Effect of geometrical design variables on implantation configuration and fixation stiffness of titling bone anchors: A parametric finite element study.

The mechanical interaction of a tilting anchor and cancellous bones of various densities was simulated using finite element modeling. The model enjoyed a sophisticated representation of the bone, as an elasto-plastic material with large deformation capability. The anchor's tilting action during implantation phase, as well as its fixation stiffness during pull-out test, were predicted by the model and a parametric study was performed to investigate the effects of the anchor's distal width and corner fillet radius, on these measures. The model predictions were validated against the results of an experimental test on ovine humerus specimens. The model could reasonably reproduce the tilting action of the anchor during the implantation phase. Comparison of the model predictions with the experimental results revealed similar trends during both the implantation and the pull-out phases, but smaller displacement magnitudes (end points: 1.4 vs. 2.1 mm and 4.6 vs. 5.2 mm, respectively). The results of the parametric study indicated substantial increase in the fixation stiffness with increasing bone density. Reducing the distal width and increasing the fillet radius improved the anchor's implantation configuration and fixation stiffness in low-density bones. For high-density bone applications, however, a larger distal width was favored for improving the fixation stiffness.

Surgical treatment of a nonunion following clavicle osteotomy in a child with a history of Erb's palsy: A case report.

INTRODUCTION AND IMPORTANCE: Erb's palsy defined as muscle weakness and loss of motion caused by a nerve condition in the shoulder and arm. Children with Erb's palsy might underwent clavicle osteotomy as an appropriate surgical treatment method. However, few number of these patients who underwent clavicle osteotomy experienced nonunion and complained of shoulder deformity and pain. The aim of the present case report was to present new surgical treatment of a nonunion following clavicle osteotomy in a child affected by Erb's palsy. CASE PRESENTATION: A six years old boy with a history of Erb's palsy who underwent clavicle osteotomy at age of 6 months was referred to hospital. There was a nonunion following clavicle osteotomy. The patient had right shoulder deformity and complained of its-related pain. To correct a nonunion following clavicle osteotomy in this case, middle third fibula auto grafting and fixing it to the cite of clavicle nonunion by pins was used. After five months of follow-up, a clavicle nonunion and shoulder deformity was thoroughly corrected. CLINICAL DISCUSSION: As clavicle osteotomy, the most commonly surgical method for Erb's palsy, has been demonstrated to not work effectively and cause nonunion in some cases, a new surgical method for correcting clavicle nonunion other than repeated clavicle osteotomy is needed. In the present case report, fibula auto grafting and fixing it to the cite of clavicle nonunion by pins was applied and demonstrated remarkable improvement. CONCLUSION: Totally, use of fibula auto grafting and fixing it to the cite of clavicle nonunion by pins might be an effective surgical treatment for such cases.

An additively manufactured titanium tilting suture anchor: a biomechanical assessment on human and ovine bone specimens.

Introduction: A novel titanium tilting suture anchor was designed and fabricated using additive manufacturing. The anchor enjoyed a nonsymmetrical structure to facilitate its insertion procedure through a weight-induced tilt, a saw-teeth penetrating edge to provide a strong initial fixation into cancellous bones of various densities, and an appropriate surface texture to enhance the longterm fixation strength through bone ingrowth. Methods: Biomechanical tests were performed on 10 ovine and 10 human cadaveric humeri to examine the insertion procedure and assess the initial fixation strength of the anchor, in comparison with a standard screw-type anchor as control. Results: This study indicated a simple yet reliable insertion procedure for the tilting anchor. All anchors survived after 400 cycles of cyclic loadings and failed in the load-to-failure step. There were no significant differences between the displacements and fixation stiffnesses of the anchors in either group. The ultimate failure load was significantly smaller (p<0.05) for tilting anchors in ovine group (273.7 ± 129.72 N vs. 375.6 ± 106.36 N), but not different in human group (311.8 ± 82.55 N vs. 281.9 ± 88.35). Also, a larger number of tilting anchors were pulled out in ovine group (6 vs. 3) but a smaller number in human group (4 vs. 6). Conclusion: It was concluded that the biomechanical performance of the designed tilting anchor is comparable with that of the standard screw-type anchors.