The research, led by Belal Abdo and Markus Rupp of the Department of Trauma, Hand and Reconstructive Surgery together with microbiologists at Justus Liebig University Giessen, was published in the Journal of Bone and Joint Infection. The team conducted a retrospective single-center study covering the years 2016 to 2023, screening 287 cases in which explanted osteosynthesis material had been analyzed by sonication. After applying strict inclusion criteria, 157 patients remained in the final analysis. Every included patient had undergone implant removal because of confirmed or suspected fracture-related infection, and every case had results from both peri-implant tissue culture and sonication fluid culture, allowing a direct, paired comparison of the two techniques in the same patients.

The technical logic behind the comparison is straightforward. Peri-implant tissue culture, the current standard, relies on surgeons taking small samples of tissue from immediately around the hardware during revision surgery. These samples are processed in the microbiology laboratory and incubated to see what grows. The weakness of this approach is that biofilm bacteria concentrate on the implant surface itself, not necessarily in the surrounding tissue, and prior antibiotic treatment can suppress growth in culture. False-negative microbiological results occur in up to 35 percent of cases despite clinically manifest infection, according to previous research cited by the authors. Sonication takes a different route: the removed implant is placed in a sterile container filled with 0.85 percent sodium chloride solution and exposed to ultrasound for one minute at 80 percent intensity. The sound waves dislodge biofilm organisms from the metal surface into the fluid, which is then centrifuged, concentrated, and inoculated into a panel of liquid and solid culture media, including aerobic, anaerobic, and fungal media, all incubated for up to 14 days.

The head-to-head results were strikingly balanced. Peri-implant tissue culture detected pathogens in 60.5 percent of the 157 cases, while sonication fluid culture achieved 57.3 percent. Statistically, the difference between the two methods was not significant, a finding confirmed by McNemar’s test for paired binary outcomes. Yet the overlap between the methods was far from complete. Sonication identified additional pathogens that tissue culture had missed in 17.8 percent of cases, while tissue culture uniquely detected organisms in 22.9 percent of cases. When the results of both methods were combined, the overall pathogen detection rate climbed to 70.1 percent. In other words, roughly one in ten additional infections were unmasked simply by running both tests rather than relying on either one alone.

The pathogen spectrum revealed by the two methods overlapped substantially, with methicillin-sensitive Staphylococcus aureus and coagulase-negative staphylococci predominating in both. Most positive cultures were monomicrobial, though polymicrobial growth was observed in 14.4 percent of sonication-positive cases and 21.1 percent of tissue-culture-positive cases, a numerical difference that did not reach statistical significance. Resistant organisms were rare but clinically important: methicillin-resistant Staphylococcus aureus appeared in four cases with each method, and one multidrug-resistant Enterobacterales strain was detected by each approach. The predominance of plate osteosynthesis systems, which accounted for 61.1 percent of removed implants, and screws at 18.5 percent, reflected the typical hardware profile of a trauma center population. The mean patient age was 57.4 years, and late infections occurring more than ten weeks after surgery were the most common presentation at 42.7 percent of cases.

One of the most clinically pressing questions the study addressed was whether prior antibiotic therapy undermines either diagnostic method. At the time of implant removal, 51 of the 157 patients were on ongoing antibiotic treatment or had received antibiotics within the previous 14 days, excluding routine perioperative prophylaxis. The concern is well founded: antibiotics circulating in tissue can suppress bacterial growth in culture, potentially producing misleading negative results. In this cohort, however, ongoing antibiotic therapy was not associated with a statistically significant difference in pathogen detection between the two methods. Tissue culture did show a numerically higher diagnostic yield than sonication among patients receiving antibiotics, but the authors caution that this observation should be interpreted carefully given the limited subgroup size. The finding contrasts with some earlier studies, including work by Dudareva and colleagues, who reported that both methods lost sensitivity after antibiotic exposure, and with the landmark 2007 study by Trampuz and colleagues, which found sonication particularly valuable after prior antibiotics in prosthetic joint infection.

The therapeutic consequences of the microbiological findings may be the most consequential part of the analysis. Antibiotic therapy was actually modified after revision surgery in 47.8 percent of cases. Most of these modifications, 38.9 percent of the entire cohort, were based on concordant findings from both diagnostic methods working together. Only 4.5 percent of patients had their treatment changed exclusively because of sonication results, and an identical 4.5 percent solely because of conventional culture findings. When the researchers asked a slightly different question, namely in how many cases a therapy modification would have been possible on microbiological grounds, the combined findings supported potential adjustment in 93 cases, with 8.3 percent attributable exclusively to sonication and 7.6 percent exclusively to tissue culture. The pattern is clear: the clinical value of each method lies less in replacing the other than in adding pieces to a diagnostic puzzle that neither can complete alone.

These results place fracture-related infection diagnostics in useful context. Sonication has long been an established component of the diagnostic algorithm for periprosthetic joint infection, where multiple studies have shown higher sensitivity than conventional tissue cultures, with reported sonication sensitivities ranging from roughly 52 to 100 percent depending on population and technique. For fracture-related infection, however, the evidence has been more contested. A 2018 systematic review by Onsea and colleagues concluded that sonication fluid culture may serve as a useful adjunct to tissue culture without strong evidence of superiority, and subsequent studies have split on which method performs better. The Giessen data align with the complementary view. Trenkwalder and colleagues similarly reported in 2023 that in septic and aseptic nonunion, sonication fluid culture showed lower sensitivity than tissue culture but higher sensitivity than histopathology, supporting a multimodal approach.

The study is honest about its limitations, and they matter for interpretation. Nearly half of the potentially eligible cases, 130 of 287, were excluded, mostly because they did not meet FRI criteria or because documentation was incomplete during a transition to a new hospital data system, so selection bias cannot be excluded. The retrospective design meant the exact number of intraoperative tissue samples could not always be verified, and because microbiological culture is itself part of the FRI Consensus Definition used as the reference standard, some incorporation bias is unavoidable. The single-center design also limits generalizability. Even so, the central conclusion stands on firm ground: nearly 30 percent of clinically confirmed infections remained culture negative even with both methods combined, underscoring that microbiology must be interpreted within the broader FRI diagnostic framework, which integrates clinical signs, intraoperative findings, histopathology, and culture results.

For surgeons and infectious disease specialists, the practical message is refreshingly concrete. When hardware comes out because of suspected infection, send the implant for sonication and take peri-implant tissue samples, and treat the two results as complementary rather than competing. The combined approach improved pathogen detection irrespective of prior antibiotic exposure, supported targeted antimicrobial management in nearly half of patients, and cost relatively little beyond standard laboratory processing. In an era when biofilm-embedded bacteria routinely defeat single diagnostic tests, the humble strategy of shaking the metal and swabbing the tissue, then reading both answers together, may be the most reliable tool clinicians have for turning invisible infections into treatable ones.

Subject of Research: Diagnostic comparison of implant sonication and peri-implant tissue culture for detecting fracture-related infection

Article Title: Sonication versus peri-implant tissue culture in fracture-related infection: diagnostic performance and therapeutic consequences in a single-center cohort

Article References: Abdo, B., Strack, D., Schäuffele, M., Tüngler, T. L., Imirzalioglu, C., Windhorst, A., Fritzenwanker, M., Heiss, C., & Rupp, M. (2026). Sonication versus peri-implant tissue culture in fracture-related infection: diagnostic performance and therapeutic consequences in a single-center cohort. Journal of Bone and Joint Infection, 11(4), 555-563. https://doi.org/10.5194/jbji-11-555-2026

Image Credits: AI Generated

DOI: 10.5194/jbji-11-555-2026

Keywords: fracture-related infection, sonication, biofilm, peri-implant tissue culture, osteosynthesis, diagnostic sensitivity, antibiotic therapy, orthopedic surgery, implant infection, microbiology, trauma surgery, pathogen detection

The biphasic plate, manufactured by 41 medical in Bettlach, Switzerland, represents a deliberate departure from decades of orthopedic philosophy. Early plate fixation pursued absolute stability after anatomic reduction, exploiting direct bone healing. Later designs, such as the Limited Contact Dynamic Compression Plate introduced by Gautier and Perren, minimized soft-tissue damage, while bridging plates allowed secondary healing through callus formation. Systems like the Less Invasive Stabilization System and retrograde nailing reduced complication rates, and dual plating has shown promise in complex distal femur fractures, although a systematic review by Tripathy and colleagues found no significant functional advantage over single plating and longer procedure times. The recurring problem is that very stiff constructs, often used in osteoporotic bone to permit early weight bearing, can shield the fracture from the mechanical stimulation that callus formation requires.

The biphasic concept answers this dilemma by building the flexibility into the plate body itself. The implant is thicker than a conventional locking plate, raising its overall stiffness and fatigue strength, but an integrated meander-shaped recess locally reduces stiffness and permits a controlled degree of elastic movement with mechanical amplitude limitation. Previous work by Hofmann-Fliri and colleagues, who adapted the plate to the ovine tibia in an animal model, demonstrated rapid and robust callus formation and improved construct strength compared with conventional locking plates, especially at higher weight-bearing levels. Epari and colleagues, testing the plate on bone substitute material with a 20-millimeter fracture gap under axial loads from 0 to 1000 newtons, found a bilinear stiffness response that delivered more consistent interfragmentary movement and greater implant strength, properties particularly relevant for distal femur fractures.

What remained missing was a bridge between these controlled characterizations and the conditions an actual patient experiences. The Saarland team closed that gap with a three-part methodology. In the laboratory arm, they obtained a cadaveric femur from a 75-year-old female body donor, created a 30-degree osteotomy mimicking an OTA/AO type 33A2 distal femur fracture, and fixed it with the biphasic plate using nine head-locking screws. The specimen was clamped in a custom-designed testing rig validated in earlier work, and a spindle-driven linear actuator applied axial compression in six steps of 0.25 millimeters each at a quasi-static rate of 0.25 millimeters per second.

Two measurement technologies made the experiment unusually informative. A camera system documented the state of the plate’s meander structure, showing it open during the flexible phase and closed once the rigid phase engaged. Meanwhile, an implantable strain sensor known as the AO Fracture Monitor, developed by the AO Foundation in Davos, was mounted directly on the plate with two screws tightened to 1.5 newton-meters. This wireless device, originally built to track bone healing progression at 10 hertz via a strain gauge and transmit data to the cloud via Bluetooth, recorded the plate’s strain response throughout loading. At the final compression step the force reached 235 newtons, at which point the meander closed and the plate transitioned from its flexible to its rigid phase, a transition the authors note becomes apparent at roughly 200 newtons.

The computational arm of the study was built to reproduce exactly this experiment. The cadaveric specimen was scanned with a Siemens Somatom Definition AS64 CT scanner at 120 kVp and 0.6-millimeter slice thickness, together with a calibration phantom, and metal artifact reduction was applied to the images. After segmenting cortical and cancellous bone in consultation with treating physicians, the team generated a finite element model using ten-node tetrahedral C3D10 elements in Abaqus. Bone material properties were derived from CT gray values through density-modulus relationships, producing 25 material classes ranging from 100 to 22,000 megapascals, while the stainless steel plate and bolts were assigned a Young’s modulus of 200 gigapascals and a Poisson’s ratio of 0.3. The meander gap was modeled with frictionless tangential and hard normal contact, and six simulation steps applied the experimental forces across the proximal femur.

Validation proceeded on two fronts. First, the simulated relative strain change across the six loading steps closely followed the smoothed curve recorded by the AO Fracture Monitor, with only minor deviations attributed to differences in force application, clamping, bone alignment, and node selection. Second, the team replicated the benchmark scenario of Epari and colleagues, applying axial loads from 0 to 1000 newtons and confirming the characteristic nonlinear load-interfragmentary movement response. In the near cortex the load rose steadily and then steepened beyond 0.2 millimeters of interfragmentary movement; in the far cortex the pronounced load increase occurred mainly beyond 1 millimeter. The von Mises stress distribution at 1000 newtons, spanning 0 to 850 megapascals, concentrated in specific plate regions and matched the earlier study’s findings, confirming that the model captured the biphasic mechanism itself.

The most striking results came from the in vivo arm. Four patient-specific models were generated from clinical CT data, incorporating each patient’s anthropometry, fracture situation, plate position, screw configuration, and individualized material properties. For one patient, sensor insoles and a motion capture system were used two days after surgery to record real gait under recommended weight-bearing conditions, and a musculoskeletal simulation in AnyBody derived the hip joint reaction force over time. The other patients’ loading profiles were drawn from the OrthoLoad database according to body weight and fracture side. Crucially, these load cases contained force components in all three anatomical planes, not just axial compression, and physiological proximal-distal forces during gait can reach approximately 2500 newtons, far exceeding the 1000-newton benchmark.

Under these realistic conditions, the stress picture inverted. Whereas axial loading distributed stresses centrally over the meander region, all four patient simulations placed maximum von Mises stresses along the lateral edge of the plate. The medial-lateral and anterior-posterior force components, together with the lever arm introduced by force transmission through the femoral head, superimpose bending and shear on axial compression, exactly as classical biomechanics described by Pauwels would predict. The authors emphasize that standardized axial test setups remain useful for implant characterization but cannot fully represent the multi-planar loading that governs implant behavior during walking, and that overly simplified in vitro or in silico setups risk missing clinically relevant stress concentrations.

The implications reach toward smarter, more individualized fracture care. Patient-specific simulations could identify implant regions exposed to elevated stresses during daily activities, informing future geometry optimization, working-length selection, and fixation strategies before clinical application. Combined with implantable sensors that continuously report plate strain as a surrogate for callus maturation, the approach points toward rehabilitation plans tailored to each patient’s actual loading environment. The team is candid about limitations: a single cadaver specimen, quasi-static axial loading capped at 1000 newtons, no biological or healing simulation, and possible segmentation errors mean the patient results should be read as model-based predictions rather than validated clinical outcomes. Even so, the study delivers what the authors identify as its key outcomes, validation and reproducibility, and demonstrates that only by integrating in vivo, in vitro, and in silico methods can the true mechanical life of a fracture implant be understood.

Subject of Research: Biomechanical evaluation of the distal femur biphasic plate using in vivo, in vitro, and in silico methodologies

Article Title: Integrated Study of the Distal Femur Biphasic Plate: Exploring In Vivo, In Vitro, and In Silico Methodologies

Article References: Integrated Study of the Distal Femur Biphasic Plate: Exploring In Vivo, In Vitro, and In Silico Methodologies. (n.d.). https://doi.org/10.1007/s10439-026-04357-6

Image Credits: AI Generated

DOI: 10.1007/s10439-026-04357-6

Keywords: biphasic plate, distal femur fracture, finite element simulation, AO Fracture Monitor, interfragmentary movement, patient-specific modeling, bone healing, osteosynthesis, biomechanics, cadaveric testing, gait loading, smart implants