Purpose
To determine the effect of insertion angle, from 45° to 135° in 15° increments, on
the number of cycles withstood, the ultimate pullout strength, and the stiffness of
threaded suture anchors subjected to load.
Methods
Threaded anchors were inserted into polyurethane foam at angles from 45° to 135°,
in 15° increments, relative to the direction of pull. Five anchors were tested at
each angle. The anchors were first cycled for 30 cycles (10 each at 100 N, 150 N,
and 200 N). The surviving specimens were then tensioned to failure. The McNemar test
was used to compare cyclic failure rates. Paired-samples t tests were used to compare load-to-failure (LTF) and stiffness data. All P values are multiplicity adjusted by the Hommel procedure.
Results
Four of 5 anchors inserted at 45° failed during cyclic testing at a mean of 27 cycles
(P = .13). One of 5 anchors placed at 60° failed after 29 cycles (P = .99). All other anchors survived cyclic testing. Mean LTF was 234 N, 243 N, 297
N, 373 N, 409 N, 439 N, and 417 N at insertion angles of 45°, 60°, 75°, 90°, 105°,
120°, and 135°, respectively. LTF was significantly less for the 60° group when compared
with the 90°, 105°, 120°, and 135° groups (P < .05). LTF was significantly less for the 75° group when compared with the 105°,
120°, and 135° groups (P < .05). For the 90° group, LTF was only significantly less when compared with the
135° group (P = .022). The differences in LTF between the 105°, 120°, and 135° groups were not
significant. Stiffness increased from 28.13 N/mm at 90° to 43.4 N/mm at 105° (P = .03), 61.48 N/mm at 120° (P = .003), and 86.83 N/mm at 135° (P = .008).
Conclusions
Anchors placed at more acute angles, that is, anchors placed closer to the so-called
deadman's angle, failed at lower loads and provided less construct stiffness than
anchors placed at angles greater than 90°. Stiffness also increased sequentially from
an angle of insertion of 90° up to our maximum angle tested of 135°. For threaded
metallic suture anchors, an obtuse insertion angle of 90° to 135° in relation to the
line of pull of the suture and rotator cuff withstands a greater LTF and provides
a stiffer construct than the more acute insertion angle advocated by the “deadman
theory.”
Clinical Relevance
This study offers a biomechanical validation for optimal placement of threaded suture
anchors at an angle of 90° or more, as anatomic restraints allow, from the vector
of pull of the attached suture and rotator cuff, rather than the 45° angle recommended
by the deadman theory.
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Article info
Publication history
Published online: May 28, 2014
Accepted:
March 21,
2014
Received:
June 7,
2013
Footnotes
The authors report that they have no conflicts of interest in the authorship and publication of this article.
Identification
Copyright
© 2014 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.
ScienceDirect
Access this article on ScienceDirectLinked Article
- The Deadman Theory Is Alive and WellArthroscopyVol. 30Issue 9
- PreviewI think it is essential that I respond to the study by Clevenger et al.,1 which is the second in a series of articles authored by largely the same investigators2 that attempt to discredit or disprove the deadman theory of suture anchors, a concept that I introduced in 1995 in an article in Arthroscopy.3 That concept was based on theoretical, yet highly intuitive considerations of trigonometry, classical mechanics, and free body analysis.
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