Radiation-Free Optical Device Speeds Multi-Angle Distal Locking in Bone Fracture Surgery

Orthopedic surgeons who fix broken long bones with intramedullary nails face one of the most frustrating steps in trauma surgery at the very end of the procedure: distal locking. Once a nail is slid down the hollow core of a fractured femur or tibia, screws must be driven through the bone and into precisely aligned holes at the nail’s far end. Because the long metal nail can deform as it is inserted, and because the surgeon cannot actually see inside the bone, this step has traditionally depended on repeated fluoroscopic imaging, a live X-ray technique that lengthens operations and bathes both patient and surgical team in ionizing radiation. A new study now reports a technical feasibility demonstration of a radiation-free alternative that combines an optical positioning device inserted inside the bone with a specially designed screw that drills and locks in a single maneuver.

The research, published in the Journal of Medical and Biological Engineering by a team from National Yang Ming Chiao Tung University and Taichung Veterans General Hospital in Taiwan, tackles a problem that has resisted a series of high-tech fixes. Electromagnetic navigation systems, laser-guided targeting devices, and mixed-reality platforms have all been proposed to reduce reliance on the C-arm fluoroscope, yet none has achieved widespread adoption. Each brings drawbacks: electromagnetic systems can be confused by the metal instruments surrounding them, laser techniques require clear lines of sight that soft tissue can block, and mixed-reality systems add cost, complexity, and a steep learning curve to busy trauma workflows. None of these approaches, the authors note, reliably handles dynamic distal locking holes, which are elongated or grooved holes deliberately designed to allow angular variability, typically up to plus or minus fifteen degrees, so that controlled axial micromotion can stimulate callus formation and speed healing.

The new system pairs two components. The first is the intramedullary endo-transilluminating device, abbreviated iMET, which is placed inside the medullary canal and projects a visible point of light through the nail’s distal screw hole onto the bone surface, marking the exact entry site for the screw without any imaging. The concept builds on earlier work by the group, which previously described the iMET device as a means of reducing radiation exposure during interlocking procedures. The second component is a cannulated boring screw, a hollow, self-drilling screw with a five-millimeter tip that matches the diameter of the screw body. A guidewire passes through the screw’s hollow core, allowing the surgeon to drill and insert the locking screw in one continuous step rather than switching between drill, tap, and screwdriver. The design eliminates separate reaming and tapping, and it remains compatible with standard orthopedic guidewires, electric drill bits, and cannulated screwdrivers.

To test whether the concept actually works, the team conducted an in vitro feasibility study using five porcine femurs harvested from eight- to twelve-month-old Taiwan Taoyuan Black pigs obtained post-mortem from a licensed abattoir, meaning no live animals were involved and no animal care committee approval was required. Porcine long bones were chosen because their cortical structure, bone density, and medullary canal geometry closely resemble those of human long bones, making them a widely accepted model for preliminary biomechanical and procedural testing. The specimens were stored at minus eighteen degrees Celsius, thawed in a controlled water bath, and stripped of all muscle, fat, and bone marrow to create a standardized testing environment. A standard 170-millimeter-long, 10-millimeter-diameter intramedullary nail was then used with five hexagonal hollow drill screws measuring 38.1 millimeters in length, with a 12.5-millimeter head, a 5.5-millimeter body diameter, and a 1.2-millimeter hollow channel.

The experimental protocol was deliberately simple. Each femur was clamped horizontally to the table, the marrow was removed, and the cavity dimensions were recorded. A three-millimeter iMET positioning needle, held by a plastic clamp, projected a visible light point through the nail’s four-millimeter screw hole after a 180-degree rotation, marking both sides of the bone at the target angle. The team tested four locking configurations across the five specimens: 60 degrees, 45 degrees, 15 degrees, and 90 degrees, with the 90-degree configuration tested twice. After marking, drilling was performed with a six-millimeter bit, a 1.0-millimeter orthopedic guidewire was inserted through the hole at the specified angle, the cannulated screw was advanced over the wire, tightened with a hexagonal screwdriver, and the wire was withdrawn. Screw position and angle were verified with a protractor and calipers, and the nail was gently shaken to confirm stable fixation. Procedural time was divided into three stages, iMET positioning, drilling, and screw locking, each with defined start and end points.

The results were striking, even allowing for the idealized setting. Successful distal locking was achieved in every specimen at every tested angle, with no repeated attempts required. The mean total locking time was 46.8 seconds with a standard deviation of 16.5 seconds, and individual procedures ranged from 27 to 68 seconds. The 90-degree configuration proved fastest, requiring only 27 to 28 seconds, while the 60-degree configuration took the longest at 68 seconds. For context, the researchers compared these figures against historically reported data for conventional fluoroscopy-guided distal locking, which averages 246 seconds with a standard deviation of 108 seconds, roughly five times longer than the new technique. No ionizing radiation was used at any point during any procedure. The authors stress that this comparison relies on historical benchmarks rather than a concurrently tested control group, so the time savings should be read as a promising trend rather than a definitive causal result.

What may matter as much as raw speed is the consistency of the workflow across angles. The sequential process of optical positioning, guidewire-assisted drilling, and cannulated screw locking remained essentially unchanged whether the target hole was oriented at 15 degrees or 90 degrees, suggesting that multi-angle alignment does not degrade procedural efficiency. The authors argue that this flattening of the learning curve could be particularly valuable in time-sensitive trauma surgery, where long operations carry their own risks. They also emphasize that the system represents an integrated targeting-and-fixation workflow rather than a navigation aid bolted onto an existing procedure: the optical device solves localization, and the boring screw solves fixation, together addressing the entire locking problem rather than a single component of it.

The study’s limitations are candid and substantial. The work was performed on cleaned porcine bones without soft tissue, an idealized environment that cannot reproduce the muscle obstruction, bleeding, and patient-to-patient anatomical variation of a real operating room, all of which would likely increase procedural times. The sample of five specimens is too small for formal inferential statistics, which the authors acknowledge would be underpowered, so all data are presented descriptively. All procedures were performed by a single operator to minimize inter-operator variability, and accuracy was assessed procedurally, defined as successful alignment of the screw trajectory with the distal hole, proper screw engagement, and stable fixation confirmed by manual testing, rather than by independent radiographic measurement. Long-term biomechanical stability under cyclical loading has not yet been verified, and the comparison against fluoroscopy inherits all the confounding factors of historical data.

Those caveats frame what comes next. The team plans cadaveric studies with soft tissue intact, larger sample sizes, concurrent control groups, and rigorous biomechanical testing to establish whether the technique holds up under realistic surgical conditions. If those validations succeed, the implications could extend beyond a single procedure. Cumulative radiation exposure is a growing concern in high-volume trauma centers, where surgeons and staff undergo repeated fluoroscopic exposure across hundreds of cases, and recent research has even documented molecular biomarkers of X-ray damage in trauma surgeons. A distal locking method that eliminates the fluoroscope entirely, works across the angular range that dynamic holes demand, uses instruments compatible with standard surgical toolkits, and completes the job in under a minute would address several persistent pain points at once. For now, the study stands as a carefully hedged but genuinely intriguing proof of concept: inside the controlled confines of a laboratory, a light shone through a metal tube and a screw that drills itself proved faster, safer, and simpler than decades of X-ray-guided guesswork.

Subject of Research: A radiation-free optical targeting method with a cannulated boring screw for multi-angle distal locking in intramedullary nailing, tested in porcine femurs.

Article Title: Advancing Intramedullary Nailing: A Novel Radiation-Free Multi-Angle Targeting Method for Dynamic Distal Locking Screw Holes: A Technical Feasibility Study

Article References: Chiang, T.-L., Shih, C.-W., Lin, Y.-T., Lu, H.-T., Hsu, Y.-F., Chen, K.-H., & Chu, W.-C. (2026). Advancing Intramedullary Nailing: A Novel Radiation-Free Multi-Angle Targeting Method for Dynamic Distal Locking Screw Holes: A Technical Feasibility Study. Journal of Medical and Biological Engineering. https://doi.org/10.1007/s40846-026-01054-6

Image Credits: AI Generated

DOI: 10.1007/s40846-026-01054-6

Keywords: intramedullary nailing, distal locking, radiation-free surgery, optical guidance, cannulated screw, fluoroscopy reduction, dynamic locking holes, orthopedic trauma, porcine femur model, surgical navigation, iMET device, feasibility study