Cannulated screw: hollow screw allowing placement over guidewire
Core: central tube around which threads are wound; may be hollow or solid
Core diameter: diameter of core portion of screw
Head: expanded portion of screw opposite tip; helps prevent inserting screw too far
Pitch: distance between threads
Pullout strength: amount of energy required to pull out or disengage screw from bone
Outer diameter (OD): diameter of outer margin of threads measured from thread tip to thread tip
Shaft: nonthreaded portion of screw
Shank: threaded portion of screw
Tap: instrument inserted through predrilled hole to create threads (channel) for screw
Tapping: process of inserting tap
Thread: inclined plane (semihorizontally oriented structure), which wraps around screw core
Converts rotational force of turning screw into linear force, driving screw forward into bone
Width of threads varies (deep or shallow) depending on screw type
Screws may be fully or partially threaded depending on whether threads traverse part of or entire core
Tip: distal end of screw 1st inserted into bone
May be blunt
Self-tapping: allows screw to be advanced without separate tapping stage
Screws cut their own path through bone
Require predrilling hole size of screw core into cortex
Non-self-tapping screws require tap to be advanced after drilling hole size of core diameter
Purpose
Screws used for fracture fixation; stabilization in surgical procedures, such as osteotomy, arthrodesis, arthroplasty, reconstruction
May be standalone devices or used in conjunction with other devices, such as plates, nails, rods, washers, prostheses
May be intended to be permanent implants, removed at later date, or as temporary stabilizing device only during surgery
Basic Screw Types
Cancellous screw
Threads are deep, widely pitched
Relatively thin core
For same OD, weaker than cortical screws
Used for fixation in metaphyseal bone
Self-tapping or non-self-tapping
Fully or partially threaded
Cortical screw
Threads are shallow, more narrowly pitched
Fully threaded
For same OD, stronger than cancellous screw
For fixation of diaphyseal bone
For same OD, larger central core than cancellous screw
Blunt tip, non-self-tapping
Used for plate fixation
Fixation often described by number of cortices engaged
Unicortical fixation crosses 1 cortex; may be used with locking plate
Bicortical fixation engages both near and far cortices, protrudes into soft tissues 1-2 mm
Tricortical and quadricortical fixation also used
Locking screw
Only used with locking plates: not standalone fixation device
Head of locking screw is threaded
Plate hole for locking screw also threaded
When locking screw inserted, threads on head engage threads in hole, "locking" screw into plate
Threads are very shallow, very narrowly pitched
Fully threaded
Specialty Screws
Headless compression screw
e.g., Herbert screw, Acutrak screw
Cannulated screw
Distal end: widely pitched threads, smaller OD
Proximal end: narrowly pitched threads, greater OD
Produces compression across fracture as inserted into bone: compression augments healing
With distal end in far fragment, proximal end in near fragment → widely pitched threads of distal end should move more quickly through far fragment
End result: far fragment pulled toward near fragment, applying compression across fracture
Occasionally used to apply compression in other circumstances: securing arthrodeses, fixing osteochondritis dissecans/osteochondral lesion fragment to parent bone
Headless profile allows use along articular surfaces in recessed fashion, no head protruding into joint
Interference screws
Fixation of tendon and bone grafts within osseous tunnel
Most commonly used in anterior cruciate ligament (ACL) reconstruction
Bullet-shaped, cannulated, and fully threaded
Radiolucent screws
Some newer hardware, including screws, made of radiolucent materials
Diminishes artifact on MR and CT, can be challenging to identify on radiographs unless small bit of metal (often nitinol) embedded
Some are designed to be bioabsorbable or more flexible and "physiologic" than metal devices
Include many materials; e.g., poly-L-lactic acid (PLLA), polyglycolic acid (PGA), polyetheretherketone (PEEK), carbon fiber hybrids
Dynamic hip screw
Cancellous lag screw within metal cannula attached to side plate
For fixation of basicervical femoral neck and intertrochanteric fractures
With weight bearing, screw slides within metal cannula, resulting in compression across fracture
Largely replaced by cephalomedullary nails for complex intertrochanteric fractures
Arthroereisis screw
Bullet-shaped
Threads are blunted
Cannulated
Used to stabilize subtalar joint in flexible flat foot
Related Hardware
Kirschner (K-) wires
Thin, sharp, smooth, stainless steel
Often used for temporary intraoperative fixation; allows control of fragments, aiding reduction and then maintaining reduction during placement of more definitive fixation
May be used for fracture fixation in small bones of hands and feet, pediatric fractures; often placed percutaneously for this application
Commonly serve as pilot for cannulated screws, which are driven into place over K-wires
Steinman pins
Threaded or nonthreaded
Larger than K-wires
Previously known as traction pins
Rarely used today
Other
Lag technique
Method of using screw, not specific screw type
Designed to produce compression between 2 bone fragments → augments healing
Screw threads only engage far fragment; as screw head contacts near fragment, continuing to turn screwdriver draws far fragment closer to near fragment
Cortical or partially threaded cancellous screws may be used to lag fragments
With cortical screws, overdrilling wide hole in near fragment prevents threads from engaging, converts to lag technique
Syndesmosis screw technique
Used to immobilize distal tibiofibular syndesmosis
Placed through fibula into tibia
May pass through fibula plate
Tricortical fixation most common
2 fibular cortices, 1 tibial cortex
IMAGING
General Features
Radiographic Findings
CT Findings
MR Findings
CLINICAL ISSUES
Presentation
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
Selected References
Guidi M et al: Intramedullary compression screw fixation of metacarpal and phalangeal fractures. EFORT Open Rev. 5(10):624-9, 2020
Ruta DJ et al: Jones fracture management in athletes. Orthop Clin North Am. 51(4):541-53, 2020
Weller WJ et al: Scaphoid fractures in athletes. Orthop Clin North Am. 51(4):511-6, 2020
Lea WB et al: Minimally invasive stabilization using screws and cement for pelvic metastases: technical considerations for the pelvic "screw and glue" technique. Semin Intervent Radiol. 36(3):229-40, 2019
Sharp JW et al: Anterior cruciate ligament fixation devices: expected imaging appearance and common complications. Eur J Radiol. 99:17-27, 2018
Jungmann PM et al: Advances in MRI around metal. J Magn Reson Imaging. 46(4):972-91, 2017
Downey MW et al: Fully threaded versus partially threaded screws: determining shear in cancellous bone fixation. J Foot Ankle Surg. 54(6):1021-4, 2015
Lee MJ et al: Overcoming artifacts from metallic orthopedic implants at high-field-strength MR imaging and multi-detector CT. Radiographics. 27(3):791-803, 2007
Douglas-Akinwande AC et al: Multichannel CT: evaluating the spine in postoperative patients with orthopedic hardware. Radiographics. 26 Suppl 1:S97-110, 2006
Related Anatomy
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Related Differential Diagnoses
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References
Tables
Tables
KEY FACTS
Terminology
Imaging
Clinical Issues
TERMINOLOGY
Definitions
Cannulated screw: hollow screw allowing placement over guidewire
Core: central tube around which threads are wound; may be hollow or solid
Core diameter: diameter of core portion of screw
Head: expanded portion of screw opposite tip; helps prevent inserting screw too far
Pitch: distance between threads
Pullout strength: amount of energy required to pull out or disengage screw from bone
Outer diameter (OD): diameter of outer margin of threads measured from thread tip to thread tip
Shaft: nonthreaded portion of screw
Shank: threaded portion of screw
Tap: instrument inserted through predrilled hole to create threads (channel) for screw
Tapping: process of inserting tap
Thread: inclined plane (semihorizontally oriented structure), which wraps around screw core
Converts rotational force of turning screw into linear force, driving screw forward into bone
Width of threads varies (deep or shallow) depending on screw type
Screws may be fully or partially threaded depending on whether threads traverse part of or entire core
Tip: distal end of screw 1st inserted into bone
May be blunt
Self-tapping: allows screw to be advanced without separate tapping stage
Screws cut their own path through bone
Require predrilling hole size of screw core into cortex
Non-self-tapping screws require tap to be advanced after drilling hole size of core diameter
Purpose
Screws used for fracture fixation; stabilization in surgical procedures, such as osteotomy, arthrodesis, arthroplasty, reconstruction
May be standalone devices or used in conjunction with other devices, such as plates, nails, rods, washers, prostheses
May be intended to be permanent implants, removed at later date, or as temporary stabilizing device only during surgery
Basic Screw Types
Cancellous screw
Threads are deep, widely pitched
Relatively thin core
For same OD, weaker than cortical screws
Used for fixation in metaphyseal bone
Self-tapping or non-self-tapping
Fully or partially threaded
Cortical screw
Threads are shallow, more narrowly pitched
Fully threaded
For same OD, stronger than cancellous screw
For fixation of diaphyseal bone
For same OD, larger central core than cancellous screw
Blunt tip, non-self-tapping
Used for plate fixation
Fixation often described by number of cortices engaged
Unicortical fixation crosses 1 cortex; may be used with locking plate
Bicortical fixation engages both near and far cortices, protrudes into soft tissues 1-2 mm
Tricortical and quadricortical fixation also used
Locking screw
Only used with locking plates: not standalone fixation device
Head of locking screw is threaded
Plate hole for locking screw also threaded
When locking screw inserted, threads on head engage threads in hole, "locking" screw into plate
Threads are very shallow, very narrowly pitched
Fully threaded
Specialty Screws
Headless compression screw
e.g., Herbert screw, Acutrak screw
Cannulated screw
Distal end: widely pitched threads, smaller OD
Proximal end: narrowly pitched threads, greater OD
Produces compression across fracture as inserted into bone: compression augments healing
With distal end in far fragment, proximal end in near fragment → widely pitched threads of distal end should move more quickly through far fragment
End result: far fragment pulled toward near fragment, applying compression across fracture
Occasionally used to apply compression in other circumstances: securing arthrodeses, fixing osteochondritis dissecans/osteochondral lesion fragment to parent bone
Headless profile allows use along articular surfaces in recessed fashion, no head protruding into joint
Interference screws
Fixation of tendon and bone grafts within osseous tunnel
Most commonly used in anterior cruciate ligament (ACL) reconstruction
Bullet-shaped, cannulated, and fully threaded
Radiolucent screws
Some newer hardware, including screws, made of radiolucent materials
Diminishes artifact on MR and CT, can be challenging to identify on radiographs unless small bit of metal (often nitinol) embedded
Some are designed to be bioabsorbable or more flexible and "physiologic" than metal devices
Include many materials; e.g., poly-L-lactic acid (PLLA), polyglycolic acid (PGA), polyetheretherketone (PEEK), carbon fiber hybrids
Dynamic hip screw
Cancellous lag screw within metal cannula attached to side plate
For fixation of basicervical femoral neck and intertrochanteric fractures
With weight bearing, screw slides within metal cannula, resulting in compression across fracture
Largely replaced by cephalomedullary nails for complex intertrochanteric fractures
Arthroereisis screw
Bullet-shaped
Threads are blunted
Cannulated
Used to stabilize subtalar joint in flexible flat foot
Related Hardware
Kirschner (K-) wires
Thin, sharp, smooth, stainless steel
Often used for temporary intraoperative fixation; allows control of fragments, aiding reduction and then maintaining reduction during placement of more definitive fixation
May be used for fracture fixation in small bones of hands and feet, pediatric fractures; often placed percutaneously for this application
Commonly serve as pilot for cannulated screws, which are driven into place over K-wires
Steinman pins
Threaded or nonthreaded
Larger than K-wires
Previously known as traction pins
Rarely used today
Other
Lag technique
Method of using screw, not specific screw type
Designed to produce compression between 2 bone fragments → augments healing
Screw threads only engage far fragment; as screw head contacts near fragment, continuing to turn screwdriver draws far fragment closer to near fragment
Cortical or partially threaded cancellous screws may be used to lag fragments
With cortical screws, overdrilling wide hole in near fragment prevents threads from engaging, converts to lag technique
Syndesmosis screw technique
Used to immobilize distal tibiofibular syndesmosis
Placed through fibula into tibia
May pass through fibula plate
Tricortical fixation most common
2 fibular cortices, 1 tibial cortex
IMAGING
General Features
Radiographic Findings
CT Findings
MR Findings
CLINICAL ISSUES
Presentation
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
Selected References
Guidi M et al: Intramedullary compression screw fixation of metacarpal and phalangeal fractures. EFORT Open Rev. 5(10):624-9, 2020
Ruta DJ et al: Jones fracture management in athletes. Orthop Clin North Am. 51(4):541-53, 2020
Weller WJ et al: Scaphoid fractures in athletes. Orthop Clin North Am. 51(4):511-6, 2020
Lea WB et al: Minimally invasive stabilization using screws and cement for pelvic metastases: technical considerations for the pelvic "screw and glue" technique. Semin Intervent Radiol. 36(3):229-40, 2019
Sharp JW et al: Anterior cruciate ligament fixation devices: expected imaging appearance and common complications. Eur J Radiol. 99:17-27, 2018
Jungmann PM et al: Advances in MRI around metal. J Magn Reson Imaging. 46(4):972-91, 2017
Downey MW et al: Fully threaded versus partially threaded screws: determining shear in cancellous bone fixation. J Foot Ankle Surg. 54(6):1021-4, 2015
Lee MJ et al: Overcoming artifacts from metallic orthopedic implants at high-field-strength MR imaging and multi-detector CT. Radiographics. 27(3):791-803, 2007
Douglas-Akinwande AC et al: Multichannel CT: evaluating the spine in postoperative patients with orthopedic hardware. Radiographics. 26 Suppl 1:S97-110, 2006
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