Fixed-angle locking assumes the fragment sits where the hole points. Real fractures are less cooperative: the piece that matters is often a few degrees off the planned trajectory, behind a tendon, or sharing space with another screw. A polyaxial head removes that constraint — the surgeon aims within the allowed cone, seats the screw in the fragment, and locks it where it lands.
The alloy is the other half of the design. Cobalt-chromium-molybdenum delivers strength at diameters where stainless or titanium screws would be fragile, so polyaxial fixation reaches the small bones and thin articular fragments that need it most. Aiming, angulation and fragment selection remain the judgement of the operating surgeon.
