title: Augmented screws in angular stable plating of the proximal humerus: what to do when revision is needed?
abstract: BACKGROUND
  Bone cement augmentation of modified cannulated locking screws shows biomechanically and clinically good results for osteoporotic fracture management. Nevertheless, complications need to be considered. Therefore implant removal should be tested for feasibility.
  
  
  METHODS
  Implant removal was simulated in 7 pairs of osteoporotic cadaveric humeri: During screw removal from an angular stable proximal humerus plate, we measured the maximum torque of 14 augmented screws and the corresponding 14 non-augmented screws on the contralateral humeri. After screw removal, specimens were cut along the screw axes to macroscopically investigate the impact of screw removal on the surrounding bone. In addition, we established a technique for cement removal in cases in which the screw head is obstructed with cement and therefore disables the insertion of the screwdriver.
  
  
  RESULTS
  The screw extraction torque measurements showed no significant differences between the two groups regarding one screw (screw 4 augmented: 1.52Nm, SD 0.25Nm vs. screw 4 non-augmented: 1.80Nm, SD 0.40Nm; P=0.20), whereas torque values for the second screw in the augmented group were lower than in the control group (screw 5 augmented: 0.72Nm, 0.31Nm vs. screw 5 non-augmented: 1.42Nm, 0.52Nm; P=0.009). Macroscopy of the bone showed no damage to the trabeculae within the humeral head due to the removal.
  
  
  CONCLUSIONS
  The removal of cannulated, polymethylmethacrylate-augmented, 2.8mm titanium screws from an angular stable plate was uncomplicated, without the need for special instruments or increased torque for screw removal. No additional damage was visible at the bone-cement interface.
authors.affiliation: Department for Trauma Surgery and Sports Medicine, Medical University of Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria. Electronic address: goetzen.michael@gmail.com.
authors.forename: Michael
authors.initials: M
authors.lastname: Goetzen
authors.affiliation: Biomedical Department, AO Foundation Research Institute, Clavadelerstrasse 8, 7072 Davos, Switzerland. Electronic address: markus.windlof@aofoundation.org.
authors.forename: Markus
authors.initials: M
authors.lastname: Windolf
authors.affiliation: Department for Trauma Surgery and Sports Medicine, Medical University of Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria. Electronic address: werner.schmoelz@uki.at.
authors.forename: Werner
authors.initials: W
authors.lastname: Schmoelz
mesh_terms: D001696:Biomechanical Phenomena; D001843:Bone Cements / Q000627:therapeutic use; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D020878:Device Removal / Q000379:methods*; D005240:Feasibility Studies; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D058430:Humeral Head / Q000601:surgery*; D010024:Osteoporosis / Q000150:complications; D058866:Osteoporotic Fractures / Q000601:surgery*; D019904:Polymethyl Methacrylate / Q000627:therapeutic use; D012086:Reoperation; D012784:Shoulder Fractures / Q000601:surgery*; D019415:Torque
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate
keywords: Augmentation; Bone cement; Implant removal; Osteoporosis; Osteoporotic fracture; PHILOS; Proximal humerus fracture