Background: Despite its well-established limitations, culture remains the gold standard for microbial identification in periprosthetic joint infection (PJI). However, there are no benchmarks for the time to positivity (TTP) on culture for specific microorganisms. This study aimed to determine the TTP for pathogens commonly encountered in PJI. Methods: This retrospective, multicenter study reviewed prospectively maintained institutional PJI databases to identify patients who underwent hip or knee revision arthroplasty from 2017 to 2021 at 2 tertiary centers in the United States and Germany. Only patients who met the 2018 International Consensus Meeting (ICM) criteria for PJI and had a positive intraoperative culture were included. TTP on culture media was recorded for each sample taken intraoperatively. The median TTP was compared among different microbial species and different specimen types. Data are presented either as the mean and the standard deviation or as the median and the interquartile range (IQR). Results: A total of 536 ICM-positive patients with positive cultures were included. The mean number of positive cultures per patient was 3.9 ± 2.6. The median TTP, in days, for all positive cultures was 3.3 (IQR, 1.9 to 5.4). Overall, gram-negative organisms (TTP, 1.99 [1.1 to 4.1]; n = 225) grew significantly faster on culture compared with gram-positive organisms (TTP, 3.33 [1.9 to 5.8]; n = 1,774). Methicillin-resistant Staphylococcus aureus (TTP, 1.42 [1.0 to 2.8]; n = 85) had the fastest TTP, followed by gram-negative rods (TTP, 1.92 [1.0 to 3.9]; n = 163), methicillin-sensitive Staphylococcus aureus (TTP, 1.95 [1.1 to 3.3] n = 393), Streptococcus species (TTP, 2.92 [1.2 to 4.3]; n = 230), Staphylococcus epidermidis (TTP, 4.20 [2.4 to 5.5]; n = 555), Candida species (TTP, 5.30 [3.1 to 10]; n = 63), and Cutibacterium acnes (TTP, 6.97 [5.9 to 8.2]; n = 197). When evaluating the median TTP according to specimen type, synovial fluid (TTP, 1.97 [1.1 to 3.1]; n = 112) exhibited the shortest TTP, followed by soft tissue (TTP, 3.17 [1.4 to 5.3]; n = 1,199) and bone (TTP, 4.16 [2.3 to 5.9]; n = 782). Conclusions: To our knowledge, this is the first study to examine the TTP of common microorganisms that are known to cause PJI. Increased awareness of these data may help to guide the selection of appropriate antimicrobial therapy and to predict treatment outcomes in the future. Nonetheless, additional studies with larger cohorts are needed to validate these benchmarks. Level of Evidence: Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Aims: Despite numerous studies focusing on periprosthetic joint infections (PJIs), there are no robust data on the risk factors and timing of metachronous infections. Metachronous PJIs are PJIs that can arise in the same or other artificial joints after a period of time, in patients who have previously had PJI.Methods: Between January 2010 and December 2018, 661 patients with multiple joint prostheses in situ were treated for PJI at our institution. Of these, 73 patients (11%) developed a metachronous PJI (periprosthetic infection in patients who have previously had PJI in another joint, after a lag period) after a mean time interval of 49.5 months (SD 30.24; 7 to 82.9). To identify patient-related risk factors for a metachronous PJI, the following parameters were analyzed: sex; age; BMI; and pre-existing comorbidity. Metachronous infections were divided into three groups: Group 1, metachronous infections in ipsilateral joints; Group 2, metachronous infections of the contralateral lower limb; and Group 3, metachronous infections of the lower and upper limb.Results: We identified a total of 73 metachronous PJIs: 32 PJIs in Group 1, 38 in Group 2, and one in Group 3. The rate of metachronous infection was 11% (73 out 661 cases) at a mean of four years following first infection. Diabetes mellitus incidence was found significantly more frequently in the metachronous infection group than in non-metachronous infection group. The rate of infection in Group 1 (21.1%) was significantly higher (p = 0.049) compared to Groups 2 (6.2%) and 3 (3%). The time interval of metachronous infection development was shorter in adjacent joint infections. Concordance between the bacterium of the first PJI and that of the metachronous PJI in Group 1 (21/34) was significantly higher than Group 2 (13/38; p = 0.001).Conclusion: The findings of this study suggest that metachronous PJI occurs in more than one in ten patients with an index PJI. Female patients, diabetic patients, and patients with a polymicrobial index PJI are at significantly higher risk for developing a metachronous PJI. Furthermore, metachronous PJIs are significantly more likely to occur in an adjacent joint (e.g. ipsilateral hip and knee) as opposed to a more remote site (i.e. contralateral or upper vs lower limb). Additionally, adjacent joint PJIs occur significantly earlier and are more likely to be caused by the same bacteria as the index PJI.Cite this article: Bone Joint J 2023;105-B(3):294–300.

Background: Periprosthetic femoral fractures are challenging complications of hip arthroplasty. They are supposed to be a rare complication, but their incidence is rapidly increasing. Surgical treatment aims to achieve early mobilization and avoid the complications of prolonged bed rest. Aim of this study is to evaluate the clinical outcomes of surgical treatment comparing two surgical approaches: revision arthroplasty (RA) versus open reduction and internal fixation (ORIF). Methods: Authors retrospectively reviewed a series of 117 patients with total hip arthroplasty treated for periprosthetic femur fractures in the period between January 2013 and March 2018 at a single tertiary referral center. Of these, 70 patients satisfied strict inclusion criteria. Patients were classified according to the Unified Classification System (UCS) and distributed in two groups according to surgical treatment. Clinical outcomes were assessed using the Oxford Hip recorded preoperatively and post operatively, Barthel Score, CIRS score (Cumulative illness rating scale), type of fracture and post-operative complications with a minimum follow up of 1 year. Results: Nominal univariate statistical analysis revealed significant differences between the post and pre-operative Oxford Hip Score (Δ Oxford) and the surgical treatment (p = 0.008) and CIRS score (p = 0.048). Moreover, we observed a significant relationship between type of treatment and type of fracture (p = 0.0001). Multivariate analyses revealed that CIRS score was independently associated with Oxford Score improvement after surgery (p = 0.024). Conclusions: Data from this case series confirmed that surgical treatment was correlated to type of fracture, according to UCS classification. Patients treated by RA had a better functional outcome than patients treated with ORIF, but these results are strongly influenced from the patients’ age, Barthel index and CIRS score. Also, authors found a correlation between functional outcome and comorbidities evaluated by CIRS score. Based on these data we suggest a multimodal approach to these patients, like those used for proximal femoral fractures.

The purpose of this article was to analyze clinical and functional results after medial patellofemoral ligament (MPFL) reconstruction and to establish if a computer-assisted physical test battery could determine a “safe timing” to return to sport. We hypothesized that “time-based” criteria to declare safe return to sport could not be reliable to predict functional recover. Fifty-eight young athletic patients were selected after isolated reconstruction of MPFL. The minimum follow-up was 8 months. All the patients were evaluated subjectively with Kujala and Short Form 36 (SF-36) scores and objectively through a standardized computer-assisted physical battery of seven tests (Back in Action, Corehab). No patient was lost at the end point of follow-up and no recurrence of patellar dislocation was reported. At 8 months, 31 patients (53.4%) returned to sport at preoperative levels, and 23 (39.6%) participated in sports at lower levels. The subjective evaluation reported an increase of Kujala (60–92.7) and SF-36 score (28.6/25.4–52.2/53.6). At computer-assisted objective assessment, only 23 patients (39.6%) fulfilled the criteria for safe return to sport, while 31 (53.4%) got an insufficient outcome and 4 (6.9%) failed to complete the test. From our data, clinical scores after MPFL reconstruction provide only little insight into return to sport. The introduction of a computer-assisted objective analysis in the decision-making process for proper return to sport is necessary to evaluate functional recovery and dynamic knee stability.