Cannulated continuous compression screw
Inventors
Gregersen, Colin S. • Fallin, T. Wade • Saltzman, Charles L. • HAGMAN, Chase
Assignees
University of Utah • University of Utah Research Foundation Inc
Publication Number
US-12023080-B1
Publication Date
2024-07-02
Expiration Date
2043-09-30
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Abstract
A bone screw may be insertable into a bone. The bone screw may have a distal member with bone-engaging threads, a proximal member configured to slidably engage the distal member, and a tension member with a proximal end coupled to the proximal member, and a distal end coupled to the distal member such that, in response to motion of the distal member away from the proximal member, the tension member elongates and urges the distal member to move toward the proximal member.
Core Innovation
The invention is a bone screw that includes a distal member with bone-engaging threads, a proximal member configured to slidably engage the distal member, and a tension member coupled to both. The tension member, which is at least partially formed from a superelastic material, elongates as the distal member moves away from the proximal member, urging the distal member to move back toward the proximal member. A length limiting mechanism prevents the screw from exceeding a maximum length or shrinking below a minimum length.
The bone screw provides continuous compressive force across bone portions by maintaining tension within the superelastic tension member. The design addresses the problem of insufficient or subsiding compression provided by existing bone screws, which can lead to fixation failures or loosening due to factors such as subsidence, resorption, motion, or multi-axial loading on the screw during healing. The present invention applies stable compression even after relative bone movement has occurred, overcoming limitations seen in conventional systems.
Problems in the prior art involve the inability of bone screws and fasteners to maintain fixation and adequate compressive pressure due to bending loads, multi-axial or off-axis forces, and relaxation or subsidence over time. The patent addresses a need for improved devices, systems, and methods for bone fixation that can provide consistent fixation strength and enhanced bone loading characteristics that promote osteogenesis and healing.
Claims Coverage
There are two independent claims, each detailing the structure and functional operation of the bone screw and its superelastic tension member.
Bone screw with superelastic tension member and length limiting mechanism
A bone screw insertable into bone, comprising: - A distal member with bone-engaging threads - A proximal member slidably engaged with the distal member - A tension member coupled to both the proximal and distal members, such that motion of the distal member away from the proximal member elongates the tension member, which urges the distal member to move toward the proximal member - The tension member is at least partially made from a superelastic material having an upper and lower plateau stress - The bone screw includes a length limiting mechanism (comprising a distal shoulder, proximal shoulder, and stop feature on the proximal member, tension member, and/or distal member) that prevents exceeding a maximum length or going below a minimum length - The tension member applies a first compressive force at the lower plateau stress (minimum length) and a second compressive force at the upper plateau stress (maximum length); the minimum and maximum lengths correspond to these stresses
Bone screw wherein superelastic tension member is actuated by temperature and length settings
A bone screw insertable into bone comprising: - A distal member with bone-engaging threads - A proximal member slidably engaged with the distal member and cooperatively defining a length limiting mechanism (prevents the screw from exceeding a maximum or minimum length) - A tension member coupled between the proximal and distal members, at least partially formed of superelastic material having an upper plateau stress at a first temperature and a lower plateau stress at a second temperature - The screw is at its minimum length when the tension member is at the lower plateau stress - The screw is at its maximum length when the tension member is at the upper plateau stress
The claims fundamentally cover a variable-length bone screw system utilizing a superelastic tension member and mechanical length stops to maintain stable compressive force across bone portions even as bone subsides or moves, with configurations allowing adjustment of stress based on length and material temperature.
Stated Advantages
Provides improved bone fixation and stabilization by delivering continuous compressive force across bone portions even after relative bone movement or subsidence.
Maintains a steady and optimal level of compression due to the superelastic property of the tension member, overcoming reduction in force present in other fixation systems.
Limits the stress in the tension member to within safe superelastic range through a defined length limiting mechanism, preventing mechanical failure.
Facilitates adaptation to bone healing by maintaining compression, thereby accelerating osteointegration, fracture healing, and lasting fixation.
Distributes and minimizes mechanical stresses using features such as load-sharing surfaces, torque transmission profiles, and a superelastic tension member.
Allows precise control of compression due to the relationship between minimum/maximum length and superelastic stress plateaus.
Enhances ease of use by allowing the screw to be driven in a conventional manner while providing advanced compression behavior.
Documented Applications
Trauma fixation procedures, such as fracture fixation requiring the alignment and securement of bone fragments using the bone screw.
Joint fusion (arthrodesis) procedures, including spine fusions, for holding bones together in compression to promote fusion.
Osteotomy procedures for realigning bones, using the screw to hold repositioned bone portions during healing.
Bone plating procedures (femur, humerus, tibial plates, etc.), intramedullary nail fixation, and bone plating in various locations.
Veterinary procedures and fixation in small bone, extremity, and correction/fusion of foot/ankle, hand/wrist, shoulder/glenoid.
Application in cranio-maxillo-facial procedures and rib plating.
Bone and implant fixation in orthopedic, spine, sports medicine, trauma, reconstruction, and amputee connection procedures.
Procedures involving osteoporotic or compromised bone where reliable compression and fixation are required.
Sarcoma procedures requiring stable bone or implant fixation.
Joint reconstruction procedures such as total hip arthroplasty and total knee arthroplasty.
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