Deadman theory revisited¹²

Article type: Review Article

Authors: Itoi, Eiji^{a; *} | Nagamoto, Hideaki^b | Sano, Hirotaka^c | Yamamoto, Nobuyuki^a | Kawakami, Jun^a

Affiliations: [a] Tohoku University School of Medicine, Sendai, Japan. E-mails: itoi-eiji@med.tohoku.ac.jp, koyomoe@med.tohoku.ac.jp, jun_gene@yahoo.co.jp | [b] Kurihara Central Hospital, Kurihara, Japan. E-mail: nagamoto@med.tohoku.ac.jp | [c] Sendai City Hospital, Sendai, Japan. E-mail: sanohirotaka@med.tohoku.ac.jp

Correspondence: [*] Corresponding author: Eiji Itoi, MD, PhD, Department of Orthopaedic Surgery, Tohoku University School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan. Tel.: +81-22-717-7245; Fax: +81-22-717-7248; E-mail: itoi-eiji@med.tohoku.ac.jp.

Note: [1] This study was performed at the Department of Orthopaedic Surgery, Tohoku University School of Medicine, Sendai, Japan.

Note: [2] A part of this article was read at the Symposium during 10th Biennial ISAKOS Congress, June 7–11, 2015, Lyon, France.

Abstract: The deadman theory is composed of two angles: θ1 and θ2, and it is recommended that both be less than or equal to 45°. Based on this theory, surgeons insert the anchor at 45°. However, the biomechanical studies show controversial data. We reviewed the original article and the biomechanical studies in the literature. We further performed three additional studies: 1) a finite element analysis to calculate the pullout strength of thread-less anchors inserted at 45°, 90°, and 135° to the polyurethane foam; 2) the same pullout test using thread-less anchors and the polyurethane foam; and 3) the same pullout test using metal threaded suture anchors and the simulated cortical bone. From the review and the additional studies, we came to the following explanations for the controversy: #1, the trigonometric calculation is not always applicable because of bone deformation; #2, insertion angle of 45° is the best for a thread-less anchor, but not for a threaded anchor; #3, θ1⩽45° is true, but it is not equivalent to inserting an anchor at 45°. In conclusion, insertion angle of 45° is the strongest for a thread-less anchor, but 90° is the strongest for a threaded anchor. The pullout strength depends on the inclination of the anchor, friction of the anchor–bone interface, and quality of the bone.

Keywords: Deadman theory, pullout strength, suture anchor, finite element model analysis, pullout test

DOI: 10.3233/BME-161586

Journal: Bio-Medical Materials and Engineering, vol. 27, no. 2-3, pp. 171-181, 2016