- increasing pin diameter:
- most important factor in fixator stability;
- adult tibia: usually requires fixation w/ 4.5 to 6.0 mm pins;
- pins must be < 1/3 bone diameter to prevent pin hole fractures;
- Biomechanical analysis of pin placement and pin size for external fixation of distal radius fractures.
- widely separated pins within single fragment;
- placement of pins near the fracture site;
- number of pins:
- three pins usually provide axial stability even w/ segmental comminution;
- little is gained w/ a 4th pin in single segment;
- short fragments fixed w/ 2 pins in same plane will provide stability in plane of pins but will be relatively unstable in plane at a right angle to the pins;
- number of support bars:
- additional planes of fixation:
- a short fragment may not allow 3 pins in single plane but may allow additional pins in a different plane;
- unilateral external fixators must stabilize the frx from an eccentric off axis position, and are most able to control frx site bending and shear when there is frx site opposition;
- multiplane fixation or circular wire fixators help limit frx site bending and shear and allow load sharing at the frx site;
- proximity to the extremity: (decreasing bone to support bar distance)
- fibular fixation:
- see frx of the tibia w/ intact fibula;
- reference: Plating of the fibula. Its potential value as an adjunct to external fixation of the tibia.
Fracture Site Motion with Ilizarov and "Hybrid" External Fixation.
- biomechanical study which compared stability of Ilizarov fixator to a Hybrid fixator in a frx model;
- in a completely unstable frx model, a four ring Ilizarov fixator has substantially more stability than a unilateral Hybrid fixator;
- weakness of study:
- most fractures have at least some bone apposition which confers load sharing;
- the frx model used in their study used longer half pins than would be used for most tibial frx;
- as would be expected, increasing the distance between the half pins and bone will decreased frx stability;
- in most cases, Ilizarov transfixation wires cannot be placed at right angles to each other, and therefore, the construct will not be as stable as the one in the biomechanical study;
- Case Example:
- 30-year-old prisoner who sustained a patellar fracture and a distal tibia fracture;
- he was treated w/ an external fixator but several treatment principles were ignored;
- the fracture was left distracted, the pins were not spread out and were placed well away from the fracture site, and the fixator bar was not near the skin;
- as might be expected, this went on to a non union
Plating of the fibula. Its potential value as an adjunct to external fixation of the tibia.
The Role of Supplemental Lag-Screw Fixation for Open Fractures of the Tibial Shaft Treated With External Fixation.
Medial external fixation with lateral plate internal fixation in metaphyseal tibia fractures. A report of eight cases associated with severe soft-tissue injury.
Fracture Site Motion with Ilizarov and "Hybrid" External Fixation
Mechanical considerations in using tensioned wires in a transosseous external fixation system.
The effect of rigidity on fracture healing in external fixation.