Suture Anchor Insertion Angle and the Deadman Theory
2009; Elsevier BV; Volume: 25; Issue: 12 Linguagem: Inglês
10.1016/j.arthro.2009.10.006
ISSN1526-3231
Autores Tópico(s)Orthopedic Surgery and Rehabilitation
ResumoI feel compelled to comment on the study by Strauss et al.1Strauss E. Frank D. Kubiak E. Kummer F. Rokito A. The effect of the angle of suture insertion on fixation failure at the tendon-suture interface after rotator cuff repair: Deadman's angle revisited.Arthroscopy. 2009; 25: 597-602Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar regarding suture anchor insertion angle, because the authors question the relevance of the deadman theory of suture anchor insertion. The article that I published in 1995 in Arthroscopy2Burkhart S.S. The deadman theory of suture anchors: Observations along a South Texas fence line.Arthroscopy. 1995; 11: 119-123Abstract Full Text PDF PubMed Scopus (209) Google Scholar developed a rationale for inserting suture anchors at 45° or less based on the principles of Newtonian mechanics. Because Strauss et al. did not question my theoretic methodology, I must assume that they are questioning Newtonian mechanics and its validity under all testing conditions. In fact, the conclusions of Strauss et al. are decidedly anti-Newtonian in that they suggest that identical forces acting on suture anchors placed at different angles will have non-identical effects, that is, that these forces will cause what they term “windshield wipering” in the 45° anchors and not in the 90° anchors.I suggest that the experimental design by Strauss et al. was not appropriate for proving or disproving the validity of the deadman theory. To do so would require intracortical fixation at all angles of insertion, which would have demanded that they use fully threaded suture anchors. Such anchors were not used.Without intracortical fixation, a common failure mechanism is cutting of the suture through bone, and this failure mode is exaggerated with more deeply placed anchors.3Bynum C.K. Lee S. Mahar A. Tasto J. Pedowitz R. Failure mode of suture anchors as a function of insertion depth.Am J Sports Med. 2005; 33: 1030-1034Crossref PubMed Scopus (54) Google Scholar Furthermore, the laser line on the inserter will give varying levels of subcortical insertion depth at different insertion angles, and variation of insertion depth has been shown to result in variations in displacement at given loads.4Mahar A.T. Tucker B.S. Upasani V.V. Oka R.S. Pedowitz R.A. Increasing insertion depth of suture anchors for rotator cuff repair does not improve biomechanical stability.J Shoulder Elbow Surg. 2005; 14: 626-630Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar Inspection of Fig 4 of the article of Strauss et al. suggests that anchor insertion depth may not have been well controlled in their study.Again, I come back to the fact that the conclusions of Strauss et al. are counter to the results that would have been anticipated by an analysis based on Newtonian mechanics. When that happens, I would caution investigators to question their methodology and their conclusions based on that methodology.For my rotator cuff repairs, I continue to use a 45° deadman angle with anchors that achieve intracortical fixation, and the study by Strauss et al. has done nothing to persuade me to change my surgical technique. I feel compelled to comment on the study by Strauss et al.1Strauss E. Frank D. Kubiak E. Kummer F. Rokito A. The effect of the angle of suture insertion on fixation failure at the tendon-suture interface after rotator cuff repair: Deadman's angle revisited.Arthroscopy. 2009; 25: 597-602Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar regarding suture anchor insertion angle, because the authors question the relevance of the deadman theory of suture anchor insertion. The article that I published in 1995 in Arthroscopy2Burkhart S.S. The deadman theory of suture anchors: Observations along a South Texas fence line.Arthroscopy. 1995; 11: 119-123Abstract Full Text PDF PubMed Scopus (209) Google Scholar developed a rationale for inserting suture anchors at 45° or less based on the principles of Newtonian mechanics. Because Strauss et al. did not question my theoretic methodology, I must assume that they are questioning Newtonian mechanics and its validity under all testing conditions. In fact, the conclusions of Strauss et al. are decidedly anti-Newtonian in that they suggest that identical forces acting on suture anchors placed at different angles will have non-identical effects, that is, that these forces will cause what they term “windshield wipering” in the 45° anchors and not in the 90° anchors. I suggest that the experimental design by Strauss et al. was not appropriate for proving or disproving the validity of the deadman theory. To do so would require intracortical fixation at all angles of insertion, which would have demanded that they use fully threaded suture anchors. Such anchors were not used. Without intracortical fixation, a common failure mechanism is cutting of the suture through bone, and this failure mode is exaggerated with more deeply placed anchors.3Bynum C.K. Lee S. Mahar A. Tasto J. Pedowitz R. Failure mode of suture anchors as a function of insertion depth.Am J Sports Med. 2005; 33: 1030-1034Crossref PubMed Scopus (54) Google Scholar Furthermore, the laser line on the inserter will give varying levels of subcortical insertion depth at different insertion angles, and variation of insertion depth has been shown to result in variations in displacement at given loads.4Mahar A.T. Tucker B.S. Upasani V.V. Oka R.S. Pedowitz R.A. Increasing insertion depth of suture anchors for rotator cuff repair does not improve biomechanical stability.J Shoulder Elbow Surg. 2005; 14: 626-630Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar Inspection of Fig 4 of the article of Strauss et al. suggests that anchor insertion depth may not have been well controlled in their study. Again, I come back to the fact that the conclusions of Strauss et al. are counter to the results that would have been anticipated by an analysis based on Newtonian mechanics. When that happens, I would caution investigators to question their methodology and their conclusions based on that methodology. For my rotator cuff repairs, I continue to use a 45° deadman angle with anchors that achieve intracortical fixation, and the study by Strauss et al. has done nothing to persuade me to change my surgical technique. Author's ReplyArthroscopyVol. 25Issue 12PreviewDr. Burkhart's statements that the findings of our recent article1 are counter to Newtonian mechanics are not correct. In fact, basic mechanical analysis resolves the tendon force vector into two force components—one acting parallel to the anchor (potential pullout) and the other perpendicular to the anchor end (potential tilting or “windshield wipering”). When the anchor position becomes more vertical (e.g., from 45° to 90°), the perpendicular force on the anchor end thus decreases, as does the cause for tilting movement of the anchor. Full-Text PDF
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