfer probe sets and targets the tuf gene of staphylococci is described here. One probe set detects the Staphylococcus genus, whereas the other probe set is specific for Staphylococcus aureus. One hundred thirty-eight cultured isolates, which contained 41 isolates of staphylococci representing at least nine species, and 100 positive blood cultures that contained gram-positive cocci in clusters were tested. This assay was 100% sensitive and 100% specific for the detection of the Staphylococcus genus and of S. aureus.

Duration of anesthesia and venous thromboembolism after hip and knee arthroplasty

OBJECTIVE To determine whether longer duration of anesthesia predisposes patients undergoing orthopedic surgery to venous thromboembolism (VTE). PATIENTS AND METHODS We conducted a secondary analysis of a retrospective case-control study that examined risk factors for postoperative VTE in postmenopausal women. We matched women aged 50 years and older with radiographically confirmed postoperative VTE (cases) by age, surgeon, year of surgery, and surgical joint (knee vs hip) with women without postoperative VTE (controls). Duration of anesthesia, operative variables, demographic data, comorbid illnesses, and laboratory data were determined by medical record review. RESULTS Eighty-eight cases were matched with 181 controls. Duration of anesthesia of 3.5 hours or longer (corresponding to the upper tertile of patients) was strongly associated with postoperative VTE compared with a shorter duration of anesthesia (odds ratio, 3.58; 95% confidence Interval, 2.11-6.16; P < .001). This relationship was maintained after controlling for multiple covariates with propensity score methods, Including type of arthroplasty, route of anesthesia, type of antithrombotic prophylaxis, and surgical approach. In multivariate analysis, the Important predictors of VTE included anesthesia duration of 3.5 hours or longer, type of antithrombotic prophylaxis, revision (vs primary) arthroplasty, and allogeneic blood transfusion. CONCLUSION We found a marked association between the duration of anesthesia and postoperative VTE in patients undergoing Joint arthroplasty. Although it is possible that unmeasured intraoperative variables account for this relationship, we suggest that duration of anesthesia may be an important risk factor for postoperative VTE after orthopedic surgery.

Molecular Identification of Bacteria from Aseptically Loose Implants

AbstractPolymerase chain reaction (PCR) assays have been used to detect bacteria adherent to failed orthopaedic implants, but some PCR assays have had problems with probable false-positive results. We used a combination of a Staphylococcus species-specific PCR and a universal PCR followed by DNA sequencing to identify bacteria on implants retrieved from 52 patients (92 implants) at revision arthroplasty. We addressed two questions in this study: (1) Is this method able to show the existence of bacterial DNA on presumed aseptic loosed implants?; and (2) What proportion of presumed aseptic or culture-negative implants was positive for bacterial DNA by PCR? Fourteen implants (15%) were believed infected, whereas 74 implants (85%) were believed aseptic. Each implant was sonicated and the resulting solution was submitted for dual real-time PCR assay and culture. All implants believed aseptically loose were culture-negative, but nine of the 74 (12%) had bacterial DNA by PCR; two (2.7%) were PCR-positive and also showed histologic findings suggestive of infection. Uniquely developed PCR and bacterial sequencing assays showed bacterial DNA on 12% of implants removed for presumed aseptic loosening. Additional studies are needed to determine the clinical importance of bacterial DNA detected by PCR but not by conventional culture. Level of Evidence: Level III, diagnostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Prospective Randomized Evaluation of the Need for Blood Transfusion During Primary Total Hip Arthroplasty with Use of a Bipolar Sealer

BACKGROUND Blood loss during total hip arthroplasty can be substantial and may lead to adverse patient outcomes and increased health-care costs. Many blood-management options are available for these procedures. The purpose of the present study was to test the hemostatic efficacy of a bipolar sealer used during total hip arthroplasty in order to determine whether its use results in significantly lower transfusion requirements and/or improved clinical, functional, and health-related quality-of-life outcomes in healthy patients. METHODS This prospective, single-center, randomized, double-blinded study was designed to enroll a total of 140 patients. Patients with a low preoperative hemoglobin level or a history of bleeding abnormalities and other medical conditions were excluded. Patients were randomized to either the treatment arm (radiofrequency energy with use of the Aquamantys 6.0 bipolar sealer) or control arm (standard Bovie electrocautery). The primary outcome measure was the transfusion requirement, and the secondary outcome measures were intraoperative estimated blood loss, postoperative hemoglobin levels, perioperative narcotic usage, length of hospital stay, postoperative pain scores, and postoperative function as measured with the Harris hip score and the Short Form-12 quality-of-life score. RESULTS Seventy-one patients were assigned to the treatment arm, and sixty-nine were assigned to the control arm. The mean number of units of blood transfused for all patients in the study and control arms were 0.38 and 0.44, respectively (p = 0.72). The transfusion requirements were similar in the two groups, with fifteen of seventy-one patients in the treatment arm and fourteen of sixty-nine patients in the control arm requiring a transfusion (p = 0.9). No significant differences were detected between the groups in terms of estimated blood loss, postoperative hemoglobin levels, perioperative narcotic usage, length of hospital stay, postoperative pain scores, Harris hip scores, or Short Form-12 scores. CONCLUSIONS In this patient population, there were no significant differences between the treatment and control groups in terms of the need for blood transfusions or overall blood loss. Given these findings, we have discontinued the use of this bipolar sealing device in uncomplicated primary total hip arthroplasty patients at our institution. LEVEL OF EVIDENCE Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.

Influence of technique with distally fixed modular stems in revision total hip arthroplasty.

Distally fixed modular implants have seen a recent increase in use, to manage proximal femoral bone loss often encountered during revision total hip arthroplasty (THA). Forty-three distally fixed modular stems implanted at our institution between 1999 and 2006 were clinically and radiographically reviewed. These patients had either a minimum 2-year follow-up (average, 2.4 years; range, 2-5.6 years) or failure (ie, explant or rerevision required). Eleven stems subsided, and 4 were rerevised (n = 4), for a rate of 9.3%. All revised stems were radiographically undersized, emphasizing the importance of the technique. Although being a valuable option in revision THA, these stems are not free of complications. The high rate of subsidence encountered in our early experience shows that there is a learning curve. This complication is preventable by avoiding undersizing.

A computer model of the position of the combined component in the prevention of impingement in total hip replacement

Dislocation remains a major concern after total hip replacement, and is often attributed to malposition of the components. The optimum position for placement of the components remains uncertain. We have attempted to identify a relatively safe zone in which movement of the hip will occur without impingement, even if one component is positioned incorrectly. A three-dimensional computer model was designed to simulate impingement and used to examine 125 combinations of positioning of the components in order to allow maximum movement without impingement. Increase in acetabular and/or femoral anteversion allowed greater internal rotation before impingement occurred, but decreases the amount of external rotation. A decrease in abduction of the acetabular components increased internal rotation while decreasing external rotation. Although some correction for malposition was allowable on the opposite side of the joint, extreme degrees could not be corrected because of bony impingement. We introduce the concept of combined component position, in which anteversion and abduction of the acetabular component, along with femoral anteversion, are all defined as critical elements for stability.

Complex prosthetic joint infections due to carbapenemase-producing Klebsiella pneumoniae: a unique challenge in the era of untreatable infections

SUMMARY Objectives Limited clinical experience exists regarding the management of prosthetic joint infection (PJI) due to multidrug-resistant (MDR) Gram-negative organisms. We review three cases of carbapenem-resistant Klebsiella pneumoniae (CRKP) complicating PJI. Methods This was a retrospective study of all patients at a tertiary care institution with CRKP complicating PJI between January 2007 and December 2010. Demographic data, procedures, organisms involved, length of stay, antibiotic treatments, and outcomes were collected. Antimicrobial susceptibility testing was performed on CRKP isolates, and the mechanism of resistance was ascertained by PCR. Results This analysis demonstrated that: (1) the CRKP possessed blaKPC and were difficult to eradicate (persistent) in PJI; (2) multiple surgeries and antibiotic courses were undertaken and patients required a prolonged length of stay; (3) resistance to colistin and amikacin emerged on therapy; (4) the same strain of CRKP may be responsible for relapse of infection; (5) significant morbidity and mortality resulted. Conclusions These cases highlight the opportunistic and chronic nature of CRKP in PJIs and the need for aggressive medical and surgical treatment. Further investigations of the management of CRKP PJI and new drug therapies for infections due to MDR Gram-negative organisms are urgently needed.

The Anatomy of the Acetabulum: What is Normal?

Published studies of the human hip make frequent reference to the normal pelvis and acetabulum. However, other than qualitative descriptions we found no clinically applicable published references describing a normal pelvis and acetabulum; such information is important for designing certain kinds of implants (eg, reconstruction cages). We describe a method to quantify, average, and apply data gathered from normal human specimens to create a standard representation of the ilium and ischium. One hundred healthy hemipelves from 50 human skeletons were evaluated. We measured angles and distances between major anatomic landmarks in the pelvis. The data collected were analyzed for variance and averaged to create a normal topographic map. Finally, we examined several commercially available acetabular reconstruction cages to determine the fit to the anatomically determined normal pelvis. These results provide a representation of true acetabular geometry and may serve as the basis for future acetabular reconstruction cage design.

Comparison of Acetabular Shell Position Using Patient Specific Instruments vs. Standard Surgical Instruments: A Randomized Clinical Trial

Total hip arthroplasty (THA) survivorship relies largely upon appropriate acetabular cup placement. The purpose of this prospective randomized controlled trial was to determine whether the use of a preoperative 3D planning software in combination with patient specific instrumentation (PSI) results in improved cup placement compared with traditional techniques. Thirty-six THA patients were randomized into standard (STD) or PSI technique. Standard approach was completed using traditional techniques, while PSI cases were planned and customized surgical instruments were manufactured. Postoperative CT scans were used to compare planned to actual results. Differences found between planned and actual anteversion were -0.2° ± 6.9° (PSI) and -6.9°±8.9° (STD) (P = 0.018). Use of 3D preoperative planning along with PSIs resulted in significantly greater anteversion accuracy than traditional planning and instrumentation.