The finite element method (FEM) represents a computer simulation method, originally used in civil engineering, which dates back to the early 1940s. Applications of FEM have also been used in numerous medical areas and in orthopedic surgery. Computing technology has improved over the years and as a result, more complex problems, such as those involving the spine, can be analyzed. The spine is a complex anatomical structure that maintains the erect posture and supports considerable loads. Applications of FEM in the spine have contributed to the understanding of bone biomechanics, both in healthy and abnormal conditions, such as scoliosis, fractures (trauma), degenerative disc disease and osteoporosis. However, since FEM is only a digital simulation of the real condition, it will never exactly simulate in vivo results. In particular, when it concerns biomechanics, there are many features that are difficult to represent in a FEM. More FEM studies and spine research are required in order to examine interpersonal spine stiffness, young spine biomechanics and model accuracy. In the future, patient-specific models will be used for better patient evaluations as well as for better pre- and inter-operative planning.

Tendons are unique forms of connective tissue aiming to transmit the mechanical force of muscle contraction to the bones. Tendon injury may be due to direct trauma or might be secondary to overuse injury and age-related degeneration, leading to inflammation, weakening and subsequent rupture. Current traditional treatment strategies focus on pain relief, reduction of the inflammation and functional restoration. Tendon repair surgery can be performed in people with tendon injuries to restore the tendon’s function, with re-rupture being the main potential complication. Novel therapeutic approaches that address the underlying pathology of the disease is warranted. Scaffolds represent a promising solution to the challenges associated with tendon tissue engineering. The ideal scaffold for tendon tissue engineering needs to exhibit physiologically relevant mechanical properties and to facilitate functional graft integration by promoting the regeneration of the native tissue.

Over the past three decades, additive manufacturing has changed from an innovative technology to an increasingly accessible tool in all aspects of different medical practices, including orthopedics. Although 3D-printing technology offers a relatively inexpensive, rapid and less risky route of manufacturing, it is still quite limited for the fabrication of more complex objects. Over the last few years, stable 3D-printed objects have been converted to smart objects or implants using novel 4D-printing systems. Four-dimensional printing is an advanced process that creates the final object by adding smart materials. Human bones are curved along their axes, a morphological characteristic that augments the mechanical strain caused by external forces. Instead of the three axes used in 4D printing, 5D-printing technology uses five axes, creating curved and more complex objects. Nowadays, 6D-printing technology marries the concepts of 4D- and 5D-printing technology to produce objects that change shape over time in response to external stimuli. In future research, it is obvious that printing technology will include a combination of multi-dimensional printing technology and smart materials. Multi-dimensional additive manufacturing technology will drive the printing dimension to higher levels of structural freedom and printing efficacy, offering promising properties for various orthopedic applications.

Steel-reinforced polymer (SRP) composite materials are very attractive due to their low weight and high strength. The ease of installation which significantly reduces repair time and expense is another major advantage. One of the main disadvantages of SRP materials is that the matrices used for their fabrication are typically organic and thus they are susceptible to fire. In this study, a newly developed retrofit system is being used. It consists of high strength steel fibers impregnated in a fireproof inorganic matrix. The objective of this study is to examine the effects of this hybrid rehabilitation system on the fatigue performance of strengthened reinforced concrete beams. Sixteen $100\mathrm{mm}\times 150\mathrm{mm}\times 1200\mathrm{mm}$ reinforced concrete beams with enough transverse reinforcement to avoid shear failure were used in this study. Nine beams were strengthened with steel fiber sheets on their tension faces. The results from the present study indicate that the fatigue life of reinforced concrete beams, subjected to the same cycling load, can be significantly extended using externally bonded sheets. A rather important finding is that although the strengthening system increases the fatigue life of the beams, the failure mechanism remains the same in both strengthened and nonstrengthened beams. Thus, it is possible to predict the fatigue life of a cyclically loaded beam using existing fatigue models. Furthermore, no delamination failures were observed due to fatigue loading.