Closing Wedge Osteotomies Stiffer Than Opening Wedge

More mechanical stiffness seen with increasing rod diameter regardless of osteotomy type

MONDAY, April 18 (HealthDay News) -- Closing wedge osteotomies (CWOs) are more mechanically stiff than opening wedge osteotomies (OWOs) in flexion-extension (FE), according to a study published in the April 15 issue of Spine.

Justin K. Scheer, from the San Francisco General Hospital, and colleagues determined the structural stiffness of OWOs and CWOs and the stiffness effect of rod diameter independent of the osteotomy type. They carried out seven OWOs and seven CWOs in cadaveric specimens and fixed 3.5 mm and 4.5 mm rods in all specimens from C4-T3. They conducted multidirectional bending tests in FE, lateral bending (LB), and axial rotation (AR).

The investigators found that, compared to 3.5 mm rods, fixation with 4.5 mm rods significantly increased stiffness in all bending modes, independent of osteotomy type. Increased stiffness of 4.5 mm rods relative to 3.5 mm rods was 31±12 percent for FE, 37±39 percent for LB, and 31±11 percent for AR across the entire site; and, at the osteotomy site, stiffness was 43±23 percent for FE, 45±36 percent for LB, and 41±17 percent for AR. CWO was significantly stiffer than OWO (construct, 42 percent; across osteotomy, 56 percent), independent of rod diameter, in FE bending only.

"Constructs with C7 closing wedge osteotomies are more mechanically stiff than those with opening wedge osteotomies in flexion-extension. Increasing rod diameter from 3.5 mm to 4.5 mm results in a significant increase in stiffness in all modes of bending," the authors write.

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