Sohrab S. Virk

Adjacent Segment Disease

EDUCATIONAL OBJECTIVES As a result of reading this article, physicians should be able to: 1. Understand the forces that predispose adjacent cervical segments to degeneration. 2. Understand the challenges of radiographic evaluation in the diagnosis of cervical and lumbar adjacent segment disease. 3. Describe the changes in biomechanical forces applied to adjacent segments of lumbar vertebrae with fusion. 4. Know the risk factors for adjacent segment disease in spinal fusion. Adjacent segment disease (ASD) is a broad term encompassing many complications of spinal fusion, including listhesis, instability, herniated nucleus pulposus, stenosis, hypertrophic facet arthritis, scoliosis, and vertebral compression fracture. The area of the cervical spine where most fusions occur (C3-C7) is adjacent to a highly mobile upper cervical region, and this contributes to the biomechanical stress put on the adjacent cervical segments postfusion. Studies have shown that after fusion surgery, there is increased load on adjacent segments. Definitive treatment of ASD is a topic of continuing research, but in general, treatment choices are dictated by patient age and degree of debilitation. Investigators have also studied the risk factors associated with spinal fusion that may predispose certain patients to ASD postfusion, and these data are invaluable for properly counseling patients considering spinal fusion surgery. Biomechanical studies have confirmed the added stress on adjacent segments in the cervical and lumbar spine. The diagnosis of cervical ASD is complicated given the imprecise correlation of radiographic and clinical findings. Although radiological and clinical diagnoses do not always correlate, radiographs and clinical examination dictate how a patient with prolonged pain is treated. Options for both cervical and lumbar spine ASD include fusion and/or decompression. Current studies are encouraging regarding the adoption of arthroplasty in spinal surgery, but more long-term data are required for full adoption of arthroplasty as the standard of care for prevention of ASD.

The temporal role of leptin within fracture healing and the effect of local application of recombinant leptin on fracture healing.

Objective: We hypothesized that leptin is expressed in a specific time sequence during fracture healing, and its deficiency leads to impaired healing. Methods: Control (C57BL/6) mice and leptin −/− obese (ob/ob) mice were used. Arm 1: Fracture callus was harvested at 1, 3, 5, 7, 10, 14, and 21 days (n = 8/time point) after closed middiaphyseal femur fractures were created in 56 C57BL/6 mice, and reverse transcriptase polymerase chain reaction analysis was then performed. Levels of leptin were tracked at each time point listed. Arm 2: Forty-two C57BL/6 controls and 42 ob/ob mice underwent open stabilized middiaphyseal femur fractures, and tissues were harvested at 14, 21, and 42 days and radiographic, histologic, and quantitative computerized tomography analyses were performed. Arm 3: Murine recombinant leptin was applied directly at the newly created fracture site in 2 separate groups (10 or 100 &mgr;g of leptin) of 42 ob/ob mice. Two-factor analysis of variance and the Student t-test were used for statistical analysis. Results: The time course of Leptin mRNA expression within a fracture callus was detected. Delay in callus maturation was demonstrated radiographically and histologically in the ob/ob mice. ob/ob fractures had an increase in total callus volume by quantitative computerized tomography (P < 0.05). Application of local leptin at both doses reversed the delay in healing. Conclusions: Leptin is expressed in a unique time course during fracture healing and leptin deficiency leads to impaired fracture healing that reverses by local application of leptin.

Cost effectiveness analysis of graft options in spinal fusion surgery using a Markov model.

Study Design: Statistical decision model. Objective: To determine the most cost-effective graft option in spinal fusion. Summary of Background Data: Spinal fusion has been shown to be an effective technique to treat lumbar degenerative spondylolisthesis. There have been significant advances in bone graft options to improve outcomes related to spinal fusion. RhBMP-2 (RhBMP), iliac crest bone graft (ICBG), local bone alone (LBG), demineralized bone matrix with local bone (DBM), local bone with corticocancellous allograft chips (CCA) have all been used as graft options. There has not been significant research in which graft option is most cost effective. Methods: A Markov decision model has been created to identify the most cost-effective graft option for use in spinal fusion to treat 1-level (L4–L5) degenerative spondylolisthesis in a cohort of 60-year-old patients. Costs and effectiveness of successful spinal fusion surgery and revision surgery associated with each graft option was estimated through published data. The quality adjusted life years (QALYs) from these surgeries were compared with the amount of QALYs associated with living with chronic back pain. Results: In the base case, the incremental cost-effective ratio for each graft option when compared with living with chronic back pain was

The top 50 Articles on Minimally Invasive Spine Surgery.

21,308/QALY for ICBG,

One-Week Staged Bilateral Total Knee Arthroplasty Protocol: A Safety Comparison of Intended and Completed Surgeries

16,595/QALY for RhBMP,

What is the Rate of Revision Discectomies After Primary Discectomy on a National Scale

21,204/QALY for LBG,

Reimbursement Related to a 90-Day Episode of Care for a One or Two-Level Anterior Cervical Discectomy and Fusion.

21,287/QALY for DBM, and

The Cost Effectiveness of Polyetheretheketone (PEEK) Cages for Anterior Cervical Discectomy and Fusion.

28,153/QALY for CCA. Therefore, the most cost-effective graft option in the base case was RhBMP. Sensitivity analysis shows that RhBMP is not the most cost-effective option if the revision rate is significantly raised. If the cost of treatment with RhBMP rises >

Experimental Design and Surgical Approach to Create a Spinal Fusion Model in a New Zealand White Rabbit (Oryctolagus cuniculus).

42,250 then LBG becomes the likely cost-effective treatment. Conclusions: RhBMP is the most cost-effective graft option for L4–L5 fusion for degenerative spondylolisthesis largely due to the reduced rate of revision spine surgery. The increased upfront cost and list of complications associated with RhBMP is offset by the reduced rate of revision surgery.

Clinical Outcomes of Single-Level Anterior Cervical Discectomy and Fusion

Study Design. Bibliometric study of current literature. Objective. To catalog the most important minimally invasive spine (MIS) surgery articles using the amount of citations as a marker of relevance. Summary of Background Data. MIS surgery is a relatively new tool used by spinal surgeons. There is a dynamic and evolving field of research related to MIS techniques, clinical outcomes, and basic science research. To date, there is no comprehensive review of the most cited articles related to MIS surgery. Methods. A systematic search was performed over three widely used literature databases: Web of Science, Scopus, and Google Scholar. There were four searches performed using the terms “minimally invasive spine surgery,” “endoscopic spine surgery,” “percutaneous spinal surgery,” and “lateral interbody surgery.” The amount of citations included was averaged amongst the three databases to rank each article. The query of the three databases was performed in November 2015. Results. Fifty articles were selected based upon the amount of citations each averaged amongst the three databases. The most cited article was titled “Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion” by Ozgur et al and was credited with 447, 239, and 279 citations in Google Scholar, Web of Science, and Scopus, respectively. Citations ranged from 27 to 239 for Web of Science, 60 to 279 for Scopus, and 104 to 462 for Google Scholar. There was a large variety of articles written spanning over 14 different topics with the majority dealing with clinical outcomes related to MIS surgery. Conclusion. The majority of the most cited articles were level III and level IV studies. This is likely due to the relatively recent nature of technological advances in the field. Furthermore level I and level II studies are required in MIS surgery in the years ahead. Level of Evidence: 5