AN IN–VITRO HUMAN CADAVERIC STUDY INVESTIGATING THE BIOMECHANICAL PROPERTIES OF THE THORACIC SPINE

I Oda, K Abumi,
BW Cunningham*,
T Takeuchi,
K Kaneda,
PC McAfee*
Hokkaido University, Sapporo, Japan
and *Union Memorial Hospital, Baltimore, MD, USA

INTRODUCTION:
The purpose of this study was to investigate the biomechanical properties of the human thoracic spine, comparing the effects of anterior and posterior sequential destabilization conditions on functional unit mechanics.

METHODS:
Sixteen thoracic functional spinal units (FSUs) with bilateral ribs were divided into two groups based on destabilization procedure:

Non–destructive biomechanical testing was performed on the intact and subsequent destabilization conditions and included flexion–extension, lateral bending, and torsion (+3 Nm). The ranges of motion (ROMs) under maximum load and neutral zone (NZ) were obtained and normalized to the intact condition for each specimen. Statistical significance was determined using a Wilcoxon Signed Rank Test at 95% confidence.[ (costovertebral joint) = (rib head joint) + (costotransverse joint)]

RESULTS:
Flexion–Extension: Discectomy significantly increased the ROM by 193% and subsequent right rib head resection further increased the ROM by 81% (p<0.05). Laminectomv + medial facetectomy lead to a 22% increase in ROM and subsequent total facetecomy resulted in 28% increase (p<0.05). Lateral Bending: Discectomy increased the ROM by 74% and subsequent right rib head resection resulted in an 84% increase (p<0.05). Laminectomy + medial facetectomy lead to a 22% change in ROM and subsequent total facetectomy further increased ROM by 15% (p<0.05). Torsion: Discectomy resulted in 111% increment in ROM and right rib head resection caused an additional 72% increase (p<0.05). Laminectomy + medial facetectomv and subsequent total facetectomy significantly increased the ROM by 30% and 15%, respectively. Discectomy and subsequent right rib head resection significantly increased the NZ in all testing modes.

DISCUSSION:
This in vitro study revealed the basic biomechanical properties of human thoracic functional spinal units. The lateral portion of the facet joints plays an important role in thoracic spinal stability and should be preserved when performing decompressive laminectomy. For scoliosis correction, anterior disc release combined with rib head resection is biomechanically more effective in producing segmental rotation compared to posterior destabilization alone, and thereby, permits greater curve correction.