OTA 2013 Posters

Scientific Poster #125 Basic Science OTA 2013

A Safe Technique for Dynamizing the Taylor Spatial Frame

Christopher Iobst, MD1; Anthony Khoury, BS2; Zachary Ingwer, BS2; David Kaimrajh, MS3; Edward Milne3; Loren L. Latta, PE, PhD2,3;
1Miami Children’s Hospital, Coral Gables, Florida, USA;
2University of Miami, Coral Gables, Florida, USA;
3Max Biedermann Institute for Biomechanics, Miami Beach, Florida, USA

Background/Purpose: Dynamization of external fixation can be achieved by allowing axial micromotion to occur with loading of the frame. The Taylor Spatial Frame (TSF) uses six obliquely oriented struts to connect the rings. These struts allow correction of deformity to occur in all planes of motion. However, attempting to dynamize the TSF by loosening the struts may not be appropriate for fracture or osteotomy healing. Our hypothesis is that dynamization of the TSF by loosening struts will create excessive shear loading on the fracture gap, but modified shoulder bolts will provide controlled axial micromotion.

Methods: Five TSF constructs were mounted on Sawbones tibiae with a proximal ostectomy. An axial load aligned to the mechanical axis of the tibia was cycled from 20 to 200 N at 0.25 Hz. 6 degrees of freedom of motion of the proximal and distal segments were tracked (Figure 1) for 8 different constructs: (1) all struts of the TSF intact; (2) strut 1 loose; (3) struts 1 and 3 loose; (4) struts 1, 3, and 5 loose; (5) all struts loose; (6) all struts intact with dynamization bolts on the proximal side; (7) all struts intact with dynamization bolts on alternating sides; and (8) threaded Ilizarov rods locked between the rings.

Results: There was no statistically significant difference in vertical displacement between the Ilizarov rods and all struts locked. There was a statistically significant difference between the modified shoulder bolts and the Ilizarov rods (P <0.01) and all struts locked (P <0.05). There was no statistically significant difference in shear values between all struts locked and the modified shoulder bolt struts. There was a statistically significant difference in shear values between one strut unlocked and all struts locked/dynamized (P <0.05) (Figure 2).

Conclusion: The modified shoulder bolts may be a safe (and easy) way to dynamize the TSF. They allow appropriate axial motion without a significant increase in shear. It is not recommended to unlock a single or multiple struts as a method of dynamizing the Taylor Spatial Frame.

Alphabetical Disclosure Listing

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.