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

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