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Principle of dynamic locking

Locking screws

Modern IM nails permit placement of locking screws through bone and nail, to improve fixation both proximally and distally. Locked nails permit stable fixation which controls length, rotation, and alignment of proximal and distal fractures. However, locking prevents impaction of distracted fractures, and interferes with their healing.
When locking nails were first introduced, their potential for impaired healing was recognized. Delayed removal of locking screws (“dynamization”) was often advised. This is usually not necessary if distraction is avoided, but may be considered when a fracture fixed with length-stable locking is healing slowly. Length-stable locking is often called “static” locking.
Some locking screw holes are designed with an oval shape so that a screw at one end of the oval will allow some fracture impaction, but still control rotation as well as limit shortening to the length of the oval. These have been called “dynamic locking” screw holes (see illustrations).

To ensure adequate fixation of acute tibial fractures, use of locking screws both proximally and distally is advisable. Dynamic (oval) rather than static (round) holes may be used when the fracture pattern prevents shortening.