Cancellous Screws Are Biomechanically Superior to Cortical Screws in Metaphyseal Bone

Abstract

Cancellous screws are designed to optimize fixation in metaphyseal bone environments; however, certain clinical situations may require the substitution of cortical screws for use in cancellous bone, such as anatomic constraints, fragment size, or available instrumentation. This study compares the biomechanical properties of commercially available cortical and cancellous screw designs in a synthetic model representing various bone densities. Commercially available, fully threaded, 4.0-mm outer-diameter cortical and cancellous screws were tested in terms of pullout strength and maximum insertion torque in standard-density and osteoporotic cancellous bone models. Pullout strength and maximum insertion torque were both found to be greater for cancellous screws than cortical screws in all synthetic densities tested. The magnitude of difference in pullout strength between cortical and cancellous screws increased with decreasing synthetic bone density. Screw displacement prior to failure and total energy absorbed during pullout strength testing were also significantly greater for cancellous screws in osteoporotic models. Stiffness was greater for cancellous screws in standard and osteoporotic models. Cancellous screws have biomechanical advantages over cortical screws when used in metaphyseal bone, implying the ability to both achieve greater compression and resist displacement at the screw-plate interface. Surgeons should preferentially use cancellous over cortical screws in metaphyseal environments where cortical bone is insufficient for fixation. [Orthopedics.2016; 39(5):e828-e832.].

Occupational injuries among pediatric orthopedic surgeons

“…These tools and instruments include needles, scalpels, a cutting saw, sharp retractors, bone hooks, osteotomes, drills, and screws. [17–20] Although wearing double gloves is encouraged among orthopedic and trauma surgeons, it has been reported that up to 10.7% of the surgeons will have their inner gloves perforated. This compromises the surgeon–patient barrier exposing surgeons to direct blood contact.…”

Biomechanical comparison of pedicle screw fixation strength in synthetic bones: Effects of screw shape, core/thread profile and cement augmentation

“…A closely spaced, shallow thread design and a larger core-to-outer diameter ratio are typical of cortical screws. In contrast, cancellous screws have widely-spaced, deep threads and a smaller core-to-outer diameter ratio [23]. However, considering pedicle screw instrumentation in spinal surgery, most of the screw anchoring power is contributed from the cortical bone in the pedicle, whereas the contribution is much smaller for the cancellous bone in the vertebral body [24].…”

Bone resorption triggered by high radial stress: The mechanism of screw loosening in plate fixation of long bone fractures

“…At present, axial pullout test is the standard method to test the fixation strength and stability of medical bone screws in biomechanical experiments on cadaveric and animal bone and in synthetic bone surrogates . This test assumes microfracture or bone resorption, caused by high axial pullout stress, to be the main reason for screw loosening.…”