Pedicle screw-rod instrumentation is considered a standard treatment for spinal instability, and titanium is the most common material for this application. Cobalt-chromium has several advantages over titanium and is generating interest in orthopedic practice. The aim of this study was to compare titanium versus cobalt-chromium rods in posterior fusion, with and without transverse connectors, through in vitro biomechanical testing and determine the optimal configuration. Six cadaveric lumbar spines (L1-S1) were used. Posterior and middle column injuries were simulated at L3-L5 and different pedicle screw constructs were implanted. Specimens were subjected to flexibility tests and range of motion, intradiscal pressure and axial rotation energy loss were statistically compared among the following conditions: intact, titanium rods (without transverse connectors), titanium rods with transverse connectors, cobalt-chromium rods (without transverse connectors) and cobalt-chromium rods with transverse connectors. The novel measurement of energy loss was examined to determine its viability in fusion investigations. All fusion constructs significantly (p0.05) were observed in axial rotation among all conditions. Intradiscal pressure significantly increased (p≤0.01) after fusion, except for the cobalt-chrome conditions in extension (p≥0.06), and no significant differences (p>0.99) were found among fixation constructs. Energy loss, differences became significant between the cobalt-chrome with transverse connector condition with respect to the cobalt-chrome (p=0.05) and titanium (p There is not enough evidence to support that the cobalt-chrome rods performed biomechanically different than the titanium rods. The use of titanium rods may be more beneficial because there is a lower probability of corrosion. The inclusion of the transverse connector only increased stability for the cobalt-chromium construct in axial rotation, which suggests that it is beneficial in complete facetectomy procedures.