Square-lashing technique in segmental spinal instrumentation: a biomechanical study

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Spinal Biomechanics

Background:

• Sublaminar wires and cables are used for spinal instrumentation in scoliosis surgery.
• Rigid scoliotic curves pose challenges, leading to sublaminar wire or cable breakage and pullout.
• The square-lashing technique was developed to mitigate these complications.

Purpose of the Study:

• To biomechanically evaluate the pullout strength and failure modes of simple sublaminar constructs versus the square-lashing technique.
• To compare the performance of monofilament wire and multifilament cables using both techniques.

Main Methods:

• Four fixation methods were tested: single wire, square-lashing wire, single cable, and square-lashing cable.
• Individual vertebrae underwent pullout testing with each construct.
• Ultimate failure load and failure mechanism were recorded for all constructs.

Main Results:

• Square-lashing constructs exhibited higher ultimate failure loads (1,239 N for wire, 1,388 N for cable) compared to single constructs (793 N for wire, 1,162 N for cable).
• Single wire constructs failed primarily by wire breakage (12/16).
• Square-lashing cable constructs consistently failed by pedicle fracture (16/16), indicating superior resistance to pullout and lamina cutout.

Conclusions:

• The square-lashing technique offers significantly higher pullout strength than simple loop constructs.
• This technique, especially with cables, minimizes lamina cutout and shows potential as an advancement in segmental spinal instrumentation for scoliosis.
• Pedicle fracture was the predominant failure mode for square-lashing cable constructs, suggesting robust fixation.