Contribution of Round vs. Rectangular Expandable Cage Endcaps to Spinal Stability in a Cadaveric Corpectomy Model

Area of Science:

• Spine surgery
• Orthopedic biomechanics
• Spinal implants

Background:

• Expandable cages are increasingly used for anterior thoracolumbar spine reconstruction post-corpectomy.
• Rectangular endcaps may reduce subsidence compared to round endcaps, but their effect on construct stability is unclear.
• This study evaluates the impact of endcap shape and fixation method on expandable cage stability.

Purpose of the Study:

• To compare the stability of expandable corpectomy cages with round versus rectangular endcaps.
• To assess the influence of anterior plate versus posterior pedicle screw fixation on construct stability.
• To determine the biomechanical contribution of endcap shape and fixation to L1 sub-total corpectomy construct stability.

Main Methods:

• Eight fresh-frozen cadaveric thoracolumbar spine specimens (T11-L3) were used.
• Multi-directional flexibility testing (6 N·m) was performed using a spine simulator.
• Testing included intact, corpectomy defect, cage-alone (round/rectangular), cage with anterior plate, and cage with posterior pedicle screws configurations.

Main Results:

• Expandable cages alone significantly reduced motion in flexion-extension and lateral bending (rectangular endcaps).
• Both endcap types showed increased axial rotation and round endcaps showed increased lateral bending compared to intact.
• Supplemental fixation (anterior plate or pedicle screws) yielded the most rigid constructs, with no significant differences between fixation types or endcap shapes.

Conclusions:

• Anterior-only fixation may be sufficient for expandable cages in sub-total corpectomy.
• Endcap selection may prioritize factors like subsidence resistance over significant differences in construct stability.
• Further research could explore long-term outcomes and patient-specific factors.