Survival analysis of the Wallis interspinous spacer used as an augment to lumbar decompression.

OBJECT: The Wallis fixed interspinous spacer may augment traditional decompression in the treatment of lumbar spinal stenosis. The aim of this study was to determine factors influencing survival of the Wallis interspinous spacer and to identify specific modes and predictors of failure. METHODS: We performed a retrospective cohort study of 244 Wallis interspinous spacers implanted in 195 consecutive patients with a mean age of 56 years (range 21-87) to augment single or multi-level decompression. We examined patient demographics, indications for surgery, surgical techniques and pathology on magnetic resonance imaging (MRI). A Kaplan-Meier survival analysis was performed. RESULTS: Median follow-up was 4.5 years (range 2-8). Sixteen patients were lost to follow-up. Repeat MRI was performed in 98 patients (50%). A recurrent stenosis was found in 21% of patients (41/195) and occurred at a similar incidence at the level of the spacer and at adjacent spinal levels. Revision decompression was performed in 19 patients (10%) at 2.8 ± 1.8 years (range 6 months-6 years) with implant removal in 15 and conversion to fusion in 4 patients. No specific patient factors or pre-operative MRI findings predicted failure. Five-year survival was 91% (95% CI: 79-96%). CONCLUSIONS: The Wallis implant is generally implanted without complication when used as an adjunct to decompression with a good medium term survival. Though disc heights were maintained, the Wallis spacer did not however appear to reduce the incidence of recurrent spinal or foraminal stenosis from that expected from decompression alone.

Modulation of spinal shape with growth following implantation of a novel surgical implant.

PURPOSE: First, to determine whether scoliosis development could be limited or reversed by growth when a novel modular hinged implant was fixed to the convexity of a scoliosis created by contralateral rib and laminar tethering and unilateral rib resection in a sheep model. Second, to assess the effect and performance of the implant in normal non-tethered sheep. METHODS: At 5 weeks, 20 Scottish Blackface lambs underwent surgery to create a right sided scoliosis by (i) tethering the left lamina of T5-L1 and the left lower six ribs and (ii) resecting a segment of their right lower six ribs [1, 2]. Twelve weeks later, through an antero-lateral thoracotomy, a mobile bi-planar hinged implant was inserted onto the right side of the spine of eight animals (group 1). For comparison, 12 sheep were tethered only but had no implant insertion (group 2). In addition, seven had no tethering but were implanted (group 3) and normal growth patterns were observed in five that had no surgery (group 4). Curve progression was assessed by plain radiography and CT over a 1-year period. RESULTS: Before implant insertion the trial animals had a scoliosis of 35º ± 16º and a lordosis of 44º ± 20º (n = 8, mean ± SD). Surgery immediately reduced these values to 25º ± 14º, p < 0.01 and 35º ± 18º, p < 0.001, with scoliosis continuing to decrease during the next three months. Spinal flexibility was retained. In the un-tethered sheep, a scoliosis of 10º ± 6º was created on the opposite side to the implant (p < 0.05) with no significant change in alignment in the sagittal plane (1º ± 6º). The implant did not cause any adverse effect on growth or affect neurological function. CONCLUSIONS: In the un-tethered animals the effect of the implant was to create a scoliotic deformity and in the tethered to improve deformity while maintaining spinal motion. We believe that the results are promising and that devices of similar construct may be of use in children with scoliosis, potentially changing current methods of clinical care.

Creation of an ovine model of progressive structural lordo-scoliosis using a unilateral laminar tether.

PURPOSE: To characterise changes in vertebral dimension in an ovine model of scoliosis and determine whether a reproducible curvature could be created that would be suitable for future testing of curve modifying surgical implants. METHODS: At a mean age of 5 weeks, 28 Scottish blackface sheep were anaesthetised. A 4 mm braided synthetic tape was laid under the left lamina of T5 and L1 and tightened to 'hand' tension. A scoliosis was then created by binding the six lowest ribs on the same side just distal to their rib angles and resecting a segment from each of the opposite ribs. Radiographs were taken at 4 weekly intervals, and CT images at 2, 5 and 7 months post tethering, to determine multi-planar curve progression. 20 animals were assessed at age 3 months, 12 at 41 weeks and 10 at 1 year with comparisons to five control animals. RESULTS: A significant bi-planar deformity was produced in all animals (scoliosis 32 ± 13º and lordosis 53 ± 21º 2 months post tethering; mean ± SD, n = 22). During the next 5 months the scoliosis decreased slightly (p = 0.08) but the sagittal deformity remained static: 21 ± 18° and 53 ± 19°, respectively (n = 12). The values at 7 months were associated with a mean 6 ± 4º rotational deformity. There was approximately twice as much growth in the right anterior aspects of the apical vertebrae as in the left posterior. CONCLUSIONS: With appropriate care it was possible to obtain a reproducible curvature in immature sheep. The methods described are suitable for use in studies of growth modulation and other spinal devices.

The effects of age, isoflurane and sevoflurane on atracurium in lambs.

OBJECTIVE: To determine the effects of age, sevoflurane and isoflurane on atracurium-induced neuromuscular blockade in 3-16 week-old lambs. STUDY DESIGN: Prospective randomized experimental trial. ANIMALS: Twenty-six Scottish blackface ewe-lambs were anaesthetized for spinal surgery when either 3-6 (mean age 4.6 weeks; n = 18) or 12-16 weeks (mean age 13.7 weeks; n = 15) of age; seven animals were anaesthetized at both ages. METHODS: After intramuscular injection of medetomidine (10 µg kg(-1)) anaesthesia was induced in the younger lambs either with isoflurane or sevoflurane in oxygen delivered by mask, and in the older lambs with ketamine (4 mg kg(-1)), and midazolam (0.2 mg kg(-1) ) administered intravenously (IV). In both groups anaesthesia was maintained with fixed end-tidal concentrations of either sevoflurane (2.8%) or isoflurane (1.8%) delivered in oxygen. Before surgery meloxicam (0.6 mg kg(-1)), morphine (0.5 mg kg(-1)) and ketamine (1 mg kg(-1) followed by 10 µg kg(-1) minute(-1) ) were administered IV. The lungs were ventilated mechanically to maintain normocapnia. Neuromuscular block was achieved with a loading dose (LD) of atracurium (0.5 mg kg(-1) IV). The peroneal nerve was stimulated (train-of-four every 12 seconds). Evoked responses in the digital extensor muscles were evaluated by palpation and observation. Maintenance doses (MD) of atracurium (0.17 mg kg(-1) IV) were administered when the first twitch (T1) returned. The onset and duration of LD action (T1 absent) and the duration of MD were recorded. Data were analysed using Student's t test, Mann-Whitney U test, repeated-measures anova, Wilcoxon's matched pairs test or Pearson correlation coefficient as relevant (p < 0.05). RESULTS: Onset of LD action developed significantly (p < 0.05) more rapidly in isoflurane compared with sevoflurane-anaesthetized lambs (55 ± 18 cf. 80 ± 37 seconds). Duration of action of LDs and MDs was longer (p < 0.05) in lambs aged 12-16 than 3-6 weeks (33 ± 5.4 cf. 25 ± 6.4 and 26 ± 4.2 cf. 18 ± 5.5 minutes) but were independent of the anaesthetic used. CONCLUSIONS AND CLINICAL RELEVANCE: The effect of atracurium is age-dependent in lambs being prolonged in older animals. The onset of neuromuscular blockade is more rapid in isoflurane compared with sevoflurane-anaesthetized lambs.

Clinical effects of isoflurane and sevoflurane in lambs.

OBJECTIVE: To compare isoflurane and sevoflurane in lambs undergoing prolonged anaesthesia for spinal surgery. STUDY DESIGN: Prospective randomised clinical study. ANIMALS: Eighteen Scottish blackface lambs 3-6 weeks of age and weighing 10-17 kg. METHODS: After intramuscular medetomidine, anaesthesia was induced and maintained with either isoflurane (group I) or sevoflurane (group S) delivered in oxygen. Meloxicam, morphine, a constant rate infusion of ketamine and atracurium were given intravenously (IV) during surgery. Lungs were ventilated to maintain normocapnia. with peak inspiratory pressures of 20-25 cmH(2) O. Ephedrine or dextran 40% was administered when mean arterial pressure (MAP) was <55 mmHg. Intrathecal morphine, and IV meloxicam and edrophonium were injected before recovery. Time to loss of palpebral reflex (TLPR) upon induction, cardiorespiratory variables, time at first swallowing and other movement, tracheal extubation, vocalisation, spontaneous head lifting (>1 minute), reunion with the ewe, and the number of MAP treatments were recorded. Statistical analysis utilised anova, Mann-Whitney, t-test or Pearson's correlation test as relevant. p < 0.05 was considered significant. RESULTS: End-tidal carbon dioxide (mean ± SD) was significantly lower in group S (5.5 ± 0.6 kPa) than in group I (5.8 ± 0.5 kPa) while MAP (70 ± 11 mmHg) and diastolic arterial blood pressure (60 ± 11 mmHg) were higher in group S than in group I (65 ± 12 and 54 ± 11 mmHg, respectively). No differences were found with TLPR and MAP treatments. Time (median, range) from end of anaesthesia to ewe-lamb reunion was briefer (p = 0.018) in group S (48, 20-63 minutes). CONCLUSION: Isoflurane and sevoflurane are both suitable for maintaining general anaesthesia in lambs although sevoflurane, as used in this study, allows a more rapid reunion with the ewe. CLINICAL RELEVANCE: The principal advantage of sevoflurane over isoflurane during prolonged anaesthesia in lambs is a more rapid recovery.

Spontaneous production of monocyte chemoattractant protein-1 and interleukin-8 by the human lumbar intervertebral disc.

STUDY DESIGN: Scoliotic and herniated human intervertebral disc tissue obtained intraoperatively was cultured, and the medium was analyzed for the production of monocyte chemoattractant protein-1 and interleukin-8. OBJECTIVES: This study was conducted to determine whether the human intervertebral disc is capable of spontaneous production of the chemokines monocyte chemoattractant protein-1 and interleukin-8. SUMMARY OF BACKGROUND DATA: Lumbar disc herniations undergo spontaneous regression with time. This is believed to occur via macrophage-mediated phagocytosis of herniated disc material. Monocyte chemoattractant protein-1, a chemotactic agent for macrophages, has recently been identified in rat intervertebral disc tissue. METHODS: Disc material obtained from patients undergoing surgery for scoliosis and sciatica was cultured using a serumless technique, and the medium was subsequently analyzed for levels of monocyte chemoattractant protein-1 and interleukin-8. RESULTS: Monocyte chemoattractant protein-1 and IL-8 were detected in both control and herniated disc specimens. Noncontained herniations produced higher levels of chemokines than those with an intact anulus. CONCLUSIONS: Human intervertebral disc tissue is capable of spontaneously producing the proinflammatory chemokines monocyte chemoattractant protein-1 and interleukin-8. These are chemotactic for macrophages and capillaries and may explain the ingrowth of granulation tissue seen in spontaneous disc herniation resorption.