Fixation

SCREWS

Instrument Sizes for Respective Screws

Screw (mm)	Thread Hole (mm)	Glide Hole (mm)	Tap (mm)	Surgical Set
1.5 Cortical	1.1	1.5	1.5	Mini fragment
2.0 Cortical	1.5	2.0	2.0	2.7
Cortical	2.0	2.7	2.7
3.5 Cortical	2.5	3.5	3.5	Small fragment
4.0 Cancellous	2.0 or 2.5	None	3.5
Partially threaded
Fully threaded
4.5 Cortical	3.2	4.5	4.5	Standard fragment
4.5 Malleolar	3.2	None	4.5	Standard fragment
6.5 Cancellous	3.2	None (4.0 in hard bone)	6.5

Cortical screws are fully threaded (historically). Tend to have fine threads with a small pitch that are designed to anchor to cortical bone.

Cancellous screws are partially threaded (historically), allowing them to be used as lag screws. The threads are coarser with a higher pitch intended to engage medullary bone.

Lag Technique

A lag screw allows compression across a fracture or osteotomy site. The head of the screw pushes down on the near fragment, and the threads pull up on the far fragment.

Example: Inserting a 2.7-mm cortical bone screw

1. Drill thread hole (2.0-mm drill bit)—near and far cortex

2. Drill glide hole (2.7-mm drill bit)—near cortex

3. Counter sink

4. Measure

5. Tap (2.7-mm tap)

6. Flush

7. Insert 2.7-mm screw (two fingers’ tightness)

PINS

Kirschner Wires (K-Wires)

Sizes (inches): 0.028, 0.035, 0.045, 0.062

Available smooth and threaded

Steinmann Pin

Larger than K-wires (usually used for rearfoot)

Sizes (inches): 5/64, 3/32, 7/64, 1/8, 9/64, 5/32, 3/16

Available smooth and threaded

WIRES

Cerclage Wire (Monofilament Wire)

Sizes: For podiatric forefoot cases, usually range between 26 and 28 gauge

Tension Band Fixation

Tension band fixation is used when there is eccentric distraction of a fracture or osteotomy site due to muscle or ligamentous pull. Tension banding converts distractive forces into compressive forces. The cerclage wire is placed on the tension side of an osteotomy/fracture, which prevents distraction on that side while also causing a corresponding compression on the opposite side. Common lower extremity uses include patellar, malleolar, and styloid process fractures.

ABSORBABLE MATERIALS

There are two main products on the market used for bioabsorbable fixation devices: PGA and PLA. PGA absorbs faster than PLA. A concern with rapidly resorbing implants is osteolysis and bone cyst formation. Absorbable materials are used for screws, anchors, and interference screws. They are nonradiopaque; so their placement is difficult to evaluate by postoperative radiographs. They tend to splinter if cut with wire or bone cutters; so absorbable devices should be cut with an oscillating saw, bovie, or scalpel.

PGA and PLA are often combined with composite materials such as hydroxyapatite (HA) and beta-tricalcium phosphate (Beta-TCP). These composite materials are osteoconductive and help bone form in the dead space as the implant dissolves. Additionally, the composite materials act as a buffer to minimize the decrease in pH associated with the resorption of these materials. The by-product of PGA and PLA degradation is lactic acid, which is acidic.

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