Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques. Micro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S4). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads.Aims
Methods
We evaluated the impact of lumbar instrumented
circumferential fusion on the development of adjacent level vertebral
compression fractures (VCFs). Instrumented posterior lumbar interbody
fusion (PLIF) has become a popular procedure for degenerative lumbar
spine disease. The immediate rigidity produced by PLIF may cause
more stress and lead to greater risk of adjacent VCFs. However,
few studies have investigated the relationship between PLIF and
the development of subsequent adjacent level VCFs. Between January 2005 and December 2009, a total of 1936 patients
were enrolled. Of these 224 patients had a new VCF and the incidence
was statistically analysed with other covariants. In total 150 (11.1%)
of 1348 patients developed new VCFs with PLIF, with 108 (72%) cases
at adjacent segment. Of 588 patients, 74 (12.5%) developed new subsequent
VCFs with conventional posterolateral fusion (PLF), with 37 (50%)
patients at an adjacent level. Short-segment fusion, female and
age older than 65 years also increased the development of new adjacent
VCFs in patients undergoing PLIF. In the osteoporotic patient, more
rigid fusion and a higher stress gradient after PLIF will cause
a higher adjacent VCF rate. Cite this article:
