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Screw Fixation
Kirkland W. Davis, MD, FACR; Jonelle M. Petscavage-Thomas, MD, MPH
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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: width 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
          • 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 and depth of threads vary, 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
            • Fully threaded, threads are very shallow, very narrowly pitched
        • 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 progeny 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
            • Diminish artifact on MR and CT; can be challenging to identify on radiographs unless small bit of metal (often nitinol) embedded
            • 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
        • 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
            • 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 cortexes, 1 tibial cortex

        IMAGING

        • General Features

          • Radiographic Findings

            • CT Findings

              • MR Findings

                CLINICAL ISSUES

                • Presentation

                  DIAGNOSTIC CHECKLIST

                  • Image Interpretation Pearls

                    Selected References

                    1. Guidi M et al: Intramedullary compression screw fixation of metacarpal and phalangeal fractures. EFORT Open Rev. 5(10):624-9, 2020
                    2. Ruta DJ et al: Jones fracture management in athletes. Orthop Clin North Am. 51(4):541-53, 2020
                    3. Weller WJ et al: Scaphoid fractures in athletes. Orthop Clin North Am. 51(4):511-6, 2020
                    4. 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
                    5. Sharp JW et al: Anterior cruciate ligament fixation devices: expected imaging appearance and common complications. Eur J Radiol. 99:17-27, 2018
                    6. Jungmann PM et al: Advances in MRI around metal. J Magn Reson Imaging. 46(4):972-91, 2017
                    7. 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
                    8. Shen C et al: Bioabsorbable versus metallic interference screw fixation in anterior cruciate ligament reconstruction: a meta-analysis of randomized controlled trials. Arthroscopy. 26(5):705-13, 2010
                    9. 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
                    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: width 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
                            • 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 and depth of threads vary, 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
                              • Fully threaded, threads are very shallow, very narrowly pitched
                          • 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 progeny 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
                              • Diminish artifact on MR and CT; can be challenging to identify on radiographs unless small bit of metal (often nitinol) embedded
                              • 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
                          • 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
                              • 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 cortexes, 1 tibial cortex

                          IMAGING

                          • General Features

                            • Radiographic Findings

                              • CT Findings

                                • MR Findings

                                  CLINICAL ISSUES

                                  • Presentation

                                    DIAGNOSTIC CHECKLIST

                                    • Image Interpretation Pearls

                                      Selected References

                                      1. Guidi M et al: Intramedullary compression screw fixation of metacarpal and phalangeal fractures. EFORT Open Rev. 5(10):624-9, 2020
                                      2. Ruta DJ et al: Jones fracture management in athletes. Orthop Clin North Am. 51(4):541-53, 2020
                                      3. Weller WJ et al: Scaphoid fractures in athletes. Orthop Clin North Am. 51(4):511-6, 2020
                                      4. 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
                                      5. Sharp JW et al: Anterior cruciate ligament fixation devices: expected imaging appearance and common complications. Eur J Radiol. 99:17-27, 2018
                                      6. Jungmann PM et al: Advances in MRI around metal. J Magn Reson Imaging. 46(4):972-91, 2017
                                      7. 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
                                      8. Shen C et al: Bioabsorbable versus metallic interference screw fixation in anterior cruciate ligament reconstruction: a meta-analysis of randomized controlled trials. Arthroscopy. 26(5):705-13, 2010
                                      9. 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