title: Suture locking of isolated internal locking knotless suture anchors is not affected by bone quality.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the mechanical performance of different suture locking mechanisms including: i) interference fit between the anchor and the bone (eg, 4.5 mm PushLock, 5.5 mm SwiveLock), ii) internal locking mechanism within the anchor itself (eg, 5.5 mm SpeedScrew), or iii) a combination of interference fit and internal locking (eg, 4.5 mm MultiFIX P, 5.5 mm MultiFIX S).
  
  
  METHODS
  Anchors were tested in foam blocks representing normal (20/8 foam) or osteopenic (8/8 foam) bone, using standard suture loops pulled in-line with the anchor to isolate suture locking. Mechanical testing included cyclic testing for 500 cycles from 10 N to 60 N at 60 mm/min, followed by failure testing at 60 mm/min. Displacement after 500 cycles at 60 N, number of cycles at 3 mm displacement, load at 3 mm displacement, and maximum load were evaluated.
  
  
  RESULTS
  Comparing 8/8 foam to 20/8 foam, load at 3 mm displacement and maximum load were significantly decreased (P<0.05) with decreased bone quality for anchors that, even in part, relied on an interference fit suture locking mechanism (ie, 4.5 mm PushLock, 5.5 mm SwiveLock, 4.5 mm MultiFIX P, 5.5 mm MultiFIX S). Bone quality did not affect the mechanical performance of 5.5 mm SpeedScrew anchors which have an isolated internal locking mechanism.
  
  
  CONCLUSIONS
  The mechanical performance of anchors that relied, even in part, on interference fit were affected by bone quality. Isolated internal locking knotless suture anchors functioned independently of bone quality. Anchors with a combined type (interference fit and internal locking) suture locking mechanism demonstrated similar mechanical performance to isolated internal locking anchors in osteopenic foam comparing similar sized anchors.
  
  
  CONCLUSIONS
  In osteopenic bone, knotless suture anchors that have an internal locking mechanism (isolated or combined type) may be advantageous for secure tendon fixation to bone.
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada.
authors.forename: Jarret M
authors.initials: JM
authors.lastname: Woodmass
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada.
authors.forename: Graeme
authors.initials: G
authors.lastname: Matthewson
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada ; Department of Orthopaedic Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Ono
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Bois
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Boorman
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada.
authors.forename: Ian Ky
authors.initials: IK
authors.lastname: Lo
authors.affiliation: Department of Surgery, Section of Orthopaedic Surgery, McCaig Institute for Bone and Joint Health, University of Calgary, Calgary, AB, Canada ; Department of Orthopaedics, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Gail M
authors.initials: GM
authors.lastname: Thornton
keywords: bone quality; knotless suture anchors; suture locking