Analysis of the influence of disc degeneration on the mechanical behaviour of a lumbar motion segment using the finite element method.

Biomechanical comparison between fusion of two vertebrae and implantation of an artificial intervertebral disc.

Study design A questionnaire study. Objective To evaluate the prevalence of wrong level surgery among spine surgeons and their use of preventive measures to avoid its occurrence. Summary of background data Wrong site surgery fails to improve the patient's symptoms and has medical, emotional, social, and legal implications. Organizations such as the North American Spine Society and the Joint Commission on Accreditation of Healthcare Organizations have established guidelines to prevent wrong site surgery. Spine surgeons' compliance with these guidelines and the prevalence of wrong-level spine surgery have not been investigated previously. Methods All members of the American Academy of Neurologic Surgeons (n = 3505) were sent an anonymous, 30-question survey with a self-addressed stamped envelope. Results A total of 415 (12%) surgeons responded. Sixty-four surgeons (15%) reported that, at least once, they had prepared the incorrect spine level, but noticed the mistake before making the incision. Two hundred seven (50%) reported that they had done 1 or more wrong level surgeries during their career. From an estimated 1,300,000 spine procedures, 418 wrong level spine operations had been performed, with a prevalence of 1 in 3110 procedures. The majority of the incorrect level procedures were performed on the lumbar region (71%), followed by the cervical (21%), and the thoracic (8%) regions. One wrong level surgery led to permanent disability, and 73 cases resulted in legal action or monetary settlement to the patient (17%). Conclusion There is a high prevalence of wrong level surgery among spine surgeons; 1 of every 2 spine surgeons may perform a wrong level surgery during his or her career. Although all spine surgeons surveyed report using at least 1 preventive action, the following measures are highly recommended but inconsistently adopted: direct preoperative communication with the patient by the surgeon, marking of the intended site, and the use of intraoperative verification radiograph.

The prevalence of wrong level surgery among spine surgeons.

The existence and importance of an accelerated adjacent segment disc degeneration (ASD) after lumbar fusion have previously not been demonstrated by RCTs. The objectives of this study were, to determine whether lumbar fusion in the long term accelerates degenerative changes in the adjacent disc and whether this affects the outcome, by using a prospective randomised design. A total of 111 patients, aged 18-55, with isthmic spondylolisthesis were randomised to exercise (EX, n = 34) or posterolateral fusion (PLF, n = 77), with (n = 37) or without pedicle screw instrumentation (n = 40). The minimum 10 years FU rate was 72%, with a mean FU time of 12.6 years (range 10-17 years). Three radiographic methods of ASD quantification were used, i.e. two digital radiographic measurement methods and the semi quantitative UCLA grading scale. One digital measurement method showed a mean disc height reduction by 2% in the EX group and by 15% in the PLF group (p = 0.0016), and the other showed 0.5 mm more disc height reduction in the PLF compared to the Ex group (ns). The UCLA grading scale showed normal discs in 100% of patients in the EX group, compared to 62% in the PLF group (p = 0.026). There were no significant differences between instrumented and non-instrumented patients. In patients with laminectomy we found a significantly higher incidence of ASD compared to non laminectomised patients (22/47 vs. 2/16 respectively, p = 0.015). In the longitudinal analysis, the posterior and anterior disc heights were significantly reduced in the PLF group, whereas in the EX group only the posterior disc height was significantly reduced. Except for global outcome, which was significantly better for patients without ASD, the clinical outcome was not statistically different in patients with and without ASD. In conclusion, the long-term RCT shows that fusion accelerates degenerative changes at the adjacent level compared with natural history. The study suggests that not only fusion, but also laminectomy may be of pathogenetic importance. The clinical importance of ASD seems limited, with only the more severe forms affecting the outcome.

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A prospective randomised study on the long-term effect of lumbar fusion on adjacent disc degeneration

Study design Systematic review of published prevalence of adjacent segment degeneration (ASD) after spine surgery. Objective To evaluate the prevalence of ASD in patients after cervical and lumbar spine surgery. Summary of background data ASD is a common complication after spine surgery in long-term follow-up. A large body of literature has been reported on the topic, but no meta-analysis of the epidemiological data on ASD has been published Methods We searched the MEDLINE until March 2012 published in English language that reported the prevalence of ASD after spine surgery. We determined the ASD rates by calculating proportions and 95% confidence interval (CI) for each study and then pooled the data to derive a pooled proportion and 95% CI. Results A total of 94 studies with 34,716 patients from 19 countries were included. The occurrence of radiograph ASD ranged from 4.8% to 92.2%, and the pooled prevalence was 29.3% (95% CI, 22.7%-35.8%) by the random-effects model. The occurrence of symptoms ASD ranged from 0.0% to 30.3%, and the pooled prevalence was 7.4% (95% CI, 6.4%-8.5%). In cervical position, the occurrence of radiograph ASD and symptoms ASD was 32.8% (95% CI, 17.8%-47.9%) and 6.3% (95% CI, 4.8%-7.8%); in lumbar position, the occurrence of radiograph ASD and symptoms ASD was 26.6% (95% CI, 21.3%-31.9%) and 8.5% (95% CI, 6.4%-10.7%). In the 0.5- to 2- or less, more than 2- to 5- or less, and more than 5- to 20- or less year diagnosis time, the radiograph ASD prevalence was 21.8% (16.0%-27.6%), 33.6% (21.8%-45.4%), and 37.4% (10.7%-64.1%), respectively; and the symptoms ASD prevalence was 6.5% (4.8%-8.1%), 12.1% (8.2%-16.0%), and 3.2% (2.5%-4.0%), respectively. Conclusion Spine surgery is associated with significant risk of ASD. These figures may be useful in the estimation of the burden of the ASD after spine surgery.

Prevalence of Adjacent Segment Degeneration after Spine Surgery: A Systematic Review and Meta-analysis.

Effects of lumbar spinal fusion on the other lumbar intervertebral levels (three-dimensional finite element analysis)

Mechanical analysis of the lumbar vertebrae in a three-dimensional finite element method model in which intradiscal pressure in the nucleus pulposus was used to establish the model.

Takashi Arai

Papers

Effects of lumbar spinal fusion on the other lumbar intervertebral levels (three-dimensional finite element analysis)

Mechanical analysis of the lumbar vertebrae in a three-dimensional finite element method model in which intradiscal pressure in the nucleus pulposus was used to establish the model.