In vitro additive effects of dalbavancin and rifampicin against biofilm of Staphylococcus aureus.

Dalbavancin is a novel glycopeptide antibiotic approved for the treatment of acute bacterial skin and skin structure infections (ABSSSIs). It is characterized by a potent activity against numerous Gram-positive pathogens, a long elimination half-life and a favorable safety profile. Most recently, its application for the treatment of periprosthetic joint infections (PJIs) was introduced. The aim of this study was to proof our hypothesis, that dalbavancin shows superior efficacy against staphylococcal biofilms on polyethylene (PE) disk devices compared with vancomycin and additive behavior in combination with rifampicin. Staphylococcus aureus biofilms were formed on PE disk devices for 96 h and subsequently treated with dalbavancin, vancomycin, rifampicin and dalbavancin-rifampicin combination at different concentrations. Quantification of antibacterial activity was determined by counting colony forming units (CFU/ml) after sonification of the PE, serial dilution of the bacterial suspension and plating on agar-plates. Biofilms were additionally life/dead-stained and visualized using fluorescence microscopy. Dalbavancin presented superior anti-biofilm activity compared to vancomycin. Additive effects of the combination dalbavancin and rifampicin were registered. Dalbavancin combined with rifampicin presents promising anti-biofilm activity characteristics in vitro. Further in vivo studies are necessary to establish recommendations for the general use of dalbavancin in the treatment of PJIs.

Effect of additional distal femoral resection on flexion deformity in posterior-stabilized total knee arthroplasty.

PURPOSE: Flexion deformity after total knee arthroplasty (TKA) is associated with poor function and dissatisfaction and should, therefore, be avoided. In the case of preoperative flexion deformity, an increased distal resection of the femur may be necessary. The degree of resection required has only been determined for cruciate-retaining (CR) prostheses to date and varies considerably from study to study. Although, for many surgeons, the algorithm for the treatment of a flexion deformity includes the resection of the posterior cruciate ligament (PCL) before additional distal resection, the degree of resection necessary for posterior-stabilized (PS)-type prostheses is not known. METHODS: Fifty consecutive patients (50 knees) who were due to undergo navigated TKA were included in this prospective study. At the end of the operation, the flexion deformity resulting from different sizes of distal femoral augmentations on the trial implants (0-8.5 mm) was determined using the navigation system. RESULTS: A linear relationship of 2.2° ± 0.3° flexion deformity per mm distal femoral augmentation was found. This was not dependent on age, sex, the preoperative coronal alignment, or the preoperative flexion deformity. CONCLUSIONS: In conclusion, after the removal of posterior osteophytes and posterior capsule release, around 5 mm of the distal femur must be further resected in the case of 10° flexion deformity and 9 mm in the case of 20° flexion deformity. LEVEL OF EVIDENCE: II (Prospective cohort study).

C-reactive protein course during the first 5 days after total knee arthroplasty cannot predict early prosthetic joint infection.

INTRODUCTION: Periprosthetic joint infection (PJI) is one of the most devastating major complications after total knee arthroplasty (TKA). The laboratory value C-reactive protein (CRP) is the inflammatory biomarker most suitable for detecting a potential postoperative (p.o.) early infection in orthopaedic surgery. However, on the basis of multiple receiver operating characteristic (ROC) analyses, CRP only has limited sensitivity and specificity. The objective of the present study was to test the hypothesis that, besides the absolute preoperative CRP value, also the absolute postoperative CRP value and its course over the first 5 days after TKA are valid indicators of periprosthetic early infection. MATERIALS AND METHODS: A total of 1068 subjects who had been treated with a unilateral primary cemented total knee replacement due to primary osteoarthritis of the knee were included in the study. Retrospectively, for all patients, the preoperative CRP value, the p.o. CRP course and a history of the medical course, including any superficial surgical site infection (SSI) or deep PJI of the knee joint operated on, were recorded; further, any follow-up operations (septic revision) were documented. Using receiver operating characteristic (ROC) analysis, an optimum preoperative CRP cutoff value for the positive prediction of a PJI was determined. RESULTS: 34 of 1068 patients developed an SSI or a PJI that had to be revised. After TKA implantation, the CRP value increased significantly and achieved its maximum between the second and third p.o. day. At no p.o. day was there a difference in CRP between patients who developed an SSI or a deep PJI and patients with a normal complication-free p.o. COURSE: In contrast, the preoperative CRP value proved to be a reliable predictor for septic revision due to an SSI or a PJI: the ROC analysis showed the optimum preoperative CRP cutoff value for a positive prediction of PJI to be 5 mg/L. CONCLUSION: The most important finding of the present study is that neither the absolute p.o. CRP value nor its course in the first 5 days after TKA is suitable for detecting an early infection. In contrast, an increased preoperative CRP value proved to be a valid predictor for septic revision due to an SSI or a PJI after TKA.

Changes of posterior condylar offset results in midflexion instability in single-radius total knee arthroplasty.

INTRODUCTION: There is no algorithm for the management of joint stability in midflexion up to now. Change in the joint line (JL) is considered to be the primary cause, although it only determines the extension gap. The purpose of this study was to determine the influence of the posterior condylar offsets (PCO), which defines the flexion gap, on midflexion instability. MATERIALS AND METHODS: Forty-two knee joints (38 patients) were included in this study, patients undergoing navigated total knee arthroplasty due to primary osteoarthritis of the knee. Changes in the JL and the PCO were determined from the navigation data. A gap tensioning device was used to determine the width of the joint gap at -5°, 0°, 30° and 60° intraoperatively. RESULTS: Within a range between 5 mm proximalization and 2 mm distalization, the JL had no influence on stability in midflexion. In contrast to this, both an increase and a decrease in PCO led to midflexion instability (R = 0.361, p = 0.019). In 16 cases (38%), the PCO was changed by more than 2 mm. This led to a midflexion instability of more than 2 mm in seven of these cases (44%). CONCLUSIONS: Whereas the joint line can be displaced by up to 5 mm without measurable changes in joint stability, reconstruction of the posterior offset within a tight range of 2 mm is necessary to avoid midflexion instability.

The C-reactive protein level after total knee arthroplasty is gender specific.

PURPOSE: Laboratory diagnostics are part of the routine before and after operations. In all specialist surgical disciplines, including orthopaedic surgery, the acute-phase protein CRP is used to detect inflammatory processes, especially infections. The potential influence of patient gender on the postoperative course of CRP after TKA implantation is still unclear. In order to achieve a more precise evaluation of the complication-free general CRP course after TKA, the objective of the present study is to test the hypothesis that the p.o. course and level of CRP is gender specific in the first 10 days after TKA. METHODS: A total of 1068 consecutive patients who had been treated with a unilateral primary cemented total knee replacement due to primary osteoarthritis of the knee over a 36-month period were retrospectively included in the study. For all patients, the preoperative CRP value and the postoperative course of CRP from postoperative days 1-10 were recorded and tested for gender specificity. RESULTS: On days 2-5 and 7-8 after surgery, men had significantly higher CRP values than women. The maximum difference was 45 mg/L on the fourth p.o. day (men 170 mg/L, women 125 mg/L, p = 0.019). CONCLUSION: The present study was able to show, for the first time, that the complication-free course of CRP in the first 10 days after TKA implantation is gender specific. The impact of the finding on diagnostic is that the gender-specific CRP course provides a more precise evaluation of the complication-free course of CRP after TKA. These results have clinical relevance to the interpretation of postoperative CRP values in order to avoid unnecessary investigations such as puncture or surgical care in female and male patients with uncomplicated TKA. Level of evidence Diagnostic study, III.

Regional differences in temperature course after knee arthroplasty.

PURPOSE: During wound healing after surgery, physiological inflammation leads to an increase in soft tissue perfusion. This is reflected by a characteristic temperature course in the skin. Although local surgical trauma also influences soft tissue perfusion, no data have been available on the regional temperature distribution after knee arthroplasty to date. This study aims at testing the hypothesis that the greatest regional difference in the temperature course is on the site of the maximum surgical trauma (medially) after knee arthroplasty implantation. This is to our knowledge the first study to present regional differences in the temperature course after TKA which would limit the diagnostic value of thermography. METHODS: Forty-two subjects who were to receive a surface replacement of the knee joint due to primary varus gonarthrosis were included in the study. In all cases, a medial parapatellar approach was chosen. Patients who underwent lateral release or a release of the lateral ligament structures were excluded. In all patients, a thermographic temperature determination was carried out on the operated knee joint every day up to the seventh post-operative day. RESULTS: On the medial side, there was no significant change in temperature between day one 34.9° ± 0.2° (34.6-35.3 °C) and seven after surgery. Thereafter, the temperature remained constant here up to the seventh day after the operation. In contrast to this, on the lateral side there was an increase in skin temperature from the second 35.0 ± 0.2 °C (34.7-35.4 °C) to the fifth 34.6° ± 0.2° (34.1-34.9 °C) post-operative day (p = 0.002). Thereafter, the temperature remained constant here up to the seventh day after the operation. CONCLUSION: This study refutes the hypothesis that the greatest regional difference in the temperature course is on the site of maximum surgical trauma (medially) after knee arthroplasty implantation. It is shown to the contrary that there is the least regional difference in the temperature course on the site of maximum surgical trauma (medially) after total knee arthroplasty implantation. It is on the site of the minimal trauma (laterally) where marked differences in the temperature course appeared. The normal temporary temperature increase typical of physiological wound healing could only be shown at a distance from the site of soft tissue preparation. This may be the result of a local compromise of perfusion. Consequently, the post-operative diagnostic application of thermography remains limited to regions distant from the surgical site. This may prevent misinterpretation of post-operative thermographic measurements for scientific or clinical reasons. LEVEL OF EVIDENCE: II.

The reversed gap technique produces anatomical alignment with less midflexion instability in total knee arthroplasty: a prospective randomized trial.

PURPOSE: No surgical technique is capable of controlling the stability of the joint in midflexion. The purpose of the present study was to present and evaluate a surgical technique that aims to reduce the need for soft-tissue release and optimize stability in midflexion. METHODS: Sixty knee joints were included in this prospective randomized study. Surgery was performed either according to a classical gap (GT) technique or using the reversed gap (RG) technique. In the RG, the femoral component was positioned parallel to the surgical transepicondylar axis using a preoperative MRI and a navigation system. The frontal alignment of the tibia was then selected to produce a symmetric flexion gap. Then, the frontal alignment of the femoral component was adjusted to produce a symmetric extension gap. Soft-tissue release was defined to be extensive if more than two steps or stabilizing structures were involved. Joint stability was measured at different flexion angles (-5° to 120°) using a gap tensioning device and the trial femoral implant. RESULTS: In the GT group, 16 knee joints (53 %) showed an instability of more than 2 mm at 5°, 30° or 60°, compared with 8 knee joints (27 %) in the RG group (p = 0.035). The RG did not lead to a reduction in the number of soft-tissue releases, but they were less extensive. CONCLUSION: RG reduced midflexion instability and the number of extensive soft-tissue releases. It may simplify the operation by reducing the extent of soft-tissue releases and avoid instability-related problems of knee arthroplasty. Nevertheless, it should only be performed under controlled conditions until long-term clinical data are available. LEVEL OF EVIDENCE: I.

The volume of the human knee joint.

INTRODUCTION: Despite its clinical relevance, particularly in septic knee surgery, the volume of the human knee joint has not been established to date. Therefore, the objective of this study was to determine knee joint volume and whether or not it is dependent on sex or body height. METHODS: Sixty-one consecutive patients (joints) who were due to undergo endoprosthetic joint replacement were enrolled in this prospective study. During the operation, the joint volume was determined by injecting saline solution until a pressure of 200 mmHg was achieved in the joint. RESULTS: The average volume of all knee joints was 131 ± 53 (40-290) ml. The volume was not found to be dependent on sex, but it was dependent on the patients' height (R = 0.312, p = 0.014). This enabled an estimation of the joint volume according to V = 1.6 height - 135. CONCLUSIONS: The considerable inter-individual variance of the knee joint volume would suggest that it should be determined or at least estimated according to body height if the joint volume has consequences for the diagnostics or therapy of knee disorders.