Effects of Spine Surgery on Paraspinal Musculature
R.G. Fessler, MD, PhD; F.D. Brown, MD; E.D. Wirth, MD, PhD

Study Design.  A commercially available muscloskeletal model of the lumbar spine was modified to study the change in muscle activation as a result of postereior lumbar surgery at the L3-4 and L4-5 segments.

Objective.  To evaluate how graded resection of the lumbar paraspinal muscles as a result of posterior lumbar surgery affects muscle activity for a variety of movement tasks.

Summary of Background Data.  Several in vivo studies compare the change in functional outcome of the paraspinal muscles following surgery.  However due to limitations that exist with current in vivo methods no study to date has been able to quantitatively examine how the function of individual muscles in the lumbar spine change in response to different levels of injury. 

Methods.  A multibody dynamic musculoskeltal model of the lumbar spine was modified to measure muscle activity using a parametric examination of change in the cross-sectional area of muscles affected by posterior lumbar surgery. 

Results. This study shows that the reduction in muscle cross-sectional area as a result of posterior lumbar surgery at L3-4 and L4-5 results in a change in trunk muscle activity where the greatest change occurs during axial rotation and lateral bending.  The results suggest that preservation of the posterior paraspinal musculature results in greater preservation of the normal muscle activity than traditional open techniques.

Conclusions.  Preservation of the paraspinal musculature associated with minimally invasive surgical approaches to the lumbar better preserve post-operative muscle activity.  This study suggests that there is a positive correlation between the reduction of paraspinal muscle cross-sectional area following posterior lumbar spine surgery and the alteration in trunk muscle activity.  

Key words: lumbar surgery; paraspinal muscle; muscle activity, trunk

Key points

• Alteration in muscle cross-sectional area as a result of lumbar spine surgery produces the greatest change in muscle activity during left and right axial rotation as well as left and right lateral bending.
  
  
• Decreases in muscle cross-sectional area as a result of posterior lumbar spine surgery produces post-operative changes in paraspinal muscle activity.
  
  
• Changes in trunk muscle activity were shown to be correlated with the percent reduction in muscle cross-sectional area.
  

A Mouse Model of Intervertebral Disc Degeneration
X. Li, MD, PhD; G. Balian, PhD; M. Cui; C.T. Laurencin; B.L. Leo

BACKGROUND CONTEXT:
Musculoskeletal disorders of the spine and low back pain are the leading source of disability in people under 45 years of age and result in national economic losses of over 90 billion dollars per year. Current treatment options, including both conservative measures such as bed rest, anti-inflammatories, analgesia, and physical therapy as well as surgical measures, target the clinical symptoms of IVD disease rather than addressing the early pathologic processes occurring in the course of degeneration. However, recent advancements in molecular biology including gene cloning and gene transfer technology have made it possible to contemplate treating the IVD at the molecular level to prevent or delay the progression of disc degeneration.

PURPOSE:
The aim of the present study was to investigate the effect of recombinant GDF-5 protein and GDF-5 cDNA on the metabolism of intervertebral disc cells in vitro and in vivo.

METHODS:
Mouse disc cells in vitro were treated with recombinant GDF-5 protein. Mouse GDF-5 cDNA was cloned into an expression vector and was used to transfect mouse disc cells in vitro. Therapy with Ad-GDF-5, GDF-5 protein and cDNA was assessed by measuring cell proliferation, proteoglycan production, and extracellular matrix gene expression in vitro and evaluating histological changes, immunostaining and extracellular matrix production in a needle puncture-induced disc degeneration model.

RESULTS:
Biochemical assays revealed an elevated GAG/DNA ratio in mouse IVD cells that were cultured in the presence of various concentrations of mGDF-5 protein. Real-time RT-PCR demonstrated that treating the cells with GDF-5 protein increased the expression of the collagen type II and aggrecan genes in a dose dependent manner while MMP-3 gene expression decreased. Immunohistochemistry showed an increase in the aggregation of mouse IVD cells that were treated with mGDF-5 in culture compared to the control group. The mouse GDF-5 gene was successfully cloned into an expression plasmid vector and GDF-5 protein production was confirmed by Western blot analysis. Type II collagen and aggrecan gene expression by the cells increased significantly in the cells that were transfected by Nucleofection with the GDF-5 plasmid compared with cells that were transfected with a control plasmid.

The production of exogenous genes could express and keep on certain strength at least 5 weeks after the injections. Quantitative measurements of %DHI and MRI image showed the Ad-GDF5 injection improves the water content and the restoration of disc height. The histology study demonstrated the chondroid cells proliferated from the annulus fibrosus (AF). In Ad-GF5 groups, the extensive and intense of cells proliferation are obviously stronger than Ad-Luc groups. The immunostaining showed more collagen II expressed in Ad-GDF5 groups. The biochemical analysis indicated the cell number of the IVD in Ad-Luc groups reduced since 4 weeks post operation and didn’t recover throughout the study.

CONCLUSIONS:
This is the first report to clone the mouse GDF-5 gene and use the Nucleofection method to transfer DNA into IVD cells. The data suggests that both recombinant protein and the cDNA forms of GDF-5 can increase the expression of genes for extracellular matrix proteins in mouse IVD cells. Compare with the GDF-5 protein injection, Ad-GDF5 could provide a stable source of GDF-5 and prolong the time of keeping an effective concentration of GDF-5 in the specific location. Our research confirmed the therapeutic effect of Ad-GDF5 for intervertebral disc degeneration in vivo. Future attempts at gene therapy to treat degenerative disc disease with a novel ex vivo gene transfer technique are needed to develop a therapy that would alleviate the condition of patients with clinically relevant axial spine pain.

Prospective Cohort Study of the COMT val 158 met Genotype and Outcome from Surgery for Degenerative Disc Disease
D.H. Kim, MD; L.G. Jenis, MD; R.J. Banco, MD; M. Max, PhD

BACKGROUND CONTEXT:
Increasing evidence suggests that the experience of pain symptoms related to lumbar degenerative disc disease (DDD) is genetically determined. Potential candidate genes conferring greater risk for development of chronic pain include the catecholamine-O-methyltransferase gene (COMT). COMT codes for a critical enzyme in catecholamine metabolism and modulates dopamine, epinephrine, and norepinephrine-mediated neurotransmission as well as µ-opioid system responses. Human studies have demonstrated that common functional genetic polymorphisms in the COMT gene affects the response to sustained pain.

PURPOSE:
To characterize the distribution of allelic variations in the COMT gene in patients undergoing surgery for lumbar DDD.

STUDY DESIGN/ SETTING:
Prospective cohort study.

PATIENT SAMPLE:
100 patients presenting for surgical treatment of lumbar DDD based on clinical evaluation and MRI. Patients were 18 years and older with moderate to severe low back pain unresponsive to at least 6 months of non-operative treatment.

OUTCOME MEASURES:
Genetic analysis.

METHODS:
A sample of venous blood was obtained from each patient for DNA extraction and sequencing. Analysis of COMT was performed with respect to 5 single nucleotide polymorphisms in non-coding regions potentially associated with pain response. Allelic frequencies for all known polymorphisms were measured and the distribution of individual patient genotypes were compared to those predicted for the general population.

RESULTS:
5 of 5 COMT loci yielded informative results for the study population. Test for Hardy-Weinberg equilibrium (HWE) revealed 2 COMT loci that diverged significantly from expected distributions. Specifically, carriers of COMT rs6269 (minor allele frequency, MAF 50%) and rs4818 (MAF 46%), both in strong linkage disequilibrium, were less likely to be homozygous for minor allele and more likely to be heterozygous than expected under HWE. Chi-square analysis for these loci yielded p-values of 0.0488 and 0.0458, respectively.

CONCLUSIONS:
As a group, patients presenting for surgical treatment of lumbar DDD demonstrate significant deviation from HWE for a set of polymorphisms with respect to the pain-modulating COMT gene. These results might suggest that allelic variations in specific genes result in predisposition to chronic pain associated with DDD. Future research regarding such potential genetic risk factors may allow development of more effective selection criteria for surgical treatment of DDD.

FDA DEVICE/DRUG STATUS:
This abstract does not discuss or include any applicable devices or drugs.

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**Current and ongoing research