American Board of Surgical Assistants (ABSA) Orthopedic Practice Test

Which statement about screws as fixation implants is false?

1. Screws alone may be used for fixation of oblique or spiral fractures of long bones

2. Cancellous bone gives the best fixation

3. They must be long enough to penetrate both cortices

4. Cortical lag screws are used to hold compression plates in place

The correct answer is: Cancellous bone gives the best fixation

The assertion that cancellous bone gives the best fixation is misleading. Generally, cortical bone provides superior fixation for screws compared to cancellous bone. This is because cortical bone is denser and offers a stronger surface for screw threads to grip, leading to greater stability. Cancellous bone, while valuable for certain applications such as securing implants in less load-bearing areas, does not provide the same level of fixation stability. It is often used in conjunction with constructs designed to optimize fixation, but it is not the optimal choice for achieving maximal stability alone. In contrast, the other statements correctly depict various aspects of screw fixation in orthopedic applications—indicating the versatility and requirements associated with using screws for fracture fixation, particularly in the context of oblique or spiral fractures, the necessity for proper screw length to ensure adequate fixation through both cortices, and the specific role of cortical lag screws in the context of compression plate stabilization.