Could isthmic approach to far lateral disc hernias cause instability?

Area of Science:

• Spinal biomechanics
• Surgical anatomy
• Orthopedic research

Background:

• The transpars (isthmic) approach involves partial resection of the pars interarticularis for distal lateral disc herniation.
• Understanding the relationship between the extent of pars resection and spinal instability is crucial for surgical outcomes.

Purpose of the Study:

• To investigate the correlation between the degree of spinal instability and the amount of isthmus excised during the transpars approach.
• To evaluate the biomechanical impact of varying pars interarticularis resection percentages on lumbar spine stability.

Main Methods:

• Thirty-six ovine lumbar spine segments were utilized.
• The isthmus was excised by 25% and 50% on the right side of each segment.
• Spinal segments underwent flexion, lateral bending, and axial rotation tests.

Main Results:

• No significant differences in flexion tests (yield moment, stiffness, ultimate load).
• Significant differences in lateral bending tests (yield moment, stiffness, maximum load) between 25% and 50% resection groups.
• No significant differences in axial rotation tests (yield torque, stiffness).

Conclusions:

• Increasing pars interarticularis resection significantly reduces spinal resistance, especially during lateral bending.
• A 50% resection led to easier fracture compared to a 25% resection.
• The pars interarticularis is vital for spinal stability; greater resection correlates with increased instability.