The retrospective, single-center cohort study included 881 consecutive patients aged 50 or older who underwent primary unilateral total hip arthroplasty for hip fracture at the Affiliated Hospital of Qingdao University between October 2022 and March 2026. Patients enrolled through September 2024 formed the development cohort of 529, with 370 assigned to model training and 159 to internal validation. A second group of 352 patients enrolled from October 2024 through March 2026 served as an independent temporal test set. Chronic postsurgical pain was defined as new or increased surgery-related pain around the operated hip that persisted for at least three months and reached at least 4 on the 0-to-10 numeric rating scale at the three-month assessment, after other identifiable causes had been excluded.

Before modeling, investigators assembled a broad set of candidate predictors covering demographics, comorbidities, perioperative factors, preoperative and early postoperative pain, long-term analgesic use, anxiety, depression, pain catastrophizing, laboratory-based nutrition and inflammation measures, and CT-derived muscle characteristics. The laboratory indicators included the Geriatric Nutritional Risk Index, Prognostic Nutritional Index, neutrophil-to-lymphocyte ratio, C-reactive protein-to-albumin ratio, and Systemic Immune-Inflammation Index. Two complementary feature-selection methods, least absolute shrinkage and selection operator regression and the Boruta algorithm, were used within the training data. Their intersection retained seven predictors: GNRI, gluteus medius/minimus muscle density, gluteus medius/minimus cross-sectional area, neutrophil-to-lymphocyte ratio, age, preoperative anxiety, and PNI.

The researchers then compared six algorithms: logistic regression, random forest, support vector machine, extreme gradient boosting, categorical boosting, and k-nearest neighbors. The support vector machine was selected after considering discrimination, sensitivity, and interpretability. Its area under the curve was 0.974 in the training set and 0.944 in the internal validation set, where sensitivity reached 0.886 and negative predictive value 0.949. Performance declined in the later temporal test set but remained above the level of random classification. The test-set precision-recall area was 0.754, calibration was described as showing agreement between predicted probabilities and observed outcomes, and decision-curve analysis indicated greater net benefit than treating everyone or no one across certain risk thresholds. In the temporal test set, positive predictive value was 0.534 and the F1 score was 0.637, indicating that the model’s positive predictions remained substantially less certain than its negative predictions.

Shapley additive explanations were used to examine how the final support vector machine assigned importance to its inputs. GNRI made the largest contribution, accounting for 35.4% of the model’s attribution, followed by gluteus medius/minimus muscle density at 13.6% and neutrophil-to-lymphocyte ratio at 12.5%. Age contributed 10.8%, preoperative anxiety 9.7%, PNI 9.5%, and gluteus medius/minimus cross-sectional area 8.4%. The direction of the model’s associations was also informative: lower GNRI, lower gluteus medius/minimus muscle density, higher neutrophil-to-lymphocyte ratio, older age, and preoperative anxiety were associated with increased predicted risk. Lower PNI and lower muscle-related parameters showed an overall trend toward greater predicted risk. These are model-derived associations, not evidence that changing any one factor would cause pain to fall or rise. The analysis explains how the algorithm uses the selected variables; it does not establish a causal mechanism for chronic postoperative pain.

The CT component introduced a two-dimensional view of the muscles around the hip. Cross-sectional area was treated as a measure of muscle quantity, while mean attenuation in Hounsfield units served as a measure of muscle quality; lower density generally indicates greater intramuscular fat infiltration. Measurements were taken from the side opposite the fracture because pain, immobilization, and local injury could alter muscle appearance around the injured hip. The gluteus maximus was assessed at the acetabular roof, the gluteus medius and minimus below the sacroiliac joint, and the rectus femoris below the lesser trochanter. Trained assessors blinded to postoperative pain outcomes performed the measurements, and repeated assessments in 20 patients showed excellent intra-observer and inter-observer reliability. Intraclass correlation coefficients ranged from 0.865 to 0.983 within observers and from 0.850 to 0.966 between observers.

Patients who developed chronic postsurgical pain in the development cohort were older and more likely to report preoperative long-term analgesic use, smoking, diabetes, anxiety, and pain catastrophizing. They also had lower gluteus maximus density, smaller gluteus medius/minimus cross-sectional area, lower gluteus medius/minimus density, lower GNRI and PNI, and higher neutrophil-to-lymphocyte ratio, C-reactive protein-to-albumin ratio, and Systemic Immune-Inflammation Index. Chronic pain occurred in 137 of 529 patients in the development cohort, an incidence of 25.9%, and in 90 of 352 patients in the temporal test cohort. The researchers did not report a statistically significant difference in event frequency between the two cohorts, with P equal to 0.913. These group differences are observational and cannot establish that malnutrition, muscle deterioration, inflammation, or anxiety caused persistent pain.

The model’s principal implication is that a single preoperative pain score may capture only part of a patient’s vulnerability to chronic postoperative pain. The strongest signal, GNRI, reflects nutritional risk using serum albumin and body-weight information, while PNI combines albumin and lymphocyte measurements and the neutrophil-to-lymphocyte ratio reflects inflammatory balance. The muscle measures add information about both the amount and quality of peri-hip tissue, and anxiety captures a psychological factor that may influence pain processing and participation in rehabilitation. The study authors describe these factors as components of preoperative recovery capacity, but the model itself does not demonstrate a biological pathway in which they interact causally. Its temporal validation and interpretability analysis strengthen the model as a risk-estimation tool without making it a treatment test. The study also did not report a direct comparison showing that this combined feature set performed better than a model limited to surgery-related information alone.

Several limits temper the findings. The study came from one hospital, and the independent test cohort was later in time but remained part of the same center, so multicenter external validation and prospective testing are still needed. All participants had complete data for the included variables, and no missing-data imputation was performed, which may restrict how the approach performs when information is incomplete. The final model also included only seven features after selection, and feature selection was not repeated within each cross-validation fold, a design choice the authors acknowledged could leave some risk of overfitting despite 19.57 outcome events per selected variable. Contralateral muscle measurements reduced local injury effects but might not represent pre-fracture muscle reserve in patients with bilateral sarcopenia, frailty, or chronic disuse. Pain is subjective, while rehabilitation adherence, treatment preferences, lifestyle, and other perioperative influences were not fully captured.

To make the model accessible, the research team built a web-based calculator that accepts the seven selected patient and imaging values and returns an individualized probability of chronic postsurgical pain. Such a tool could help clinicians identify higher-risk patients before discharge and prompt closer attention to recovery planning, but its practical value has not yet been established in a clinical trial. The study did not test whether nutritional optimization, psychological support, rehabilitation changes, or other interventions reduce pain, and it cannot show that acting on a model prediction improves outcomes. The results instead provide a prediction framework for a defined population of adults with hip fracture undergoing primary unilateral arthroplasty at one hospital. Larger prospective multicenter cohorts, objective functional outcomes, longitudinal pain trajectories, and intervention studies will be needed before that framework can guide patient care.

Subject of Research: Machine-learning prediction of chronic postsurgical pain after total hip arthroplasty in adults with hip fracture

Article Title: Nutritional status, inflammatory burden, and CT-derived muscle phenotypes for predicting chronic postsurgical pain after total hip arthroplasty: an explainable machine learning study

Article References: Jia, X., Han, X., Cui, X., Zhao, Y., Zhang, Y., & Xu, K. (2026). Nutritional status, inflammatory burden, and CT-derived muscle phenotypes for predicting chronic postsurgical pain after total hip arthroplasty: an explainable machine learning study. Frontiers in Nutrition, 13, Article 1958865. https://doi.org/10.3389/fnut.2026.1958865

Image Credits: AI Generated

DOI: 10.3389/fnut.2026.1958865

Keywords: chronic postsurgical pain, total hip arthroplasty, hip fracture, machine learning, nutritional risk, inflammation, skeletal muscle, preoperative anxiety, CT imaging, clinical prediction, Nutritional, status

The study, led by Madhur Mangalam of the University of Nebraska at Omaha with colleagues at the University of Nebraska Medical Center, reanalyzed gait data from 80 healthy adults and 106 patients with unilateral hip osteoarthritis, assessed before and six months after total hip arthroplasty. The dataset originated from a pre-registered clinical trial conducted in Dijon, France, in which overground walking was recorded with eight optoelectronic cameras tracking 34 reflective markers placed across the body. Rather than examining isolated joint angles, the researchers treated the body as an interacting network, computing statistical dependencies between the displacement of every marker pair while mathematically removing the motion of the body’s center of mass.

The central innovation is a signed decomposition. Conventional movement-network analyses take the absolute value of coupling strengths, collapsing positive and negative relationships into a single number. That practice, the authors argue, obscures a mechanically critical distinction. Positive couplings link segments whose displacement amplitudes rise and fall together—covarying coordination, such as the shared rhythm of loading across the body. Negative couplings link segments whose amplitudes trade off: one displaces little while the other displaces a great deal, a signature the researchers call segmental differentiation. A healthy gait requires both modes, but a magnitude-only analysis sees only their sum.

When the signed decomposition was applied, hip osteoarthritis revealed itself as two pathologies in one. The covarying network lost its normal modular structure and small-world organization—the characteristic architecture in which segments cluster into specialized groups while remaining globally connected—while the trading-off network moved in the opposite direction, becoming more locally clustered and more small-world than in healthy walkers. Global efficiency fell in both networks. The authors interpret this pattern as consistent with pain-driven splinting: the body consolidates a few fixed trading-off configurations and rigid covarying motion to avoid displacements that provoke pain.

Surgery, it turns out, acts almost exclusively on one of these two layers. Six months after hip replacement, the covarying network had partially recovered: modularity roughly halved toward healthy values, characteristic path length dropped by about 45 percent, and local clustering measures moved back toward the healthy range. The trading-off network, by contrast, remained essentially stuck. Its local clustering, transitivity, and small-world organization showed no meaningful change between the pre-surgical and six-month assessments, and its global efficiency deficit remained statistically indistinguishable from the pre-surgical value.

The most striking single finding concerns the participation coefficient, a measure of how broadly each segment spreads its trading-off partners across different functional modules of the body. Before surgery, trading-off participation in patients was statistically indistinguishable from healthy adults. By six months after surgery, it had dropped significantly below healthy values—a deficit that emerged during recovery rather than being present beforehand. In other words, as patients recovered under standard post-surgical care, their trading-off relationships became concentrated among an increasingly narrow set of partners. This finding also resolves an apparent paradox in the team’s earlier magnitude-based analysis, in which participation had unexpectedly decreased after surgery: the signed decomposition shows that decrease was driven specifically by the trading-off network while the covarying network partially recovered.

Asymmetry analysis added further nuance. All four asymmetry measures were elevated before surgery on both networks and partially recovered by six months, with the trading-off network carrying the larger disruption in internal and overall asymmetry. Middle asymmetry—side-to-side imbalance in how the limbs couple to the trunk, pelvis, and head—was almost entirely a covarying phenomenon, consistent with the hypothesis that pain-driven splinting biases trunk and pelvis displacement toward the unaffected side. In patients with left-hip osteoarthritis, the researchers observed a previously unreported dissociation: within-limb trading-off densities deteriorated further during the recovery window even as the corresponding covarying densities recovered or even overshot healthy values, suggesting that post-surgical adaptation reinforces cohesive within-limb motion at the cost of segmental differentiation.

Amid these persistent structural deficits, one metric recovered completely. The researchers introduced a node-level sign-balance measure, capturing the proportion of each segment’s total coordination carried by covarying rather than trading-off relationships. Pre-surgical patients showed a small but significant downward shift, carrying proportionally more trading-off coordination per segment than healthy controls. By six months after surgery, sign balance had returned to values statistically indistinguishable from healthy adults—the only metric in the entire analysis to recover fully. Because it is a ratio, it can normalize even while the underlying magnitude and topology of both networks remain altered, making it a coarse-grained recovery indicator that conceals exactly what the separated network analyses reveal.

The clinical implication is a sharpened rehabilitation hypothesis rather than a prescription. Standard post-arthroplasty protocols emphasize strengthening, range of motion, and symmetric bilateral exercises—activities the authors note plausibly align with covarying coupling, the mode already recovering on its own. Comparatively little targets amplitude differentiation between segments. Exercises that explicitly train trunk–pelvis dissociation, split-stance work with contralateral reach, step-ups with opposite-arm drive, and reciprocal arm-swing retraining map naturally onto the observed deficits. Because the trading-off participation deficit emerged during the recovery window rather than before it, the authors suggest that timing may matter, though they caution that their observational design cannot establish whether standard care produces the consolidation or whether earlier intervention would prevent it.

The authors also stress the limits of their kinematic, model-free approach. The networks describe statistical dependencies among segment displacements, not neural drive or muscular coupling, so interpretations such as splinting and motor persistence remain hypotheses consistent with the data rather than demonstrated mechanisms. The six-month window cannot speak to longer-term trajectories, the healthy comparison group was on average younger than the patient cohort, and concurrent pathology outside the operated hip—contralateral degeneration, knee osteoarthritis, lumbar disease—may independently shape whole-body coordination, meaning persistent abnormalities should not necessarily be read as surgical failure. Still, the broader message stands: recovery from hip replacement is not one trajectory but two, and at the mid-recovery checkpoint the lagging one—segmental differentiation—is the mode most closely tied to fluid, unguarded gait. Whether targeted training can reverse its consolidation is now a testable question for future intervention trials.

Subject of Research: Network analysis of whole-body gait coordination before and after total hip arthroplasty for unilateral hip osteoarthritis

Article Title: Network analysis reveals that total hip arthroplasty restores shared segmental motion before segmental differentiation

Article References: Mangalam, M., Schlattmann, B., Deans, C., & Wellsandt, E. (2026). Network analysis reveals that total hip arthroplasty restores shared segmental motion before segmental differentiation. Frontiers in Network Physiology, 6, Article 1916345. https://doi.org/10.3389/fnetp.2026.1916345

Image Credits: AI Generated

DOI: 10.3389/fnetp.2026.1916345

Keywords: hip osteoarthritis, total hip arthroplasty, gait analysis, network physiology, segmental differentiation, covarying coordination, small-world networks, motor recovery, biomechanics, rehabilitation, signed networks, whole-body coordination

The study was conducted at a high-volume academic tertiary centre that specializes in the treatment of prosthetic joint infections, a complication that affects a small but meaningful fraction of the growing population of patients living with artificial joints. The researchers reviewed the records of 100 patients who underwent DAIR for acute infections of total hip replacements between 2008 and 2021, each with a minimum of two years of follow-up. Acute infections were defined using the 2018 criteria of the Musculoskeletal Infection Society, and included both infections occurring within six weeks of the original hip operation and sudden hematogenous infections, in which bacteria travel through the bloodstream and seed the implant after a symptom-free period. The average age of the patients was nearly 69 years, and more than half were women.

DAIR is the least invasive surgical option for an acute prosthetic joint infection. Rather than removing the entire implant — as required in single- or two-stage revision surgery — surgeons open the joint, thoroughly wash out the infected tissue with at least six litres of saline, exchange the modular components that bacteria can colonize, and then treat the patient with targeted antibiotics. Compared with full revision, DAIR carries less morbidity, costs less, and is technically simpler. But its Achilles heel is the biofilm: once bacteria have built a mature, protective layer on the metal and plastic surfaces of the implant, neither the immune system nor systemic antibiotics can reliably eradicate them, and the only cure is to remove the hardware entirely.

That biological reality is what makes timing so critical. Preclinical work has shown that immature Staphylococcus aureus biofilms can begin forming on implant surfaces as early as three hours after bacterial attachment, and that mature biofilms can develop within 24 hours. Although those laboratory timelines have not been directly translated to patients, they provide a sobering backdrop for the clinical data. Previous studies had already shown that in infected knee replacements, delays of more than 48 hours from admission to DAIR were associated with higher rates of septic reoperation and postoperative complications. In hip fracture care, too, surgery within 48 hours of admission is a well-established benchmark for reducing death and complications. What remained unknown was whether the same clock governed infected hip replacements.

The answer, according to the new analysis, appears to be yes. The mean time from hospital admission to DAIR in the cohort was 46.4 hours, with a wide spread ranging from 3 to 240 hours, and 27 percent of patients waited more than two days for surgery. Using multivariate regression to untangle the effects of age, health status, infection severity, and other variables, the researchers found that each additional hour of delay from admission to the operating room was associated with roughly a 2 percent increase in the odds of death within 90 days — an odds ratio of 1.02 with a confidence interval of 1.00 to 1.03 and a p-value of 0.04. Notably, the time from the onset of symptoms to surgery showed no significant relationship with any outcome, a finding the authors attribute to the inherent subjectivity and unreliability of patient-reported symptom timelines.

The study also identified other, less modifiable risk factors that shaped patient fates. Increasing age raised the risk of death within one year, with each additional year of life corresponding to a 6 percent increase in odds. Patients classified as McPherson host grade C — those with the poorest overall systemic health — faced dramatically elevated risks compared with grade A patients: a nearly thirteenfold increase in one-year mortality and a more than sevenfold increase in postoperative complications. Low preoperative haemoglobin emerged as a significant predictor of reoperation, with each gram-per-litre decrease raising the odds by about 4 percent. The severity of the local extremity condition also mattered, with grade II extremities carrying more than three times the risk of complications compared with grade I.

The raw outcomes of the cohort were sobering. Just over half of the patients — 52 percent — eventually required reoperation for stubborn infection that DAIR could not cure, and patients averaged 1.5 additional hip surgeries after the initial procedure. Thirty percent were readmitted within 90 days, and mortality reached 3 percent at 30 days, 6 percent at 90 days, and 12 percent at one year. Nearly 70 percent experienced postoperative complications, the vast majority of them severe enough to require surgical intervention. The authors caution that their centre is a regional referral hub for the most complex prosthetic joint infections, which likely inflates these failure rates compared with the 58 to 78 percent success rates reported in broader literature. Indeed, 89 percent of the cohort carried an ASA classification of III or IV, indicating severe systemic disease, and the average body mass index of 31 placed most patients in the obese category.

The microbiology added another layer of complexity. Intraoperative cultures revealed a high prevalence of difficult-to-treat pathogens, including polymicrobial infections, methicillin-resistant Staphylococcus aureus, and gram-negative organisms such as Enterococcus, Klebsiella, Enterobacter, and E. coli. Among the patients who died within a year, a quarter had polymicrobial cultures, and Enterococcus and Enterobacter species each appeared in nearly 17 percent of cases — consistent with prior research linking Enterococcus infections after hip replacement to increased mortality. Antibiotic therapy itself was a long haul: the mean initial regimen lasted 37 days, 42 percent of patients required chronic suppressive antibiotics afterwards, and the total antimicrobial exposure averaged more than 333 days per patient. Interestingly, delays beyond 48 hours did not prolong antibiotic courses, suggesting that the harm of waiting manifests through biology rather than through treatment intensity.

Perhaps the most actionable part of the study is its dissection of why delays happen. The mean time from admission to DAIR was about 6.6 hours longer than in a comparable knee infection cohort from the same institution, and the reasons for the longest delays included operating room availability, the need to optimize medical comorbidities, and the management of anticoagulant medications. Many of these barriers are modifiable. Patients on direct oral anticoagulants or warfarin typically wait days for their blood to thin back to a safe range, but reversal agents could be deployed earlier in time-critical infections. Surgeon availability and familiarity with the procedure also contributed, pointing to the value of streamlined protocols, better resource allocation, and clear institutional pathways to the operating suite.

The authors are careful to acknowledge the limits of their work. The retrospective design introduces selection bias, the single-centre cohort of 100 patients produced wide confidence intervals for some estimates, and the 13-year study window spanned changes in electronic records, surgical technique, and implant technology. The study also could not define a precise cutoff — such as the 48-hour benchmark established in knee and hip fracture care — beyond which outcomes deteriorate. Still, the central message is difficult to ignore: in infected hip replacements, the time between admission and surgery is an objective, measurable, and modifiable factor tied to survival. For hospitals, the implication is that prosthetic joint infections deserve the same urgency as hip fractures, with rapid access to the operating room treated not as a convenience but as a clinical imperative. For patients and their families, the takeaway is simpler still — when an artificial joint becomes infected, hours matter.

Subject of Research: The effect of timing from hospital admission to DAIR surgery on mortality and outcomes in acute total hip prosthetic joint infections

Article Title: Timing from admission to debridement, antibiotic, and implant retention (DAIR) affects mortality risk in total hip prosthetic joint infections

Article References: Legler, J., Morgan, S., Beaulé, P., Abdelbary, H., Grammatopoulos, G., & Garceau, S. (2026). Timing from admission to debridement, antibiotic, and implant retention (DAIR) affects mortality risk in total hip prosthetic joint infections. Journal of Bone and Joint Infection, 11(4), 463-477. https://doi.org/10.5194/jbji-11-463-2026

Image Credits: AI Generated

DOI: 10.5194/jbji-11-463-2026

Keywords: prosthetic joint infection, total hip arthroplasty, DAIR, surgical timing, mortality, biofilm, debridement, antibiotics, implant retention, reoperation, orthopaedic surgery, tertiary referral centre

The research team, led by Sebastian Simon and corresponding author Jochen G. Hofstaetter, combed through a prospectively maintained institutional arthroplasty registry covering 8,476 primary total hip arthroplasties performed through the direct anterior approach between 2013 and 2024. Within this cohort, they identified 36 patients, or 0.4 percent, who developed a chronic periprosthetic joint infection, defined as an infection occurring more than four weeks after the index operation, and subsequently underwent a two-stage septic revision in which both stages were performed through the same anterior route. Diagnosis was standardized using the 2018 International Consensus Meeting criteria for periprosthetic joint infection, with 83.3 percent of patients scoring at or above the threshold of six that defines an infected joint.

The two-stage protocol remains the gold standard for chronic periprosthetic joint infection, and its logic is straightforward. In the first stage, all prosthetic components are removed, infected tissue is thoroughly debrided, and an antibiotic-loaded cement spacer is implanted to maintain joint space while delivering high local concentrations of antimicrobial drugs. Patients then receive systemic antibiotic therapy tailored to the organisms identified from tissue samples and implant sonication, continuing for a minimum of twelve weeks. Once clinical signs, inflammatory markers such as C-reactive protein, and microbiological parameters indicate that the infection is controlled, a second operation removes the spacer and implants a new prosthesis. The Vienna team performed reimplantation at least six weeks after the first stage, with the timing decided jointly with an infectious disease specialist based on the infecting organism, wound status, and laboratory trends.

The headline result is encouraging. After a median follow-up of 6.2 years, 28 of the 36 patients, or 77.8 percent, had undergone successful second-stage reimplantation and remained free of infection. Two additional patients, 5.6 percent, were deemed medically unfit for a second major operation and were treated definitively with a so-called 1.5-stage procedure, in which an articulating antibiotic-loaded permanent prosthesis was left in place; they too remained infection free. Among the 32 patients who actually received a new prosthesis, 87.5 percent stayed infection free, while four patients, 12.5 percent, developed recurrent infection requiring further septic revision. Two patients with persistent infection at the first stage ultimately required a Girdlestone procedure, a salvage operation that leaves the hip without a prosthesis. These reinfection figures fall squarely within the 8 to 32 percent range reported in the broader literature for two-stage hip revision, most of which has been generated using posterior or direct lateral approaches.

Just as important as the infection outcomes are the mechanical complications, and here the direct anterior approach showed distinct advantages. Spacer-related complications, a persistent worry in two-stage surgery, occurred in only two patients, 5.6 percent: one spacer dislocation and one spacer fracture, both in the subgroup receiving preformed spacers. Notably, none of the 25 patients who received custom-made antibiotic-loaded spacers experienced any spacer complication, an observation the authors attribute to the superior fit and stability of spacers fashioned intraoperatively from antibiotic-loaded cement. The overall spacer complication rate compares with a systematic review reporting mechanical spacer complications such as dislocation in roughly 10.8 percent of cases, and with spacer fracture rates of around 8 percent in prior series.

Dislocation after reimplantation is the other Achilles heel of two-stage hip revision, with published rates ranging from 9 to as high as 30 percent when posterior or direct lateral approaches are used. In the Vienna cohort, four patients experienced a dislocation after the second stage, and three of them, 8.3 percent, required surgical revision with head and liner exchange at a median of 22 days after reimplantation; the fourth was successfully managed with closed reduction. The authors suggest that the inherent stability of the direct anterior approach, which avoids cutting through the posterior soft-tissue sleeve that stabilizes the hip, may partly explain these low rates, echoing the reduced dislocation risk documented for primary hip replacement through the same route.

Fracture risk during implant removal was also lower than expected. Only one patient, 2.8 percent, sustained an intraoperative fracture at the calcar region during explantation, and one patient suffered a postoperative periprosthetic fracture eight days after reimplantation, both far below the 10 to 15 percent fracture rates reported in comparable two-stage series. The researchers credit their liberal use of femoral osteotomy, a controlled cutting of the femur performed in 19.4 percent of cases to facilitate safe stem removal, which deliberately converts a potential uncontrolled fracture into a planned, fixable one. All fractures and osteotomies were stabilized with cable wires, and remarkably, every fracture was managed through the anterior approach itself, demonstrating the versatility of the technique even in hostile surgical fields.

The microbiological findings add an intriguing layer to the story. Of the 52 microorganisms detected at the first stage, Cutibacterium species accounted for 28.8 percent and coagulase-negative staphylococci for 26.9 percent, with Gram-negative organisms making up 23.1 percent, a spectrum that earlier work by the same group has linked to the anterior approach. Fourteen of the second-stage cultures were positive, and in a striking 64.3 percent of these the organism differed from that found at the first stage, while only 21.4 percent harbored the same pathogen. All four patients who ultimately failed had culture-positive second stages, whereas patients with positive second-stage cultures who did not fail typically grew low-virulence organisms such as Cutibacterium or coagulase-negative staphylococci detected only after enrichment culture. This pattern suggests that positive second-stage cultures carry very different prognostic weight depending on the organism involved, a nuance that could refine how clinicians interpret cultures at reimplantation.

One further finding carries practical weight: patients who achieved successful reimplantation and remained infection free were significantly younger, with a median age of 66 years, than those who never received a new prosthesis, whose median age was 81 years, a difference that was highly statistically significant. Age-related medical fitness, rather than the virulence of the infecting organism, appears to be the decisive factor separating patients who complete the two-stage journey from those who must settle for spacer retention or a Girdlestone salvage. No significant difference in the distribution of high- versus low-virulence microorganisms was found between the reimplantation and non-reimplantation groups, reinforcing the point that patient physiology often trumps microbiology in determining outcomes.

The authors are candid about the limitations of their work. The retrospective, single-center design carries an inherent risk of selection bias, the sample of 36 patients limits statistical power, particularly for subgroup analyses of spacer type and microbiology, and the cohort is heterogeneous. Nevertheless, the study offers something genuinely scarce in the literature: five-year-plus follow-up data on two-stage revision performed entirely through the direct anterior approach, using a standardized diagnostic and treatment protocol. As the anterior approach continues to dominate primary hip replacement in many registries, an increasing share of infected replacements will present with anterior incisions, and reusing the same route preserves muscle that infection and prior surgery have already compromised. With reinfection, dislocation, spacer, and fracture rates all at the favorable end of published ranges, the Vienna data make a compelling case that the direct anterior approach is not merely an acceptable option for two-stage septic revision, but potentially an advantageous one.

Subject of Research: Two-stage revision surgery for chronic hip periprosthetic joint infection using the direct anterior approach

Article Title: Reinfection and complication rates in two-stage revision for chronic hip periprosthetic joint infections using the direct anterior approach

Article References: Simon, S., Mitterer, J. A., Frank, B. J. H., Huber, S., Sebastian, S., Gardete-Hartmann, S., & Hofstaetter, J. G. (2026). Reinfection and complication rates in two-stage revision for chronic hip periprosthetic joint infections using the direct anterior approach. Journal of Bone and Joint Infection, 11(4), 513-521. https://doi.org/10.5194/jbji-11-513-2026

Image Credits: AI Generated

DOI: 10.5194/jbji-11-513-2026

Keywords: periprosthetic joint infection, total hip arthroplasty, direct anterior approach, two-stage revision, antibiotic-loaded spacer, reinfection rate, hip dislocation, revision surgery, Cutibacterium, coagulase-negative staphylococci, orthopedic surgery, infection-free survival

The scale of the underlying problem is set to grow. The annual number of total hip arthroplasties is projected to rise substantially over the coming decades, driven by population growth and increasing utilization. Although revision rates per implant have gradually declined thanks to better bearing surfaces and fixation, the absolute number of revision procedures continues to climb. Meanwhile, the true incidence of both major complications is likely underestimated. Joint registries capture only fractures requiring stem revision, yet more than half of periprosthetic femoral fractures are treated without stem revision, yielding an estimated true incidence of 0.92 per 1000 prosthesis years. Infection figures suffer from incomplete reporting and failure to update preoperative diagnoses with intraoperative culture results. With an ageing, increasingly comorbid population living longer with prosthetic joints, the absolute burden of both complications is expected to increase sharply.

The coexistence of the two conditions is rarer still, and the authors stress a crucial distinction: a fracture occurring around a chronically infected implant is fundamentally different from an acute infection developing after fracture-fixation surgery. Chronic infection involves a mature biofilm on the implant surface, a microbial fortress that antibiotics alone cannot penetrate, and typically arises in the setting of longstanding infection and septic loosening. Because implant loosening is a well-established risk factor for periprosthetic fracture, septic loosening may further increase fracture susceptibility, although robust data on this relationship remain limited. Existing evidence-based guidelines cover fractures, joint infection, and fracture-related infection separately, but integrating fracture stabilization, infection eradication, and definitive reconstruction in often frail patients has remained an unsolved challenge.

The first patient, a 74-year-old woman with multiple comorbidities, had undergone hip replacement in 2019 for a femoral neck fracture, followed by an Escherichia coli joint infection treated with repeated surgeries, and then presented in 2022 after a low-energy fall. Imaging showed a Vancouver type C fracture around a loosened cemented stem. Fluoroscopy-guided hip aspiration revealed a synovial white blood cell count of 15,880 cells per microliter with 97 percent neutrophils and a positive alpha-defensin test, meeting European Bone and Joint Infection Society criteria for infection; cultures confirmed methicillin-resistant Staphylococcus epidermidis. After multidisciplinary discussion and shared decision-making, the team proceeded with a two-stage revision.

The first stage follows a disciplined dirty-then-clean logic. In the dirty phase, surgeons explant the prosthesis through an extensile approach, perform thorough debridement and lavage, and remove infected tissue and foreign material. In the clean phase, the fracture is stabilized, here with cerclage wiring and a plate-screw construct, and a custom-made antibiotic-loaded cement spacer is implanted to bridge the fracture and deliver high local antibiotic concentrations. For this patient, the spacer was lengthened from a prefabricated device and loaded with meropenem because of her history of ESBL-producing E. coli. Targeted antibiotics were de-escalated to oral minocycline, wounds healed uneventfully, and C-reactive protein normalized. Ten weeks later, the second stage removed the spacer and hardware, confirmed healthy tissues and fracture healing, applied fresh plate fixation to reinforce the femur, and implanted a definitive cemented stem with a dual mobility cup. Three and a half years on, imaging showed complete healing, infection markers stayed normal, and the patient reported better mobility than before her fall.

The second case illustrates how unpredictable these scenarios become. A 56-year-old man with a history of hip resurfacing, early infection, and a two-stage revision for Staphylococcus aureus and Pseudomonas aeruginosa sustained a fracture whose plate fixation failed through non-union. At referral, his synovial fluid showed 59,800 white cells per microliter with 99 percent neutrophils, though cultures were negative, likely suppressed by ongoing antibiotics from the referring hospital. During the first stage, surgeons encountered frank pus along the plate and in the joint; the stem was so well fixed that extraction required an extended trochanteric osteotomy, a controlled cut of the greater trochanter to gain access. Cultures grew P. aeruginosa, treated with eight weeks of oral levofloxacin. At the second stage, with the fracture and osteotomy not yet healed, a new plate construct and a modular revision stem were implanted, but six samples unexpectedly grew Candida albicans, prompting six months of fluconazole alongside the antibacterial course. Two years later, radiographs and CT showed complete healing and normalized inflammatory markers, although patient-reported outcome measures remained poor, a sobering reminder that eradication does not guarantee subjective recovery in complex, comorbid patients.

The third patient, a 76-year-old woman, presented with a draining skin fistula over her anterior incision and a Vancouver B2 fracture after a fall. The fistula was traced and excised down to the implant, the prosthesis was explanted, and the fracture stabilized with a plate extending to the trochanter plus a long antibiotic spacer. Cultures identified Cutibacterium avidum, a slow-growing skin bacterium, treated with oral amoxicillin. Eight weeks after the first stage, all second-stage cultures were negative, a new plate and an uncemented dual mobility cup with a modular fluted titanium revision stem were implanted, and the patient completed twelve weeks of total antibiotic therapy. Seven months after reimplantation she reported no problems, and her patient-reported scores were essentially perfect across pain, symptoms, activities, functioning, and quality of life.

Beyond the outcomes, the paper distills hard-won technical lessons. Diagnosing infection amid a fracture is treacherous: hemarthrosis and local inflammation can produce false-positive synovial white cell counts, especially when the fracture extends into the joint, so the authors reserve the first milliliter of aspirate for cell analysis to minimize blood contamination, and note that molecular diagnostics can add value. Timing matters too: recent studies found no clear correlation between the interval from trauma to definitive surgery and outcomes, including mortality, so postponing surgery until an experienced revision and septic-surgery team is available appears safe. Fracture-related infection principles demand stable fixation that preserves bone biology, and the authors advise leaving spare screw holes or using the shortest adequate plate at the first stage to preserve options for reconstruction. Surgeons must also consider adjacent prosthetic joints, since metachronous infection of a same-side knee replacement has been reported in up to 20 percent of cases.

The interval between stages must be individualized, balancing the risk of septic failure against premature reimplantation compromising fracture healing. The team generally targets a window of roughly six weeks without an antibiotic-free interval, extended when fracture healing needs more time, and weighs wound status, C-reactive protein trends, spacer tolerance, and acetabular erosion. Conceptually, they treat the second stage as a single-stage exchange of the spacer, replacing all components including the first-stage plate, reasoning that organisms introduced during the long first procedure may not have been covered by targeted therapy, and that plate exchange is straightforward once the fracture is reduced and partially healed. The authors acknowledge the limits of their evidence: three heterogeneous patients, no control group, and a framework grounded in expert opinion. They call on large musculoskeletal infection centers to build prospective databases and on international societies to forge consensus algorithms. For now, their framework offers surgeons confronting this rare collision of broken bone and entrenched biofilm a tested, reproducible path through it.

Subject of Research: Two-stage surgical management of periprosthetic femoral fractures around chronically infected total hip arthroplasties

Article Title: Periprosthetic fractures around chronically infected total hip arthroplasties: a case series and pragmatic two-stage treatment framework

Article References: Vles, G. F., Metsemakers, W.-J., Aerden, L., Geurts, J., Borens, O., & Ghijselings, S. (2026). Periprosthetic fractures around chronically infected total hip arthroplasties: a case series and pragmatic two-stage treatment framework. Journal of Bone and Joint Infection, 11(4), 547-554. https://doi.org/10.5194/jbji-11-547-2026

Image Credits: AI Generated

DOI: 10.5194/jbji-11-547-2026

Keywords: periprosthetic fracture, periprosthetic joint infection, total hip arthroplasty, two-stage revision, antibiotic-loaded cement spacer, biofilm, fracture-related infection, septic loosening, revision stem, orthopaedic surgery, case series, debridement

That reliance on experience carries real risk. Biomechanical studies cited by the research team show that a femur can fracture under a bending moment of about 137 newton-metres, and the sciatic nerve can be damaged by a force of roughly 530 newtons. Excessive manipulation during surgery has been linked to complications including ankle fractures and nerve injuries. Yet despite the stakes, no quantitative safety index exists for how a leg should be moved on the operating table, and no system has been able to continuously record the forces acting on a patient’s lower limb throughout a procedure. A team of Japanese engineers and orthopaedic surgeons has now built the foundations of exactly such a system, and their results are published in the International Journal of Computer Assisted Radiology and Surgery.

The research, led by Risa Shoji, Motoki Takagi, Tomonori Baba and Akihiko Hanafusa of the Shibaura Institute of Technology and Juntendo University School of Medicine, rests on a three-part architecture: a sensor-equipped traction operating table, a physical dummy human model, and a virtual human model running in musculoskeletal simulation software. The traction table, a commercially available device called LECURE made by Surgical Alliance, holds the patient’s foot in a boot connected to a traction mechanism that can pull the leg, rotate it internally and externally, extend it, and swing it into abduction or adduction. Between the traction device and the sole of the boot, the team installed a six-axis force sensor capable of measuring forces up to 1,000 newtons and moments up to 30 newton-metres in every direction, capturing the complete mechanical conversation between table and limb.

Because forces at the sole alone cannot reveal what is happening to the muscles and tissues deep around the hip joint, the researchers also built a dummy human model with unsettling ingenuity. Starting from a real adult skeletal specimen, they added clay to approximate the length and mass of a human lower limb, 760 millimetres from ankle to hip and 6.9 kilograms in total. The crucial innovation lies in six silicone tubes, with an outer diameter of 15 millimetres and a Young’s modulus of 3.5 megapascals, threaded inside the thigh to mimic four key muscles: the sartorius, rectus femoris, semitendinosus and gluteus medius. Unlike earlier prototypes in which the artificial muscles sat exposed on the outside of the thigh, these tubes follow the anatomical paths of the real muscles they represent. Tension sensors rated at 500 newtons were embedded within three of the muscle models, allowing the team to measure directly how much strain each simulated muscle experiences as the leg is manipulated.

The third pillar is computational. Using OpenSim, the open-source musculoskeletal simulation platform developed at Stanford University and funded by the US National Institutes of Health, the team constructed a virtual human model containing 40 muscles around the hip joint, scaled to match the dimensions of the dummy. The muscle model employed, known as Millard2012 Equilibrium Muscle, improves on the classical Hill muscle model and offers the computational efficiency and numerical stability needed for complex lower limb analysis. The hip joint was modelled in a dislocated state, mirroring surgical reality, with three translational and three rotational degrees of freedom, while the knee and ankle were fixed. The researchers also imported a computer-aided design model of the traction table itself, defining slider joints for linear motion and pin joints for rotation, so that the entire surgical setup could be reproduced digitally and driven by the same movements recorded in the laboratory.

To validate the simulation against physical reality, the team recorded the dummy’s movements with an optical three-dimensional motion analysis system, using 34 infrared reflective markers distributed across the dummy, the table and the surrounding workspace. Two categories of surgical motion were analysed. The first was basic traction, in which the leg is pulled by roughly 150 millimetres by turning the traction handle twenty revolutions. The second, more demanding test was the so-called stem procedure, the combined movement used to widen the surgical field when inserting the artificial hip stem into the femur: external rotation of 125 degrees, extension in two stages totalling about 30 degrees, and internal rotation of 30 degrees, performed in sequence.

The comparison between measurement and simulation delivered a mixture of encouraging agreement and instructive disagreement. For the force in the traction direction, the dominant component at the sole, the dummy’s sensors and the OpenSim simulation told essentially the same story, both during simple traction and during the staged extension of the stem procedure, where the force rose in two steps and then fell during adduction. Muscle tensions also behaved consistently during traction and extension: in both the physical and virtual models, all measured muscles stretched and the semitendinosus emerged as the most heavily loaded of the three instrumented muscles, with the same ordering of semitendinosus, sartorius and rectus femoris in both systems. For a field in which safety thresholds have never been quantified, this alignment between a silicone-muscled cadaveric dummy and a 40-muscle computer model is a genuine milestone.

The discrepancies were just as revealing. During external rotation, the dummy registered a clear increase in the twisting moment about the vertical axis, but the simulation barely moved, because the virtual model defines no frictional resistance between limb and table, no joint rotational resistance, and its wire-like muscles generate tension but not torsion. During adduction, the measured tensions in the sartorius and rectus femoris rose while the simulation predicted a fall in all three muscles, a mismatch the team attributes to differences in how muscle paths are defined. The knee joint of the dummy also could not be fully fixed, tilting the sole and introducing force components the rigid virtual knee could not produce. And the absolute magnitudes diverged in opposite directions: the dummy’s peak traction-direction force of 115 newtons fell short of the 200 to 300 newtons clinicians observe during real surgery, while the virtual model overshot at roughly 420 newtons, signalling that muscle parameters on both sides need refinement.

Perhaps the most powerful demonstration of the hybrid approach came from the simulation’s ability to see what the dummy cannot. When the team examined the ten muscles with the largest simulated tension changes during the stem procedure, eight reached their maximum during extension, but the gluteus minimus and tensor fasciae latae peaked during adduction. More strikingly, the adductor longus and adductor magnus, muscles that originate at the pubic bone and run down the inner thigh, showed larger tension swings than any of the four muscles physically represented in the dummy, pointing the way to which artificial muscles should be added in the next iteration. This is the essential logic of the paired system: the dummy provides physical realism and a training platform on a real traction table, while the simulation provides completeness, evaluating every muscle without any physical experiment at all.

The team is candid that this is a first foundation rather than a finished product. Consultation with surgeons indicates that clinical attention currently centres on the traction-direction force, and because both models reproduce its trends, the system appears suitable for evaluating intraoperative manoeuvres. The researchers plan to collect traction force data from the sensor-equipped boot during actual operations, use those measurements as a gold standard to calibrate both models, and ultimately define force limits and motion ranges for the traction table itself, turning surgical intuition into enforceable safety boundaries. If they succeed, the centuries-old craft of judging how far a leg can safely stretch will gain something it has never had: a number, measured continuously, that tells the surgeon when to stop.

Subject of Research: Quantitative evaluation of lower limb loads during total hip arthroplasty using dummy and virtual human body models

Article Title: Development of a support system for total hip arthroplasty: evaluation of lower limb loads using virtual and dummy human body models

Article References: Shoji, R., Takagi, M., Baba, T., & Hanafusa, A. (2026). Development of a support system for total hip arthroplasty: evaluation of lower limb loads using virtual and dummy human body models. International Journal of Computer Assisted Radiology and Surgery. https://doi.org/10.1007/s11548-026-03791-0

Image Credits: AI Generated

DOI: 10.1007/s11548-026-03791-0

Keywords: total hip arthroplasty, direct anterior approach, lower limb traction table, musculoskeletal simulation, OpenSim, dummy human model, virtual human model, muscle tension, biomechanics, surgical support system, orthopaedics, force sensors