The value of (18)F-fluoride PET/CT in the assessment of screw loosening in patients after intervertebral fusion stabilization.

PURPOSE: We evaluated (18)F-fluoride PET/CT for the diagnosis of screw loosening after intervertebral fusion stabilization and compared the results with those from functional radiography. METHODS: A group of 59 patients with pain in the region of previous intervertebral fusion stabilization and suspicion of implant instability due to screw loosening were investigated with (18)F-fluoride PET/CT and functional radiography, 30.1 ± 3.4 and 29.3 ± 3.2 months, respectively, after surgery. The criterion for loosening was increased focal uptake surrounding the screw entry point and shaft. SUVmax and SUVmean were measured in a region of interest (ROI) drawn around each screw (334 screws analysed). The final diagnosis was established by surgical exploration in 27 patients and clinical follow-up after intervertebral fusion stabilization in 32 patients. RESULTS: Of the 59 patients, 20 were proven positive for implant failure due to screw loosening and 39 were confirmed negative. The sensitivity, specificity and accuracy of (18)F-fluoride PET/CT were 75%, 97.4% and 89.8% in the patient-based analysis, and 45.6%, 100% and 80% in the screw-based analysis, respectively. The positive and negative predictive values were 93.8% and 100 % in the patient-based analysis, and 88.4 and 76% in the screw-based analysis, respectively. CT signs in PET/CT allowed screw breakage to be detected in three patients. SUVmax, SUVmean and SUVmax/SUVmean ratios in screw ROIs and respective values in reference regions were all found to be significantly different between screws positive for loosening (58 screws) and screws negative for loosening (276 screws). The ratio between SUVmax in screw ROIs and the values in reference regions was the most significant parameter for distinguishing screws positive and screws negative for loosening. CONCLUSION: (18)F-Fluoride PET/CT imaging is useful for the diagnosis of screw loosening in patients with persistent symptoms after intervertebral fusion stabilization.

Postoperative and preincisional electrical nerve stimulation TENS reduce postoperative opioid requirement after major spinal surgery.

BACKGROUND AND OBJECTIVE: Preincisional and postoperative transcutaneous electrical nerve stimulation (TENS) administration reduces postoperative opioid demand in abdominal surgery. Aim of this study was to find out whether a comparable effect of TENS applies in major spinal surgery. METHODS: Thirty-eight patients of both sex scheduled for lumbar interbody fusion were enrolled and divided randomly into 3 groups. Group A received TENS preincisional and postoperative, group B received this treatment postoperative only, and group C was the sham controlled. The postoperative demand on piritramid to achieve a visual anlog scale pain score <3 was delivered either by nurse or by a patient-controlled analgesia pump, when the patients were alert. The setting of the patient-controlled analgesia pump, bolus of piritramid 2 mg intravenously (IV), lockout time of 20 minutes, and maximum dose of piritramid 15 mg within 4 hours, the coanalgesic therapy diclofenac 75 mg IV, and the rescue medication metamizol 1 g IV was identical for all patients. The total amount of piritramid administered over the first 24 hours after surgery and an optional rescue medication were recorded. RESULTS: All groups were compared by pairs. The postoperative demand on piritramid differed significantly A versus B (P<0.05), A versus C (P<0.05), and B versus C (P<0.05). Neither sex, body mass index, current, duration, and type of operation nor the occurrence of hypotensive phases showed any significant association with postoperative piritramid demand. The necessity of rescue medication was significantly higher in group C than in group A. CONCLUSIONS: Postoperative TENS as well as the combination of preincisional and postoperative TENS therapy reduce the postoperative demand of piritramid in major spinal surgery in a safe and simple way free of systemic side effects.

Surgical instrumentation for the in vivo determination of human lumbar spinal segment stiffness and viscoelasticity.

The definition of spinal instability is still controversial. For this reason, it is essential to better understand the difference in biomechanical behaviour between healthy and degenerated human spinal segments in vivo. A novel computer-assisted instrument was developed with the objective to characterize the biomechanical parameters of the spinal segment. Investigation of the viscoelastic properties as well as the dynamic spinal stiffness was performed during a minimally invasive procedure (microdiscectomy) on five patients. Measurements were performed intraoperatively and the protocol consisted of a dynamic part, where spinal stiffness was computed, and a static part, where force relaxation of the segment under constant elongation was studied. The repeatability of the measurement procedure was demonstrated with five replicated tests. The spinal segment tissues were found to have viscoelastic properties. Preliminary tests confirmed a decrease in stiffness after decompression surgery. Patients with non-relaxed muscles showed higher stiffness and relaxation rate compared to patients with relaxed muscles, which can be explained by the contraction and relaxation reflex of muscles under fast and then static elongation. The results show the usefulness of the biomechanical characterization of the human lumbar spinal segment to improve the understanding of the contribution of individual anatomical structures to spinal stability.

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.