Related Experiment Video
Updated: Jun 1, 2026
An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model
Published on: May 31, 2017
The "Rescue screw" as a freehand revision strategy for implant loosening: a technical note and comparative
Mazda Farshad1, Aron Alakmeh1, Ramon Rohner2
1University Spine Center Zurich, Balgrist University Hospital, University of Zurich, 8008 Zurich, Switzerland.
Background Context:
Depending on bone mineral density, implant loosening occurs in up to 54% of cases after spinal instrumentation. This leads to compromised healing, instability and mechanical pain, often requiring surgical revision. Revision strategies strongly depend on the remaining bone stock within the pedicle and include the use of larger diameter or dual pitch screws, implant cementation, alternative screw trajectories such as the cortical bone trajectory (CBT), impaction grafting, and extension to the intact adjacent segment.
Purpose:
This study biomechanically compares screws with a 2 mm larger diameter (LD), CBT screws, and craniocaudal "rescue screws" (RS) in the setting of loosened cemented and native index pedicle screws.
Study Design:
Biomechanical study on human cadavers.
Methods:
The vertebral bodies of 5 human cadaveric lumbar spines were dissected. After randomization and simulated screw loosening with a 1 mm larger tapping, each test trajectory was tested in alternating order on all lumbar levels. RS and LD screws were analyzed for cemented and uncemented index pedicle screws. The respective contralateral pedicle was instrumented with a conventional pedicle screw as an intrasample reference. Maximum bending load-to-failure [Nm] in flexion was recorded for all screws in a biomechanic testing machine.
Results:
In total, revision screws showed a significantly higher (+25.9%; p=.006) maximum torque (34.0 Nm) than controls (27 Nm). In native index screws, LD screws showed the highest median torque (35.3 Nm; +19.5%). Rescue screws showed an 11.6% torque increase (32.1 Nm) compared to contralateral controls. In cemented index screws, this effect was even greater for both LD (45.1 Nm, +59.2%) and rescue screws (48.9 Nm; +41%). CBT screws did not restore the mechanical strength of the index screw in the context of prior screw loosening (29.4 Nm; -2.7%).
Conclusions:
Followed by rescue pedicle screws, LD screws showed the best mechanical performance in this cadaveric screw loosening model for cemented and native index pedicle screws. CBT screws are not useful in the context of pedicle screw loosening.
Clinical Significance:
In light of the increasing number of revision surgeries, the rescue pedicle screw offers a biomechanically robust and technically simple revision strategy using standard implants and infrastructure if larger diameter screws are no longer applicable due to significant bone loss.
