Consequences of patient position in the radiographic measurement of artificial disc replacement angles

Accurate clinical measurement of spinal range of motion (ROM) is essential in the evaluation of artificial disc performance. The effect of patient placement with respect to the X-ray beam source is yet to be reported and may be an influencing factor in radiographic artificial disc angle measurements. This study aims to evaluate how radiographic patient placement influences artificial disc angle measurements. An anatomically accurate synthetic L4-L5 motion segment was instrumented with an artificial disc and two pins. The instrumented motion segment was mounted onto a frame allowing for independent rotation and elevation while holding the artificial disc angle and anatomical position between L4 and L5 fixed. Analyses included descriptive statistics, evaluation of uncertainty, intra- and inter-observer, and a 2-way analysis of variance (ANOVA). The mean angle measurement range at the various positions was 1.26° for the pin, and 2.74° for the artificial disc endplates. The centered patient position had the highest inter- and intra-observer reliability. ANOVA results showed elevation effects to be statistically significant (P=0.021), and rotational effects to be extremely statistically significant (P<0.0001) for the pin angles. In terms of the mean artificial disc angle, however, the ANOVA showed a highly statistically significant interaction term (P=0.002). A significant difference was found in the angle measurements of a fixed artificial disc prosthesis based on a sample of patient radiographic placement positions. Since it is important to assess the success of an artificial disc replacement by evaluating the relatively small ROM present, it is crucial to aim at minimizing the error by placing the patient parallel to the plate with the beam centered not at the mid lumbar spine, but at the level of the arthroplasty, for both flexion and extension view

Minimally invasive versus open transforaminal lumbar interbody fusion: evaluating initial experience

The aim of this study was to compare our experience with minimally invasive transforaminal lumbar interbody fusion (MITLIF) and open midline transforaminal lumbar interbody fusion (TLIF). A total of 36 patients suffering from isthmic spondylolisthesis or degenerative disc disease were operated with either a MITLIF (n = 18) or an open TLIF technique (n = 18) with an average follow-up of 22 and 24months, respectively. Clinical outcome was assessed using the visual analogue scale (VAS) and the Oswestry disability index (ODI). There was no difference in length of surgery between the two groups. The MITLIF group resulted in a significant reduction of blood loss and had a shorter length of hospital stay. No difference was observed in postoperative pain, initial analgesia consumption, VAS or ODI between the groups. Three pseudarthroses were observed in the MITLIF group although this was not statistically significant. A steeper learning effect was observed for the MITLIF grou

Impact of iliac crest bone graft harvesting on fusion rates and postoperative pain during instrumented posterolateral lumbar fusion

This study aims to evaluate the influence of bone harvesting on postoperative pain and fusion rates. Group 1 patients received iliac crest bone graft (ICBG) either alone or augmented with local bone. Group 2 received only local bone. No statistical significance was found in radiological union or in the Oswestry Disability Index scores. Visual Analogue Scale scores showed less pain in group 2. Logistic regression showed no correlation between residual pain and occurrence of fusion. Harvesting ICBG did not appear to increase fusion rates and no relation was found between radiological non-union and pai

Posterolateral lumbar spine fusion using a novel demineralized bone matrix: a controlled case pilot study

Introduction: Intertransverse posterolateral fusion along with instrumentation is a common technique used for spinal fusion. Iliac crest bone graft (ICBG) offers good fusion success rates with a low risk for disease transmission but is, however, linked with certain morbidity. In an effort to eliminate or reduce the amount of iliac graft needed, bone substitutes including demineralized bone matrix (DBM) have been developed. This study evaluates a novel DBM (Accell Connexus®) used in one or two-level instrumented posterolateral lumbar fusion. Materials and methods: A total of 59 consecutive patients were studied as two groups. Group 1 consisted of 33 patients having Accell Connexus® used to augment either ICBG or local decompression material. Group 2 consisted of 26 consecutive patients, operated prior to the introduction of this novel DBM, having either ICBG alone or local decompression material. Fusion was assessed by two independent observers, blinded to graft material, using standardized criteria found in the literature. All adverse events were recorded prospectively. Results: The results show no statistically significant differences between the two groups in fusion rates, complications, surgery duration, ODI, or pain on VAS. Logistical regression showed no relation between fusion and age, smoking status or comorbidities. Furthermore, no adverse events related to the use of the novel DBM were observed. Conclusion: The results from this study demonstrate that the novel DBM presented performs equally as well as that of autologous bone, be it either ICBG or a local decompression material, and can therefore be used as a graft extende

Lymphocoele: a rare and little known complication of anterior lumbar surgery

Lymphocoele is a rare and little known complication with only a handful of reports available. We report two cases of lymphocoele after anterior lumbar surgery that have occurred in two different centres and discuss diagnosis and management options. The first case is that of a 53-year-old male patient undergoing two level anterior lumbar interbody fusion (ALIF) for disabling back pain due to disc degeneration in the context of an old spondylodiscitis. He developed a large fluid mass postoperatively. Fluid levels of creatinin were low and intravenous urography ruled out a urinoma suggesting the diagnosis of a lymphocoele. Following two unsuccessful drainage attempts he underwent a laparoscopic marsupialization. The second case was that of a 32-year-old female patient developing a large fluid mass following a L5 corpectomy for a burst fracture. She was treated successfully with insertion of a vacuum drain during 7days. Lymphocoele is a rare complication but should be suspected if fluid collects postoperatively following anterior lumbar spine procedures. Chemical analysis of the fluid can help in diagnosis. Modern treatment consists of laparoscopic marsupialization. Lymph vessel anatomy should be borne in mind while exposing the anterior lumbar spin

Is spinal stenosis assessment dependent on slice orientation? A magnetic resonance imaging study

Introduction: Lumbar spinal stenosis (LSS) treatment is based primarily on the clinical criteria providing that imaging confirms radiological stenosis. The radiological measurement more commonly used is the dural sac cross-sectional area (DSCA). It has been recently shown that grading stenosis based on the morphology of the dural sac as seen on axial T2 MRI images, better reflects severity of stenosis than DSCA and is of prognostic value. This radiological prospective study investigates the variability of surface measurements and morphological grading of stenosis for varying degrees of angulation of the T2 axial images relative to the disc space as observed in clinical practice. Materials and methods: Lumbar spine TSE T2 three-dimensional (3D) MRI sequences were obtained from 32 consecutive patients presenting with either suspected spinal stenosis or low back pain. Axial reconstructions using the OsiriX software at 0°, 10°, 20° and 30° relative to the disc space orientation were obtained for a total of 97 levels. For each level, DSCA was digitally measured and stenosis was graded according to the 4-point (A-D) morphological grading by two observers. Results: A good interobserver agreement was found in grade evaluation of stenosis (k=0.71). DSCA varied significantly as the slice orientation increased from 0° to +10°, +20° and +30° at each level examined (P<0.0001) (−15 to +32% at 10°, −24 to +143% at 20° and −29 to +231% at 30° of slice orientation). Stenosis definition based on the surface measurements changed in 39 out of the 97 levels studied, whereas the morphology grade was modified only in two levels (P<0.01). Discussion: The need to obtain continuous slices using the classical 2D MRI acquisition technique entails often at least a 10° slice inclination relative to one of the studied discs. Even at this low angulation, we found a significantly statistical difference between surface changes and morphological grading change. In clinical practice, given the above findings, it might therefore not be necessary to align the axial cuts to each individual disc level which could be more time-consuming than obtaining a single series of axial cuts perpendicular to the middle of the lumbar spine or to the most stenotic level. In conclusion, morphological grading seems to offer an alternative means of assessing severity of spinal stenosis that is little affected by image acquisition techniqu

A CT-based study investigating the relationship between pedicle screw placement and stimulation threshold of compound muscle action potentials measured by intraoperative neurophysiological monitoring

Purpose: Neurophysiological monitoring aims to improve the safety of pedicle screw placement, but few quantitative studies assess specificity and sensitivity. In this study, screw placement within the pedicle is measured (post-op CT scan, horizontal and vertical distance from the screw edge to the surface of the pedicle) and correlated with intraoperative neurophysiological stimulation thresholds. Methods: A single surgeon placed 68 thoracic and 136 lumbar screws in 30 consecutive patients during instrumented fusion under EMG control. The female to male ratio was 1.6 and the average age was 61.3years (SD 17.7). Radiological measurements, blinded to stimulation threshold, were done on reformatted CT reconstructions using OsiriX software. A standard deviation of the screw position of 2.8mm was determined from pilot measurements, and a 1mm of screw—pedicle edge distance was considered as a difference of interest (standardised difference of 0.35) leading to a power of the study of 75% (significance level 0.05). Results: Correct placement and stimulation thresholds above 10mA were found in 71% of screws. Twenty-two percent of screws caused cortical breach, 80% of these had stimulation thresholds above 10mA (sensitivity 20%, specificity 90%). True prediction of correct position of the screw was more frequent for lumbar than for thoracic screws. Conclusion: A screw stimulation threshold of >10mA does not indicate correct pedicle screw placement. A hypothesised gradual decrease of screw stimulation thresholds was not observed as screw placement approaches the nerve root. Aside from a robust threshold of 2mA indicating direct contact with nervous tissue, a secondary threshold appears to depend on patients' pathology and surgical condition

Miniature probe for the delivery and monitoring of a photopolymerizable material

Photopolymerization is a common method to cure materials initially in a liquid state, such as dental implants or bone or tissue fillers. Recent advances in the development of biocompatible gel- and cement-systems open up an avenue for in situ photopolymerization. For minimally invasive surgery, such procedures require miniaturized surgical endoscopic probes to activate and control photopolymerization in situ. We present a miniaturized light probe in which a photoactive material can be (1) mixed, pressurized, and injected, (2) photopolymerized/photoactivated, and (3) monitored during the chemical reaction. The device is used to implant and cure poly(ethylene glycol) dimethacrylate-hydrogel-precursor in situ with ultraviolet A (UVA) light (365 nm) while the polymerization reaction is monitored in real time by collecting the fluorescence and Raman signals generated by the 532 nm excitation light source. Hydrogels could be delivered, photopolymerized, and monitored by the probe up to a curing depth of 4 cm. The size of the photopolymerized samples could be correlated to the fluorescent signal collected by the probe, and the reproducibility of the procedure could be demonstrated. The position of the probe tip inside a bovine caudal intervertebral disc could be estimated in vitro based on the collected fluores- cence and Raman signal

Photo-polymerization, swelling and mechanical properties of cellulose fibre reinforced poly(ethylene glycol) hydrogels

The application of hydrogels as load-bearing biomedical components is often limited by their mechanical properties. Often an attempt to improve a hydrogel's stiffness is accompanied by a loss of toughness and swelling properties. In this work, we show that the addition of nanofibrillated cellulose (NFC) provides a mean to tailor both the swelling and the mechanical properties of the hydrogel. Various volume fractions of NFC were added to poly(ethylene glycol) dimethacrylate (PEGDM) precursors with two different molecular weights (6 and 20 kDa). The viscosity measurements of the precursor solutions indicated that the dispersed NFCs form a network-like structure in the hydrogel precursor. Such a structure, as observed in the photo-rheology experiments, serves as a light-scattering source when the solution is illuminated by UV light, which provides a uniform polymerization of the hydrogel in three-dimension and reduces the curing time. Mechanical properties of the neat and composite hydrogels were characterized using monotonic and cyclic compression tests. NFC reinforcement increases the hydrogel's stiffness by a factor 2 and 3.5 for the PEGDM matrixes with molecular weights of 6 and 20 kDa respectively without compromising their toughness. Moreover, the desired stiffness and swelling properties can be simultaneously achieved by adapting the reinforcement concentration and the hydrogel cross-link density. The obtained composite hydrogels offer enhanced and tuneable properties and are proposed for injectable and photo-curable load-bearing implants