Orthopedic Posterior Spinal Fixation Segment

This assembly represents a gold-standard, micro-engineered spinal implant cluster used to securely immobilize and fuse a single damaged motion segment of the human spine (such as two adjacent lumbar or thoracic vertebrae).

• Polyaxial Pedicle Screws: The four large threaded screws at the base feature dual-threaded designs for maximizing bone-purchase and a distinctive anodized green coating. This color is typically used by medical manufacturers to visually indicate a specific screw diameter size (e.g., $5.5\text{ mm}$ or $6.5\text{ mm}$) to the surgical team mid-operation. The pivoting “tulip” heads allow multidirectional adjustments.

• Fixation Rods: Two short, horizontal cylindrical bars run parallel through the open slots of the screw tulips, locked permanently into place using top-threading set screws.

• Adjustable Transverse Connector (Crosslink): The central bridging assembly features an oblong, interlocking slide slot secured by a central nut. This adjustable “telescoping” crosslink bridges the left and right rods, drastically reducing parallelogram deformation and enhancing torsional (rotational) rigidity of the construct under physiological loading (Cornaz et al., 2022; Han et al., 2022; Lehman et al., 2015).

• Material: Constructed entirely from high-grade, biocompatible titanium alloy ($Ti\text{-}6Al\text{-}4V$) or cobalt-chromium (CoCr) to withstand long-term mechanical stress without suffering fatigue failure or inducing an immune response.