The anatomical problem at the heart of the research is known as a high-riding vertebral artery, or HRVA. In a subset of patients, the vertebral artery, which normally threads through openings in the cervical vertebrae on its way to the brain, climbs unusually high on the axis. That leaves the bony channel, or pedicle, of the C2 vertebra too narrow to accept a standard pedicle screw safely. When surgeons drill a tract for the screw, a millimeter or two of misdirection can lacerate the artery, causing hemorrhage or, in the worst cases, stroke. Because of this, many surgeons abandon pedicle screws altogether in HRVA patients and switch to alternative fixation strategies that sacrifice some biomechanical strength.

The research team, led by Changjiang Ou, Yongjun Tong, and Qibin Zhang, with senior authors Yilei Chen, Junhui Liu, and Fengdong Zhao, asked whether ultrasonic bone drilling could widen the safe corridor. Unlike a high-speed drill, which spins a burr at thousands of revolutions per minute, an ultrasonic device cuts bone through high-frequency mechanical vibrations. The technology has a long history in oral and maxillofacial surgery, where piezoelectric instruments were prized for their ability to distinguish between mineralized and soft tissue, and it has been increasingly adopted in spinal surgery for decompression and laminectomy. Whether that soft-tissue selectivity translates into fewer arterial injuries during C2 screw tract preparation had not been rigorously tested.

To find out, the investigators assembled an integrated clinical and experimental program. The clinical arm was a retrospective cohort of 33 patients with 43 pedicles affected by high-riding vertebral artery anatomy, comparing outcomes between those treated with ultrasonic drilling and those treated with high-speed drilling. The primary clinical endpoints were conversion to an alternative fixation method, substantial bleeding from the venous plexus surrounding the artery, and outright vertebral artery injury. The experimental arms were designed to probe the mechanisms behind the clinical signal: a three-dimensional-printed C2 model perfused with porcine arteries allowed standardized breaches of one, two, and three millimeters to be created deliberately, while a paired rabbit model tracked bone temperature, acute osteonecrosis, healing on micro-computed tomography, and screw pull-out strength at zero, four, and twelve weeks.

The clinical results favored ultrasonic drilling on the measures of intraoperative feasibility. Only 3.8 percent of cases in the ultrasonic group required conversion to alternative fixation, compared with 35.3 percent in the high-speed drilling group, a difference that reached statistical significance. Substantial venous plexus bleeding followed the same pattern, occurring in 7.7 percent of ultrasonic cases versus 35.3 percent of high-speed cases. One minor vertebral artery injury occurred, and it was in the high-speed drilling group, but the authors were careful to note that such events are rare enough that the study lacked the statistical power to draw a firm conclusion about arterial injury rates specifically.

The benchtop experiments lent mechanistic support to the clinical signal. When the researchers created standardized breaches in the perfused model, high-speed drilling produced more frequent full-thickness perforations of the porcine arteries at the two-millimeter and three-millimeter breach depths. In other words, when the drill strayed from its intended path by a small but clinically realistic margin, the spinning burr was more likely to cut all the way through the vessel wall than the vibrating tip of the ultrasonic device. This is consistent with the selectivity principle that has made ultrasonic instruments attractive near nerves and vessels: the oscillating tip cuts bone preferentially and tends to stop when it encounters softer, non-mineralized tissue.

But the animal experiments revealed a genuine trade-off. In the paired rabbit model, ultrasonic drilling generated higher peak bone temperatures and produced deeper acute osteonecrosis, the death of bone cells caused by heat, than high-speed drilling. There was also a trend toward delayed bone healing in the ultrasonic group on micro-CT imaging. The consequences showed up in the biomechanical testing: screw pull-out strength was significantly lower in the ultrasonic group at four weeks after surgery. By twelve weeks, the difference between groups was no longer statistically significant, suggesting that the early fixation deficit may resolve as the bone remodels, but the finding underscores that thermal injury is not a cosmetic concern.

Thermal osteonecrosis has a well-established threshold literature. Classic studies in rabbits and subsequent reviews of dental implant and cortical bone drilling have identified temperature and exposure-time combinations above which bone regeneration is impaired, and the authors of the new study situate their rabbit findings squarely in that tradition. Heat-damaged bone resorbs before it remodels, which can loosen an implant precisely during the early postoperative window when fixation matters most for fusion. The authors conclude that their results highlight the need for optimized drilling parameters and effective irrigation when ultrasonic devices are used in the C2 pedicle, since cooling could potentially blunt the thermal penalty while preserving the vascular advantages.

The study has clear limitations that the authors themselves acknowledge. The clinical cohort was retrospective and modest in size, with only 33 patients and 43 affected pedicles, so the arterial injury comparison in particular rests on a single event and cannot be considered definitive. The benchtop model, while elegant, uses porcine arteries in a printed replica rather than living human tissue, and the rabbit model captures healing biology but not the exact geometry of a human C2 pedicle. Prospective validation in a larger, controlled clinical trial will be needed before ultrasonic drilling can be recommended as a standard approach for HRVA anatomy.

Even so, the work is notable for the way it triangulates a single surgical question across three levels of evidence, from patient outcomes to perfused models to animal histology. For surgeons, the practical message is nuanced: ultrasonic bone drilling appears to make the narrow C2 corridor more navigable in high-riding vertebral artery patients, reducing the need to abandon pedicle screws and reducing troublesome venous bleeding, but it does so at the cost of more heat and weaker early screw fixation. The next generation of ultrasonic devices, with better irrigation and tuned vibration parameters, may be able to keep the vascular benefits while erasing the thermal debt. Until then, the study gives spine surgeons the kind of quantitative trade-off data they rarely get when choosing between two tools at the edge of the safety envelope.

Subject of Research: Comparative safety of ultrasonic versus high-speed drilling for C2 pedicle screw placement in high-riding vertebral artery anatomy

Article Title: Ultrasonic Versus High-Speed Drilling for C2 Pedicle Screw Placement with High-Riding Vertebral Artery: A Comparative Study of Vascular Safety and Thermal Injury

Article References: Ou, C., Tong, Y., Zhang, Q., Huang, B., Kong, X., Jin, J., Cai, Z., Chen, J., Chen, Y., Liu, J., & Zhao, F. (2026). Ultrasonic Versus High-Speed Drilling for C2 Pedicle Screw Placement with High-Riding Vertebral Artery: A Comparative Study of Vascular Safety and Thermal Injury. Annals of Biomedical Engineering. https://doi.org/10.1007/s10439-026-04389-y

Image Credits: AI Generated

DOI: 10.1007/s10439-026-04389-y

Keywords: ultrasonic bone drilling, high-speed drilling, C2 pedicle screw, high-riding vertebral artery, vertebral artery injury, thermal osteonecrosis, spine surgery, atlantoaxial fixation, pull-out strength, vascular safety, biomedical engineering, surgical instrumentation