Minimally invasive intraoperative stiffness measurement of lumbar spinal motion segments.

OBJECTIVE: To test a new tiny-tipped intraoperative diagnostic tool that was designed to provide the surgeon with reliable stiffness data on the motion segment during microdiscectomy. A decrease in stiffness after nuclectomy and a measurable influence of muscle tension were assumed. If the influence of muscle tension on the motion segment could at least be ruled out, there should be no difference with regard to stiffness between women and men. If these criteria are met, this new intraoperative diagnostic tool could be used in further studies for objective decision-making regarding additional stabilization systems after microdiscectomy. METHODS: After evaluation of the influence of muscle relaxation during in vivo measurements with a spinal spreader between the spinous processes, 21 motion segments were investigated in 21 patients. Using a standardized protocol, including quantified muscle relaxation, spinal stiffness was measured before laminotomy and after nuclectomy. RESULTS: The decrease in stiffness after microdiscectomy was highly significant. There were no statistically significant differences between men and women. The average stiffness value before discectomy was 33.7 N/mm, and it decreased to 25.6 N/mm after discectomy. The average decrease in stiffness was 8.1 N/mm (24%). CONCLUSION: In the moderately degenerated spine, stiffness decreases significantly after microdiscectomy. Control for muscle relaxation is essential when measuring in vivo spinal stiffness. The new spinal spreader was found to provide reliable data. This spreader could be used in further studies for objective decision-making about additional stabilization systems after microdiscectomy.

Influence of thread design on pedicle screw fixation. Laboratory investigation.

OBJECT: The authors conducted a study to determine the thread properties that provide optimal screw fixation in cancellous bone, when screws of the same external screw diameter are used. METHODS: Three compliance engineering-certified screws in clinical use, all of the same external diameter and length, were compared in an axial pullout experiment with respect to advantageous thread properties. As test material, standardized Sawbone blocks with 3 different densities (0.12, 0.16, and 0.32 g/cm3) were used. RESULTS: Screw thread Type 1, whose flank overlap area (FOA; 261 mm2) results from narrowing the conical core in the thread area, showed significantly better holding strength than the other types. Screw thread Type 2 (FOA 326 mm2) with a conical but thicker core and a smaller thread pitch was found to be the only one without increase of pull-out forces when test materials density changed from 0.12 to 0.16 g/cm3. A screw tested as control, with a constant (cylindrical) core diameter (Type 3; FOA 206 mm2), had the same thread pitch as Type 1 but without the compressive effect on the surrounding bur hole wall material. Nevertheless, it showed higher pullout forces in the 0.16-g/cm3 material than screw Type 2. CONCLUSIONS: By reducing the core diameter of a screw toward the tip, while maintaining a constant nominal (external) diameter, one achieves frictional connection due to compression of surrounding material. In addition, the FOA is increased, which, in summary, leads to better fixation, as shown by screw Type 1.

Prognosis of multifactorial outcome in lumbar discectomy: a prospective longitudinal study investigating patients with disc prolapse.

OBJECTIVES: Although previous research has shown that certain medical data and psychosocial factors predict postoperative pain, it remains unclear whether they also contribute to a more distinct outcome measure that is based on classification of self-reported outcome criteria. To assess the prognostic power of somatic, psychologic, and social predictors when evident outcome criteria of surgical treatment are investigated, this study used a prospective longitudinal design examining preoperative factors associated with outcome six months after lumbar discectomy. METHODS: Forty-eight out of 58 consecutive patients were included (60% male, 40% female, mean age 47 years). Preoperative data comprised of Lasegue sign (straight leg raising test), pain duration, paresis and radicular distribution, depression, pain disability, pain coping strategies, and qualitative descriptions of pain. Additionally, sociodemographic and occupational characteristics were observed. Six months' postoperative classification of outcome included pain intensity, pain locations, functional capacity, return to work, and health-related quality of life. RESULTS: From a surgical point of view, lumbar discectomy was successfully carried out on all patients. But, when subjective criteria of outcome were investigated, 56% of patients benefited from lumbar discectomy, whereas 44% of patients had poor results. Lasegue sign, depression, and sensory pain descriptions proved to be significant predictors, whereas pain cognition and pain coping strategies had no significant influence on evident outcome classification. DISCUSSION: Classification of patients regarding their individual outcome profiles showed that patients responded differently to lumbar disc-surgery. High risk factors for poor outcome of surgery are Laseque-sign and depression.