Influence of surgical intervention at the level of the dorsal spinous processes on the biomechanics of the equine thoracolumbar spine.
Authors: Baudisch, Singer, Jensen, Eichler, Meyer, Lischer, Ehrle
Journal: Equine veterinary journal
Summary
# Overriding Dorsal Spinous Processes: What Surgical Intervention Actually Changes in Spinal Biomechanics Overriding dorsal spinous processes remain a contentious diagnosis in equine practice, with two competing surgical approaches—interspinous ligament desmotomy and partial spinous process ostectomy—commonly advocated despite limited biomechanical evidence. Baudisch and colleagues investigated how these procedures alter thoracolumbar spine mobility using 12 cadaveric specimens mounted on a mechanical testing rig, measuring spinous process separation and spinal range of motion across multiple planes before and after surgery at two or five levels. Desmotomy failed to increase the distance between spinous processes significantly (median 7.2 mm to 7.4 mm), whereas ostectomy produced a substantial widening (8.8 mm to 13 mm); however, both procedures increased axial rotation markedly—up 28% at T14/T15—whilst having no meaningful effect on flexion, extension, or lateral bending. Importantly, dissection revealed that desmotomy invariably caused trauma to the multifidus muscles at every surgical site, raising questions about the tissue cost of this less invasive approach. These findings suggest that neither procedure mechanically resolves spinous process impingement in the way clinical practice might assume, though both do enhance rotational mobility, which may have clinical relevance for horses with performance limitations related to axial stiffness rather than simply overcrowded dorsal spines.
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Practical Takeaways
- •Cranial wedge ostectomy is more effective than desmotomy alone at mechanically increasing spacing between overriding spinous processes in the thoracolumbar region
- •Both procedures increase rotational mobility, which may improve spinal mechanics, but this occurs without gains in other planes of motion
- •Desmotomy causes documented injury to the paraspinal muscles (Musculi multifidi) that practitioners should consider when planning postoperative rehabilitation
Key Findings
- •Interspinous ligament desmotomy did not significantly increase spacing between spinous processes (7.2 mm to 7.4 mm, p=0.09) but cranial wedge ostectomy did (8.8 mm to 13 mm, p<0.001)
- •Both surgical procedures significantly increased axial rotational range of motion by 28.1% at T14/T15 level (6.4° to 8.2°, p=0.02)
- •Neither procedure increased spinal range of motion during flexion, extension, or lateral bending
- •Musculi multifidi injury was present at all desmotomy sites during anatomical dissection