What is the evidence/rules for locking implants in small animal surgery?

Prior to locking plates, most fractures were repaired with internal fixation using standard plating techniques. Concepts of fracture fixation were outlined by the AO/ASIF (Arbeitskreis Osteosynthese/ Association for the Study of Internal Fixation), with the emphasis on anatomic reconstruction and rigid internal fixation. Over the last years, surgeons have moved from a mechanical approach to fracture treatment with the objective of anatomically reconstructing the bone, towards a biological one in which the approach to the fracture site is less necessary. Primary goal is to restore the alignment of the axis of the skeletal segments. So called „biological osteosynthesis” involves the use of bridging implants such as external fixators, interlocking nails and both standard and locking plates. To date, multiple locking plate systems exist although many still only allow the screws to be placed at fixed angles relative to the plate. Newer advancements have led to the development of angle variable locking systems, allowing a limited angulation of the screw while still locking into the plate. Nowadays the most notable locking systems in Veterinary Medicine are the Synthes LCP, Kyon ALPS, Trauma Vet Fixin, Orthomed SOP, Aesculap PLS, Koenigssee NCP and the Securos PAX.

Numerous advantages over conventional plating systems have been cited and include enhanced preservation of periosteal blood supply, improved fracture site stability, reduced risk of altering fracture reduction during screw placement, a less precise anatomic plate contouring needed and locking screws having a larger core diameter that increases their bending shear strength. These features also make locking plates particularly amenable for the use in minimally invasive plate osteosynthesis (MIPO) applications.

Few, if any studies, prospectively evaluate clinically locking versus non-locking plates and the overall complication rate of fracture repair is low, so definitely conclusions regarding the superiority of locking plates is still lacking. [...]