###### 1 Introduction  
Fixation with suture anchors is a common method of securing bone and soft tissue during orthopedic surgery, and is particularly prevalent in endoscopic surgery. Various designs of suture anchor have been proposed, including different materials, shapes and sizes, with the intent of ensuring a secure fixation between the soft tissue and bone until healing is complete [1; 2; 3]. Although metallic suture anchors with nonabsorbable sutures are routinely used and provide a good initial fixation, clinical studies have reported anchor-associated complications such as migration, loosening, breakage, and interference from surrounding tissues [4; 5].  
[PERSON] et al. [6] reported that 10% of fixation failures with suture anchors used for rotator repair are associated with anchor loosening or migration. However, early bone healing around the anchor may increase the pull-out strength and reduce migration or loosening. Thus, 3D printing allows for the rapid development of hollow or perforated structures which can be tailored to different orthopedic applications to improve bone ingrowth. [PERSON] et al. [7] designed a perforated 3D printed structure with a porous outer surface which demonstrated good bone ingrowth when implanted in an ovine model. In a 24-month follow-up study, [PERSON] et al. [8] reported no cases of implant breakage, migration or subsidence in 51 sacroiliac joint fusion cases when using 3D-printed triangular titanium implants. [PERSON] et al. [9] used 3D-printed technology to develop a suture anchor with barbs and their results indicated that the 3D-printed technology could make the anchor maximum strength to hold reshaped tissue structures.  
Progressing previous research on a 3D-printed triangular titanium implant [7], our research team developed a novel 3D-printed titanium suture anchor with rectangular cross-section, surface fenestration and a porous central core. When compared to the circle cross-section implant, the rectangular cross-section shape minimizes rotation by the press-fit with four corners. Moreover, the structural fenestrations and porous structure (70% porosity and 600 \(\upmu\)m pore size) allow for bone ingrowth to the central core, leading to permanent fixation. When inserted into a predrilled round hole, the surface roughness of the implant and friction generated between the implant and bone allow for a press-fit insertion, removing the need for a threaded outer surface for initial fixation strength. The press-fit action also forces surrounding cancellous bone into the pores and fenestrations. The small footprint of our anchor also allows for more bone stock to be preserved, which is highly beneficial in cases of revision surgery [10]. In comparison with the traditional thread suture anchor with circle cross-section our design concept is to provide higher anti-rotation ability, a smaller footprint, porous structure allows for bony on growth and ingrowth.  
Pull-out testing gives a good indicator of initial purchase strength after implantation, and is a critical step when designing novel implants. The pullout test consists of applying a tensile force until the anchor pulls out of the substrate, with the maximum force generated being taken as the pull-out force. Loading is typically applied at 0\({}^{\circ}\), 90\({}^{\circ}\), and 135\({}^{\circ}\) relative to the long-axis of anchor, however, a loading angle of 0\({}^{\circ}\) is not commonly experienced by suture anchors in vivo [11; 12; 13]. [PERSON] et al. [14] indicated that the pull-out strength of a threadless anchor was greatest when loading was applied at 90\({}^{\circ}\).  
It is difficult to directly compare fixation techniques in cadavers and animal models due to variations in bone quality, bone anatomy, and fixation location. Hence, the purpose of this study is to compare the pull-out properties of a threadless rectangular suture anchor and a traditional threaded suture anchor when inserted in a synthetic testing block at 90\({}^{\circ}\) and 135\({}^{\circ}\), simulating common in vivo insertion angles.