Daniel Chan

A Radiological Comparison of Anterior Fusion Rates in Anterior Lumbar Interbody Fusion

Aim To compare anterior fusion in standalone anterior lumbar interbody fusion (ALIF) using cage and screw constructs and anterior cage–alone constructs with posterior pedicle screw supplementation but without posterior fusion. Methods Eighty-five patients underwent single- or two-level ALIF procedure for degenerative disk disease or lytic spondylolisthesis (SPL). Posterior instrumentation was performed without posterior fusion in all cases of lytic SPL and when the anterior cage used did not have anterior screw through cage fixation. Results Seventy (82%) patients had adequate radiological follow-up at a mean of 19 months. Forty patients had anterior surgery alone (24 single level and 16 two levels) and 30 had front-back surgery (15 single level and 15 two levels). Anterior locked pseudarthrosis was only seen in the anterior surgery–alone group when using the STALIF cage (Surgicraft, Worcestershire, UK) (37 patients). This occurred in five of the single-level surgeries (5/22) and nine of the two-level surgeries (9/15). Fusion was achieved in 100% of the front-back group and only 65% (26/40) of the anterior surgery–alone group. Conclusion Posterior pedicle screw supplementation without posterolateral fusion improves the fusion rate of ALIF when using anterior cage and screw constructs. We would recommend supplementary posterior fixation especially in cases where more than one level is being operated.

Bovine and degenerated human annulus fibrosus: a microstructural and micromechanical comparison.

The complex structure of the annulus fibrosus is strongly related to its mechanical properties. Recent work showed that it is possible to observe the relative movement of fibre bundles in loaded cow tail annulus; the aim of this work was to describe and quantify annulus fibrosus micromechanics in degenerated human disc, and compare it with cow tail annulus, an animal model often used in the literature. Second harmonic generation was used to image the collagen matrix in twenty strips of annulus fibrosus harvested from intervertebral disc of seven patients undergoing surgery. Samples were loaded to 6% tensile strain in 1% steps. Elastic modulus was calculated from loading curves, and micromechanical strains were calculated from the images using custom software. The same protocol was applied to twenty strips of annulus harvested from cow tail discs. Significant morphological differences were found between human and cow tail samples, the most striking being the lack of collagen fibre crimp in the former. Fibres were also observed bending and running from one lamella to the other, forming a strong flexible interface. Interdigitation of fibre bundles was also present at this interface. Quantitative results show complex patterns of inter-bundle and inter-lamellar behaviour, with inter-bundle sliding being the main strain mechanism. Elastic modulus was similar between species, and it was not affected by the degree of degeneration. This work gives an insight into the complex structure and mechanical function of the annulus fibrosus, which should be accounted for in disc numerical modelling.

The effects of needle damage on annulus fibrosus micromechanics

Needle puncture of the intervertebral disc can initiate a mechanical and biochemical cascade leading to disc degeneration. Punctures mechanical effects have been shown near the puncture site, mechanical effects should be observed far, relative to needle size, from the puncture site, given the disc-wide damage induced by the stab. The aim of this work was to quantify these far-field effects, and to observe the local structural damage provoked by the needle. Strips of cow tail annulus fibrosus underwent two consecutive mechanical loadings to 5% tensile strain; fifteen samples were punctured in a radial direction with a randomly assigned needle between the two loadings (needle gauges between 19 and 23). Ten samples (control group) were not punctured. During loading, the tissue strains were imaged using second harmonic generation microscopy in a <600×800µm region about 4.4mm from the puncture site. After mechanical testing, the puncture site was imaged in 3D. Puncture had no significant effect on annulus elastic modulus. Imaging showed a modest change in the shearing between fibre bundles however, the linear strain between bundles, intra-bundle shear and linear strain were not significantly affected. At the puncture site, detached lumps of tissue were present. These results suggest that the mechanical effects observed in intact discs are due to the depressurization of the disc, rather than the local damage to the annulus. Needle profiles could be designed, aiming at separating fibre bundles rather than cutting through them, to avoid leaving dying tissue behind. STATEMENT OF SIGNIFICANCE Needle puncture of the intervertebral disc can initiate a mechanical and biochemical cascade leading to disc degeneration, but the link between the local damage of the puncture and the disc-wide effects is not well understood. This work aimed at determining the micro-mechanical effects of the puncture far from its site, and to observe the damage induced by the puncture with high resolution imaging. Results show that the puncture had modest effect far from the puncture, but lumps of tissue were left by the needle, detached from the disc; these could cause further damage through friction and inflammation of the surrounding tissues. This suggests that the cascade leading to degeneration is probably driven by a biochemical response rather than disc-wide mechanical effects.

Erect radiographs to assess clinical instability in patients with blunt cervical spine trauma.

BACKGROUND Computed tomography (CT) and magnetic resonance imaging (MRI) are sensitive modalities for the assessment of the spine, but certain injuries remain poorly assessed with supine radiographs. We describe four cases in which cervical spine injuries were proven as unstable with erect radiographs after being previously evaluated with supine radiographs and CT scans. METHODS A retrospective review of medical records and images was used to identify four patients who presented to a teaching hospital from April to December 2010 with unstable cervical spine injuries that were only demonstrated on erect radiographs. RESULTS All four patients sustained either C4-C5 or C5-C6 injuries. Prior to diagnosis, each had been evaluated with supine radiographs that did not demonstrate instability. Computed tomography identified the osseous injuries that were present but did not provide suitable assessment of stability. Three patients successfully underwent anterior cervical discectomy and fusion. The fourth was managed with a Halo jacket because of major comorbidities. CONCLUSIONS Despite major advances in imaging, these cases highlight the importance of physiological loading and radiographs. The controlled use of erect radiographs to test for clinical instability in patients with cervical spine injuries should be considered except in cases in which instability is already evident on other imaging modalities and/or surgical treatment is already indicated.

Respiratory failure due to a displaced fracture of the odontoid

Fractures of the odontoid peg are relatively common in elderly people. Often they are minimally displaced and can be treated with a collar. However, a fracture which is displaced significantly may be difficult to manage. We describe the case of an 80-year-old man with a fracture of the odontoid peg which was completely displaced and caused respiratory distress. After initial closed reduction and application of a halo jacket, open and internal fixation was undertaken and relieved his symptoms. It is a safe and effective way to manage this injury.

Do Growing Rods for Idiopathic Early Onset Scoliosis Improve Activity and Participation for Children

Objective To investigate whether growing rod surgery for children with progressive idiopathic early onset scoliosis (EOS) effects activity and participation, and investigate factors that may affect this. Study design Multicenter retrospective cohort study using prospectively collected data on 60 children with idiopathic EOS and significant scoliosis (defined as a Cobb angle >40°). Thirty underwent brace treatment, and 30, growth rod surgery. Questionnaire and radiographic data were recorded at 1 year. The validated Activities Scale for Kids performance version (ASKp) questionnaire was used to measure activity and participation. Results In the brace group, Cobb angle increased from 60° to 68°. There was no change in ASKp score. In the operative group, Cobb angle decreased from 67° to 45°. ASKp decreased from 91 to 88 (P < .01). Presence of spinal pain correlated with greater reduction in activity and participation scores in both groups, as did occurrence of complications in the operative group (P < .05). Both treatments permitted growth of the immature spine. Conclusions In children with significant idiopathic EOS (Cobb angle>40°), growth rod surgery was associated with a reduction in activity and participation and Cobb angle, whereas brace treatment was associated with an increase in Cobb angle and no change in activity and participation. Pain was the most important factor affecting activity and participation in both groups.

Recommendations for Lengthening of Magnetically Controlled Growing Rods in Children With Pacemakers.

Purpose of the Study: Pacemakers are currently identified as a contraindication for the use of magnetic growth rods (MGRs). This arises from concern that magnetic fields generated by the MGR external remote controller (ERC) during lengthening procedures may induce pacemaker dysfunction. We investigated (1) whether MGR lengthening affects pacemaker function, and (2) if the magnetic field of a pacemaker affects MGR lengthening. Methods: MGRs were tested in conjunction with an magnetic resonance imaging-compatible pacemaker, which was connected to a virtual patient under continuous cardiac monitoring. To determine whether pacemaker function was affected during MGR lengthening, the electrocardiogram trace was monitored for arrhythmias, whereas an ERC was applied to lengthen the MGRs at varying distances from the pacemaker. To investigate if MGR lengthening was affected by the presence of a pacemaker, at the start and end of the experiment, the ability of the rods to fully elongate and shorten was tested to check for conservation of function. Results: When the pacemaker was in normal mode, <16 cm away from the activated ERC during MGR lengthening, pacemaker function was affected by the ERC’s magnetic forces. At this distance, prophylactically switching the pacemaker to tonic mode before lengthening prevented occurrence of inappropriate pacing discharges. No deleterious effect of the pacemaker’s magnetic field on the MGR lengthening mechanism was identified. Conclusions: Magnetic resonance imaging-compatible pacemakers appear safe for concomitant use with MGRs, provided a pacemaker technician prophylactically switches the pacemaker to tonic function before outpatient lengthening procedures. Clinical Relevance: This experiment was designed to provide the first safety information on MGR lengthening in children with pacemakers. Although currently a rare clinical scenario, with increasing use of MGRs, this clinical scenario may arise more frequently in the future.

Anterior lumbar discectomy and fusion for acute cauda equina syndrome caused by recurrent disc prolapse: report of 3 cases

There is a lack of information and consensus regarding the optimal treatment for recurrent disc herniation previously treated by posterior discectomy, and no reports have described an anterior approach for recurrent disc herniation causing cauda equina syndrome (CES). Revision posterior decompression, irrespective of the presence of CES, has been reported to be associated with significantly higher rates of dural tears, hematomas, and iatrogenic nerve root damage. The authors describe treatment and outcomes in 3 consecutive cases of patients who underwent anterior lumbar discectomy and fusion (ALDF) for CES caused by recurrent disc herniations that had been previously treated with posterior discectomy. All 3 patients were operated on within 12 hours of presentation and were treated with an anterior retroperitoneal lumbar approach. Follow-up ranged from 12 to 24 months. Complete retrieval of herniated disc material was achieved without encountering significant epidural scar tissue in all 3 cases. No perioperative infection or neurological injury occurred, and all 3 patients had neurological recovery with restoration of bladder and bowel function and improvement in back and leg pain. ALDF is one option to treat CES caused by recurrent lumbar disc prolapse previously treated with posterior discectomy. The main advantage is that it avoids dissection around epidural scar tissue, but the procedure is associated with other risks and further evaluation of its safety in larger series is required.

Letter to the Editor concerning “Virtually bloodless posterior midline exposure of the lumbar spine using the ‘paramidline’ fatty plane” by Moghimi MH, Leonard DA, Cho CH, et al. (Eur Spine J (2016) 25;956–962)

To the Editor, Recently, the European Spine Journal published an interesting article describing a ‘virtually bloodless posterior midline exposure of the lumbar spine using the paramidline fatty plane’ [1]. The authors described a ‘paramidline’ approach to the posterior lumbar spine using ‘a virtually avascular surgical plane not previously described in the literature.’ In this approach, the deep lumbar fascia is longitudinally incised on either side of the spinous processes instead of directly in the midline, which reveals the paramidline fatty plane. This fatty plane is universally present on preoperative MRI. The authors prospectively analyzed 50 consecutive patients undergoing primary lumbar surgery on 1–3 levels and reported no blood loss during the approach for all procedures. Furthermore, the average blood loss for the entire procedure was 60 ml (20–200 ml). The case in which 200 ml of blood was lost was an L2–5, multi-level laminectomy, and fusion. We thank the authors for reporting their results with this approach, particularly their abilities to minimize blood loss (and therefore transfusion requirements); however, we note that the exposure lateral to the facets is not well described in their report. We have been using this same approach at our institution for many years. Weatherley et al. [2] describe the thoracolumbar fascia being incised lateral to the supraspinous ligament, and the paraspinal muscles raised laterally off the spinous processes, laminae, and facet joints subperiosteally with a Cobb elevator and a gauze swab. To expose the transverse processes for a posterolateral fusion, the dissection continues down the lateral side of the superior facet and onto the transverse process, in a fatty plane between the tendons of longissimus and multifidus, which attach to the accessory and mamillary processes of the facet joint, respectively [2]. While we have found that the dissection out to the facet joints is fairly avascular, the dissection lateral to the facet joint is less precise and associated with more bleeding. Wiltse and Spencer have noted similar difficulty with haemostasis in this area with a paraspinal approach [3]. Macnab and Dall [4] have described the arterial pattern lateral to the superior articular processes and at the base of the transverse process. These vessels are a continuation of the lumbar segmental arteries, passing posteriorly on each side around the waist of each vertebra. The location of the vessels is constant, although their identification at operation is difficult because of their placement in the depth of the exposure with the overhang of the facet joints and, lateral to the muscular attachments of multifidus to the mammillary, and longissimus to the accessory processes. Division of these tendons close to their attachments, and identification of the intervening fatty plane may enable easier visualization of these lateral facet vessels for cauterization. Weatherley et al. [2] did not formally measure blood loss; however, we consider this approach to be ‘a minimally avascular approach,’ with some blood loss being inevitable, particularly on dissection lateral to the facets. & Mathew David Sewell matbuzz1@hotmail.com

Retroperitoneal haematoma in a postoperative ALIF patient taking rivaroxaban for atrial fibrillation

BackgroundNovel oral anticoagulants (NOACs) are being increasingly used in the secondary prevention of thromboembolic stroke in patients with atrial fibrillation. Patients taking NOACs are difficult to manage perioperatively, and several unexpected complications have been reported in these patients.Case reportWe report a case of a rivaroxaban-induced retroperitoneal haematoma in a 72-year-old man who underwent an L5/S1 anterior lumbar interbody fusion (ALIF) for grade 1 spondylolytic spondylolisthesis. The patient suffered from atrial fibrillation and was taking rivaroxaban, a factor Xa inhibitor, for thromboembolic risk reduction. In accordance with perioperative Novel Oral Anticoagulant (NOAC) guidelines, rivaroxaban was stopped 2 days preoperatively and restarted on the third postoperative day. The patient presented on the ninth postoperative day, complaining of severe left iliac fossa pain, nausea, and vomiting, accompanied by swelling and bruising around the surgical site. A computed tomography (CT) scan showed a large expanding retroperitoneal haematoma. The patient was taken back to theatre for an evacuation of the haematoma and subsequently recovered without any further complications.ConclusionThis is the first case of a rivaroxaban-induced retroperitoneal haematoma reported in the literature, secondary to elective spinal surgery. This report adds to the body of evidence on the risk of postoperative bleeding in patients taking NOACs. If patients on NOACs present with abdominal symptoms following anterior approach to the lumbar spine, treating clinicians should have a high index of suspicion for retroperitoneal haematoma.