Knotless anchors with sutures external to the anchor body may be at risk for suture cutting through osteopenic bone

Abstract

Objectives: This study evaluated the mechanical performance, under low-load cyclic loading, of two different knotless suture anchor designs: sutures completely internal to the anchor body (SpeedScrew) and sutures external to the anchor body and adjacent to bone (MultiFIX P).

Methods: Using standard suture loops pulled in-line with the rotator cuff (approximately 60°), anchors were tested in cadaveric bone and foam blocks representing normal to osteopenic bone. Mechanical testing included preloading to 10 N and cyclic loading for 500 cycles from 10 N to 60 N at 60 mm/min. The parameters evaluated were initial displacement, cyclic displacement and number of cycles and load at 3 mm displacement relative to preload. Video recording throughout testing documented the predominant source of suture displacement and the distance of 'suture cutting through bone'.

Results: In cadaveric bone and foam blocks, MultiFIX P anchors had significantly greater initial displacement, and lower number of cycles and lower load at 3 mm displacement than SpeedScrew anchors. Video analysis revealed 'suture cutting through bone' as the predominant source of suture displacement in cadaveric bone (qualitative) and greater 'suture cutting through bone' comparing MultiFIX P with SpeedScrew anchors in foam blocks (quantitative). The greater suture displacement in MultiFIX P anchors was predominantly from suture cutting through bone, which was enhanced in an osteopenic bone model.

Conclusions: Anchors with sutures external to the anchor body are at risk for suture cutting through bone since the suture eyelet is at the distal tip of the implant and the suture directly abrades against the bone edge during cyclic loading. Suture cutting through bone may be a significant source of fixation failure, particularly in osteopenic bone.Cite this article: Y. Ono, J. M. Woodmass, A. A. Nelson, R. S. Boorman, G. M. Thornton, I. K. Y. Lo. Knotless anchors with sutures external to the anchor body may be at risk for suture cutting through osteopenic bone. Bone Joint Res 2016;5:269-275. DOI: 10.1302/2046-3758.56.2000535.

Keywords: Bone quality; Knotless suture anchor; Rotator cuff; Suture cutting through bone.

Conflict of interest statement

ICMJE conflict of interest: I. K. Y. Lo is a consultant for Arthrex Inc. and Artho Care Corp.

© 2016 Lo et al.

Figures

Fig. 1

Two major designs of knotless suture anchors according to the way the sutures are handled with respect to the anchor body: (left) internal knotless suture anchor (e.g. SpeedScrew anchor), (right) external knotless suture anchor (e.g. MultiFIX P anchor).

Mechanical performance of knotless suture anchors in cadaveric bone: a) initial displacement from the preload to the peak of the first cycle; b) cyclic displacement from the peak of the first cycle to the peak of the 500th cycle; c) number of cycles at 3 mm displacement relative to the preload; d) load at 3 mm displacement relative to the preload.*MultiFIX P different than SpeedScrew (p

Mechanical performance of knotless suture anchors in foam (20/8, 15/8, 8/8): a) initial displacement from the preload to the peak of the first cycle; b) cyclic displacement from the peak of the first cycle to the peak of the 500th cycle; c) number of cycles at 3 mm displacement relative to the preload; d) load at 3 mm displacement relative to the preload. “n = 1” indicates one observation because four out of five MultiFIX P anchors in 8/8 foam failed during cyclic loading.*MultiFIX P different than SpeedScrew (p post hoc analysis).

Fig. 4

‘Suture cutting through bone’ during cyclic loading of knotless suture anchors in 15/8 foam.*MultiFIX P different than SpeedScrew (p sd, standard deviation.