Influence of Spinal Deformity Construct Design on Adjacent-Segment Biomechanics

Area of Science:

• Spinal biomechanics
• Orthopedic surgery
• Deformity correction

Background:

• Adjacent level degeneration is a known complication after adult spinal deformity surgery.
• The influence of surgical construct design on adjacent level degeneration risk is not well understood.
• This study investigates the biomechanical effects of different spinal deformity correction constructs on adjacent segment motion.

Purpose of the Study:

• To biomechanically profile common adult spinal deformity correction constructs.
• To assess the impact of construct design on adjacent level biomechanics.
• To compare the range of motion at adjacent levels for different surgical techniques.

Main Methods:

• Nondestructive flexibility tests were performed on 21 cadaveric spinal specimens.
• Fourteen specimens featured pedicle subtraction osteotomies (PSOs) and seven featured anterior column realignment (ACR) constructs.
• Range of motion (ROM) at the adjacent free level was measured in flexion, extension, axial rotation, and lateral bending.

Main Results:

• ACR constructs demonstrated a significantly lower change in ROM during flexion at the proximal adjacent level compared to PSO constructs (1.02 vs. 1.32, P < 0.01).
• Lateral lumbar interbody fusion adjacent to PSO with four rods reduced ROM more effectively than transforaminal interbody fusion with two rods.
• Anchoring ACR interbody fusions with two screws reduced proximal adjacent level ROM in flexion.

Conclusions:

• ACR constructs result in less adjacent level ROM change compared to PSO constructs.
• Specific construct configurations, such as lateral lumbar interbody fusion with four rods for PSO, offer greater adjacent segment motion reduction.
• Deformity construct design significantly influences the biomechanics of the proximal adjacent segment.