Adjacent segment degeneration: observations in a goat spinal fusion study

Area of Science:

• Orthopedics
• Spinal Surgery
• Biomedical Engineering

Background:

• Ongoing debate exists regarding the cause of adjacent segment degeneration (ASD) after spinal fusion: increased biomechanical load or pre-existing degenerative disease.
• Animal models allow for the isolation of factors contributing to ASD by studying non-degenerated spines.

Purpose of the Study:

• To evaluate the development of adjacent segment disc degeneration in vivo using a goat lumbar spinal fusion model.
• To differentiate between biomechanical effects and natural degeneration progression in ASD.

Main Methods:

• 13 skeletally mature goats underwent spinal fusion at L3-L4 and L1-L2 segments, followed for 3 or 6 months.
• Adjacent (T13-L1, L4-L5), interjacent (L2-L3), and control (L5-L6) intervertebral discs were analyzed using MRI, macroscopy, and histology.
• Results were compared to 6 non-operated control goats.

Main Results:

• No significant degenerative changes were observed in the intervertebral discs adjacent or interjacent to the fused segments.
• Severe degenerative changes were unexpectedly found in the L5-L6 control discs after 6 months.

Conclusions:

• Large animal fusion models are valuable for in vivo ASD research due to the absence of pre-existing degeneration.
• The study suggests that adjacent disc degeneration does not occur in this specific goat spinal fusion model.
• An increased risk of intervertebral disc degeneration at the L5-L6 level was noted, with an unclear underlying mechanism.