Objectives:

After listening to this episode, we hope that you can:

1. Differentiate primary from secondary bone healing.
2. Describe the difference between cortical and cancellous screws.
3. Contrast the use of a lag screw by design versus by technique.
4. Identify different plate types and their specific indications.

Resources

https://naileditortho.com/heres-what-med-students-should-know-about-orthopedic-plates-and-screws-part-1/

Summary:

- Screw = composed of a head, a shaft, threads that surround the shaft, and a tip.

- Types of screws:cortical, cancellous, cannulated

- Cortical: “fully threaded along the shaft, with a smaller pitch than their cancellous counterparts. The threads themselves are small, thus lowering their threaded to core diameter ratio, which helps them to anchor inside dense cortical bone.”

- Cancellous screws: “ have a large thread to core diameter ratio, so that their coarse threads can anchor in soft cancellous bone. They are often partially threaded, meaning the first part of their shaft has no thread, allowing them to act as a lag screw (more on this in a moment!) Notably, cancellous screws are also self-tapping, allowing the threads to achieve a better grip as the screw is driven into the bone”

- Cannulated screws: “ hollow on the inside, allowing it to be inserted over a K-wire that has been placed in the correct position. While these screws can be placed with more precision than non-cannulated screws, this comes with the tradeoff of slightly diminished pullout strength.”

- Lag screw technique

- One very important principle in orthopedic fixation is the lag screw technique. A lag screw compresses two fragments of bone together, which can be done in a couple different ways. We hinted at this before when discussing the cancellous screw: because it’s partially threaded, when the screw is driven into the bone, the threaded portion will engage bone only on the far side of the fracture, pulling it closer towards the near side, where the unthreaded portion is not engaged. Think of it like a fish hook attached to a line dangling from a fishing rod: every turn of the lag screw to drive it into the bone is like reeling in the line to bring the hook (and your fish) closer to the rod, or the proximal and distal fragments of bone closer together.

https://orthopaedia.com/two-main-types-of-bone-healing/

- Primary healing: “Primary bone healing involves a direct attempt by the cortex to re-establish itself after interruption, without the formation of a fracture callus. Usually only seen after surgical plating”

- Secondary bone healing: occurs when the ends of the fractured bones are near enough to heal** but not perfectly opposed, or when there is some motion at the fracture site. This motion is commonly seen with cast immobilization or with the placement of an intramedullary nail or rod.

https://www.youtube.com/watch?v=AydMRUqzJOo&ab_channel=Dr.AhmedYoussif

Mastering the principles of Orthopaedic Surgery, one break at a time.

Hosted by Dr. Kaid van Kampen
Produced by the UBC Orthopaedic Continuing Professional Development Program

In Collaboration with COSSNET and the Canadian Orthopaedic Association

In this episode, we cover one of the most common injuries encountered in orthopaedic practice: the distal radius fracture. We unpack crucial diagnostic steps, including patient history, physical examination, and imaging, to classify fractures accurately. We then explore surgical approaches and management techniques, providing a clear blueprint for handling these prevalent injuries on your rotation.

https://ota.org/sites/files/2021-06/General%20A5%20Locked%20Plating.pdf

LOCK PLATING

• Definitions
  • Locking screw: screw with “male” threads that engage with matching “female” threads on a plate.
  • Locking plate: plate with screw holes that have “female” threads
  • When coupled together = screw is locked into the plate
• Types of Locking Plates
  • Fixed angle (Monoaxial): Screw can be locked to the plate only in ONE designed direction
    • guides threading into the hole , necessary for drilling
  • Variable angle (Polyaxial): “The screw can be locked within 10 °-15°cone” this is particularly useful for periarticular fractures where you are being very specific about the trajectory of the screw across the jont line
  • Locking plates vs Non-locked plating

Locking | Non-locked
In situations with high failure of failure with non-locked plating:poor bone qualitylimited surface areabone defectsbicortical fixation not possible“Relies on fixed angle construct, and NOT on friction between plate and bone”Biological fixation“Blood supply to bone and fracture site is PRESERVED when applied with locked screws only as the periosteum under the plate is not compressed” “Can be applied off the bone”“HOWEVER, if locking plate first secured with non-locking screw, this biological principle is lost”Disadvantages“No tactile feedback of screw purchase & bone quality”“Locking Plates usually thicker vs non-locking plates: May cause symptoms” Cold welding makes removal problematic (an issue with some titanium alloys) •More expensive than non-locking plates: Should be used when beneficial | Relies on FRICTION generated by the screws, between the plate and bone


Failure mechanism: All screws will cut out and fail in unison, requires a larger force to disrupt
| Failure mechanism: Each screw would fail individual due to loosening and pull out

Mastering the principles of Orthopaedic Surgery, one break at a time.

Hosted by Dr. Kaid van Kampen
Produced by the UBC Orthopaedic Continuing Professional Development Program

In Collaboration with COSSNET and the Canadian Orthopaedic Association