Anterior shear strength of the porcine lumbar spine after laminectomy and partial facetectomy

Abstract

Degenerative lumbar spinal stenosis is the most common reason for lumbar surgery in patients in the age of 65 years and older. The standard surgical management is decompression of the spinal canal by laminectomy and partial facetectomy. The effect of this procedure on the shear strength of the spine has not yet been investigated in vitro. In the present study we determined the ultimate shear force to failure, the displacement and the shear stiffness after performing a laminectomy and a partial facetectomy. Eight lumbar spines of domestic pigs (7 months old) were sectioned to obtain eight L2–L3 and eight L4–L5 motion segments. All segments were loaded with a compression force of 1,600 N. In half of the 16 motion segments a laminectomy and a 50% partial facetectomy were applied. The median ultimate shear force to failure with laminectomy and partial facetectomy was 1,645 N (range 1,066–1,985) which was significantly smaller (p = 0.012) than the ultimate shear force to failure of the control segments (median 2,113, range 1,338–2,659). The median shear stiffness was 197.4 N/mm (range 119.2–216.7) with laminectomy and partial facetectomy which was significantly (p = 0.036) smaller than the stiffness of the control specimens (median 216.5, 188.1–250.2). It was concluded that laminectomy and partial facetectomy resulted in 22% reduction in ultimate shear force to failure and 9% reduction in shear stiffness. Although relatively small, these effects may explain why patients have an increased risk of sustaining shear force related vertebral fractures after spinal decompression surgery.

The impact of bone mineral density and disc degeneration on shear strength and stiffness of the lumbar spine following laminectomy

“…Our findings are in line with results reported in other in vitro and finite element studies, which also showed reduced shear strength and stiffness of the spine after laminectomy [11, 19, 20]. However, declines found in the present study (44.2% for SFF and 19.9% for SS) were much larger than those found in a similar study using porcine specimens (22% for SFF and 9% for SS), even though facetectomy was performed in addition to laminectomy in the latter study [20].…”

“…However, declines found in the present study (44.2% for SFF and 19.9% for SS) were much larger than those found in a similar study using porcine specimens (22% for SFF and 9% for SS), even though facetectomy was performed in addition to laminectomy in the latter study [20]. With facetectomy, a larger reduction of strength and stiffness could be expected.…”

“…In addition, laminectomy as well as removal of posterior elements substantially reduces spinal strength in shear loading [11, 19, 20]. In vitro experiments have also shown that shear loading can lead to bony failure of the posterior elements of the spine, with fracturing of the pars interarticularis most often reported [1].…”

Which factors prognosticate spinal instability following lumbar laminectomy?

“…All articulating parts were kept free. The casting mould was placed in a hydraulic materials testing machine (Instron©, model 8872, Norwood, Canada) [1, 23, 24]. The caudal vertebral body was fixed on a plateau that allowed movement in axial and transverse directions only.…”

The feasibility of modal testing for measurement of the dynamic characteristics of goat vertebral motion segments

“…The stiffness of the spine may also be altered by spinal surgery. For example, surgery targeting spinal stenosis often implicates that the overlying lamina and the supraspinous ligament of the motion segment are removed, which might destabilise the spine (Tai et al, 2008;Subramaniam et al, 2009;Van Solinge et al, 2010).…”